Abstract
The NaZr(2)P(3)O(12) family of materials have shown low and tailorable thermal expansion properties. In this study, SrZr(4)P(6)O(24) (SrO·4ZrO(2)·3P(2)O(5)), CaZr(4)P(6)O(24) (CaO·4ZrO(2)·3P(2)O(5)), MgZr(4)P(6)O(24) (MgO·4ZrO(2)·3P(2)O(5)), NaTi(2)P(3)O(12) [½(Na(2)O·4TiO(2)·3P(2)O(5))], NaZr(2)P(3)O(12) [½(Na(2)O·4ZrO(2)·3P(2)O(5))], and related solid solutions were synthesized using the organic-inorganic steric entrapment method. The samples were characterized by in-situ high-temperature X-ray diffraction from 25 to 1500°C at the Advanced Photon Source and National Synchrotron Light Source II. The average linear thermal expansion of SrZr(4)P(6)O(24) and CaZr(4)P(6)O(24) was between -1 × 10(-6) per °C and 6 × 10(-6) per °C from 25 to 1500°C. The crystal structures of the high-temperature polymorphs of CaZr(4)P(6)O(24) and SrZr(4)P(6)O(24) with R3c symmetry were solved by Fourier difference mapping and Rietveld refinement. This polymorph is present above ∼1250°C. This work measured thermal expansion coefficients to 1500°C for all samples and investigated the differences in thermal expansion mechanisms between polymorphs and between compositions.