Dielectric and Raman investigations in the temperature and frequency ranges 300–550K and 102 – 104Hz respectively show that M2(SO4). Te(OH)6 with (M = K, Rb and Cs) materials present three phase transition. The first transition observed at 480, 440 and 460K respectively for M = K, Rb and Cs and should be probably of order-disorder type. The second one was observed only for Rb2(SO4). Te(OH)6 and Cs2(SO4). Te(OH)6 respectively at 510 and 495K. The third peak observed at 490, 520 and 510K for M = K, Rb and Cs respectively can be attributed to a ferroelectric-paraelectric phase transition.

Dielectric and Raman investigations on M2(SO4).Te(OH)6 (M =K, Rb and Cs)

Electric and dielectric measurements have been used to study the superionic conductivity and the ferroelectricity respectively in Rb0.8(NH4)0.2HSO4 single crystal. This material presents a high level of conductivity at high temperature. Activation energies were determined from the temperature dependence of the alternating-current conductivity in the regions 440-560 K and beyond 560 K; they are respectively 0.15 and 0.10 eV. The dielectric measurements show an intense anomaly at 285 K indicating a ferroelectric-paraelectric phase transition. This phase transition is accompanied by a significant dispersion of the real part of the dielectric constant in the frequency region investigated, in accordance with the high level of conductivity of this material.

https://iopscience.iop.org/article/10.1088/0953-8984/13/37/308/pdf

H+-ion conductivity and ferroelectric properties of rubidium ammonium hydrogen sulphate

A crystal of Cs1—x (NH4)xHSO4 (x=0.1) has been prepared by slow evaporation at room temperature. This crystal is of about.(1x1x0.5) mm3 and is monoclinic at room temperature. DSC, dielectric, optical and infrared measurements allow us to detect a second-order or slightly first-order phase transition at 346 K and a first-order phase transition: superionic protonic phase transition (SPT) at 410 K.

Dielectric, optical and infrared studies of the mixed caesium-ammonium acid sulphate Cs0.9(NH4)0.1HSO4

The phase transition in the mixed Cs 0.9 (NH 4 ) 0.1 HSO 4 were characterized by differential scanning calorimetry and Raman spectroscopy studies at temperatures ranging from 300 to 500 K. The I-II transition is characterized by the conversion of infinite (HSOj) n chains into cyclic (HSO 4 - ) 2 dimers. The II-III phase transition corresponds to a superprotonic phase transition (STP) where protons and SO 2- 4 ions contribute to the unusually high conductivity. The activation energy was determined from the plot of Δυ 1/2 as a function of temperature for the υ S-OH bands and from the conductivities. The two values have the same order of magnitude.

A. Daoud

Papers

Synthesis Characterization and Protonic Conduction in Mixed Caesium-Ammonium Hydrogenosulphate Cs0.95(NH4)0.05HSO4