Reductive lithium insertion into B-cation deficient niobium perovskite oxides

Abstract

Reaction between LiH and the A(n)B(n-1)O(3n) cation deficient perovskite phases Ba(5)Nb(4)O(15), Ba(6)TiNb(4)O(18) and Ba(3)LaNb(3)O(12) proceeds by reductive lithium insertion, leading to the formation of Ba(5)LiNb(4)O(15), Ba(6)LiTiNb(4)O(18) and Ba(3)LaLiNb(3)O(12) respectively. During lithium insertion into Ba(5)Nb(4)O(15) and Ba(6)TiNb(4)O(18) 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 Ba(3)LaNb(3)O(12) 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 Ba(5)LiNb(4)O(15) and insulating behaviour for Ba(6)LiTiNb(4)O(18) and Ba(3)LaLiNb(3)O(12). Detailed analysis of the crystal structure of Ba(6)LiTiNb(4)O(18) suggests crystallographic charge ordering in this phase.

Conversion of Li2FeSbO5to the Fe(III)/Fe(V) Phase LiFeSbO5via Topochemical Lithium Extraction

“…This differs from the stacking sequence of Li 2 FeSbO 5 , revealing that on lithium deintercalation the Li 2– x Sb 2 O 5 blocks slide relative to each other to generate octahedral coordination sites for the iron centers, which are occupied with a minor rearrangement of the Fe centers, to generate the structure shown in Figure . Similar shifting of close packed blocks has been observed during intercalation of lithium into layered, cation-deficient perovskite oxides and other related reactions . This large structural change observed on lithium removal is probably responsible for the apparent irreversibility of the chemical delithiation of Li 2 FeSbO 5 , as noted above.…”