Synthesis and characterization of mixed-valence barium titanates

A single-crystal barium oxotitanate(III, IV) of approximate composition Ba-5.93(Ti-11.86(3+) Ti-28.14(4+))O-80, 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,L-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,L-3 and O K energy-loss near-edge structure (ELNES) of Ba-5.93(Ti-11.86(3+) T-28.14(4+))O-80 with those obtained from a K1.54Mg0.77Ti7.23O16 single crystal with hollandite structure, containing only Ti4+, revealed a shift in the Ti L-2,L-3 edge by 0.4-0.5eV 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,L-3 edges can be used to interpret coordination and bonding in related compounds.