Crystal Growth and Conductivity Investigations on BiVO4 Single Crystals

Some oxides with the scheelite structure are well known mixed ionic and electronic conductors. This structure family, with the general composition ABO(4), can be described as a layer structure derivative of the fluorite structure. The relations between the structural and the electrical transport properties of these materials have been investigated. The model system used in this work was BiVO(4), which shows both electronic and ionic conduction. Single crystals of bismuth vanadate (BiVO(4)) were grown using the Czochralski technique. Single crystal boules up to 55 mm in diameter and up to 30 mm long were produced. The crystallographic orientation was determined by the Lane method, and they were cleaved along [001] planes and polished to optically perfect cubes with an edge length of 5 mm. Two-point ac impedance measurements in the temperature range between 550 degrees C and 700 degrees C were performed. The conductivities were measured as a function of the crystal orientation and showed strong anisotropy as expected from the crystal structure.