Crystal structure of new Li+ ion conducting perovskites: Li2xCa0.5−xTaO3 and Li0.2[Ca1−ySry]0.4TaO3
Solid State Sciences, Volume 6, Issue 9, September 2004, Pages 923-929
Quoc Nghi Pham, Marie-Pierre Crosnier-Lopez, Françoise Le Berre, François Fauth, Jean-Louis Fourquet
Abstract
Two new solid solutions—Li2xCa0.5−xTaO3 (0.05<x<0.25) and Li0.2[Ca1−ySry]0.4TaO3 (0<y<0.15)—based on the A defective ABO3 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 Image , 2ap, Image (ap, primitive cubic cell parameter). The distortion of the cubic aristotype arises from the three tilts system a+b−b− of the TaO6 octahedra. For the same lithium content (x=0.10), the Sr2+ substitution to Ca2+ 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 Li0.2Ca0.4TaO3 and Li0.2[Ca0.9Sr0.1]0.4TaO3, respectively).