Crystal structure of new Li + ion conducting perovskites: Li 2 xCa 0.5− xTaO 3 and Li 0.2[Ca 1− ySr y] 0.4TaO 3

Abstract

Two new solid solutions—Li 2 x Ca 0.5− x TaO 3 (0.05⩽ x⩽0.25) and Li 0.2[Ca 1− y Sr y ] 0.4TaO 3 (0< y⩽0.15)—based on the A defective ABO 3 perovskite structural type, are synthesized. The crystal structures of these Li + ion conducting compounds are solved from synchrotron radiation and conventional X-ray powder diffraction data. The unit cells exhibit a classical orthorhombic distortion of the cubic perovskite model (space group Pnma No. 62) with parameters close to 2 a p , 2 a p, 2 a p ( a p, primitive cubic cell parameter). The distortion of the cubic aristotype arises from the three tilts system a + b − b − of the TaO 6 octahedra. For the same lithium content ( x=0.10), the Sr 2+ substitution to Ca 2+ is found to enhance the electrical conductivity by quasi-one order of magnitude (at 200 °C, bulk dc conductivity values are close to 2.3×10 −6 and 1.1×10 −5 S cm −1 for Li 0.2Ca 0.4TaO 3 and Li 0.2[Ca 0.9Sr 0.1] 0.4TaO 3, respectively).