Lattice Constants of CsH₃(SeO₃)₂and CsD₃(SeO₃)₂

Abstract

The temperature variation of the lattice constants below room temperature has been measured on an X-ray four-circle diffractometer for antiferroelectric CsH 3 (SeO 3 ) 2 and CsD 3 (SeO 3 ) 2 . The results confirm that the -65°C transition in CsD 3 (SeO 3 ) 2 corresponds to the -128°C antiferroelectric transition in CsH 3 (SeO 3 ) 2 . It is shown that the monoclinic modification of CsD 3 (SeO 3 ) 2 exists in as-grown crystals at room temperature in addition to the triclinic modification and that the monoclinic modification transforms to a triclinic one on cooling.