抄録
Structural phase changes in K2SeO4 have been found at 129.5°K and 93°K by introducing free radical SeO4− as a probe.
The structure in the temperature range between 129.5°K and 93°K is expected to be orthorhombic with the crystallographic axes coincident with those of room temperature. The unit cell may contain twelve molecules located at three different sites. A superstructure, a tripled lattice parameter along the a axis, has been found by X-ray diffraction method and an expected space group is Pnam. It is ferroelectric along the c axis below 93°K. A possible unit cell contains twelve molecules located at six different sites and is monoclinic in the space group P21, in which the superstructure is maintained. The crystal probably consists of fine twins with the common c axis and they are related with each other by mirror planes. The higher transition is of second order and the lower of first order. Conformations of radicals SeO2− and SeO3− in the crystal lattice are illustrated.
