Thermal expansion of NASICON materials

Our and others' results on the thermal expansion of compounds and the crystal-chemical information about their structure have been used to properly select compositions of new NASICON materials with small thermal expansion and low thermal expansion anisotropy: M (x) M1-x 'Ti-2(PO4)(3) (M and M' are alkali metals, 0 a parts per thousand currency sign x a parts per thousand currency sign 1), MaEuro(3)FeTi(PO4)(3) (MaEuro(3) is an alkaline-earth metal), and Ca0.5(1 + x)Fe (x) Ti2 - x (PO4)(3) (0 a parts per thousand currency sign x a parts per thousand currency sign 1). Such materials have been synthesized through salt coprecipitation from aqueous solutions and their thermal expansion has been assessed by high-temperature X-ray diffraction. We have determined their unit-cell parameters as functions of temperature and correlated their thermal expansion parameters and composition. The K0.5Rb0.5Ti2(PO4)(3) and Rb0.8Cs0.2Ti2(PO4)(3) materials obtained combine small volumetric thermal expansion and near-zero thermal expansion anisotropy.