Grain-sized influence on the phase transition of Bi26Mo9WO69: an X-ray diffraction and impedance spectroscopy study

In order to investigate the microstructure dependence of the monoclinic–triclinic phase transition of Bi26Mo9WO69, dense samples with different grain sizes were produced by isostatic pressing and controlling sintering temperature and time. The structural and electrical properties were studied by X-ray diffraction (at room and at high temperature) and impedance spectroscopy, respectively. The influence of the microstructural properties on the triclinic–monoclinic phase transition and on the electrical properties of the Bi26Mo9WO69 were described by the following parameters derived from the fitting of impedance diagrams: depression angle, relaxation frequency and total electrical conductivity. Impedance spectroscopy results are in agreement with the high-temperature X-ray diffraction data; both techniques show that phase transition kinetics depends on the microstructural properties, remarkably on the grain size.