抄録
X-ray scattering from K2SeO4 crystal at temperatures near Tm=129.5 K is measured to elucidate the nature of the mechanism of the structural phase transition. On approaching Tm the super-lattice reflection at (2/3, 0, 4) decreases slowly, indicating that the transition at Tm is of the second order. The diffuse intensity near (2/3, 0, 4) increases near Tm and its distribution shows a strong anisotropy elongating along the a*-direction. It is suggested that the transverse optical phonon polarized along the c-direction softens at q=(2π⁄3a, 0, 0) near Tm.
