Intensive Widmannstätten Nanoprecipitates Catalyze SnTe With State‐of‐the‐Art Thermoelectric Performance

Abstract

Nanoprecipitates play a vital role in designing high‐performance thermoelectric materials, particularly for those with short phonon mean‐free paths. However, their effectiveness in reducing lattice thermal conductivity is hindered by the uncontrollable intensity, poor interfacial coherence, and suboptimal morphology. To address these limitations, AgPbSbTe₃ is used to alloy SnTe to form intensive Ag₂Te Widmannstätten nanoprecipitates for obtaining state‐of‐the‐art thermoelectric performance. Advanced microscopy characterizations reveal the crystallographic orientation relationships between SnTe and Ag₂Te to guide the lath‐shaped morphology of Ag₂Te, leading to the formation of the high‐intensity Widmannstätten nanoprecipitates, which effectively scatter phonons to reduce the lattice thermal conductivity. Togethering the optimized electrical properties through carrier concentration adjustment, band convergence, and the energy filtering effect, a maximum figure of merit ZT of 1.5 at 723 K and an average ZT of 1.1 between 423 and 823 K is achieved in (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20, enabling a single‐leg device and two‐pair module with energy‐conversion efficiency of 7.22% and 4.26% under a temperature difference of 450 K, respectively. The findings highlight the potential of intensive Widmannstätten nanoprecipitates as effective phonon scattering centers, providing a new pathway to enhance the thermoelectric performance of chalcogenides.

The intensive lath‐shaped Ag₂Te Widmannstätten nanoprecipitates are in situ generated in SnTe via AgPbSbTe₃ alloying, and align with the formation of the parallel type and twin type interfaces. These Widmannstätten nanoprecipitates effectively scatter phonons to reduce the lattice thermal conductivity, resulting in a significantly enhanced average ZT, more suitable for mid‐temperature applications.

1. Introduction

Owing to their ability to directly convert waste heat into electricity or operate in reverse, thermoelectric materials hold great promise for power generation and solid‐state refrigeration.^{[ 1} , ² , ^{3 ]} The performance of a thermoelectric device is primarily determined by its energy‐conversion efficiency, which is closely linked to the figure of merit of thermoelectric materials, ZT = S ² σT/κ,^{[ 4 ]} in which, S represents the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature (in Kelvin), and κ is the total thermal conductivity, comprising lattice thermal conductivity (κ _L) and electronic thermal conductivity (κ _e).^{[ 5} , ⁶ , ^{7 ]} The interdependence of S, σ, and κ _e makes improving ZT a challenging task.^{[ 8 ]} In contrast, κ _L, which is governed by phonon transport, can be more independently tuned compared to electronic properties. This makes the κ _L a critical target for enhancing thermoelectric performance.^{[ 9 ]} Strategies to suppress the κ _L typically fall into two main categories. The first involves identifying materials with intrinsically low κ _L, which can result from complex structures,^{[ 10 ]} anharmonic lattice vibrations,^{[ 11 ]} or liquid‐like phonon transport mechanisms,^{[ 12} , ^{13 ]} among other factors.^{[ 14} , ^{15 ]} The second focuses on disrupting phonon transport by introducing structural features such as 0D point defects,^{[ 16 ]} 1D dislocations,^{[ 17 ]} 2D grain boundaries,^{[ 18 ]} or 3D nanoprecipitates.^{[ 19 ]} This approach has been widely applied to chalcogenide compounds, including Group IV‐VI and V₂VI₃‐based alloys.^{[ 20} , ²¹ , ^{22 ]}

Heavy chalcogenides exhibit metavalent bonding,^{[ 23 ]} a unique bonding mechanism where ≈1 electron is shared between neighboring atoms, forming a half‐filled σ‐bond.^{[ 24 ]} In these systems, the κ _L is primarily determined by heat‐carrying phonons with mean free paths ≈10 nm,^{[ 25 ]} making nanoprecipitates particularly effective in reducing the κ _L. A pivotal factor in the design of effective nanoprecipitates lies in the contrast between the chemical bonding mechanisms of the host matrix and the secondary phase. When the bonding nature differs substantially, phase separation becomes thermodynamically favored over the formation of a solid solution.^{[ 26 ]} This disparity not only facilitates the formation of well‐defined nanoprecipitates but also generates chemically and structurally mismatched interfaces that act as efficient phonon‐scattering centers. Traditionally, nanoprecipitates are introduced via either ex situ or in situ methods. Ex situ techniques often result in nanoprecipitates with uncontrolled distributions, poor coherency, and undesirable growth due to effects like Ostwald ripening or high interfacial energy. In contrast, in situ methods offer a more promising pathway, particularly through the exsolution of Widmannstätten structural nanoprecipitate, a well‐known metallurgical microstructure that is frequently observed in certain steels and meteorites. This approach leverages the contrast in chemical bonding mechanisms and the temperature‐dependent solubility behavior to precisely tailor the characteristics of nanoprecipitates, thereby effectively minimizing the κ _L.

The nature of chemical bonding plays a critical role in governing interfacial phonon scattering. In addition, the interfaces of nanoprecipitates are often non‐periodic, making factors such as intensity, interface coherence, and morphology critical for maximizing phonon scattering.^{[ 27 ]} High‐intensity nanoprecipitates create abundant scattering centers, while coherent interfaces with low interfacial energies suppress coarsening, ensuring the precipitates remain nanoscale and thermodynamically stable. These coherent interfaces also enhance phonon scattering without significantly disrupting carrier transport.^{[ 28 ]} In terms of morphology, lath‐shaped nanoprecipitates provide much larger interfacial areas compared to spherical ones with the same volume fraction, making them more effective at blocking phonon transport.^{[ 29 ]} Designing high‐intensity, coherent, and lath‐shaped Widmannstätten nanoprecipitates (referred to as intensive Widmannstätten nanoprecipitates) is therefore essential for achieving high thermoelectric performance. However, controlling the morphology, intensity, and size of Widmannstätten nanoprecipitates remains the challenge. Previous studies have shown that in situ formation of Ag₂Te precipitates in Group IV–VI compounds effectively scatters phonons and reduces the κ _L.^{[ 30 ]} However, most Ag₂Te precipitates exhibit spherical or irregular shapes at the nano‐ to micron‐level,^{[ 31 ]} with the PbTe‐Ag₂Te system being a notable exception.^{[ 32 ]} The process for constructing lath‐shaped Widmannstätten‐structured nanoprecipitates in thermoelectric materials remains poorly understood, requiring further investigation.

Understanding mechanisms that drive the nucleation and growth of Widmannstätten nanoprecipitates is essential. High‐intensity Widmannstätten nanoprecipitates depend on a temperature‐dependent solid solubility curve, which allows for high solubility at elevated temperatures but promotes exsolution as the temperature decreases.^{[ 33 ]} This conforms to the principle of “high‐temperature miscibility, low‐temperature immiscibility.” According to classical nucleation and growth theory, the morphology and size of precipitates are influenced by the strain energy at the interfaces, which is determined by the degree of lattice mismatch between the matrix and the precipitates. A larger lattice mismatch leads to higher strain energy,^{[ 34 ]} prompting precipitates to grow preferentially in directions that allow the formation of coherent interfaces. This maximizes the interface area of specific crystal planes, minimizing strain energy. To achieve a lath‐shaped morphology, a significant difference in crystal structure and lattice parameters between the matrix and the precipitates is required, along with the presence of specific crystal planes that can form coherent interfaces. These conditions are critical for enabling the unique morphology and optimizing the functional performance of Widmannstätten nanoprecipitates.

As demonstrated in SnTe, a lead‐free analog of PbTe, its high κ _L significantly limits ZT enhancement.^{[ 35 ]} The short phonon mean free path in SnTe underscores the potential of Widmannstätten nanoprecipitates to effectively reduce the κ _L.^{[ 25 ]} Given the chemical bonding‐induced phase separation behavior, Ag₂Te represents a suitable candidate for nanoprecipitate design in SnTe, owing to the distinct bonding nature between the two phases (metavalent bonding in SnTe vs. iono‐covalent bonding in Ag₂Te).^{[ 36} , ^{37 ]} Additionally, crystallographic analysis reveals a specific orientation relationship between SnTe and Ag₂Te. This relationship features a substantial lattice parameter mismatch alongside well‐matched crystal planes that form coherent interfaces. These factors guide the exsolution of Ag₂Te along a specific crystallographic plane, defining the habit plane for its growth and fulfilling the criteria for forming lath‐shaped Widmannstätten nanoprecipitates. Despite these favorable conditions, the phase diagram of the Sn‐Ag‐Te system indicates limited Ag solubility in SnTe, which exhibits ≈3% at ≈870 K, with complete exsolution as the temperature drops to ≈720 K. This restricts the intensity of Widmannstätten nanoprecipitates (Figure 1a). Previous studies have shown that significantly more Ag (>7%) can be dissolved into SnTe upon AgSbTe₂‐alloying,^{[ 36 ]} due to the same chemical bonding mechanism between AgSbTe₂ and SnTe. Additionally, Ag exhibits greater solid solubility (≈7−8%) in PbTe at elevated temperatures, which exsolves as the temperature decreases (Figure 1a). The temperature‐dependent solid solution of Ag in PbTe has been indicated experimentally in previous studies.^{[ 38} , ^{39 ]} This suggests that alloying with AgPbSbTe₃ could significantly increase the intensity of Ag₂Te Widmannstätten nanoprecipitates in SnTe. Building on these insights, this study aims to systematically investigate the formation mechanisms, orientation relationships, interfacial structures, and thermoelectric performance impacts of intensive Widmannstätten nanoprecipitates in SnTe.

Figure 1.

Design strategy for achieving high‐performance SnTe‐based materials and devices. a) Illustration of the design strategy for forming intensive Widmannstätten nanoprecipitates in SnTe. b) Schematic representation of Widmannstätten‐structured nanoprecipitates. c) Diagram of the induced “parallel type” and “twin type” interfaces between the matrix and nanoprecipitates. d) Comparison of the minimum lattice thermal conductivity (κ _L) achieved in this work with previously reported studies.^{[ 41} , ⁴² , ⁴³ , ⁴⁴ , ⁴⁵ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ⁴⁹ , ^{50 ]} e) Comparison of the average ZT value (ZT _ave) calculated across the full temperature range and the mid‐temperature range (423–823 K) between this work and literature.^{[ 27} , ³⁶ , ⁴³ , ⁴⁴ , ⁴⁷ , ⁴⁸ , ⁵⁰ , ⁵¹ , ⁵² , ⁵³ , ⁵⁴ , ⁵⁵ , ⁵⁶ , ⁵⁷ , ^{58 ]} The inset is also visibly displayed in Figure S1 (Supporting Information). f) Energy‐conversion efficiency (η) of a single‐leg SnTe‐based device under various temperature differences (ΔTs), compared with previously reported works.^{[ 59} , ^{60 ]}

2. Results and Discussion

By applying the concept of two‐phase miscibility guided by chemical bonding mechanisms and phase diagram engineering,^{[ 26} , ^{40 ]} a high‐performance thermoelectric system, (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x , was successfully designed, characterized by intensive Widmannstätten Ag₂Te nanoprecipitates. These nanoprecipitates, with lengths of 400–500 nm and widths of 50–100 nm, are embedded within the SnTe matrix, as illustrated schematically in Figure 1b. High‐angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) analysis identifies two types of interfaces, parallel and twin types, that enhance the stability and compatibility between the matrix and nanoprecipitates, dictating the specific growth orientation of Ag₂Te (Figure 1c). Additionally, Ag₂Te twin structures and interfacial dislocations are observed, contributing to further phonon scattering. This unique microstructure significantly reduces the κ _L, achieving a low κ _L of 0.32 W m⁻¹ K⁻¹ at 773 K in the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample (Figure 1d). AgPbSbTe₃‐alloying increases the hole carrier concentration (n _H) by regulating Sn vacancies and enhances the density‐of‐state effective mass ($m_{\mathrm{d}}^{\ast }$) through band convergence and energy filtering effects, leading to an optimized power factor (S ² σ). As a result, the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample achieves a maximum ZT value of 1.5 at 723 K and an impressive average ZT (ZT _ave) value of 1.1 across the temperature range of 423–823 K (Figure 1e), making it well‐suited for mid‐temperature applications. A single‐leg thermoelectric device fabricated from this sample demonstrates an output power density (ω) of 221 mW cm⁻² and an energy‐conversion efficiency (η) of 7.22% under a temperature difference (ΔT) of 450 K, representing good performance for SnTe‐based devices (Figure 1f). Meanwhile, a two‐pair TE module is also conducted on this sample and PbTe‐based material, which exhibits a maximum η of 4.26% under a ΔT of 450 K. This work highlights the effectiveness of incorporating intensive Widmannstätten nanoprecipitates to enhance phonon scattering, providing a novel strategy for improving thermoelectric performance.

2.1. Microstructure Investigations

X‐ray diffraction (XRD) analysis was performed to investigate the phase composition of all (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x samples (Figure S2a, Supporting Information). The diffraction peaks align well with the standard JCPDS#46–1210, corresponding to the rock‐salt structure of SnTe (space group $Fm\overline{3}m$).^{[ 61 ]} A closer look at the diffraction peaks between 28.0 and 28.8° (Figure S2b, Supporting Information) shows a gradual shift of the (200) plane peak toward higher angles as the AgPbSbTe₃ content increases, indicating lattice contraction. To quantify this, Rietveld refinement was performed on the XRD data, and the lattice parameters (a) were calculated, with the refined results presented in Figures S2c and S3 (Supporting Information). The a systematically decreases with increasing AgPbSbTe₃ content, shrinking from 6.326 Å for pristine SnTe to 6.267 Å for the x = 0.25 sample (Figure S4, Supporting Information). Similarly, the refined 2θ value of the (200) plane follows the same trend observed in the XRD patterns (Figure S4, Supporting Information). These findings confirm that AgPbSbTe₃‐alloying induces lattice contraction. According to Lange's Handbook of Chemistry, the ionic radii of Ag⁺ (1.15 Å) and Pb²⁺ (1.19 Å) are close to that of Sn²⁺ (1.18 Å), whereas Sb³⁺ (0.76 Å) has a significantly smaller ionic radius.^{[ 62 ]} Thus, the primary cause of the lattice contraction is attributed to the incorporation of Sb. However, the degree of contraction observed suggests that additional factors may also contribute, warranting further investigation.

XRD analysis confirms the presence of a pure phase with no detectable secondary phases. This finding contradicts the initial assumption that Ag₂Te precipitates would form due to the differing chemical bonding mechanisms between the two phases, which typically result in low miscibility.^{[ 26 ]} To further investigate, STEM and energy‐dispersive spectroscopy (EDS) were employed to analyze the microstructure and elemental distributions in (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20, as shown in Figure S5 (Supporting Information). The results reveal regions with significant contrast differences, indicating the formation of abundant lath‐shaped Widmannstätten nanoprecipitates.^{[ 29 ]} EDS analysis confirms that these nanoprecipitates are enriched in Ag and Te, corresponding to the Ag₂Te compound, as determined through quantitative analysis (Figure S6, Supporting Information). In contrast, the SnTe matrix exhibits a uniform distribution of all elements, with SnTe identified as the main phase. The apparent discrepancy between the XRD and STEM results arises because the Ag₂Te nanoprecipitates form in situ within the SnTe grains, making them undetectable by XRD. The exsolution of Ag₂Te nanoprecipitates from the matrix leads to a deviation of the actual chemical composition from the nominal stoichiometry, resulting in the formation of numerous cation vacancies. These vacancies further contribute to the observed reduction in the a.

The complex microstructure arising from the distinct chemical bonding mechanisms between SnTe and Ag₂Te plays a critical role in governing thermoelectric performance. To investigate the defects in the nanoprecipitates and the interface characteristics of the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample, TEM characterization was performed. The HAADF‐STEM image (Figure 2a) reveals nanoprecipitates embedded within the matrix. These nanoprecipitates exhibit an intensive, lath‐shaped Widmannstätten structure (Wid laths), with lengths of ≈400–500 nm and widths of 50–100 nm, uniformly distributed throughout the matrix. EDS analysis identifies these Wid laths as Ag₂Te nanoprecipitates, consistent with the low‐resolution HAADF‐STEM results shown in Figure S5 (Supporting Information). High‐resolution STEM images in Figure 2b,c further highlight distinct phases separated by a well‐defined interface. EDS mapping of Figure 2c (presented in Figure S7, Supporting Information) confirms that the region to the left of the interface corresponds to the Ag₂Te Wid laths, while the region to the right represents the SnTe matrix. Additionally, twin bands were observed in the Ag₂Te Wid laths region (marked with a yellow oval), a feature that is relatively rare in Ag₂Te precipitates reported in previous studies.^{[ 30 ]} These unique twin structures may have significant implications for the thermoelectric properties of the material.^{[ 63 ]}

Figure 2.

TEM microstructural characterization of (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample. a) Low‐resolution scanning transmission electron microscopy (STEM) imaging and energy‐dispersive spectroscopy (EDS) elemental mapping for Sn, Te, Ag, Pb, and Sb. b) High‐resolution imaging reveals distinct contrasts separated by a well‐defined interface. c) High‐resolution STEM image highlights the interface and twin bands within the nanoprecipitates. d) High‐resolution STEM image displays the atomic‐scale microstructure. e) Fast Fourier transform (FFT) analysis of d shows the diffraction patterns corresponding to SnTe and Ag₂Te phases. f) Close‐up of the matrix region reveals an atomic configuration consistent with cubic SnTe. Insets include FFT analysis and interplanar spacing measurements. g) Atomic‐scale imaging of the nanoprecipitate region reveals a twin interface. h) A magnified image of g shows an atomic arrangement that aligns well with the Ag₂Te atomic model along the [$0\overline{2}1$]direction. i) Atomic‐scale EDS mapping illustrates the elemental distribution within the region.

To investigate the phase structures of the matrix and nanoprecipitates, as well as their interface characteristics and crystallographic orientation relationships, atomic‐resolution STEM analysis was performed. Figure 2d shows a region encompassing both phases, their interface, and twin structures, each with distinct atomic configurations. A transition zone spanning several atomic layers is observed near the interface, indicating local lattice strain.^{[ 64 ]} This strain originates from minor lattice distortions in one phase to accommodate the crystal planes of the adjacent phase. The fast Fourier transform (FFT) of Figure 2d, presented in Figure 2e, reveals complex diffraction patterns containing three distinct sets of crystallographic information. The diffraction pattern within the yellow square corresponds to cubic SnTe along the [001] direction, as confirmed by the close‐up atomic‐scale image, which matches well with the SnTe atomic model (Figure 2f). Meanwhile, the diffraction patterns in the red and blue rectangles correspond to monoclinic Ag₂Te and its twin along the [$0\overline{2}1$] direction, respectively. Further FFT analysis of the Ag₂Te and its twin regions corroborates these observations, as shown in Figures 2g and S8 (Supporting Information). In this direction, Ag₂Te exhibits a unique planar atomic structure characterized by triatomic layers separated by significant interlayer gaps. Within this arrangement, Ag atoms occupy the central atomic plane exclusively, while Ag and Te alternate on the adjacent planes. Comparison with the Ag₂Te atomic model (Figure 2h) and atomic‐scale EDS mapping (Figure 2i) confirms that the nanoprecipitates are monoclinic Ag₂Te, belonging to the P2₁/c space group, which represents the thermodynamically stable structure at temperatures below ≈413 K.^{[ 65 ]} The SnTe matrix is oriented along the [001] direction, while Ag₂Te nanoprecipitates are aligned along the [$0\overline{2}1$] direction. The (200) plane of SnTe (d‐spacing = 3.217 Å, inset in Figure 2f) connects with the (200) plane of Ag₂Te (d‐spacing = 3.387 Å), resulting in a lattice mismatch of ≈5%. This mismatch induces lattice distortion, forming the observed transition zone, which facilitates structural compatibility between the two phases. However, the observed [$0\overline{2}1$]_Ag2Te does not represent the simplest atomic configuration, complicating the interpretation of the phase relationship. Further analysis is needed to fully understand this complexity and its implications for the overall system.

To analyze the orientation relationships between the SnTe matrix and Ag₂Te nanoprecipitates, the zone axis was regulated to better understand the growth mechanism of the lath‐shaped Widmannstätten structure. Figure 3a shows the atomic configuration, revealing a well‐defined interface separating the SnTe matrix from the Ag₂Te nanoprecipitate. FFT analysis indicates that the left region corresponds to cubic SnTe along the [$1\overline{1}0$] direction (Figure 3b), while the right region aligns with the atomic model of monoclinic Ag₂Te along the [010] direction. This establishes the crystallographic orientation relationship as [$1\overline{1}0$]_SnTe‖[010]_Ag2Te. Notably, the [010] orientation of Ag₂Te is derived from a rotation of the [$0\overline{2}1$] direction around the a‐axis, which is indicated by the crystal structure visualization and analysis tool. Interestingly, this crystallographic orientation relationship has also been observed in the PbTe‐Ag₂Te system.^{[ 37 ]} We speculate that PbTe and SnTe share the same rock‐salt structure with the space group of $\mathrm{Fm}\overline{3}m$, and Pb²⁺ and Sn²⁺ have similar ionic radius, which creates similar conditions for the growth of Ag₂Te. In addition, two types of interfaces are observed between the SnTe matrix and Ag₂Te nanoprecipitates: the “parallel type” and the “twin type.” Figure 3c highlights the “parallel type” interface, showing the structural transition from the triple‐layer motif of Ag₂Te, aligned with the (200) plane, to the alternating Sn‐Te motif parallel to the (002) plane, forming the relationship (002)_SnTe‖(200)_Ag2Te. Atomic models in Figure 3d further illustrate this interface structure, where the central Ag atom layer in the triple‐layer motif of Ag₂Te aligns with the interstitial sites in SnTe. Similarly, Ag atoms on adjacent planes correspond to Sn atom positions, while Te atoms transition seamlessly across the interface from Ag₂Te to SnTe. The interplanar distance of the (200) plane in Ag₂Te is 3.387 Å, while the (002) planes in SnTe have a slightly smaller value of 3.217 Å. This minor lattice mismatch induces a transition zone, facilitating a pseudo‐coherent interface that determines the habit plane for Ag₂Te growth.

Figure 3.

Interface structural characterization by TEM for (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample. a) Atomic‐resolution image showing the crystallographic orientation relationship between the SnTe matrix and Ag₂Te nanoprecipitates, with two types of interfaces identified: “parallel type” and “twin type.” b) FFT analysis of area 1 reveals the diffraction pattern of SnTe along the [$1\overline{1}0$] direction. c) Atomic structure of the “parallel type” interface. d) Atom model illustrating the interface connection. e) The intensity profile scanned along the blue arrow spans the interface from SnTe to Ag₂Te, revealing compositional transitions. f) Atomic structure of the “twin type” interface. g) Schematic diagram illustrates phonon scattering mechanisms at the interfaces. h) Geometric phase analysis (GPA) of the “twin type” interface highlights the presence of local strain at the interfaces. Figure c,f are captured from distinct, high‐resolution regions in the same sample where the atomic arrangements at the respective “parallel type” and “twin type” interfaces could be clearly resolved, not the close‐up images of figure a.

Figure 3e presents the intensity profile scanned across the interface from SnTe to Ag₂Te along the direction parallel to (002)_SnTe and (200)_Ag2Te, as indicated in Figure 3c. The profile reveals an interplanar distance of 2.292 Å corresponding to the (220) plane of SnTe, and 2.255 Å corresponding to the ($\overline{2}04$) plane of Ag₂Te. This observation confirms the presence of an additional interface characterized by the relationship (220)_SnTe‖($\overline{2}04$)_Ag2Te, exhibiting complete coherence. Further analysis of the interface, as shown in Figure S9a (Supporting Information), indicates a transition from the (002)_SnTe‖(200)_Ag2Te interface to the (220)_SnTe‖($\overline{2}04$)_Ag2Te interface. In Figure S9b (Supporting Information), a lath‐shaped Ag₂Te nanoprecipitate is observed to be interspersed within the SnTe matrix, viewed along the [$1\overline{1}0$]_SnTe‖[010]_Ag2Te direction, with a schematic atomic model provided in Figure S9c (Supporting Information). The analysis shows that the (220)_SnTe‖($\overline{2}04$)_Ag2Te interface occupies a significant portion of the nanoprecipitate, suggesting that Ag₂Te predominantly grows along the [001] direction. This specific growth direction is attributed to the differing structural characteristics of the interfaces. The long axis of the lath‐shaped nanoprecipitate, spanning several hundred nanometers, aligns with the (220)_SnTe‖($\overline{2}04$)_Ag2Te interface exhibiting complete coherence and minimal interfacial energy, which restricts growth in this direction. In contrast, the shorter dimension, measuring tens of nanometers, corresponds to (002)_SnTe‖(200)_Ag2Te interface with lattice mismatch and higher interfacial energy, facilitating growth in this direction. This anisotropic growth behavior accounts for the formation of the lath‐shaped Widmannstätten nanoprecipitates and is strongly influenced by the orientation relationships and interfacial compatibility between the SnTe matrix and Ag₂Te nanoprecipitates.

Mirrored Ag₂Te nanoprecipitates with distinct twin structures are also observed, indicating that the twin bands identified in Figure 2c primarily consist of Ag₂Te. As previously discussed, the small lattice mismatch between (200)_Ag2Te and (002)_SnTe generates elastic strain energy, which drives the spontaneous formation of twin Ag₂Te nanoprecipitates. These twins form “twin‐type” interfaces, as shown in Figure 3f, which enhance coherence between the two phases, thereby improving interfacial compatibility and stability.^{[ 64 ]} Figure 3g provides a schematic representation of the twin boundaries in Ag₂Te and their associated “twin‐type” interfaces. These interfaces induce localized strain, as revealed by geometric phase analysis (GPA) in Figure 3h, which effectively enhances phonon scattering. Additionally, dislocations are observed at the interfaces and near the Ag₂Te nanoprecipitates (Figure S10, Supporting Information). The formation of intensive Widmannstätten nanoprecipitates introduces a high intensity of phonon scattering centers and creates a large interfacial area, significantly enhancing phonon scattering. These structural features play a critical role in effectively suppressing κ _L, thereby improving thermoelectric performance.

2.2. Effect of Microstructure on Thermoelectric Performance

The thermoelectric performance of all (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x samples is systematically analyzed, with a focus on the effects of incorporation of AgPbSbTe₃ and the formation of intensive Widmannstätten nanoprecipitates. Figure 4a presents the temperature‐dependent κ for all samples, showing a clear reduction in κ with increasing AgPbSbTe₃ content. For instance, the room‐temperature κ decreases from 7.29 W m⁻¹ K⁻¹ for pristine SnTe to 3.77 W m⁻¹ K⁻¹ for the x = 0.05 sample, and further to 1.17 W m⁻¹ K⁻¹ for the x = 0.25 sample. This significant decrease in κ indicates effective suppression of thermal transport, contributing to enhanced thermoelectric performance. The κ consists of contributions from lattice vibrations (κ _L) and carrier transport (κ _e). The latter is estimated using the Wiedemann–Franz law, κ _e = LσT, where L is the Lorenz number, calculated using the universal formula L = 1.5 + exp(−|S|/116).^{[ 66 ]} Figure S11 (Supporting Information) shows the temperature‐dependent curves for L and κ _e. By subtracting κ _e from the total κ, the κ _L as a function of temperature is determined. As depicted in Figure 4b, the κ _L exhibits a similar decreasing trend to κ, gradually reducing with higher AgPbSbTe₃ content. For example, at room temperature, the κ _L decreases by ≈79%, from 2.95 W m⁻¹ K⁻¹ for pristine SnTe to 0.62 W m⁻¹ K⁻¹ for the x = 0.25 sample. Notably, the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample achieves a minimum κ _L of 0.32 W m⁻¹ K⁻¹ at 773 K. This value is lower than the theoretically predicted κ _Lmin of 0.4 W m⁻¹ K⁻¹, calculated using the Debye–Cahill model,^{[ 67 ]} and closely matches the estimated value based on the diffusion model incorporating the Born–Karmann approximation (Figure 1d).^{[ 68 ]} A comparison of κ _L versus temperature between this work and data from the literature is presented in Figure 4c.^{[ 41} , ⁴² , ⁴³ , ⁴⁴ , ⁴⁵ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ⁴⁹ , ^{50 ]} The results demonstrate that the κ _L achieved in this study is lower than those reported for most SnTe‐based materials, underscoring the effectiveness of nanoprecipitate engineering in suppressing κ _L.

Figure 4.

Thermal and electrical transport performance of (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x samples. Temperature dependence of a) total thermal conductivity (κ) and b) lattice thermal conductivity (κ _L). c) Temperature‐dependent κ _L of this work compared to previously reported works.^{[ 41} , ⁴² , ⁴³ , ⁴⁴ , ⁴⁵ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ⁴⁹ , ^{50 ]} Temperature dependence of d) electrical conductivity (σ) and e) Seebeck coefficient (S). f) Schematic diagram of band convergence and energy filtering effect. g) Pisarenko relationship calculated using a single parabolic band (SPB) model. h) Power factor (S ² σ) as a function of temperature. i) Relationship between S ² σ and 1/κ _L at 300 and 723 K in this work, compared with values reported in the literature.^{[ 36} , ⁴² , ⁴³ , ⁴⁵ , ⁴⁸ , ⁴⁹ , ⁵⁰ , ^{69 ]}

The reduction in κ _L is primarily attributed to the manipulation of phonon transport achieved through sophisticated microstructural modifications. Specifically, the dominant mechanism involves strong interfacial phonon scattering facilitated by intensive Widmannstätten nanoprecipitates, which can be explained by two key factors. First, classical scattering theory indicates that the scattering rate of phonons is influenced by the intensity of scattering sources and the effective scattering cross‐section. TEM analysis reveals that AgPbSbTe₃‐alloying promotes the exsolution of Ag₂Te nanoprecipitates from the SnTe matrix, forming intensive Widmannstätten structures (Figure S5, Supporting Information). The high intensity of these nanoprecipitates significantly increases the concentration of phonon scattering centers. Additionally, the lath‐shaped morphology of the nanoprecipitates provides a much larger interfacial area compared to spherical counterparts.^{[ 29 ]} This simultaneously increases the intensity of scattering centers and the effective scattering cross‐section, making this morphology more effective in phonon scattering. Second, the change in chemical bonding leads to distinct variations in physical properties,^{[ 70 ]} which in turn intensify interfacial phonon scattering. SnTe is characterized by metavalent bonding,^{[ 36 ]} while Ag₂Te exhibits iono‐covalent bonding.^{[ 37 ]} This bonding transition across the interface induces a pronounced contrast in local force constants, which significantly affects phonon dispersion, as illustrated by a simplified model of semi‐infinite 1D chains.^{[ 71 ]} These bonding‐induced disparities result in phonon dispersion mismatch, thereby promoting stronger phonon scattering at the interfaces.

Several additional factors also contribute to the suppression of κ _L: i) The alloying of AgPbSbTe₃ introduces point defects, which generate significant mass and strain field fluctuations at the atomic level. These effectively scatter high‐frequency phonons. ii) The formation of dislocations and twin structures enhances phonon scattering. iii) The increased concentration of cation vacancies removes electrons from bonding states, leading to lattice softening.^{[ 49 ]} iv) The heavier atomic masses of the dopants (Pb and Sb) compared to the host element Sn slow down phonon transport. The latter two effects are further evidenced by the reduction in sound velocity (v) with increasing AgPbSbTe₃ content, as shown in Figure S12 (Supporting Information). These combined factors provide a comprehensive explanation for the significant suppression of κ _L and underscore the effectiveness of intensive Widmannstätten nanoprecipitates in improving thermoelectric performance.

For electrical transport properties, the precipitation of Ag₂Te introduces abundant cationic vacancies that act as acceptors, contributing holes to the matrix and significantly increasing the n _H, as shown in Figure S13a (Supporting Information) (upper panel). The enhanced n _H is dominated by the regulation of Sn vacancies due to the AgPbSbTe₃ alloying belong to the charge‐balanced doping, which Pb²⁺ acts as an isovalent dopant, Ag⁺ and Sb³⁺ doping effects counterbalance each other without yielding any net charge carriers to the first order. Traditional strategies for improving ZT often focus on aliovalent doping or increasing the formation energy of Sn vacancies to reduce the n _H, thereby enhancing the S.^{[ 36 ]} However, this approach often overlooks the critical role of n _H in determining σ, as doping typically induces impurity scattering, which reduces the µ _H.^{[ 36 ]} In this study, the interface characterizations between the matrix and nanoprecipitates exhibit coherent arrangements. This may primarily scatter phonons with minimal impact on carrier transport. However, the AgPbSbTe₃ alloying introduces exotic elements into the matrix, which creates a structurally ordered but chemically disordered system to increase carrier scattering.^{[ 27 ]} Consequently, the µ _H decreases with the increasing AgPbSbTe₃ content (Figure S13a, Supporting Information, lower panel). Under these conditions, increasing n _H becomes crucial to offset the negative effect of reduced µ _H on σ. By optimizing the Ag‐to‐Sb ratio, a remarkable room‐temperature σ of 166 919 S m⁻¹ is achieved in the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample (Figure 4d). This value is exceptional among mid‐temperature thermoelectric materials and plays a significant role in achieving high thermoelectric performance.

Figure 4e presents the S as a function of temperature for (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x samples. It is observed that S increases with higher AgPbSbTe₃ content. For instance, the room‐temperature S increases from 31 µV K⁻¹ for the pristine SnTe to 115 µV K⁻¹ for the (SnTe)_0.75(AgPbSbTe₃)_0.25 sample. Notably, this trend contradicts the conventional relationship where S is inversely proportional to n _H. For degenerate semiconductors, the S is also proportional to the effective mass ($m_{\mathrm{d}}^{\ast }$), as described by the Pisarenko relationship:^{[ 15 ]}

$$S=\frac{8{\pi }^2{k}_{\mathrm{B}}^2}{3e{h}^2}{m}_{\mathrm{d}}^{\ast }T{\left(\frac{\pi }{3n_{\mathrm{H}}}\right)}^{2/3}$$ (1)

where e is the electron charge and h is the Planck constant. The Pisarenko curve for pristine SnTe, calculated using a two‐band model, is displayed in Figure S14a (Supporting Information), alongside literature data for comparison. Pristine SnTe aligns well with the calculated curve, whereas alloyed samples deviate above the line, indicating an increased $m_{\mathrm{d}}^{\ast }$ upon AgPbSbTe₃‐alloying. As illustrated in Figure 4f, two factors contribute to the enhancement of $m_{\mathrm{d}}^{\ast }$: i) Band convergence induced by AgPbSbTe₃ alloying, which is indicated by the density functional theory (DFT) calculations of band structures, as shown in Figure S15 (Supporting Information), and ii) carrier energy filtering effects at the matrix‐nanoprecipitate interfaces.^{[ 72 ]} The S‐n _H relationship, fitted using the single parabolic band (SPB) model under the assumption of acoustic phonon scattering, further reveals a gradual increase in $m_{\mathrm{d}}^{\ast }$ with higher AgPbSbTe₃ content. As shown in Figure 4g and Figure S17 (Supporting Information), $m_{\mathrm{d}}^{\ast }$ increases from 0.86 m ₀ for SnTe to 4.46 m ₀ for the x = 0.20 sample and further to 7.50 m ₀ for the y = 0.05 sample. The significant increase in $m_{\mathrm{d}}^{\ast }$ after regulating the Ag‐to‐Sb ratio stems from the enhanced n _H, which shifts the Fermi level deeper into the valence band. This shift allows for the activation of deeper valence bands, increasing band degeneracy (N _v). The significant increase in $m_{\mathrm{d}}^{\ast }$ offsets the adverse impact of high n _H on S, resulting in a S of 186 µV K⁻¹ at 723 K for the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample. Furthermore, despite the optimized Ag‐to‐Sb ratio slightly reduces S at lower temperatures due to the enhanced n _H, their efficacy in suppressing the bipolar effect maintains high S values across elevated temperatures.

The AgPbSbTe₃‐alloying achieves both a high σ and an optimized S, leading to a significant enhancement in S ² σ, particularly at elevated temperatures (Figure 4h). A maximum S ² σ of 27.0 µW cm⁻¹ K⁻² at 723 K is observed in the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample, which is more than double the S ² σ of pristine SnTe (12.5  µW cm⁻¹ K⁻² at 723 K). Comparisons with literature data reveal that the S ² σ values in this study surpass those reported for many advanced SnTe‐based alloys (Figure S18, Supporting Information). The combined effects of substitutions and the formation of intensive Widmannstätten nanoprecipitates enable the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample to achieve both an optimized S ² σ of 10.7  µW cm⁻¹ K⁻² and a reduced κ _L of 0.80 W m⁻¹ K⁻¹ at 300 K (Figure 4i). At 723 K, the sample maintains a high S ² σ of 27.0 µW cm⁻¹ K⁻² and a further reduced κ _L of 0.35  W m⁻¹ K⁻¹ (Figure 4i). These results demonstrate the synergistic contributions of AgPbSbTe₃ and nanoprecipitate engineering to enhancing thermoelectric performance.

Achieving a high ZT value requires precise regulation of complex interactions among defects, carriers, and phonons. The overall influence of microstructural modifications on thermoelectric performance is evaluated using the thermoelectric quality factor (β), which quantifies the balance between electrical and thermal transport properties. Notably, the β is independent of n _H optimization, providing a direct measure of the effectiveness of structural enhancements. The β factor is defined as:^{[ 73 ]}

$$\beta ={\left(\frac{k_{\mathrm{B}}}{e}\right)}^2\frac{8\pi e{\left(2m_0{k}_{\mathrm{B}}T\right)}^{3/2}T}{3h^3}\frac{{\mu }_{\mathrm{W}}}{{\kappa }_{\mathrm{L}}}$$ (2)

where m ₀ is the electron mass and µ _W is the weight mobility, a descriptor of the ability of electrical transport properties. The µ _W is defined as a function of the measured S and the electrical resistivity (ρ):^{[ 73 ]}

$$\begin{array}{ccc}\hfill {\mu }_{\mathrm{W}}& =& 331\frac{{\mathrm{cm}}^2}{\mathrm{Vs}}\left(\frac{\mathrm{m}\mathrm{\Omega }\mathrm{cm}}{\rho }\right){\left(\frac{T}{300\mathrm{K}}\right)}^{-3/2}\hfill \\ & & \left[\frac{\exp \left[\frac{\left|S\right|}{k_{\mathrm{B}}/e}-2\right]}{1+\exp \left[-5\left(\frac{\left|S\right|}{k_{\mathrm{B}}/e}-1\right)\right]}+\frac{\frac{3}{{\pi }^2}\frac{\left|S\right|}{k_{\mathrm{B}}/e}}{1+\exp \left[5\left(\frac{\left|S\right|}{k_{\mathrm{B}}/e}-1\right)\right]}\right]\hfill \end{array}$$ (3)

Figure 5a illustrates the variation in the β with increasing AgPbSbTe₃ content (β vs. temperature is shown in Figure S19, Supporting Information). The results indicate a significant enhancement in β for the alloyed samples compared to pristine SnTe, particularly at higher temperatures. For instance, the β of pristine SnTe is 0.25 at 723 K, which increases to 0.99 for the x = 0.20 sample and further rises to 1.40 with a higher Ag‐to‐Sb ratio. Notably, the β is temperature‐dependent and directly proportional to µ _W/κ _L, emphasizing the decoupling of electrical and thermal transport properties. Specifically, the µ _W/κ _L values at 300 and 723 K are highlighted in Figure 5a, showing an increase from 81 (300 K) and 41 (723 K) for pristine SnTe to 211 (300 K) and 230 (723 K) for the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 sample. These findings demonstrate that element‐doping, combined with the formation of intensive Widmannstätten nanoprecipitates, effectively suppresses phonon transport while maintaining excellent electrical performance. Advanced characterization techniques such as spatially resolved frequency‐domain thermoreflectance (FDTR) and correlative EBSD–PPMS–APT measurements enable direct probing of interfacial effects on phonon and carrier transport, respectively.^{[ 74} , ^{75 ]} While these methods provide valuable insights, their implementation requires specialized instrumentation and expertise beyond our current capabilities. Nevertheless, studies on TAGS–Ag₂Te systems have demonstrated that interfacial bonding contrasts between the matrix and precipitates can significantly enhance phonon scattering, thereby reducing κ _L.^{[ 76 ]} Furthermore, comparative analyses of direct current (DC) and optical conductivity offer complementary insights into interfacial charge transport, owing to their sensitivity to distinct carrier relaxation mechanisms and frequency‐dependent responses. These approaches represent promising directions for future investigation.

Figure 5.

Performance evaluation of (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x samples. a) Composition‐dependent thermoelectric quality factor (β) at 723 K, and the ratio of weight carrier mobility to lattice thermal conductivity (µ _W/κ _L) at 300 and 723 K, respectively. b) ZT as a function of temperature. c) ZT as a function of temperature for this work compared to data reported in the literature.^{[ 27} , ³⁶ , ⁴³ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ⁵⁰ , ⁵¹ , ⁵² , ⁵⁴ , ⁵⁶ , ⁵⁷ , ⁵⁸ , ^{77 ]} d) Relationships among ZT, reduced Fermi energy (η _Fer), and β, show the optimal doping level. Current‐dependent e) output power (P) and f) energy‐conversion efficiency (η) of a single‐leg (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x device under various ΔTs.

Figure 5b shows the temperature‐dependent ZT for the studied samples. A maximum ZT value of 1.5 at 723 K is achieved in (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20, which is higher than that of pristine SnTe (ZT = 0.2 at the same temperature). This value is comparable to or surpasses most advanced SnTe‐based materials at similar temperatures (Figure 5c).^{[ 27} , ³⁶ , ⁴³ , ⁴⁶ , ⁴⁷ , ⁴⁸ , ⁵⁰ , ⁵¹ , ⁵² , ⁵⁴ , ⁵⁶ , ⁵⁷ , ⁵⁸ , ^{77 ]} The significant ZT enhancement is mainly attributed to the intensive Widmannstätten nanoprecipitates, which substantially increase phonon scattering, leading to a dramatic reduction in κ _L while maintaining excellent electrical performance. To better understand the enhanced performance, the relationships between ZT, β, and the reduced Fermi level (η _Fer) were evaluated (Figure 5d). For pristine SnTe, deviations in η _Fer from the optimal value and a lower β contribute to its limited ZT at both 300 and 723 K. In contrast, AgPbSbTe₃‐alloying shifts the η _Fer toward the optimal range and increases the β, demonstrating that the optimized n _H and enhanced $m_{\mathrm{d}}^{\ast }$ significantly contribute to the improved ZT. Moreover, tuning the Ag‐to‐Sb ratio effectively suppresses the detrimental bipolar effect at higher temperatures, ensuring a high ZT across a broader temperature range. This leads to a notable improvement in the ZT _ave, as shown in Figure S21 (Supporting Information). A maximum ZT _ave of 0.90 between 300 and 823 K is achieved for (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20. Remarkably, a higher ZT _ave of ≈1.1 is obtained over the temperature range of 423–823 K, making this material highly suitable for mid‐temperature applications. Comparisons with literature further validate the state‐of‐the‐art ZT _ave achieved in this work (Figure 1e).^{[ 27} , ³⁶ , ⁴³ , ⁴⁴ , ⁴⁷ , ⁴⁸ , ⁵⁰ , ⁵¹ , ⁵² , ⁵³ , ⁵⁴ , ⁵⁵ , ⁵⁶ , ⁵⁷ , ^{58 ]} These findings underscore the effectiveness of in situ generation of intensive Widmannstätten nanoprecipitates in SnTe for achieving high‐performance thermoelectric applications. Despite trace amounts of Pb are introduced, its content is reduced by an order of magnitude relative to conventional lead‐chalcogenides. This approach reflects a deliberate effort to mitigate toxicity concerns while acknowledging the inherent trade‐off between environmental impact and thermoelectric performance, as achieving high ZT values remains critical for practical applications.

2.3. Mechanical Property and Device Performance

The mechanical properties of thermoelectric materials are critical for their manufacturability, operational stability, and economic feasibility. In this study, the in situ generation of intensive Widmannstätten nanoprecipitates in SnTe significantly improves mechanical strength. As shown in Figure S25a (Supporting Information), the Vickers hardness increases from 50 kgf mm⁻² for pristine SnTe to 135 kgf mm⁻² for (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20. Meanwhile, the compressive strength increases with the rising content of AgPbSbTe₃ alloying (Figure S25b, Supporting Information), showing a trend consistent with that of Vickers hardness. It is well established that the mechanical strength of polycrystalline alloys primarily arises from lattice resistance to dislocation motion. In this work, the incorporation of AgPbSbTe₃ contributes to both secondary strengthening and solid solution strengthening, effectively impeding dislocation movement and thus enhancing both the Vickers hardness and compressive strength. Interestingly, although an increase in Vickers hardness is often associated with a reduction in fracture toughness, our results show that the fracture toughness remains nearly unchanged with increasing AgPbSbTe₃ content, within the measurement uncertainty (Figure S25c, Supporting Information), which phenomenon is different from the observation in PbTe.^{[ 78 ]} Generally, the fracture toughness depends on organization structure, chemical composition, and internal stress. Therefore, this stability is likely due to the formation of intensive nanoprecipitates, which induce microstructure change and hinder the propagation of microcracks, thereby maintaining fracture toughness. Such improvements enhance material durability and processability, making it more suitable for practical thermoelectric applications.

To leverage enhanced thermoelectric performance and mechanical strength, a single‐leg device was fabricated using the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.2 sample, and its performance was evaluated on a custom‐built measurement platform. Figure S26 (Supporting Information) illustrates the relationship between current (I) and open‐circuit voltage (U) at various temperature differences (ΔT), with the cold‐side temperature (T _c) fixed at 285 K. The open‐circuit voltage (U) decreases linearly with increasing I and rises significantly as ΔT increases from 250 to 450 K. The dependence of output power (P) and η on I under different ΔTs is shown in Figure 5e,f, respectively. Both P and η initially increase with rising I, reaching a peak when the external load resistance (R _load) matches the internal resistance (R _in), and then decline. Under a ΔT of 450 K, the single‐leg device achieves a peak ω of 221 mW cm⁻² and a maximum η of 7.22%. However, the experimental η is lower than the theoretical prediction of 9.08%, likely due to factors such as imperfect soldering, heat losses in the experimental setup, deviations from ideal thermoelectric behavior, inaccuracies in device dimensions, and measurement errors.^{[ 79 ]} Addressing these challenges will require advancements in fabrication techniques and the development of more accurate testing methodologies to fully realize the material's theoretical potential. Furthermore, a two‐pair TE module is also fabricated based on this sample (p‐type leg) and the PbTe‐based material (n‐type leg), which indicates a peak P of 137 mW and a maximum η of 4.26% under a ΔT of 450 K. as shown in Figure S27 (Supporting Information).

3. Conclusion

In this study, the (SnTe)_{1− x} (Ag_{1+ y} PbSb_{1− y} Te₃) _x system was synthesized to explore its structural evolution and impact on thermoelectric performance. High‐intensity Ag₂Te Widmannstätten nanoprecipitates were observed, and their crystallographic orientation relationships between SnTe and Ag₂Te were identified to clarify the nanoprecipitate growth behavior. It was found that the (220) plane of SnTe and the ($\overline{2}04$) plane of Ag₂Te exhibit complete coherence, while the (002) plane of SnTe and the (200) plane of Ag₂Te have a small lattice mismatch. This supports the growth of Ag₂Te nanoprecipitates along the [001] direction, forming their characteristic lath‐shaped morphology. These intensive Widmannstätten nanoprecipitates, combined with point defects and dislocations, significantly enhance phonon scattering, leading to an ultra‐low κ _L of 0.32 W m⁻¹ K⁻¹ at 773 K in the (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 alloy. Furthermore, the exsolution of Ag₂Te from SnTe creates Sn vacancies, increasing the n _H. The introduction of AgPbSbTe₃ also facilitates band convergence, while the high intensity of interfaces induces an energy filtering effect, enhancing the $m_{\mathrm{d}}^{\ast }$. These factors collectively improve the S ² σ. Consequently, (SnTe)_0.80(Ag_1.05PbSb_0.95Te₃)_0.20 achieves a maximum ZT value of 1.5 at 723 K, a state‐of‐the‐art ZT _ave value of 1.1 across 423 to 823 K, and the peak η of 7.22% and 4.26% under a ΔT of 450 K in a single‐leg device and two‐pair module, respectively. These results highlight the critical role of intensive Widmannstätten nanoprecipitates in phonon scattering and ZT enhancement in SnTe, presenting a promising pathway for high‐performance thermoelectric materials and applications, particularly in chalcogenides.

Conflict of Interest

The authors declare no conflict of interest.

Supporting information

Supporting Information

Lyu T., Shi X.‐L., Hu L., et al. “Intensive Widmannstätten Nanoprecipitates Catalyze SnTe With State‐of‐the‐Art Thermoelectric Performance.” Adv. Mater. 37, no. 33 (2025): 37, 2503918. 10.1002/adma.202503918

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.