Reductive lithium insertion into B-cation deficient niobium perovskite oxides

Abstract

Reaction between LiH and the A_nB_n−1O_3n 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.