Thermal Properties of the Frustrated Rb0.52(ND4)0.48D2PO4 System at Low Temperatures

Specific heat and thermal conductivity data, 1.5–35 K, are reported on the mixed (frustrated) ferroelectric-antiferroelectric crystal Rb0.52(ND4)0.48D2PO4. A glasslike linear term in the specific heat is resolved below 5 K and ascribed to random electric fields caused by the random distribution of Rb ions, in good agreement with the theory of McWhan et al. A maximum in C/T3 at 13.5 K is attributed to dispersionless motions of the deuterium ions, by analogy with KDP. In contrast to the specific heat, the thermal conductivity is not glasslike, displaying a maximum at 12.5 K of 37 mW cm-1K-1. At lower temperatures, the behavior of the thermal conductivity is tentatively ascribed to resonant phonon scattering from the Rb–ND4 system. The Debye temperature for the crystal is 303 K, in reasonably good agreement with extrapolations based on θD for KDP.