Thermal expansion of lattice parameters of La3Nb0.5Ga5.5O14, La3Ta0.5Ga5.5O14 and La3SbZn3Ge2O14

The thermal expansion of trigonal La3Nb0.5Ga5.5O14 (LNG), La3Ta0.5Ga5.5O14 (LTG) and monoclinic La3SbZn3Ge2O14 (LSZG) was studied with Xray powder diffraction technique. The trigonal crystal structures of LNG and LTG are stable under elevated temperature and no phase transition was detected up to 1123 K, whereas the monoclinic LSZG undergoes a phase transition at temperature 523(50) K, presumably to trigonal space group P321. The thermal expansion of LNG, LTG and LSZG is anisotropic. This can be explained by the layer structure of title compounds. The mean coefficients in the monoclinic a, b and c directions for LSZG from room temperature to 523(50) K are 8.20, 8.47 and 6.22 [10(-6)/K], respectively. The mean coefficients in the trigonal a and c directions are 8.141 and 6.162 [10(-6)/K] for LNG; 7.653 and 5.344 [10(-6)/K] for LTG from room temperature to 1123 K.