Showing papers by "Yoshihiro Ishibashi published in 1976"
TL;DR: In this article, the Curie-Weiss constant is unusually small and this fact directly accounts for a possible sign change of the spontaneous polarization by only a slight variation of model parameters with temperature.
Abstract: Dielectric properties of two nonequivalent sublattice polarizations are studied. Assuming a strong coupling favoring an antiparallel alignment of polarizations, the model reveals some new features of a ferroelectric transition with no multiple change of the unit cell volume. The Curie-Weiss constant is unusually small and this fact directly accounts for a possible sign change of the spontaneous polarization by only a slight variation of model parameters with temperature. The model also can describe a para-ferroelectric phase transition followed by an isomorphous phase transition between two ferroelectric phase with no change of symmetry. Temperature dependence of susceptibility is derived with the emphasis on the critical region in which the applied pressure or electric field smears out the difference between two isomorphous phases. The model can explain some properties of ammonium sulfate, dicalcium strontium and lead propionate.
81 citations
TL;DR: In this article, the phase transition in ammonium Rochelle salt is discussed from the symmetry point of view and the role of identity representation in the theory of phase transitions is briefly discussed.
Abstract: Recent progress in the understanding of the improper ferroelectric phase transitions is reviewed. The phase transition in ammonium Rochelle salt is discussed from the symmetry point of view. The phase transitions in some improper ferroelectrics, such as langbeinite, boracite and dicalcium strontium propionate, are discussed and several problems on these materials, which are still controversial, are pointed out. In connection with the isomorphous phase transition recently discovered in dicalcium strontium propionate, the role of identity representation in the theory of phase transitions is briefly discussed.
23 citations
TL;DR: In this paper, the dilatometric measurements for CsSrCl 3 by means of differential transformer, and measurements of pressure dependence of three transition points were carried out, and the expressions for spontaneous strains in each phase and for pressure coefficients of the transition temperatures are phenomenologically derived.
Abstract: The dilatometric measurements for CsSrCl 3 by means of differential transformer, and measurements of pressure dependence of three transition points were carried out. It has turned out that the pressure coefficients of three transition points are 10.1, 11.0 and 9.2 deg/kb. The expressions for spontaneous strains in each phase and for pressure coefficients of the transition temperatures are phenomenologically derived.
14 citations
TL;DR: In this article, the Raman scattering spectra of Ca 2 Sr(C 2 H 5 CO 2 ) 6 and Ca 2 Pb (C 2H 5 CO 6 ) 6 were studied in the frequency range up to 2000 cm -1 and in the temperature range between -200°C and 150°C.
Abstract: Raman scattering spectra of Ca 2 Sr(C 2 H 5 CO 2 ) 6 and Ca 2 Pb(C 2 H 5 CO 2 ) 6 were studied in the frequency range up to 2000 cm -1 and in the temperature range between -200°C and 150°C. No soft mode was observed. As a result, it is concluded that the phase transition of both materials is of order-disorder type.
12 citations
TL;DR: In this article, the phase diagram of the Ca 2 Pb x Sr 1-x (C 2 H 5 CO 2 ) 6 mixed system is presented on the basis of dielectric and dilatometric anomalies.
Abstract: The phase diagram of the Ca 2 Pb x Sr 1- x (C 2 H 5 CO 2 ) 6 mixed system is presented on the basis of dielectric and dilatometric anomalies. By the continuity of the phase in the mixed crystal system to those of two end members the space groups of Ca 2 Pb(C 2 H 5 CO 2 ) 6 are identified to be D 4 4 (D 8 4 ) and C 2 4 (C 4 4 ) at high, intermediate and low temperatures, respectively.
9 citations
TL;DR: In this paper, the second-order Raman spectra of CsCl single crystals have been measured at room temperature for different Raman polarizations and crystal orientations, with the help of the calculated selection rules for a csCl-type lattice, observed nineteen peaks and shoulders were assigned by the critical point analysis based on the neutron scattering data.
5 citations
TL;DR: In this paper, the elastic constants in Cd 3 Mg and Cd 2 Mg were measured at room temperature by using ultrasonic technique and the temperature dependences of c 11 and c 33 were also measured in the ordered phase as well as in the disordered phase.
Abstract: All the elastic constants in Cd 3 Mg and Cd 2 Mg were measured at room temperature by using ultrasonic technique. The temperature dependences of c 11 and c 33 were also measured in the ordered phase as well as in the disordered phase. The results are compared with those so far reported for crystals with different compositions.
4 citations
TL;DR: The far-infrared optical properties of CsCl at 300 and 80 K have been calculated by assuming the two-phonon summation-and difference-relaxations of k = 0 TO mode as mentioned in this paper.
Abstract: The far-infrared optical properties of CsCl at 300 and 80 K have been calculated by assuming the two-phonon summation- and difference-relaxations of k =0 TO mode. The frequency-dependent damping and frequency shift, due to cubic anharmonicity, have been calculated by using the eigenfrequencies and eigenvectors obtained from a simple shell model. Using the frequency shift and damping, the refractive index, the extinction coefficient and the reflectivity are calculated, and the results are compared with the experimental values obtained from the far-infrared reflection spectra. It is shown that the observed dip in the far-infrared reflection spectrum is due to the strong peak at 135 cm -1 in the damping spectrum (300 K).
2 citations