The volume ratio of domains in the tetragonal phase of KMnF3

The previous results on the domain volume distribution in the tetragonal phase of KMnF3 with the space group I4/mcm have been re-examined by X-ray and neutron single-crystal diffraction in a temperature range down to 110 K; the transition temperature between the cubic and tetragonal phases is 186.6 K. For a smaller specimen examined with X-rays, the distribution is fairly constant in a temperature region close to the transition, whereas it shows a gradual change at lower temperatures. For a larger specimen examined with neutrons, the distribution is nearly constant over the whole temperature range. The difference in the behaviour can be attributed to the size or shape effect and/or to the different distributions of defects. All the previous data can be explained on the basis of the present results.