Rb_1−x(NH₄)_x.H₂P_1−yAs_yO₄ (RADPA-xy) crystal: Randomly competing interaction and frustration

Abstract

Proton glass phases of Rb_1−x (NH₄) _x H₂P_1−y As _y O₄ (RADPA-xy) crystals are studied by dielectric and pyroelectric measurements for x=0.55 / y=0.65 and x=0.61 / y=0.46. For both x=0.55 and x=0.61 the a-cut samples are observed to have the lower onset temperatures of glassy freezing and larger dielectric constants as compared with the c-cut samples, implying that the effective field of antiferroelectric ordering proportional to x=[NH⁺ ₄] may be larger than that of the competing ferroelectric ordering proportional to 1 − x=[Rb⁺] in the Curie-Weiss regime before the onset temperature of freezing. The dielectric loss dependence on temperature and frequency in the proton glass was analyzed by Vogel-Fulcher scaling to obtain the distribution function f(E) of E, the energy barrier parameter of the Vogel-Fulcher law, v _˚ the Raman attempt frequency and T_˚ the static freezing temperature of the Vogel-Fulcher law: v _˚ ⋍ 1.6 × 10¹² Hz and T_˚ ⋍ 19.7 K for RADPA-xy (x=0.55, y=0.65) crystal. RADPA-xy (x=0.61) crystal was observed to show a thermal hysteresis in the dielectric measurements, and the pyroelectric measurements of the zero-field-cooled polarization P _ZFC were found to replicate the low frequency dielectric constant measured in the warming-up cycle.