STRUCTURAL DISORDER IN AGBR ON THE APPROACH TO MELTING

The powder neutron diffraction pattern of AgBr has been measured at nine temperatures between 293 K and 703 K (melting point Tm=701 K). The structure factors have been analysed using the reverse Monte Carlo modelling technique to produce three-dimensional distributions of ions which show the thermally induced structural disorder in AgBr. Anisotropic mean squared displacements about lattice sites and occupancy of interstitial ( 1/4, 1/4, 1/4) sites by Ag+ ions have been calculated for each temperature, giving a quantitative description of the development of the structural disorder associated with premelting.