Browsing by Author "Xue, Z.-Q."

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Hypersonic studies in CsD2AsO4 and Cs0.84(ND4)0.16D2AsO4 single crystals
(1998-11) Tu, Chi-Shun; Schmidt, V. Hugo; Xue, Z.-Q.
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.
Phases in antiferroelectric‑side Rb1-x(ND4)xD2AsO4 mixed crystals by light scattering
(1998-09-01) Tu, Chi-Shun; Gao, S.-S.; Jaw, R.-J.; Xue, Z.-Q.; Hwa, L.-G.; Schmidt, V. Hugo
The Raman spectra of A1,B2, and E symmetries and the longitudinal [100] Brillouin backscattering have been measured as a function of temperature in the mixed ferroelectric (FE)-antiferroelectric (AFE) system Rb1−x(ND4)xD2AsO4 (DRADA-x) for ammonium concentrations x=0.39, 0.55, 0.69, and 1.0. Successive phase transitions [paraelectric (PE) phase⃗ coexistence of PE and AFE phases⃗ AFE phase] were observed in both x=0.55 and 0.69 as the temperature decreases. Taking into account earlier dielectric results, a phase coexistence of the deuteron-glass state and the AFE order is confirmed in x=0.39. In addition, a broad damping peak (that is associated with a Landau-Khalatnikov-like maximum in x=0.55 and 0.69) was observed in the Brillouin phonon spectra of x=0.39, 0.55, and 0.69. Such an anomaly is attributed to dynamic order-parameter fluctuations. Using previous results for ferroelectric-side DRADA-x, a phase diagram (ND4 concentration x vs T) with qualitative phase boundaries is also given.