B. Hilczer

Electric conductivity in crystal group Me3H(SeO4)2 (Me: NH+4, Rb+, Cs+)

Abstract Electric conductivity measurements were made by means of impedence spectroscopy for crystals of the Me 3 H(SeO 4 ) 2 (Me: NH 4 , Cs, Rb) group. All the crystals are superionic in the high temperature phase. Basic conductivity characteristics were estimated. The results well agree with structural studies.

Electric conductivity of tgs, pure and with lattice defects

The temperature dependence of dc steady state conductivity was measured in the three crystallographic directions for pure and y-irradiated TGS single crystals. An exponential law is obeyed from 20 to 80°C, with a change in activation energy at Tc. The electric conductivity is the highest along the c-axis. The three activation energies increase slowly with increasing defect concentration in the paraelectric state. In the ferroelectric phase, they increase initially up to about 0.5 MR and then decrease. Various radiation-induced changes in the three axes may suggest that the electric conductivity in TGS can vary in type from different crystallographic directions.

Structural aspects of fast proton transport in (NH4)3H(SeO4)2 single crystals

Though it is generally accepted that fast proton transport in superionic hydrogen sulphate and selenate crystals proceeds via Grotthuss mechanism and conditions of intra- and intermolecular proton transport were discussed considerably, there was no structural data support available. We report here results of X-ray studies of (NH 4 ) 3 H(SeO 4 ) 2 single crystals in superionic phases II and I. Mean thermal amplitudes of the O(2) oxygens from neighbouring SeO 4 in the (001) plane were calculated on the basis of riding model analysis of experimentally obtained anisotropic temperature factors. It is shown that thermal excitations of SeO 4 tetrahedra in the superionic phases result in a variety of O(2)-O(2) separation length conditioning both the near barrierless proton transfer and breaking of hydrogen bonds in the (001) plane.

Ferroelasticity of M 3 H(XO 4 ) 2 Crystals: FT NIR Raman, Ferroelastic Domain and Pretransitional Effects Studies

Temperature studies of Raman spectra and ferroelastic domain structure of Rb 3 H(SeO 4 ) 2, Rb 3 H(SO 4 ) 2 and (NH 4 ) 3 H(SO 4 ) 2 crystals are presented. Anomalous behaviour of frequencies and line width of bands related to the internal vibrations of SO 4 and SeO 4 in the vicinity of superprotonic phase transitions T S was found. Significant changes in the ferroelastic domain patterns just below T S are also presented. It was found that Rb 3 H(SO 4 ) 2 is not a ferroelastic in low conductivity phase. The role of ferroelasticity in the superprotonic phase transition is discussed.

Ferroelastic domain structure and thermal behavior of some Me3H(XO4)2 crystals in the vicinity of superprotonic phase transitions

Abstract Thermal evolution of ferroelastic domain structure and differential scanning calorimetric (DSC) investigations of Rb 3 H(SeO 4 ) 2 (TRHSe), Cs 3 H(SeO 4 ) 2 (TCHSe) and (NH 4 ) 3 H(SO 4 ) 2 (TAHS) in the vicinity of the superprotonic phase transition are presented. It was established that new domain structure appears in Rb 3 H(SeO 4 ) 2 crystals at ( T s −5.8) K, and another fine domain arises at ≈( T s −1.8) K. In Cs 3 H(SeO 4 ) 2 and (NH 4 ) 3 H(SO 4 ) 2 crystals, a very dense domain pattern appears at 1.3 and 0.6 K, respectively, below the superprotonic phase transitions. DSC measurements show anomalies at similar temperatures at which changes in the ferroelastic domain pattern were observed. The anomalous behavior of domain structure indicates that the transition to superprotonic phase is more complicated than that described in the literature.

Electric conductivity of some ferroelectric crystals

Abstract Steady state conductivity vs. temperature was measured for Pb5(Ge,Si)3O11 mixed crystals and, moreover, for TGS and LAS pure and deuterated crystals. Change in activation energy at Tc was observed with activation energy in the ferroelectric phase higher than in the paraelectric phase. In case of TGS the second change in activation energy at low temperatures was found with low temperature activation energy close to those of the paraelectric phase.

Proton ordering model of superionic phase transition in (NH4)3H(SeO4)2 crystal

Abstract The microscopic proton ordering model is developed for the description of the phase transition sequence from superionic phase II to ferroelastic phases III and IV in the (NH4)3H(SeO4)2 crystal. Symmetry analysis of proton orderings in phases III and IV is performed using structural data. The equilibrium states of the proton subsystem are studied and the corresponding phase diagram determining the necessary conditions for the existence of different proton orderings is constructed within the frame of the mean-field approximation taking into account long-range proton interactions. Investigations of thermodynamic functions as well as the temperature dependence of proton average occupation numbers are performed numerically. The resulting picture corresponds to experimental data for the network of hydrogen bonds in these crystal phases. The results are compared with the conclusions which follow from the phenomenological approach based on the Landau expansion.

Dynamic pyroeffect and resonance phenomena in pvdf based diaphragm-type systems: Physical and application aspects

Abstract Frequency dependence of pyroelectric response of polarized P(VDF/TFE) (0.98/0.02) 70 μm foil was studied and its amplitude-phase analysis is provided. A low frequency pyroelectric resonance is discovered. The resonance is observed in the case of thermal excitation of the foil close to the electrode being grounded during poling. The effect is explained by nonhomogeneous distribution of pyro- and piezoelectric activity. Moreover, influence of acoustic and electric field on the pyroelectric response is discussed from the application point of view.

Superionic phase transition in Rb4LiH3(SO4)4, Rb4LiH3(SeO4)4 and K4LiH3(SO4)4 single crystals

Abstract DTA studies of a new family of ferroelastic crystals of Me4LiH3(XO4)4 stoichiometry revealed at Ts another phase transition in the paraelastic phase, accompanied by an anomalous increase in the capacitance. Complex impedance method was used to study temperature variation of electric conductivity and its anisotropy of Rb4LiH3(SO4)4, Rb4LiH3(SeO4)4 and K4LiH3(SO4)4 single crystals. The bulk conductivity of the crystals varies from 10−6 to 10−4 (ωm)−1 in the temperature range from ∼ 400 K to temperatures below melting. The conductivity σc is ∼ one order of magnitude lower than σa ∽ σb. At Ts the activation energy Wa ∽ Wb decreases from 0.94 – 1.35 eV below Ts to 0.27 –0.28 eV at T > Ts. Comparison of the data with the crystallographic structure allowed us to classify the transition as superionic.

Structure and phase transitions in Cu2P2O7

X-ray diffraction studies of the temperature variation of the Cu2P2O7 crystal structure were performed in the vicinity of the transition from the α-phase (C2/c space group) to the β-phase (C2/m space group). These results as well as those of Raman spectroscopy studies and temperature variation of the electric capacitance point to the existence of an intermediate phase in the temperature range 347–363 K.