Hypersonic studies in CsD2AsO4 and Cs0.84(ND4)0.16D2AsO4 single crystals

Abstract

The longitudinal (LA) Brillouin back-scattering spectra along the [1 0 0] (a-axis) phonon direction have been measured as a function of temperature (80–300 K) for both CsD2AsO4 (DCDA) and Cs0.84(ND4)0.16D2AsO4 (DCADA-0.16) single crystals. As the temperature decreases the acoustic phonon frequencies of both DCDA and DCADA-0.16 show a hardening (whose steepness is weaker in DCADA-0.16). A Landau–Khalatnikov-like maximum was observed in a pure crystal of DCDA and the polarization relaxation time is estimated to be τ∼2.0×10−11/Tc–T/s, where Tc∼206 K is the ferroelectric transition temperature. In DCADA-0.16, the temperature-dependent frequency shift shows a gradually rising anomaly associated with a damping maximum near ∼175 K. This phenomenon is attributed to coexistence of ferroelectric and paraelectric phases.