MAXIMUM-ENTROPY ANALYSIS OF THE CUBIC PHASES OF KOH AND KOD, NAOH AND NAOD

The maximum-entropy method (MEM) for structure determination is applied on the plastically crystalline phases of KOH and KOD characterized by delocalized H+ or D+ ions in a simple rock salt structure. The structure factors measured by neutron diffraction already give a consistent picture of the hydrogen distribution by conventional Fourier and modelling methods, which helps to understand the merit of the MEM. Owing to the negative sign of the scattering length of hydrogen, the MEM can, in a limited sense 'model free', separate off the hydrogen density distribution. It is found, however, that the MEM cannot be applied naively for these compounds and reasons are given why the uniform density as a priori information has to be given up in the present case. The a priori information procedure to be used is discussed. In addition, and perhaps unexpectedly, the deuterium density is also obtained.