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-tri clinic phase transition of Bi26Mo9WO69, dense samples with different grain sizes were produced by isostatic pressing and controlling sintering tempera ture and time. The structural and electrical properties were studied by X-r ay diffraction (at room and at high temperature) and impedance spectroscopy , respectively. The influence of the microstructural properties on the tric linic-monoclinic phase transition and on the electrical properties of the B i26Mo9WO69 were described by the following parameters derived from the fitt ing of impedance diagrams: depression angle, relaxation frequency and total electrical conductivity. Impedance spectroscopy results are in agreement w ith the high-temperature X-ray diffraction data; both techniques show that phase transition kinetics depends on the microstructural properties, remark ably on the grain size. (C) 2001 Elsevier Science B.V. All rights reserved.