Structural Study of Ferroelastic Phase Transition in TlH₂PO₄

Abstract

Ferroelastic phase transition in TlH ₂ PO ₄ has been investigated by means of neutron diffraction using single-crystal sample. The average structures of TlH₂PO ₄ in the phases I and II have been determined. The crystal analysis with anisotropic thermal parameters in the phase I has been carried out for the 2-site model of O atom that the oxygen atoms forming the PO ₄ tetrahedron are disorder while other atoms are order. The result means that the ferroelastic phase transition is mainly caused by the rotational motion of PO ₄ tetrahedra.

Keywords:

• Ferroelastic
• TlH₂PO₄
• phase transition
• crystal structure
• neutron