Reductive lithium insertion into B-cation deficient niobium perovskite oxides.

Reaction between LiH and the AnBn-1O3n cation deficient perovskite phases Ba5Nb4O15, Ba6TiNb4O18 and Ba3LaNb3O12 proceeds by reductive lithium insertion, leading to the formation of Ba5LiNb4O15, Ba6LiTiNb4O18 and Ba3LaLiNb3O12 respectively. During lithium insertion into Ba5Nb4O15 and Ba6TiNb4O18 the respective ccchh and cccchh stacking sequences are converted into entirely cubic stacking sequences, while the B-cation vacancy order of the two phases is faithfully converted into Li-Nb or Li-Nb/Ti cation order in the lithiated products. In contrast lithium insertion into Ba3LaNb3O12 leads to no gross change in structure, with the inserted lithium cations displacing some of the niobium cations leading to a cation disordered material. Transport measurements indicate semiconducting behaviour consistent with variable range hopping for Ba5LiNb4O15 and insulating behaviour for Ba6LiTiNb4O18 and Ba3LaLiNb3O12. Detailed analysis of the crystal structure of Ba6LiTiNb4O18 suggests crystallographic charge ordering in this phase