Structural filiations in the new complex titanates SrLiMTi4O11 (M=Cr, Fe)

Two new titanates of strontium, lithium and a 3d metal, with the composition SrLiMTi4O11 (M=Cr, Fe), have been discovered. Single crystals were obtained by spontaneous crystallization from a high-temperature solution with LiBO2 as the solvent. The structure of SrLiCrTi4O11 was refined in the orthorhombic space group Pnma (Z=4), while SrLiFeTi4O11 appeared to adopt a four-times larger orthorhombic unit cell with Pbcn (Z=16). The structures can be described by a close-packed arrangement of Sr and O atoms. The unit cell contains six ;compact planes' perpendicular to [100] in the layer sequence ABACBC [(chc)2]. Ti and Cr or Fe atoms occupy some of the interstitial octahedral sites created, whereas Li atoms are in tetrahedral sites. Depending on the synthesis conditions of SrLiCrTi4O11, the distribution of Cr and Ti atoms on the four possible crystallographic sites is not the same. Having a similar compact-planes sequence, SrLiCrTi4O11 and SrLiFeTi4O11 structures differ in the arrangement of Sr and O atoms per layer of close packing, which also induces a correlated variation in the Li-tetrahedra distribution.