A rapid chemical route to niobates: hydrothermal synthesis and transport properties of ultrafine Ba5Nb4O15

A rapid synthetic route to ultrafine Ba5Nb4O15 powders is reported in which the compound is hydrothermally prepared at 240 degrees C in 3 h. It was ch aracterized by powder X-ray diffraction, transmission electron microscopy, Raman, IR spectroscopy and thermal analysis-thermogravimetry. The influence s of various hydrothermal conditions such as reaction time and temperature on the formation, morphology and grain size of products were investigated. The product has a narrow distribution of particle size with particles ca. 1 00 nm in diameter. The electrical conductivity of Ba5Nb4O15 was investigate d from 300 to 800 degrees C by a complex impedance technique under differen t atmospheres. A mixed proton and electron conductivity was observed in a w et atmosphere. Electronic conduction originates from oxygen loss and ioniza tion of oxygen vacancies, whereas proton conduction arises from reaction of water molecules with oxygen vacancies. The conductivity and corresponding activation energy for Ba5Nb4O15 at 800 degrees C were 1.1 x 10(-4) S cm(-1) and 0.62 eV, respectively.