Structural, thermal, and radiation shielding properties of antimony-doped zinc borate glasses

Abstract

Antimony zinc borate glasses with compositions (45–m)ZnO–(55–n)B₂O₃–(m + n)Sb₂O₃ (0 ≤ m, n ≤ 15 mol%) were synthesized via the melt-quenching technique to investigate the impact of Sb₂O₃ substitution on structural, thermal, and radiation shielding properties. X-ray diffraction confirmed the amorphous nature of the synthesized glass samples. Fourier-transform infrared spectroscopy revealed significant structural rearrangements, including an increase in non-bridging oxygen content with rising Sb₂O₃ concentrations, as evidenced by the shifting and intensification of characteristic absorption bands. Differential thermal analysis demonstrated that the glass transition temperature decreased from 580 °C to 490 °C with increasing Sb₂O₃, while the thermal stability parameter (ΔT) improved from 144 °C to 256 °C, particularly when B₂O₃ was replaced. Density increased from 3.121 g/cm³ to 3.836 g/cm³, and molar volume expanded from 24.01 cm³/mol to 31.16 cm³/mol. Radiation shielding performance was significantly enhanced: at 10 MeV, the linear attenuation coefficient increased from 0.0768 cm⁻¹ to 0.1142 cm⁻¹ (~ 49%) when replacing B₂O₃ and to 0.0983 cm⁻¹ (~ 28%) when replacing ZnO. The half-value layer decreased from 9.02 cm to 6.07 cm at 15 mol% Sb₂O₃, confirming improved photon attenuation. Overall, this work offers valuable insights into the interplay between composition, structure, and functional properties in Sb₂O₃-doped zinc borate glasses.

https://orcid.org/0000-0001-6425-936X.

Introduction

The pursuit of advanced materials for radiation shielding and related applications has driven significant research interest in specialized glass compositions. Borate glasses have emerged as particularly promising candidates due to their exceptional versatility in accommodating various structural modifications while maintaining desirable properties such as high thermal stability, superior glass-forming ability, and remarkable optical transmission characteristics^1,2. These fundamental attributes, combined with their relatively low melting points, position borate glasses at the forefront of materials science innovation, enabling their deployment across diverse technological domains, from optical devices to radiation protection systems³.

The incorporation of zinc oxide into borate glass networks has revolutionized their structural and functional properties, marking a significant advancement in glass engineering. When introduced into the borate network, ZnO exhibits a fascinating dual nature - functioning both as a network modifier and as a network former, according to its coordination environment⁴. As a modifier, it disrupts the continuous B-O-B bonds, creating non-bridging oxygen atoms that significantly influence the glass’s physical properties. Alternatively, when acting as a network former, ZnO forms tetrahedral ZnO₄ units that integrate into the glass network⁵, enhancing structural stability and improving thermal characteristics. This multifaceted behavior offers opportunities to finely tune the overall structural arrangement, thermal expansion, chemical stability, and optical responses of borate-based glass formulations. Consequently, zinc borate glasses, with their relatively low melting point and adaptable structural network, have been employed for plasma display panels, low-temperature co-fired ceramics (LTCC), and numerous high-performance optoelectronic devices^6–8.

Recent investigations have demonstrated the efficacy of incorporating heavy metal oxides such as TeO₂, Bi₂O₃, and PbO into zinc and borate glass matrices to enhance radiation shielding properties, thermal stability, and optical properties^9–12. Notably, these heavy metal oxides can act as both network formers and network modifiers, depending on their coordination environment, thereby offering tunability in optical, mechanical, and radiation-attenuating characteristics. Nevertheless, there remains a continuous demand for identifying alternative heavy metal oxides that can offer comparable or superior multifunctional performance while maintaining cost-effectiveness and ease of processing.

Despite the progress made with TeO₂, Bi₂O₃, and PbO dopants, comparatively fewer investigations have focused on incorporating antimony trioxide (Sb₂O₃) into borate glasses. Sb₂O₃ exhibits heavy metal oxide characteristics, contributing high density, broad optical transmission, and strong radiation attenuation potential^13,14. Although Sb₂O₃ alone has a relatively weak glass-forming ability, its integration into borate networks can significantly alter the structural arrangement and lower the glass transition temperature without sacrificing overall stability^15,16. These attributes suggest that Sb₂O₃-containing glasses could be highly beneficial for applications requiring a combination of excellent thermal stability and radiation shielding performance.

In light of these considerations, the present study aims to examine how substituting Sb₂O₃ for ZnO and B₂O₃ alters the structural, physical, thermal, and radiation-shielding attributes of zinc borate glasses. By adjusting the amount of Sb₂O₃ introduced, we elucidate the underlying structural transformations and correlate these changes with the observed property enhancements. The outcomes of this investigation are anticipated to facilitate the design of next-generation borate-based glasses that combine strong thermal stability with effective radiation protection for emerging technological applications.

Materials and methods

A series of ZnBSb glasses with the nominal composition (45–m)ZnO–(55–n)B₂O₃–(m + n)Sb₂O₃ (m, n = 0–15 mol%) was synthesized via the well-established melt-quench method, as outlined in Table 1. High-purity zinc oxide (ZnO, Reachim), boric acid (H₃BO₃, Etimaden), and antimony trioxide (Sb₂O₃, Sigma-Aldrich) were precisely weighed and homogenized. The batch mixture was preheated in a muffle furnace at 250 °C for one hour to dehydrate boric acid, ensuring complete conversion to boron trioxide (B₂O₃). The resulting dry mixture was then transferred into a standard 60-mL corundum crucible and melted in a SiC rod-heated furnace (model Nabertherm HTCT 01/16 C) at 1280 °C for one hour, thereby facilitating complete fusion. The resulting melts were cast into molds to form ZnBSb glass samples in two different shapes: sticks with dimensions of 5 × 5 × 50 mm³ and disks with a diameter of 30 mm and a thickness of 2.5 mm. The samples were then annealed at 510–590 °C in a SNOL 7.2/900 muffle furnace for ten hours to eliminate any residual stresses. Finally, at a carefully controlled rate of 50 °C per hour, the ZnBSb samples were refrigerated to ambient temperature.

Table 1.

Comprehensive glass chemical composition (mol%), along with density (ρ) and molar volume (V_m) for ZnBSb glasses.

Sample identifier	ZnO	B2O3	Sb2O3	ρ, (g/cm3)	Vm, (cm3/mol)
45Z40B15S	45	40	15	3.836	28.206
30Z55B15S	30	55	15	3.415	31.165
35Z50B15S	35	50	15	3.543	29.091
40Z45B15S	40	45	15	3.699	29.091
45Z45B10S	45	45	10	3.610	26.898
35Z55B10S	35	55	10	3.328	28.823
40Z50B10S	40	50	10	3.461	27.886
45Z50B5S	45	50	5	3.367	25.544
40Z55B5S	40	55	5	3.267	26.145
45Z55B	45	55	0	3.121	24.010

Thermal analysis of the ZnBSb glasses was systematically assessed using a MOM Q-1500 Derivatograf (Paulik-Paulik-Erdey, Hungary) at a constant heating rate of 5 °C per minute for all samples in Pt crucibles, with high-purity α-Al₂O₃ (Thermo Fisher) as a reference. The following characteristic temperatures were recorded from each DTA curve: T_g.t.—the glass transition temperature, T_o – the onset of crystallization (the point at which the exothermic reaction begins), T_p—the peak temperature of crystallization (the maximum reaction rate), and T_m.t.—the melting temperature. These values provide insight into the glass’s thermal stability and crystallization behavior. Further examination of the samples was conducted using a dilatometer (model GT-1000) at a heating rate of 3 °C per minute to determine the glass transition (T_g.t.) temperature, the dilatometric (T_dil) softening point, and the coefficient (CTE) of linear thermal expansion¹⁷. The amorphous structure of the as-prepared glasses and the presence of crystalline phases (detection threshold ~ 2 wt%) after heat treatment were verified using a DRON-3 M diffractometer. The crystallization analysis was further enhanced through field emission scanning electron microscopy (FE-SEM), which provided detailed insights into the morphological characteristics of the heat-treated ZnBSb samples.

Infrared spectral analysis was performed with an FT-IR spectrometer (IRSpirit-X) over the range of 1600–400 cm⁻¹ at a resolution of 2 cm⁻¹ (40 scans, SqrTriangle apodization) using the potassium bromide pellet technique. The density of the ZnBSb glass sample was measured at standard ambient temperature using the Archimedes principle with distilled water as the immersion liquid¹⁸, utilizing a Radwag АЅ analytical balance with 0.0001-gram precision. Density values are reproducible within ± 0.001 g/cm³ for repeated measurements of the same sample. The assessment of the radiation shielding efficacy of the fabricated ZnBSb glasses was accomplished by employing the PSD/Phy-X software¹⁹. This analysis provided theoretical calculations for an array of shielding-related metrics²⁰, including the linear attenuation coefficient (LAC), the tenth-value layer (TVL), the half-value layer (HVL), and the effective atomic number (Z_eff) across gamma-ray energies spanning from 0.015 MeV to 15 MeV. These parameters were used to evaluate the impact of Sb₂O₃ content on the attenuation capabilities of the ZnBSb glasses.

Results and discussion

Structural analysis

The utilization of X-ray diffraction analysis in the examination of ZnBSb glass specimens has led to the discernment of their amorphous structural nature, as illustrated by the XRD patterns displayed in Fig. 1a. The diffractogram manifests a distinctive broad hump traversing the 2-theta range of 27° to 42°²¹, a phenomenon that contrasts with the sharp, well-defined peaks commonly observed in crystalline materials. This feature is a hallmark of amorphous glassy structures, where atoms are arranged in a disordered, non-crystalline configuration. Regarding the coloration effect, the images of the ZnBSb glass samples in Fig. 1b show a progressive yellowing as the Sb₂O₃ content increases. The base zinc-borate (45ZnO·55B₂O₃) glass is clear, but with the introduction of Sb₂O₃, the samples acquire a yellow tint that becomes more pronounced with higher Sb₂O₃ concentrations.

Fig. 1.

XRD results and corresponding visual representation of ZnBSb glass samples.

Figure 2 depicts the FT-IR absorption spectra of 45ZnO·55B₂O₃ glass and its modifications resulting from the replacement of varying amounts of ZnO and B₂O₃ with Sb₂O₃. These spectra exhibit prominent absorption bands corresponding (Table 2) to the vibrational modes of the borate network. The bands observed in the spectral region between 1600 and 400 cm⁻¹ are attributed to various borate structural units, including tetrahedral BO₄ and triangular BO₃ groups, as well as vibrations associated with zinc and antimony oxide contributions. The spectra demonstrate systematic changes increasing Sb₂O₃ content, suggesting significant structural rearrangements in the glass matrix. The base 45Z55B glass exhibits characteristic absorption peaks at 1372, 1256, 1084, 1022, 882, 688, 466, and 424 cm⁻¹, associated with BO₄ tetrahedra, BO₃ triangles, B–O–B linkages, and Zn–O vibrations, in agreement with prior studies²².

Fig. 2.

FT-IR spectra of ZnBSb glasses.

Table 2.

Wavenumbers and corresponding assignments for FTIR spectra of ZnBSb samples.

Wavenumber (cm−1)	Assignment	References
1372–1354	Stretching vibrations of non-bridging B–Ø bonds in metaborate units	22,23
1256–1238	Stretching vibrations of bridging B–O bonds in pyroborate units	22,23
1084–1078	Stretching vibrations of B–O bonds in tetrahedral BO4 units from tri-, tetra-, and pentaborate groups	23,24
1022–1012	Stretching vibrations of B–O bonds in tetrahedral BO4 units from diborate groups	22,25
882–878	Symmetric B–O–B stretching of pyroborates dimers	23,26
692–688	B–O–B bending modes of triangular borate units and symmetric stretching vibrations of Sb–O bonds in SbO3 pyramidal structures	27–29
468–466	Bending vibrations of Zn–O bonds within ZnO4 units	24,25
424–418	Vibration of zinc (Zn2+) cations	8,30

The spectra exhibit a series of well-defined absorption bands, which can be assigned to specific vibrational modes based on prior literature. In the high-frequency region (1600 –1200 cm⁻¹), the substitution of B₂O₃ with Sb₂O₃ leads to more pronounced changes in the absorption bands at 1372–1354 cm⁻¹ and 1256–1238 cm⁻¹, corresponding to non-bridging B-Ø bonds in metaborate units and bridging B-O bonds in pyroborate units, respectively. This effect is particularly evident in samples where B₂O₃ content decreases from 55 to 40 mol%, suggesting that Sb₂O₃ preferentially disrupts the borate network connectivity. In contrast, when ZnO is replaced by Sb₂O₃, these bands show more subtle shifts, indicating that zinc’s network-modifying role is gradually assumed by antimony without drastically altering the fundamental borate structure. The presence of BO₄ tetrahedral units is confirmed by characteristic absorption bands in the 1084–1078 cm⁻¹ and 1022–1012 cm⁻¹ ranges, corresponding to B–O stretching vibrations in tri-, tetra- and pentaborate groups, as well as diborate units, respectively. The increase in Sb₂O₃ concentration is associated with a gradual shift of these peaks, suggesting structural rearrangements in the borate framework. The band at 882–878 cm⁻¹, attributed to pyroborate dimers, exhibits enhanced definition with increasing Sb₂O₃ content, particularly in compositions where it replaces B₂O₃. The vibrational modes observed in the 692–688 cm⁻¹ range indicate contributions from B–O–B bending modes in diverse borate triangles, along with symmetric stretching vibrations of Sb–O bonds within SbO₃ pyramids. The appearance of bands associated with Sb–O bonds suggests the integration of antimony into the glass network, leading to structural rearrangements. These findings are consistent with studies on antimony-doped borate glasses, which report similar structural transformations²⁷. Notably, in the low-wavenumber region, bands at about 466 cm⁻¹ correspond to bending vibrations of Zn–O within ZnO₄ units, and the shoulder near 420 cm⁻¹ stems from vibrations of Zn<Superscript>2+</Superscript> cations. Overall, the observed FT-IR spectral trends suggest that Sb₂O₃ incorporation induces a reorganization of the borate network, primarily through the creation of non-bridging oxygens and structural rearrangements in tetrahedral BO₄ and triangular BO₃ units.

Thermal and crystallization behavior

Differential Thermal Analysis (DTA) provides a precise way to examine the thermal behavior of glass materials by measuring the temperature difference between a sample and a reference under identical heating. It reveals key thermal events³¹ - such as glass transition (T_g.t.), crystallization (T_o and T_p), and melting (T_m.t.) - thus offering crucial insights into a glass’s stability and crystallization tendencies.

The DTA curves in Fig. 3 illustrate the influence of Sb₂O₃ on the thermal properties of 45ZnO·55B₂O₃ glass when replacing either ZnO or B₂O₃. As the concentration of Sb₂O₃ increases from 0 to 15 mol% in place of ZnO, a downward trend is observed in both the glass transition (T_g.t.) and the onset of crystallization (T_o) temperatures. For instance, the T_g.t. decreases from 580 °C in the base composition (45Z55B) to 550 °C in the 40Z55B5S sample and subsequently to 495 °C in the 30Z55B15S sample. A comparable decline is observed in the T_o values, which shift from 724 °C in the base composition to 644 °C in the 30Z55B15S sample. Similarly, the crystallization peak (T_p) temperature also decreases, with a notable change from 790 °C in the 45Z55B sample to 662 °C in the 30Z55B15S sample. Samples with lower ZnO content (e.g., 30Z55B15S) exhibit two crystallization exotherms and multiple endothermic transitions, indicating multi-stage crystallization due to the partial destabilization of the zinc borate network as Zn<Superscript>2+</Superscript> is replaced by Sb³⁺. This leads to the formation of multiple phases across distinct temperature ranges, a phenomenon previously reported in zinc-deficient borate glasses³². The curves also show a progressive reduction in melting temperature (T_m.t.), reflecting Sb₂O₃’s fluxing effect, which lowers the viscosity and the melting point of the glass matrix. Conversely, when Sb₂O₃ partially replaces B₂O₃, an increase in both the T_o and T_p is observed with an increase in the Sb₂O₃ content. As an illustration, the T_o value shifts from 724 °C in the 45Z55B sample to 748 °C in the 45Z40B15S sample, while the T_p rises from 790 °C to 802 °C. This suggests that Sb₂O₃ enhances the thermal stability of the glass network when replacing B₂O₃, making it more resistant to crystallization. Furthermore, the decreasing crystallization peak intensity with increasing Sb₂O₃ content demonstrates that replacing B₂O₃ with Sb₂O₃ reduces the crystallization tendency of the glass. However, the T_m.t. and T_g.t. decreases slightly, indicating that Sb₂O₃ still acts as a flux, reducing the glass’s viscosity.

Fig. 3.

DTA thermograms of ZnBSb glasses.

Using the Dietzel³³ criterion (ΔT = T_o – T_g.t.) as a measure of thermal stability, it becomes clear that Sb₂O₃ influences the thermal stability differently depending on whether it replaces ZnO or B₂O₃. When Sb₂O₃ substitutes ZnO, T_g.t. and T_o both decrease, but ΔT shows a slight increase, indicating a marginal enhancement in thermal stability despite the reduced absolute temperature values. For example, the base composition (45Z55B) has ΔT = 144 °C. Replacing 5 mol% ZnO with Sb₂O₃ (40Z55B5S) results in ΔT = 150 °C, and further substitution to 10 mol% Sb₂O₃ (35Z55B10S) increases ΔT to 165 °C. When Sb₂O₃ replaces B₂O₃, the glass shows a more pronounced increase in ΔT, signifying a significant enhancement in thermal stability. The introduction of 10 mol% of Sb₂O₃ in lieu of B₂O₃ (45Z45B10S) results in an increase in the ΔT to 244 °C. At the highest level of substitution, 15 mol% Sb₂O₃ (45Z40B15S), the ΔT reaches 256 °C. This significant increase suggests that Sb₂O₃ strengthens the glass network when replacing B₂O₃, acting as a stabilizing agent against crystallization. The enhanced stability can be attributed to structural modifications in the glass network. Sb³⁺ ions, due to their higher polarizability and larger ionic radius compared to B³⁺, may contribute to increased network rigidity, requiring greater thermal energy for structural reorganization. Additionally, Sb₂O₃ may enhance network connectivity through the formation of Sb–O–B linkages or by modifying the distribution of non-bridging oxygens, leading to a more resistant glass matrix. This structural reinforcement effectively delays the onset of crystallization, widening the temperature range between T_g.t. and T_o, thereby improving the glass’s resistance to devitrification and enhancing its overall thermal stability.

Figure 4 provides a combined analysis of X-ray diffraction (XRD) patterns (left side) and scanning electron microscopy (SEM) images (right side) for three glass samples after controlled heat treatment. This heat treatment process, which involved heating the samples to their respective crystallization temperatures (identified from DTA analysis) for 5 h, was conducted to understand the crystallization behavior and phase evolution of these materials. Such understanding is crucial for applications where these glasses might experience elevated temperatures during service, such as in radiation shielding components near heat-generating sources or in sealing applications for electronic devices.

Fig. 4.

XRD patterns and SEM micrographs of heat-treated ZnBSb samples: 45Z55B (a), 40Z55B5S (b), and 35Z55B10S (c), showing crystallization phases and corresponding microstructural evolution.

The heat-treated samples − 45Z55B, 40Z55B5S, and 35Z55B10S - show distinct crystallization patterns that provide valuable insights into their thermal stability and phase transformation behavior. The sharp peaks in the XRD patterns indicate the formation of well-defined crystalline phases during heat treatment, contrasting with the broad, diffuse patterns of the original glasses (shown earlier in Fig. 1a). This controlled crystallization study helps predict how these materials might behave in high-temperature applications and allows us to understand the role of Sb₂O₃ in influencing phase evolution. The 45Z55B sample, subjected to a heat treatment at 790 °C for a period of 5 h, displays the presence of peaks corresponding to Zn₄B₆O₁₃ and Zn₄B₂O₇, indicative of the formation of these crystalline phases during the aforementioned heat treatment. The substitution of ZnO with Sb₂O₃ in the 35Z55B10S and 30Z55B15S samples results in the emergence of Sb₂ZnO₄, which emerges alongside those of ZnB₂O₄. This substitution alters the crystallization dynamics, promoting phases that include Sb₂ZnO₄ at the expense of the zinc-borate phases seen in 45Z55B.

The SEM findings (see Fig. 4, right side) serve to supplement the XRD data by elucidating the microstructural changes associated with the varying compositions. In Fig. 4a (45Z55B), the crystal morphology consists predominantly of larger, well-defined hexagonal and rectangular crystals with smooth surfaces interspersed with smaller rod-like crystals. Figure 4b (40Z55B5S) shows notable morphological changes with the introduction of 5 mol% Sb₂O₃. The crystals are larger and exhibit enhanced faceting compared to the undoped sample, suggesting improved crystallization kinetics. The rods appear less prominent, replaced by a denser arrangement of well-faceted hexagonal crystals. When the Sb₂O₃ concentration is increased to 10 mol% in the 35Z55B10S sample (see Fig. 4c), the morphology becomes more complex, with an increased number of smaller rod-like or needle-like formations intertwined with the larger crystals. This suggests that a higher Sb₂O₃ content introduces additional crystalline phases or facilitates the preferential growth of these secondary structures, leading to a more intricate and interconnected network.

Figure 5 illustrates the alterations in dilatometric properties (CTE, T_g.t., and T_dil) that arise from the substitution of ZnO and B₂O₃ with Sb₂O₃ in the initial 45Z55B glass composition. The base composition (45Z55B) demonstrates a CTE of 4.65 ppm/°C, a T_g.t. of 586 °C, and a T_dil of 611 °C. An increase in the Sb₂O₃ content results in a notable alteration of these parameters. The substitution of B₂O₃ with Sb₂O₃ while maintaining the ZnO content (e.g., 45Z50B5S and 45Z40B15S) has been observed to result in a notable reduction in both T_g.t. and T_dil, while simultaneously exhibiting a significant increase in CTE. The 45Z50B5S composition (5 mol% Sb₂O₃) exhibits a T_g.t. of 554 °C, a T_dil of 579 °C, and a higher CTE of 5.01 ppm/°C in comparison to the base glass. Upon further increasing the concentration of Sb₂O₃ in the 45Z40B15S composition (to 15 mol%), the T_g.t. and T_dil values decrease to 497 °C and 529 °C, respectively, while the CTE rises to 5.95 ppm/°C. The substitution of ZnO for Sb₂O₃ while holding the B₂O₃ content constant also leads to a reduction in T_g.t. and T_dil, along with an augmentation in CTE. When 5 mol% Sb₂O₃ replaces ZnO (45Z50B5S), the CTE increases to 5.05 ppm/°C, while the T_g.t. and T_dil temperatures decrease to 557 °C and 582 °C, respectively. A further increase in Sb₂O₃ content to 15 mol% (30Z55B10S) continues this trend, with the CTE rising to 5.9 ppm/°C, while T_g.t. and T_dil are further lowered to 503 °C and 539 °C, respectively.

Fig. 5.

Dilatometry results of ZnBSb glasses.

The underlying mechanism driving these changes can be traced to the fundamental role of Sb₂O₃ as a network modifier within the glass structure. As Sb₂O₃ is incorporated into the glass structure, it disrupts the existing boron-oxygen network by breaking B–O–B linkages and generating non-bridging oxygen (NBO) sites³⁴. This structural depolymerization process reduces the overall network connectivity, manifesting as lower glass transition and dilatometric softening temperatures. Concurrently, the diminished network rigidity facilitates increased molecular mobility, directly translating to enhanced thermal expansion characteristics. These observations regarding increasing CTE with higher Sb₂O₃ content closely parallel the findings of Šubčík et al.³⁵ on antimony-doped zinc borophosphate glasses, where the CTE likewise rose proportionally with Sb₂O₃ concentration due to the progressive weakening of chemical bonds in the glass network.

Density and molar volume

The density and molar volume of glasses are fundamental physical properties that provide critical insights into the structural modifications occurring within the glass network³⁶. The substitution of ZnO and B₂O₃ with Sb₂O₃ in the 45ZnO·55B₂O₃ glass composition induces notable variations in density and molar volume, as depicted in Fig. 6a and b. The higher molar mass of Sb₂O₃ (291.51 g/mol), compared to ZnO (81.41 g/mol) and B₂O₃ (69.62 g/mol), primarily accounts for the marked increase in density. For instance, in the 45Z40B15S sample, which contains 15 mol% Sb₂O₃, the density reaches 3.836 g/cm³, the highest recorded value. In contrast, the base composition without Sb₂O₃ (45Z55B) has a much lower density of 3.120 g/cm³. This trend can be visualized in Fig. 6a, where the density contours shift toward higher values as the Sb₂O₃ concentration increases. Accompanying this rise in density is a systematic increase in the molar volume, as illustrated in Fig. 6b. At 0 mol% Sb₂O₃ (45Z55B), the molar volume is the lowest at 24.010 cm³/mol, indicating a relatively compact glass network. With the substitution of 5 mol% Sb₂O₃ (45Z50B5S), the molar volume increases to 25.544 cm³/mol, and at 15 mol% Sb₂O₃ (45Z40B15S), it peaks at 28.206 cm³/mol. This increase reflects the larger ionic radius (0.76 Å) and structural influence of Sb³⁺ ions, which expand the glass network and reduce overall packing efficiency. Overall, Fig. 6a and b reveal a clear trend: introducing Sb₂O₃ into the 45ZnO·55B₂O₃ glass composition tends to increase both the density and the molar volume of the glass. The specific values depend on which oxide (ZnO or B₂O₃) is being replaced and by how much, but the overall effect is a systematic shift toward higher density and molar volume as Sb₂O₃ substitution increases.

Fig. 6.

Density (a) and Molar volume (b) results of ZnBSb glasses.

Radiation shielding performance

Figure 7 compares the linear attenuation coefficients (LAC) of 45ZnO·55B₂O₃ glass when B₂O₃ (Fig. 7a) and ZnO (Fig. 7b) are partially substituted by Sb₂O₃ over the photon energy range extending from 15 keV to 15 MeV. In Fig. 7a, reducing B₂O₃ content from 55 to 40 mol% and replacing it with up to 15 mol% Sb₂O₃ (indicated by the transition from black to blue curves) significantly enhances the LAC values at all photon energies. Similarly, Fig. 7b shows that decreasing ZnO from 45 to 30 mol% while increasing Sb₂O₃ to 15 mol% consistently raises the LAC. Both substitution series reveal a consistent improvement in photon attenuation with each increment of Sb₂O₃. In the low-energy range (< 0.1 MeV), photoelectric absorption dominates³⁷, yielding very high LAC values. As energy increases, the curves decrease and converge, reflecting a shift toward Compton scattering (CS) and, ultimately, pair production (PP) at higher energies^38,39. Nonetheless, glasses with more Sb₂O₃ invariably show higher LACs. For instance, at 10 MeV, the LAC increases from 0.0768 cm⁻¹ in 45Z55B to 0.1142 cm⁻¹ in 45Z40B15S for the B₂O₃ substitution series; likewise, it rises from 0.0768 cm⁻¹ in 45Z55B to 0.0983 cm⁻¹ in 30Z55B15S for the ZnO substitution series. Overall, the results confirm that increasing Sb₂O₃ content improves gamma-ray attenuation across the full energy range. This improvement is consistent with previous research indicating that Sb₂O₃ enhances gamma-ray attenuation in sodium-boro-silicate glasses⁴⁰.

Fig. 7.

Impact of substituting B₂O₃ (a) and ZnO (b) with Sb₂O₃ in 45ZnO·55B₂O₃ glass on LAC values.

Figure 8a shows the variation of the half-value layer (HVL) with increasing photon energy for ZnBSb glass samples with different substitutions of B₂O₃ and ZnO with Sb₂O₃ in the 45ZnO·55B₂O₃ glass composition. Figure 8b illustrates the corresponding trend for the tenth-value layer (TVL). Both HVL and TVL exhibited an increasing trend with photon energy, thus indicating the energy-dependent attenuation behavior of the glass samples. At lower energies (e.g., 0.015–0.1 MeV), the glass samples demonstrate smaller HVL and TVL values, reflecting higher attenuation due to the dominance of the photoelectric effect. For instance, the HVL at 0.1 MeV energy for 45Z55B is approximately 0.7741 cm, while for 45Z40B15S, it is around 0.2293 cm, reflecting a decrease of about 70%. Similarly, the TVL values at the same energy are 2.5714 cm for 45Z55B and 0.7618 cm for 45Z40B15S, indicating a marked improvement in attenuation performance with Sb₂O₃ addition. This reduction indicates enhanced photon attenuation due to the higher atomic number of Sb, which boosts photoelectric absorption. As photon energy increased, both HVL and TVL values rose for all glass samples, driven by the reduced effectiveness of photoelectric absorption and the dominance of CS and PP. However, even at higher energies, samples with higher Sb₂O₃ content maintained lower HVL and TVL values compared to those without Sb₂O₃. For example, at 10 MeV, the HVL for 45Z55B is 9.0215 cm compared to 6.0714 cm for 45Z40B15S, showing a reduction of about 33%. This behavior demonstrates the energy-dependent attenuation characteristics of the glass and underscores the significant role of Sb₂O₃ in enhancing the radiation shielding capabilities of the material.

Fig. 8.

Variation in HVL (a) and TVL (b) values with photon energy for ZnBSb glasses, showing the effects of substituting varying amounts of B₂O₃ and ZnO with Sb₂O₃.

Figure 9 illustrates the alteration of the Z_eff values with photon energy for ZnBSb glasses, showing the impact of partial substitution of B₂O₃ (Fig. 9a) and ZnO (Fig. 9b) with Sb₂O₃ in the 45ZnO·55B₂O₃ glass composition. The Z_eff demonstrates a distinct dependence on photon energy, showing a marked increase surrounding 0.040 MeV due to the K-absorption edge of antimony atoms^41,42, where the photon energy is sufficient to eject inner-shell electrons, thereby increasing attenuation. At lower energies (e.g., 0.1 MeV), the Z_eff values for glasses with 15 mol% Sb₂O₃ substitution (e.g., 45Z40B15S in Figs. 9a and 30Z55B15S in Fig. 9b) are notably higher, at approximately 32.3062 and 30.6701, respectively, compared to their counterparts with no Sb₂O₃ substitution, which exhibit values of approximately 14.6243. The notable increase in Z_eff with Sb₂O₃ incorporation can be attributed to the higher atomic number (Z = 51) of antimony, which enhances the dominance of the photoelectric effect at low photon energies. This effect is particularly pronounced in the 0.015–0.1 MeV range, where photoelectric absorption is the predominant interaction mechanism⁴³. Moreover, the substitution of B₂O₃ for Sb₂O₃ (see Fig. 9a) results in a more substantial enhancement of Z_eff compared to the replacement of ZnO. This is attributable to the lower atomic number of boron (Z = 5) relative to zinc (Z = 30), thereby amplifying the effect of the substitution on enhancing the overall photon attenuation efficiency. The energy-dependent behavior of Z_eff values exhibits a distinct pattern. After reaching a peak around 0.040 MeV – attributed to the K-edge absorption of Sb – the Z_eff values gradually decrease as the photon energy increases, reaching a minimum at approximately 1 MeV. This trend is a result of the transition from photoelectric absorption (which dominates at lower energies and is highly dependent on the atomic number) to Compton scattering, which becomes the predominant interaction in the intermediate energy range. Beyond this point, a slight increase in Z_eff is observed up to 15 MeV, indicating the gradual transition from Compton scattering to pair production, where heavier elements continue to exhibit better attenuation characteristics. The improvements in LAC, HVL, TVL, and Z_eff underscore the pivotal role of Sb₂O₃, with its higher atomic number, in boosting photon attenuation, making these glasses highly effective for radiation shielding applications.

Fig. 9.

Impact of substituting B₂O₃ (a) and ZnO (b) with Sb₂O₃ in 45ZnO·55B₂O₃ glass on Z_eff values.

Conclusions

The investigation of antimony-doped zinc borate glasses demonstrated significant improvements in structural, thermal, and radiation shielding properties with increasing Sb₂O₃ content. The results confirmed that the amorphous nature of the glass was maintained across all compositions, with Sb₂O₃ incorporation leading to significant structural rearrangements, as evidenced by FT-IR analysis. The thermal characteristics showed remarkable improvement, particularly when B₂O₃ was replaced with Sb₂O₃. The thermal stability parameter (ΔT) increased substantially from 144 °C in the base composition to 256 °C at 15 mol% Sb₂O₃ substitution, demonstrating enhanced crystallization resistance. The coefficient of thermal expansion increased from 4.65 to 5.95 ppm/°C, indicating reduced network rigidity and enhanced flexibility of the glass matrix. The density and molar volume exhibited systematic increases with Sb₂O₃ content, reaching maximum values of 3.836 g/cm³ and 28.206 cm³/mol for the 45Z40B15S composition, attributable to the higher atomic mass and ionic radius of antimony. Most significantly, the radiation shielding capabilities show marked enhancement across the entire studied energy spectrum. The linear attenuation coefficient at 10 MeV increased by 49% (from 0.0768 cm⁻¹ to 0.1142 cm⁻¹) when substituting B₂O₃ with Sb₂O₃, while the half-value layer decreased by approximately 28% (from 9.02 cm to 6.07 cm). These improvements were particularly pronounced when B₂O₃ was replaced with Sb₂O₃, rather than substituting ZnO, due to the greater contrast in atomic numbers. These comprehensive findings establish Sb₂O₃-doped zinc borate glasses as exceptional candidates for advanced applications requiring both structural integrity and radiation protection. The demonstrated ability to fine-tune thermal, structural, and radiation shielding properties through controlled Sb₂O₃ substitution opens new possibilities for deployment in specialized technical applications, particularly in environments demanding robust radiation protection and thermal stability.

Author contributions

YH conceptualization, investigation, visualization, writing – original draft, writing – review & editing; AZ methodology, investigation, formal analysis. All authors have read and approved the final manuscript.

Data availability

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

Declarations

Competing interests

The authors declare no competing interests.