Low-Temperature Spark Plasma Sintering of ZrW

Area of Science:

• Materials Science
• Solid State Chemistry
• Nanotechnology

Background:

• Molybdenum-doped zirconium tungstate (ZrW₂₋ₓMoₓO₈) is known for its significant negative thermal expansion (NTE).
• Limitations in density and sinterability hinder its practical production and use.
• Developing methods to improve these properties is crucial for wider applications.

Purpose of the Study:

• To fabricate high-density, single-phase molybdenum-doped zirconium tungstate.
• To investigate the effect of molybdenum doping on the phase transition temperature and NTE behavior.
• To establish a correlation between material structure and NTE properties.

Main Methods:

• Spark plasma sintering of ZrW₂₋ₓMoₓO₇(OH)₂·2H₂O precursor powders.
• High-temperature X-ray diffraction (HT-XRD) for phase transition analysis.
• Thermomechanical analysis (TMA) to quantify thermal expansion.
• Rietveld structure refinement for detailed structural analysis.

Main Results:

• Achieved relative density >90% for single-phase ZrW₂₋ₓMoₓO₈ (0.0 ≤ x ≤ 1.0) via spark plasma sintering at 500–600 °C.
• Phase transition temperature decreased with increasing molybdenum content (x), from 170 °C (x=0) to below room temperature (x≥0.7).
• Tunable NTE coefficients were observed, ranging from -7.85 × 10⁻⁶ °C⁻¹ to -9.01 × 10⁻⁶ °C⁻¹ before transition and -3.22 × 10⁻⁶ °C⁻¹ to -2.50 × 10⁻⁶ °C⁻¹ after transition.

Conclusions:

• Spark plasma sintering successfully produced high-density, single-phase molybdenum-doped zirconium tungstate.
• Molybdenum doping effectively controls the phase transition temperature and NTE properties.
• The tunable NTE behavior is linked to the thermodynamic instability of terminal oxygen atoms.