Phase Transition In K2SeO4 Research Articles

Kinetic process of the commensurate-incommensurate phase transition in K2SeO4

Abstract The kinetic process of the commensurate-incommensurate phase transition in K2SeO4 has been studied by the measurements of the time evolutions of polarization and dielectric constant during the field-induced transition. The time evolutions are qualitatively similar to those observed for Rb2ZnCl4, and can be explained by our theory of the time evolution of discommensuration lattice during the commensurate-incommensurate transition.

Effect of Electric Field on the IC-C Phase Transition in K2SeO4

The effect of electric field on the IC-C phase transition in K2SeO4 has been investigated by measuring the ESR spectra and the crystal current in the ESR circuit. It has been found that time development of the crystal current after the application of static electric field shows two different time dependencies; one is rapid and reversible and the other is slow and irreversible. The slow change of the crystal current can be represented well as t0.21. The peak of the crystal current which corresponds to that of the dielectric loss shifts to higher temperature with increase of the frequency of applied microwave. From the quantitative analysis of the shift, it is shown that the polarization fluctuation around Tc in K2SeO4 can be explained by the relaxational model with a temperature dependent activation potential.

Optical second harmonic study of the ieicommensuirate phase in K2SeO4and (NH4)2BeF4crystals

Abstract Second harmonic generation was studied in the region of phase transition in K2SeO4 and (NH4)2BeF4. Symmetry-forbidden harmonic generation was observed in the incommensurate phases near Tc. The experimental results are explained under assumption that the unipolar domain-like structure with C2v symmetry appears in the incommensurate phase.

Influence of external electric field on incommensurate-commensurate phase transition in K2SeO4and (NH4)2BeF4crystals. I. Static properties

The author presents a study of the influence of an external electric field on the incommensurate-commensurate phase transition in K2SeO4- and (NH4)2BeF4-like crystals. Within the constant-amplitude approximation the same type of thermodynamic potential is found in both cases. The phase diagram in the E-T phase plane is found and should exhibit a Lifshitz point. The susceptibility of the incommensurate phase diverges at the transition point while that of the commensurate phase remains finite.

Vanishing of the phase transitions and quantum effects in K2SeO4at high pressure

Abstract The effects of pressure on the dielectric properties and phase transition in K2SeO4 were investigated. The incommensurate-to-commensurate ferroelectric transition vanishes at 0.73 GPa, and the paraelectric-to-incommensurate transition is expected to vanish at ∼ 1.13 GPa. These large pressure effects can be understood in terms of the delicate balance between Coulomb and short-range interactions. The results show the increased influence of quantum effects on approaching the displacive limit (i.e. Tc = O K), and they confirm the existence of a γ = 2 regime in the temperature dependence of the susceptibility, as predicted by recent theories.

Stress dependence of Tc for the incommensurate phase transition in K2SeO4

Abstract We have measured the uniaxial stress dependence of the frequency of the zone center A1 soft mode in the low temperature phase of K2SeO4. The frequency shows a strong decrease with stress. We infer from this a similar decrease of the incommensurate phase transition temperature Tc. This behavior is explained by detailed lattice dynamical calculations for K2SeO4 which reveal the unusual balance between Coulomb and short-range forces in this structure. Our calculations show that this balance is changed by stress in such a way that the quasi-harmonic normal mode frequencies harden drastically. Tc is reduced by this purely volume dependent effect. This unusual balance between Coulumb and short-range forces also provides a natural explanation for the occurence of an incommensurate phase transition in K2SeO4. We infer that similar transitions are likely in isomorphous structures.