DEHYDRATION OF MOO3 . 2H2O - A NEUTRON THERMODIFFRACTOMETRY STUDY

A neutron powder thermodiffractometric study of the dehydration reactions MoO3 · 2H2O → MoO3 · H2O → MoO3 has been carried out in order to investigate the topotactic mechanism previously reported. The topotactic character of the reactions is confirmed and an approximate model for the crystal structure of MoO3 · H2O is proposed. Quantitative data about the relative amount of the existing phases, as a function of temperature, have been deduced from multiphase profile analysis. The anomalous behavior of the cell parameters of MoO3 · H2O, at about 100°C, indicates the existence of a new phase transition. The evolution of the crystallite size of MoO3 has also been obtained from the broadening of Bragg reflections at high temperature. The preferred direction of growth is along [021]. © 1993 Academic Press, Inc.