Phases in antiferroelectric-sideRb1−x(ND4)

Abstract

The Raman spectra of A 1 , B 2 , and E symmetries and the longitudinal ͓100͔ Brillouin backscattering have been measured as a function of temperature in the mixed ferroelectric ͑FE͒-antiferroelectric ͑AFE͒ system Rb 1Ϫx (ND 4) x D 2 AsO 4 ͑DRADA-x͒ for ammonium concentrations xϭ0.39, 0.55, 0.69, and 1.0. Successive phase transitions ͓paraelectric ͑PE͒ phase→coexistence of PE and AFE phases→AFE phase͔ were observed in both xϭ0.55 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 xϭ0.39. In addition, a broad damping peak ͑that is associated with a Landau-Khalatnikov-like maximum in xϭ0.55 and 0.69͒ was observed in the Brillouin phonon spectra of xϭ0.39, 0.55, and 0.69. Such an anomaly is attributed to dynamic orderparameter fluctuations. Using previous results for ferroelectric-side DRADA-x, a phase diagram (ND 4 concentration x vs T͒ with qualitative phase boundaries is also given. ͓S0163-1829͑98͒09033-X͔

Peculiarities of Ferro-Antiferroelectric Phase Transitions 9. Can the Substances with Coexisting Ferroelectric and Antiferroelectric Phases Mimic the Dipole-Glass Behavior?

“…15) may be related to the formation of complex FE+AFE domains in the paraelectric matrix of the substance. The dependence of the Brillouin shift on the temperature in this case has to be similar to the one found in [33] and shown in Fig. 15. …”

“…The same investigations for this system of solid solutions with compositions corresponding to the AFE side of diagram have been carried out in [33]. Authors attributed the anomalies of physical properties of the solid solutions with x = 0.10 near the temperature 160K to the onset of short-range AFE order caused by the freezing-in of (ND) 4 reorientations and imply a growth of local structure competition (between FE and AFE ordering).…”

“…Temperature dependencies of the same parameters for the solid solution with x = 0.55 [33] are given in the Fig. 15 on the right for illustration purpose.…”

“…For this reason, it seems expedient to analyze some experimental results obtained during investigations of phase transitions in the K 1-x (NH 4 [30], diagram for Rb 1-x (NH 4 ) x D 2 AsO 4 [33], the line T seg is added by authors of the present paper based on results of [31][32][33][34], and diagram for Rb 1-x (NH 4 ) x H 2 PO 4 [35].…”

“…The most complete presentation of results of investigation of phase coexistence in the systems under discussion are presented in [31][32][33][34]37] where Rb 1-x (ND 4 ) x D 2 AsO 4 solid solutions are considered as an example (phase diagram is presented in Fig. 12 we believe that it necessary to point out the resemblance of the Rb 1-x( ND 4 ) x D 2 AsO 4 -phase diagram and diagrams depicted in the Fig.…”