Structural studies of deuterated CsH₂AsO₄in its paraelectric and ferroelectric phases

Abstract

The crystal structure of deuterated CsH2AsO4 (DCsDA) has been determined by neutron diffraction at room temperature and at Tc+5K in the tetragonal (paraelectric) phase using single-crystal samples. The structure has also been determined at 77K in the orthorhombic (ferroelectric) phase using an unpoled, unconstrained-and, so, poly-domained-sample. The results for both phases are compared with those obtained from similar studies of KD2PO4. Whilst the structures (and the way they change through the transition) are very alike in most respects, there are some interesting differences. In particular, the 'disordered' D(H) sites in the tetragonal phase are significantly further apart in DCsDA (by approximately 0.05 AA), yet the O-D(H)-O bondlengths are the same within error and the transition temperatures differ by only approximately 20K. This is remarkably like the relationship that obtains between RbH2PO4 and KH2PO4.