Crystal structure solution and high-temperature thermal expansion in NaZr₂(PO₄)₃-type materials

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• The NaZr2P3O12 family is known for low and tailorable thermal expansion.
• Understanding thermal expansion mechanisms is crucial for high-temperature material applications.

Purpose of the Study:

• To synthesize and characterize SrZr4P6O24, CaZr4P6O24, MgZr4P6O24, NaTi2P3O12, NaZr2P3O12, and related solid solutions.
• To measure their thermal expansion properties up to 1500°C.
• To investigate the structural changes and thermal expansion mechanisms of these materials at high temperatures.

Main Methods:

• Organic-inorganic steric entrapment method for synthesis.
• In-situ high-temperature X-ray diffraction (HT-XRD) from 25 to 1500°C.
• Fourier difference mapping and Rietveld refinement for crystal structure analysis.

Main Results:

• SrZr4P6O24 and CaZr4P6O24 showed average linear thermal expansion between -1 x 10^-6 /°C and 6 x 10^-6 /°C.
• High-temperature polymorphs of CaZr4P6O24 and SrZr4P6O24 with R3c symmetry were identified above ~1250°C.
• Thermal expansion coefficients were measured for all synthesized compositions up to 1500°C.

Conclusions:

• The synthesized zirconium phosphate materials possess low and tailorable thermal expansion properties.
• High-temperature polymorphs exhibit distinct structural characteristics influencing thermal expansion.
• This research provides valuable insights into the thermal behavior of these materials for advanced applications.