Protocol for the reactive synthesis of double-A-layer MAX phase Ti₂Bi₂C in a sealed quartz ampule

Summary

Ti₂Bi₂C is a ternary atomically layered carbide MAX phase with potential applications in radiation shielding under elevated temperature conditions. Here, we present a protocol for synthesizing the double-A-layer MAX phase Ti₂Bi₂C from elemental Ti, Bi, and C powders. The approach involves steps for powder mixing and homogenization, pressing, vacuum sealing in quartz ampules, and high-temperature solid-state reaction at 1,000°C for 48 h. Powder X-ray diffraction confirms Ti₂Bi₂C formation as the predominant (>70 wt %) synthesis product.

For complete details on the use and execution of this protocol, please refer to Kushnir et al.¹

Graphical abstract

Highlights

• •Procedure for Ti₂Bi₂C MAX phase synthesis from powders in a sealed quartz ampule
• •Instructions for mixing and compacting precursors into a stable green body
• •Steps for sealing quartz ampules using a rotary system and oxy-hydrogen torch
• •Confirmation of Ti₂Bi₂C phase product by XRD and morphological analysis

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Ti₂Bi₂C is a ternary atomically layered carbide MAX phase with potential applications in radiation shielding under elevated temperature conditions. Here, we present a protocol for synthesizing the double-A-layer MAX phase Ti₂Bi₂C from elemental Ti, Bi, and C powders. The approach involves steps for powder mixing and homogenization, pressing, vacuum sealing in quartz ampules, and high-temperature solid-state reaction at 1,000°C for 48 h. Powder X-ray diffraction confirms Ti₂Bi₂C formation as the predominant (>70 wt %) synthesis product.

Before you begin

MAX phases are a class of atomically layered ternary carbides and nitrides with a unique combination of metallic and ceramic properties, including high thermal stability, electrical conductivity, and machinability.^2,3 Among them, Ti₂Bi₂C stands out as one of only two double A-layer MAX phases known to have been produced in bulk (powder) form via reactive synthesis.¹ Furthermore, it is the first synthesized MAX phase to adopt long-range rhombohedral symmetry. The traditional MAX phase characteristics, along with the presence of an abundant high-Z element like bismuth, make Ti₂Bi₂C a promising candidate for applications such as radiation shielding in high-temperature environments.

However, the synthesis of Bi-containing MAX phases, and more broadly, materials incorporating volatile elements with low melting points and high vapor pressures, is particularly challenging. Under conventional high-temperature synthesis in inert atmosphere flow conditions used for conventional MAX phases, such elements tend to evaporate, condense in undesired areas, and therefore do not partake in the reaction leaving it incomplete. As a result, retaining volatile components during synthesis is critical to enable forming the desired phase in meaningful purity and quantity.

This protocol addresses that challenge by using vacuum-sealed quartz ampules to contain volatile elements during synthesis. It enables the preparation of Ti₂Bi₂C and is broadly applicable to other systems containing low melting point elements such as Sn, Ga, Se, and Te. The protocol has been successfully used to synthesize not only MAX phases, but also van der Waals solid transition metal carbo-chalcogenides (TMCCs), a newly emerging and exciting family of layered materials,⁴ that not only share structural and chemical traits with MAX phases, but can also be transformed into two-dimensional forms for potential applications in electronics and energy storage.^5,6 Access to specialized equipment, such as a rotary ampule sealing system, an oxy-hydrogen torch, and an X-ray diffractometer, is essential for successful execution and reproducibility of this protocol.

Innovation

The protocol presented here offers a practical solution to a challenge in high-temperature solid-state synthesis: the incorporation of volatile, low melting point elements such as Bi, Sn, Ga, Se, and Te. These elements exhibit high vapor pressures and are prone to evaporation under conventional flow-based inert atmosphere synthesis, often resulting in incomplete reactions and poor phase purity. By sealing the precursor mixture in a vacuum-sealed quartz ampule, this protocol effectively retains volatile species during extended high-temperature treatment, enabling thermodynamically favorable reactions to proceed to completion.

While vacuum ampule techniques are used for volatile systems, they are rarely applied to MAX phase synthesis due to the typically required temperatures (>1,200°C) exceeding quartz’s thermal limits. This work demonstrates a successful adaptation of ampule-based synthesis to the MAX phase domain by identifying a Bi-containing MAX phase, Ti₂Bi₂C, that forms at a lower temperature (1,000°C), within quartz’s safe operating range. Therefore, making the approach both practical and reproducible.

Beyond Ti₂Bi₂C, the protocol can be generalized to other layered materials containing volatile elements. The method offers clear guidance on precursor preparation, sealing procedures, and heat treatment, enabling high-yield synthesis of layered phases.

Precursor selection and batch planning

Timing: 1–2 h

• 1.
  Evaluate elemental powders for synthesis.

  • a.
    Use high-purity (>99%) elemental powders of Titanium (Ti), Bismuth (Bi), and Carbon (C) as precursors.

    Note: Do not use TiC as a substitute for Ti, even though it is commonly used as a MAX phase precursor in other Ti-based systems. In the Ti–Bi–C system, TiC does not result in MAX phase formation.

  • b.
    Choose precursor powders with small (larger than 100 mesh, ≤150 μm) and relatively similar particle sizes to improve mixing uniformity and enhance reaction kinetics during synthesis.
  • c.
    Perform X-ray diffraction (XRD) analysis on each precursor to confirm phase purity and identify potential contaminant phases.

    CRITICAL: Residual oxide phases or impurities in the precursors will interfere with the synthesis and significantly hinder or reduce the MAX phase yield (see problem 5).

• 2.
  Stoichiometric calculation and precursor mass planning.

  • a.
    Calculate the molar mass of the desired phase by summing the atomic weights of its constituent elements.
  • b.
    Determine the number of moles of the desired phase based on the total target mass of the precursor mixture.
  • c.
    Multiply the number of moles of the target phase by the stoichiometric ratio of each element to determine the required moles of each precursor.
  • d.
    Convert the required moles of each precursor to mass using their respective molar masses.

Note: According to our previous study,¹ the highest yield of Ti₂Bi₂C was obtained using a starting atomic ratio of Ti:Bi:C = 2:1:1, rather than Ti:Bi:C = 2:2:1. Increasing the Bi content beyond the ratio of Ti:Bi:C = 2:1:1 ratio led to a reduced formation of the double A-layer MAX phase and a higher amount of residual elemental Bi in the final product.

Key resources table

REAGENT or RESOURCE	SOURCE	IDENTIFIER
Chemicals, peptides, and recombinant proteins
Ti powder 99.5%, ∼45 μm (325 mesh)	Eckart	CAS- 7440-32-6
Bi powder 99.99% ∼150 μm (100 mesh)	Sigma-Aldrich	CAS- 7440-69-9
Calcined petroleum coke powder, crystalline, 99%, ∼45 μm (325 mesh)	Thermo Scientific - Alfa Aesar	CAS- 64743-05-1
2-Propanol (Isopropanol)	Merck	CAS- 67-63-0
Argon gas 99.999%	Air and Argon Factories Inc., Israel	general-grade gas
Deposited data
Crystallographic Information File (CIF) of Ti2Bi2C	Cambridge Crystallographic Data Center (CCDC)	Deposition Number 2449275
Other
Laboratory diffractometer	Malvern Panalytical	Cat# Aeris Research
Analytical balance AS 60/220.R2 PLUS	RADWAG	Cat# WL-104-1052
Agate mortar and pestle	Lichen, China	N/A
50 mL centrifuge tube High-RCF	Romical, Israel	Cat# 424-CFT312500
Rolling ball mill mixer	TENCAN	Model number: QM-5
Stainless steel mixing balls (3–5 mm)	N/A	N/A
Circular pressing die (5 mm)	TMAX Battery Equipment	Cat# 20201217112226
Cylindrical alumina crucible, 99.7% Al2O3	Toho Ceramic Technology Co., Ltd	N/A
Quartz tube (fused silica), 99.99% SiO2	A.Rom Agancies	N/A
Flame Sealing Mechanical Pump Rotary Quartz Ampule Tube Vacuum Sealing System	Okay Energy	Model number: OH800
Silicone Ace O-rings	Sigma-Aldrich	Cat# Z504017
Hose connector clamp	Sigma-Aldrich	Cat# Z147281
Muffle furnace	TMAX Battery Equipment	Model number: KF1700

Materials and equipment

Quartz tube

• •Use high-quality quartz tubes (>99% SiO₂).
• •Outer diameter should be compatible with the rotary ampule sealing system.
• •Inner diameter should accommodate the alumina crucible containing the sample.
• •For high-grade quartz tubes, a wall thickness of ∼1 mm is sufficient for the heat treatment conditions described in this protocol (1,000°C, 48 h).

Rolling ball mill

• •A rolling ball mill was used for powder homogenization in this protocol, offering efficient mixing of precursor powders.

Alternatives: 3D powder mixers (such as TURBULA mixers) can be used, particularly for larger batch sizes or when a gentler, non-impact mixing method is preferred. For precursors requiring more intensive mixing or slight mechanical activation, a planetary ball mill may also be suitable, though care should be taken to avoid excessive energy input that could alter the powder characteristics.

Stainless steel mixing balls

• •The choice of milling media is important to avoid contamination.

Alternatives: ZrO₂ or Al₂O₃ mixing balls can be used to minimize potential metallic contamination.

Muffle furnace

• •This protocol uses a box-type muffle furnace, but the specific furnace type is not critical provided it offers precise temperature control, a heating rate of at least 5°C/min, and can maintain extended heat treatments up to 48 h at the target temperature.

Alternatives: Tube furnace, vacuum furnace, and graphite resistance furnace.

Step-by-step method details

Green body sample preparation from Ti, Bi, and C powders

Timing: 25–26 h

This section outlines how to prepare a homogeneous powder mixture from precursor elemental Ti, Bi, and C and their compaction into a green body.

• 1.Carefully weigh on an analytical balance each precursor according to the calculated values from precursor selection and batch planning step (Figure 1A). Aim for at least ±0.1% precision in the targeted weights.
• 2.
  Manual grinding to break agglomerates and homogenize the precursor mixture.

  • a.
    Transfer all weighed precursors into a clean agate mortar (Figure 1B).
  • b.
    Grind the mixture thoroughly using an agate pestle for 5–10 min to ensure uniform mixing and to break up any agglomerates (Figure 1C).

CRITICAL: Insufficient grinding may leave agglomerates in the mixture, which can hinder mixture uniformity and full precursor reaction during synthesis, reducing the yield or purity of the target phase (see problem 5).

• 3.
  Mechanical mixing of the powder using a rolling ball mill mixer.

  • a.
    Transfer the ground precursor powder into a 50 mL centrifuge tube.
  • b.
    Add 5–7 stainless steel mixing balls of varying diameters (3–5 mm) to the tube (Figure 1D).
  • c.
    Insert the centrifuge tube into the rolling ball mill mixer and position it at a 20°–45° angle relative to the rolling ball mill’s rotation axis (Figure 1E).

    Note: For MAX phase synthesis, steel balls are preferred because of their higher mass and the limited iron contamination is unlikely to interfere with MAX phase formation.

    CRITICAL: Aligning the tube parallel to the rolling ball mill’s rotation axis limits powder mobility, resulting in poor mixing, particularly in narrow containers. Tilting the tube at a 20°–45° angle introduces a helical motion of the milling balls, which enhances three-dimensional mixing and increases shear and impact events. This configuration improves powder homogeneity.

  • d.
    Operate the rolling ball mill mixer at 180–200 rpm for 24 h to ensure uniform mixing.

    Note: For MAX phase synthesis, stainless steel balls are preferred because of their higher mass and the limited iron contamination is unlikely to interfere with MAX phase formation.

    CRITICAL: Improper tube angle or insufficient rotation speed can result in poor mixing and non-uniform precursor distribution, which may hinder the formation of the desired MAX phase during synthesis (see problem 5).

• 4.
  Cold press the mixed powder into a green body pellet.

  • a.
    Mix the powder with 1 mL of isopropanol (per ∼1 g of mixed powder) to form a moist powder mixture using the agate pestle and mortar (it should have a texture resembling the plasticity and granularity of wet sand).

    Note: The powder mixture should be moist but not wet, ensuring it remains cohesive without excess liquid after compaction in the pressing die, as demonstrated in Figure 2A.

    Note: Elemental carbon acts as a natural lubricant, which may lead to brittleness, crumbling or delamination of the green body. Using isopropanol helps reduce this effect by promoting particle cohesion, thereby preventing mechanical failure during green body formation. A green body prepared without sufficient isopropanol (or other similar solvent) may appear fractured, as shown in Figure 2D, while a properly formed pellet is shown in Figure 2E (see problem 1).

  • b.
    Load the full volume of the moist powder mixture into the circular pressing die of 5 mm (Figures 2B and 2C).
  • c.
    Apply a uniaxial pressure of 200 MPa for 30–60 s to form a dense green body and ensure intimate contact between precursor particles.

    CRITICAL: Rapid stress release can cause delamination or cracking of the green body due to the elastic rebound of compressed powder (spring-back effect).^7,8 This effect is evident in the fractured green body shown in Figure 2D (see problem 2). In contrast, Figure 2E presents a structurally intact green body prepared under controlled pressing conditions.

  • d.
    Gradually release the applied stress to prevent sudden expansion of the pellet and avoid the spring-back effect.
  • e.
    Insert the 5 mm green body pellet into a cylindrical alumina crucible.
    Dry the green body in the alumina crucible for ∼20 min using a vacuum oven, desiccator, or hot plate to remove residual isopropanol.

    CRITICAL: Residual isopropanol will burn up during ampule sealing and the byproducts like CO gas will condense as carbon residue on the inner quartz walls, significantly complicating and prolonging the sealing process (see problem 3 and 5).

    Note: The alumina crucible acts as a thermal and chemical barrier, preventing direct contact and reaction between the pellet and the quartz ampule during synthesis.

Figure 1.

Powder mixing and homogenization process

(A) Analytical balance measurement of elemental Ti, Bi, and C powders according to calculated stoichiometric ratios.

(B) Elemental precursor powders placed in an agate mortar before manual grinding.

(C) Thoroughly mixed precursor powder shown alongside stainless steel mixing balls and a 50 mL centrifuge tube.

(D) Powder and mixing balls loaded into the centrifuge tube, prepared for mechanical mixing and homogenization.

(E) Centrifuge tube positioned at a 20°–45° angle relative to the rolling ball mill mixer rotation axis before the 24 h mixing step.

Figure 2.

Formation of the pressed green body from precursor powder

(A) Precursor powders mixed with 1 mL isopropanol using an agate mortar and pestle to form a moist powder mixture.

(B) Components of the 5 mm circular pressing die shown prior to assembly.

(C) Assembled pressing die loaded with the prepared powder mixture and ready for uniaxial pressing.

(D) Defective green body exhibiting crumbling and delamination, resulting from insufficient isopropanol or rapid stress release.

(E) Intact and well-formed green body with no visible cracks or separation, indicating proper moisture content and stress management.

Quartz ampule sealing for reactive synthesis

Timing: 30–60 min

In this stage the compacted powder pellet is encapsulated in a vacuum-sealed quartz ampule to isolate it from oxygen during high-temperature synthesis. Preconditioning the quartz tube and maintaining vacuum integrity are essential for successful sealing.

Note: Use a high-quality quartz (>99% SiO₂) tube for prolonged high-temperature exposure to avoid ampule quartz failure during the heat treatment.

• 5.
  Precondition the quartz tube.

  • a.
    Connect an empty quartz tube to the rotary quartz ampule sealing system as seen in Figure 3A.
  • b.
    Wear protective goggles and insulative gloves turn on the oxy-hydrogen generator.

    CRITICAL: Always shut off the oxy-hydrogen torch immediately when not in use to avoid safety hazards.

  • c.
    Turn on the rotary ampule sealing system and the mechanical vacuum pump.

    • i.
      Ignite the torch and evenly heat the entire length of the empty quartz tube to promote desorption of residual moisture from the inner walls.

      Note: Water vapor trapped inside the quartz tube will act as an oxidizer during high-temperature synthesis, reacting with sensitive precursors such as Bi that are highly prevalent to oxidation and hinder MAX phase formation (see problem 5).

    • ii.
      After heating, allow the quartz tube to cool for 5 min.
  • d.
    Once cooled, dismantle the quartz tube from the sealing setup.

    • i.
      Place two silicone O-rings at the sealed end of the quartz tube and secure it with a hose connector clamp.
    • ii.
      Insert the alumina crucible containing the green body pellet into the quartz tube.
    • iii.
      Reconnect the loaded quartz tube to the sealing system.
    • iv.
      Immediately start the vacuum rotary pump to evacuate the quartz tube.
• 6.
  Seal the quartz ampule under vacuum after Ar purging.

  • a.
    Perform 5 purge cycles by alternately flushing the ampule with Ar and pulling vacuum.
  • b.
    After the final purge cycle, maintain the ampule under vacuum for the remainder of the sealing process.
  • c.
    Turn on the rotation of the ampule sealing system and ignite the oxy-hydrogen torch.
  • d.
    Heat the full length of the quartz tube to remove residual moisture from the inner walls.

    CRITICAL: Do not direct the flame at the alumina crucible or hose connector clamp. Bismuth melts at 271°C and can vaporize or oxidize if directly exposed to torch heat flux.

  • e.
    Pause the rotation and hang a ∼300 g weight from the hose connector clamp (Figure 3B).

    Note: The added weight promotes neck formation during softening of the quartz and ensures a smooth seal, as shown in Figure 3C.

  • f.
    Resume rotation at 60 RPM and aim the torch at a 90° angle to the quartz tube and begin sealing, as illustrated in Figure 3B and demonstrated in Methods Video S1.

    • i.
      Gradually slow the rotation (∼18 RPM) as the quartz softens and a neck begins to form during the sealing process, as shown in Figure 3C.
    • ii.
      Once the ampule is fully sealed, extinguish the torch and allow the ampule to cool. The resulting tip of the ampule will be very sharp, as seen in Figure 3D.
    • iii.
      Use the torch to carefully smooth the sharp quartz tip formed at the end of the ampule, as demonstrated in Figure 3E.

      Note: Smoothing the tip helps eliminate stress concentrations that could otherwise act as initiation points for crack propagation and lead to ampule failure during handling or heat treatment.

    • iv.
      After cooling, remove the hose connector clamp and silicone ace O-rings. Place the sealed ampule in an alumina crucible to support vertical orientation during the subsequent heat treatment, as seen in Figure 3F.

Figure 3.

Procedure of sealing the green body in a quartz ampule

(A) Setup of the ampule sealing system prior to preconditioning, with an empty quartz tube connected and ready for flame heating to remove residual moisture.

(B) Close-up image showing a 300 g weight attached to the quartz tube, with the torch positioned at a 90° angle relative to the tube.

(C) Formation of a quartz neck during softening of the tube under heating and pumping while rotating.

(D) Sealed quartz ampule tip after torch sealing, showing a sharp conical shape.

(E) Tip smoothing using a torch to reduce stress concentration.

(F) Sealed ampule placed inside an alumina crucible for vertical support during heat treatment.

Methods video S1. Ampule sealing process, related to Step 6.f

This video demonstrates the sealing of a quartz tube containing the green body. The torch is applied while the ampule is rotated to form a neck and complete the seal.

High-temperature treatment in a muffle furnace for reactive synthesis of Ti–Bi–C precursors inside the sealed quartz ampule

Timing: 52 h

This step facilitates the reactive synthesis by subjecting the sealed sample to a high temperature for an extended duration.

• 7.
  Set up the muffle furnace and program the heat treatment profile.

  • a.
    Place the sealed quartz ampule horizontally in the center of the muffle furnace.

    Optional: Place the sealed quartz ampule inside a supporting alumina crucible to maintain vertical orientation during the heat treatment.

  • b.
    Program the furnace with the following thermal profile as illustrated in Figure 4:

    • i.
      Ramp from 25°C to 1,000°C at a rate of 10°C/min.
    • ii.
      Hold at 1,000°C for 48 h.
    • iii.
      Cool from 1,000°C back to 25°C at a rate of 10°C/min.
    • iv.
      Once the furnace reaches 25°C, allow the ampule to cool to room temperature inside the furnace.
  • c.
    Carefully remove the ampule and break it open.

    Note: Break the ampule gently, far enough from the crucible within to avoid quartz fragments contaminating the sample (see problem 4).

    • i.
      Extract the alumina crucible and remove the synthesized product.
    • ii.
      Use an agate mortar and pestle to manually grind the reaction product back into powder form for analysis. The resulting powder should take on a darker complexion (relative to the precursor powder mixture), as seen in Figure 5.

Figure 4.

Furnace heating profile for the high-temperature synthesis of Ti₂Bi₂C used for the reactive synthesis, showing ramp-up to 1,000°C, 48 h dwell, and controlled cooling

Figure 5.

Reaction synthesis product after grinding to a powder in an agate mortar

Post-synthesis analysis of the reaction product powder

Timing: 1–2 h

This final step evaluates the success of the synthesis using XRD and scanning electron microscopy (SEM) to evaluate the MAX phase crystal structure and morphology, respectively.

• 8.
  Perform XRD to assess the MAX phase formation and presence of other byproducts.

  • a.
    Collect powder XRD data on the synthesized powder using any standard laboratory diffractometer.
  • b.
    Compare the experimental diffraction pattern to the reference pattern of Ti₂Bi₂C published in the CCDC database⁹ (shown in Figure 6) to confirm phase identity.
  • c.
    Rietveld refinement¹⁰ using dedicated software (e.g., GSAS, FullProf) can be performed to determine the exact phase composition of the reaction products.

Figure 6.

CIF model of the Ti₂Bi₂C double-A-layer MAX phase, crystallizing in the rhombohedral space group symmetry R-3m

Expected outcomes

This protocol should result in successful synthesis of the Ti₂Bi₂C double A-layer MAX phase. Under optimized conditions thus far, the reaction typically yields Ti₂Bi₂C with >70 wt % phase purity. The resulting XRD pattern (Figure 7A) should match the CCDC reference for Ti₂Bi₂C, confirming formation of the targeted rhombohedral structure (space group R-3m, #166). The post-synthesis powder should comprise particle agglomerates with a diameter of ∼50–100 μm (Figure 7B). More importantly, higher magnification imaging by SEM should reveal the characteristic laminated morphology of MAX phases (Figure 7C), consistent with successful formation of layered Ti₂Bi₂C.

Figure 7.

Structural and morphological characterization

(A) Powder XRD pattern of the synthesized product after heat treatment at 1000°C for 48 h, showing predominant Ti₂Bi₂C MAX phase. The diffraction peaks of Ti₂Bi₂C are indexed with their corresponding (hkl) planes.

(B) Low magnification SEM micrograph of the recovered powder exhibiting particles with a size of 50–100 μm.

(C) High magnification SEM micrograph displaying the characteristic laminated morphology of the Ti₂Bi₂C MAX phase. The smaller submicron particles are residual carbides, typically byproducts for reactive synthesis of MAX phases.

Limitations

This protocol enables the synthesis of Ti₂Bi₂C as the predominant phase using high-purity elemental precursors and a controlled reaction synthesis in a sealed quartz ampule. However, it does not result in a completely phase-pure product. Typically, >70 wt % purity is achieved, with residual or byproduct phases such as unreacted elemental Bi or TiC remaining in the final powder.

This partial purity reflects the sensitivity of the synthesis to several key parameters, including precursor elemental powder quality, mixing uniformity, moisture removal and proper ampule sealing to prevent oxidation. While the conditions described here have been optimized for reproducibility, further refinement, such as adjusting stoichiometry or extending the temperature and holding time, may allow to realize better results (higher MAX phase purity). Users aiming for higher phase purity should consider these parameters as potential tuning points for optimization.

Additionally, high-temperature synthesis protocols such as this one are strongly dependent on the specific equipment used. Differences in furnace calibration, temperature uniformity, sealing system configuration, and vacuum integrity may influence the reaction environment and outcome. As a result, reproducibility may vary across laboratories, and users are encouraged to carefully validate and adapt the protocol to their own instrumentation.

Troubleshooting

Problem 1 (step 4)

The green body does not remain rigid after pressing and fractures, delaminates, or disintegrates into powder when removed from the pressing die.

Potential solution

Add more isopropanol to the mixed powder to create a moister powder prior to pressing. The additional isopropanol improves particle rearrangement and acts as a binding agent to help the powder compact remain more cohesive and retain its shape after pressing. Avoid adding excessive amounts of isopropanol since a wet powder will not bind properly and the green body will delaminate, fracture, or disintegrate after compaction.

Problem 2 (step 4)

The green body shows visible cracks or delamination after pressing.

Potential solution

Reduce the applied pressing load. Excessive pressure can cause internal stress buildup and lead to cracking or delamination, especially in dry or loosely bonded powders. Additionally, release the applied load more gradually to minimize elastic rebound (spring-back), which can further damage the compacted green body.

Problem 3 (step 6)

A dark condensation appears on the inner wall of the quartz tube during the sealing process, see Figure 8. This will impede the ampule sealing process and, moreover, as the contamination is not readily evacuated it serves as a detrimental impurity that can react during the high temperature treatment and hinder the synthesis process.

Figure 8.

Burnt isopropanol residue on quartz tube wall during sealing

Dark condensation on the inner wall of the quartz tube, likely a result of burnt isopropanol, indicating insufficient drying of the green body prior to sealing.

Potential solution

This is likely a carbon-based condensation byproduct of burnt residual isopropanol, indicating that the sample was not fully dried before sealing. Ensure the green body is thoroughly dried in a vacuum oven, desiccator, or on a hot plate to remove all residual isopropanol before sealing. If the ampule takes too long to seal, the risk of sample oxidation increases, especially due to high susceptibility of Bi to oxygen at elevated temperatures.

Problem 4 (step 7)

Upon opening the quartz ampule after heat treatment, glass shards become mixed with the reaction powder.

Potential solution

To avoid uncontrolled shattering, gently score the surface of the quartz tube with a sharp and hard tool (e.g. alumina or carbide based) at the desired breaking point. This promotes localized crack initiation and propagation. Then apply bending pressure at the scored line to produce a controlled fracture, minimizing the risk of quartz fragments contaminating the sample (see Figure 9).

Figure 9.

Controlled opening of the sealed quartz ampule

(A) Sealed quartz ampule after heat treatment, showing a marked scoring line at the intended break point.

(B) Clean fracture of the ampule following manual breakage along the score line, minimizing glass contamination of the sample.

Problem 5 (step 8)

The synthesis does not yield a predominantly pure phase of Ti₂Bi₂C.

Potential solution

There are several factors that may affect the formation of a high-purity Ti₂Bi₂C phase.

• •Inadequate manual grinding may leave initial agglomerates intact, leading to incomplete reactions.
• •Poor mechanical mixing can result in non-uniform precursor distribution.
• •Insufficient preconditioning of the quartz ampule may leave residual moisture, introducing an oxidizing environment.
• •A prolonged sealing process increases the likelihood of Ti and Bi oxidation prior to the synthesis reaction, especially if the system is not under sustained vacuum or rapid sealing is not achieved.

Carefully verify each of these steps to ensure optimal phase purity.

• •Check the quality and purity of the starting elemental powders. Low-grade or contaminated precursors have been observed to hinder Ti₂Bi₂C formation. If possible, use powders sourced from reliable commercial suppliers (e.g., Sigma-Aldrich, Alfa Aesar etc.) with certified purity and consistent particle size. Inadequate precursors will lead to the synthesis product consisting of Bi, TiC, Bi oxides, or Bi-Ti intermetallics instead of the desired Ti₂Bi₂C MAX phase.

Resource availability

Lead contact

Further information and requests for resources and reagents should be directed to and will be fulfilled by the lead contact, Maxim Sokol (sokolmax@tauex.tau.ac.il).

Technical contact

Technical questions on executing this protocol should be directed to and will be answered by the technical contact, Yiftach Kushnir (yiftachk@mail.tau.ac.il).

Materials availability

Not available.

Data and code availability

This protocol did not generate any new datasets or code.

Acknowledgments

This work was supported by the Israel Science Foundation (grant no. 2527/22).

Author contributions

Y.K. and A.N. conceptualized the study, developed the protocol, performed the experiments, and wrote the manuscript. B.R. assisted in writing the manuscript. O.M. and B.F. contributed to data analysis and manuscript editing. M.S. supervised the project and reviewed the manuscript.

Declaration of interests

The authors declare no competing interests.

Declaration of generative AI and AI-assisted technologies in the writing process

During the preparation of this work, the authors used ChatGPT by OpenAI to assist with grammar refinement. All content was subsequently reviewed and edited by the authors, who take full responsibility for the final version of the publication.