Wataru Kinase

Periodic 2D electron lattice model in the high-Tc superconductivity of the layered oxide materials

Abstract The high-Tc superconductivity in the layered oxides is discussed by the model of the two dimensional electron system arranged periodically. The electrons in the Cu—O plane form themselves into the square lattice of lattice length D by the condition D = √e/σ for the surface density σ of the positive back ground. The lattice length D corresponds to the incommensurate periodicity which has been discovered in the materials such as Bi, Ca compounds. When the surface density σ on the Cu—O plane increases and the lattice length D decreases as the temperature goes down, the electron pairing takes place accompanied by the enhancement of the covalency between the electrons. It is proposed that the square electron lattice changes into the hexagonal lattice at the critical temperature Tc where the superconductive phase is realized.

Theory of the domain wall in NaNO2 and the relation with the incommensurate structure

Two types of domain walls (a- and c-axes rotation) in NaNO2 are discussed. The mechanism of stability micro-domain is discussed taking account of the neutralizing charges. The discussion about the incommensurate phase is also made considering the electron-lattice interaction.

Domain Structure and Surface Electrons of Ferroelectrics in Incommensurate State

The periodicity of the incommensurate state in ferroelectrics is explained by considering that the area of the surface neutralization by one electron corresponds to the area of the microdomain in ferroelectrics, namely, NaNO2, K2SeO4 and Sr2Nb2O7. The state of the surface electrons is obtained quantum-mechanically, and the incommensurate phase transition is also discussed taking account of the interaction between the surface electrons and the ionic lattice.

The incommensurate character of the 2d electron system and its relation with ferroelectricity and superconductivity

Abstract The micro-domain structure of the high-T c superconductor Re-Ba-Cu-O system is discussed on the basis of a 2D electron lattice model taking into account that this material shows ferroelectricity between 240 K and T sc. The superconductive state is considered to be brought about by the change of lattice structure in the 2D electron system accompanied by the change of charge carrier density. The influence of the grain boundaries on the electrical conductivity is also discussed.

Theory of double refraction and kerr effect in BaTiO3

The mechanism of the double refraction in the tetragonal phase of BaTiO3 is explained considering the spontaneous Kerr effect due to the local field acting on the respective ions by a microscopic way of quantum mechanics. By using the variational method the change of the electronic polarizabilities of the constituent ions due to the local field is calculated by the determination of the change of the Slater-type orbitals of the constituent ions. It is found that the birefringence obtained Δn = -0.051, which is in good agreement with the experimental value-0.054. Furthermore the coefficient d33 of the optical SHG obtained from the calculated Kerr coefficients is also calculated as -42.6 × 10-9 CGSesu, which explains well the experimental value -(42 ± 3) × 10-9 CGSesu.

Theory of electrooptic effect in BaTiO3

The mechanism of electrooptic effect in BaTiO3 is discussed taking account of the dipole interaction among the constituent ions and their electronic polarizabilities. Three contributions are considered, namely; the first is caused by modified Lorentz correction for the dipole interaction, whose ratio to the whole contribution is estimated as 0.19; the second is due to the change of electronic polarizabilities due to the piezoelectric deformation, whose ratio is estimated as 0.81-(eclamp/efree); the third contribution is related to the spontaneous Kerr effect, whose ratio is regarded as eclamp/efree.

Theoretical study of temperature dependence of spontaneous polarization, optical properties and linear electro-optic coefficients of tetragonal KNbO3

The microscopic mechanisms of refractive indices, birefringence, spontaneous polarization and linear electro-optic effects are examined for KNbO3 using a microscopic model which takes into account a quantum method based upon the orbital approximation and the dipole-dipole interaction due to the local field acting on the constituent ions. It is found that the electronic polarizabilities play a major role in these calculations and that the birefringence n and the linear electro-optic coefficients are in good agreement with the experimental data.

Theory of the Successive Phase Transition in BaTiO3

The successive cubic-tetragonal-orthorhombic-rhombohedral phase transitions in BaTiO 3 are discussed quantitatively from the microscopic free energy based upon the mean field approximation, where the Ti ions shift in the lattice having the spontaneous deformation. It is shown that the effect of the spontaneous lattice deformation is essential to the appearance of the ferroelectric three phases and the experimental values of the transition entropies are well explained by this model of the displacive-type concerning the Ti ions.

Quantum theory of electrooptic effect in BaTiO3

The electrooptic effect in BaTiO3 is discussed based upon the non-linear electronic polarizabilities for the respective ions calculated by the variational method in quantum mechanics. The Pockels constants r33 are obtained as 41.4 × 10-8 in the clamped state and 265.6 × 10-8 in the free state respectively. The correlation between the Kerr effect and the piezoelectric effect is also discussed.

The random barrier model and the resistance anomalies in ferroelectric ceramics

The theory of the low-and high field conductivity of ferroelectric ceramics in the region of the positive temperature coefficient of the resistivity (PTCR) is reformulated on the basis of the random barrier model. For the low-field conductivity the model gives the temperature dependence of the conductivity essentially similar to that which follows from the Heywang equivalent-barrier model. The fluctuation of the barrier heights plays an important role for high fields where the shape of the current-voltage characteristic appears to be quite different from that given by the equivalent-barrier model. The experimental data on the high-field conductivity of (BaCe)TiO 3 -ceramics are in agreement with the predictions of the random barrier model.