Thermal expansion of MZr2(AsO4)3 and MZr2(TO4)x(PO4)3–x (M = Li, Na, K, Rb, Cs; T = As, V)

The thermal expansion parameters of the MZr 2 (AsO 4 ) 3 (M = Li, Na, K, Rb, Cs) arsenates and MZr 2 (TO 4 ) x (PO 4 ) 3– x (T = As, V) arsenate phosphate and vanadate phosphate solid solutions with the NaZr 2 (PO 4 ) 3 (NZP) structure have been determined by high-temperature X-ray diffraction. The effects of the size of the alkali metal cation and arsenic or vanadium substitution for phosphorus on the thermal expansion of the arsenates and solid solutions have been studied systematically. The potassium-, rubidium-, and cesium-containing arsenates, arsenate phosphates, and vanadate phosphates are low-expansion materials (αav < 2 × 10 –6 °C –1 ); sodium zirconium arsenate and sodium zirconium and lithium zirconium arsenate phosphates and vanadate phosphates have intermediate thermal expansion (3 × 10 –6 °C –1 < αav < 7 × 10 –6 °C –1 ); and lithium zirconium arsenate is a high-expansion material (αav = 9.9 × 10 –6 °C –1 ). The present results demonstrate that, increasing the size of the alkali metal cation in the arsenates and varying the composition of the solid solutions, one can produce NZP materials with controlled linear thermal expansion coefficients and extremely low thermal expansion anisotropy.