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

A new quaternary oxide, BiGaTi₄O₁₁ (bismuth gallium tetratitanium undeca-oxide), 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. ABi³⁺ site is coordinated by nine O² anions, and three oxygen-coordinated octahedral sites are statistically occupied by Ga³⁺ and Ti⁴⁺ 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 x 10⁴ and 1.14 x 10⁴ Scm¹, 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.