Showing papers by "Yoshihiro Ishibashi published in 1972"

A Theory of the Phase Transition in ADP

Abstract: A four-sublattice theory is presented to explain the phase transition of ADP, where the dipole-dipole interaction is taken into account. The theory shows that the phase transition is of first order and the sublattice polarization is saturated below the transition temperature. These conclusions seem to be in good agreement with experimental observations.

Computer Experiment on Linear Chain of Atoms Lying in Double Minimum Potential

Abstract: Computer experiments have been carried out on the model which simulates Takahasi model of BaTiO 3 in the paraelectric phase. The lattice vibrations are studied on the monatomic linear chain in which each atom is in double minimum potential and is connected to nearest neighbor atoms by springs with the spring constant L . By tracing tracing the motions of all the atoms by Fourier analysis of the motions the k –ω dispersions are obtained. It has turned out that the increase of L induces many low frequency vibrations especially in the range of small k . The inherent relations to actual ferroelectric crystals are discussed.

The Role of Lorentz Factors in Rochelle Salt

Abstract: Mitsui's local field model of phase transitions in Rochelle salt is reexamined. The region for β and β', Lorentz factors, which yield spontaneous polarization only in intermediate temperatures, is extended. The cases that Mitsui treated where β and β' are both positive are included as a part of the present result. It has turned out that the sum of β and β' must be positive in order that a ferroelectric phase should appear either at low temperature side or at some intermediate temperatures.

Microscopic Theory of the Phase Transitions in Rochelle Salt

Abstract: Local field at general positions in Rochelle salt crystals is considered on the basis of the symmetry. The variation in dipole moments on each sublattice caused by applied electric field is obtained. The conditions for the instability of dipole arrangement are given for P2 1 2 1 2, P2 1 11, P12 1 1, P112 crystals in terms of susceptibility of dipolar radicals and Lorentz factors. The nature of electrostatic interaction energy of Rochelle salt is clarified, by taking into account the dipole-dipole interaction as well as the dipole-charge interaction between sublattices and also the electronic polarizability of ions situated on the two-fold axes along the c direction. Some coefficients which appear in Mitsui theory are reexamined under the light of the present results.