Synthesis and characterization of mixed-valence barium titanates

A single-crystal barium oxotitanate(III, IV) of approximate composition , containing mixed-valence Ti, was grown from a borate flux. The crystal structure was identified as hollandite type by single-crystal X-ray diffractometry. Electron-energy-loss spectroscopy of Ti L 2,3 and O K edges was used to determine chemical shifts related to the presence of mixed-valence Ti in the crystal. Comparison of Ti L 2,3 and O K energy-loss near-edge structure (ELNES) of with those obtained from a K 1.54 Mg 0.77 Ti 7.23 O 16 single crystal with hollandite structure, containing only Ti 4+ , revealed a shift in the Ti L 2,3 edge by 0.4-0.5 eV towards lower energy losses whereas only slight intensity variations without a detectable energy shift of the edge onset occur at the O K ELNES. In addition, valence-specific multiplet structures of the Ti L 23 ELNES are used as valence fingerprints. The observed fine structures of O K and Ti L 2,3 edges can be used to interpret coordination and bonding in related compounds.