Synthesis, crystal structure and properties of a quaternary oxide with a new structure type, BiGaTi4O11

A new quaternary oxide, BiGaTi4O11 (bismuth gallium tetratitanium undecaoxide), was prepared by heating a mixture of the binary oxides at 1373 K in air. BiGaTi4O11 melts at 1487 K and prismatic single crystals were obtained from a sample melted at 1523 K and solidified by furnace cooling. The structure of BiGaTi4O11 was analyzed using single-crystal X-ray diffraction to be of a new type that crystallized in the space group Cmcm. A Bi3+ site is coordinated by nine O-2 anions, and three oxygen-coordinated octahedral sites are statistically occupied by Ga3+ and Ti 4+ cations. A relative dielectric constant of 46 with a temperature coefficient of 57 ppm K1 in the temperature range 297-448 K was measured for a polycrystalline ceramic sample at 150 Hz-1 MHz with a dielectric loss tan of less than 0.01. Electrical resistivities measured at 1073 K by alternating-current impedance spectroscopic and direct-current methods were 1.16 10 4 and 1.14 10 4 S cm 1, respectively, which indicates that electrons and/or holes were conduction carriers at high temperature. The optical band gap estimated by the results of diffuse reflectance analysis was 2.9-3.0 eV, while the band gap obtained from the activation energy for electrical conduction was 3.5 eV.