Yuji Shiro

Coulomb interactions and optically-active vibrations of Ionic crystals—I: Theory and application to NaNO3

Abstract A method is given for polarizable-ion model calculations of optically-active vibration frequencies of ionic crystals together with an illustrative application. Frequency splittings originating from Coulomb interactions between induced dipoles are explained satisfactorily by the calculations. Important discrepancies remaining in rigid-ion treatments are considerably reduced by taking into account the electronic polarizabilities. Some effects of anisotropy of the ionic polarizabilities on crystal vibrations are discussed briefly.

Ionicity scale and piezoelectricity of crystals with zincblende- and wurtzite-type structure

Abstract We have tried to determine the ionicity of crystals with a dynamical effective ionic charge defined by the observed TO - LO splitting. We find excellent agreement between our results and the ionicity scale derived by Phillips from band gap theory. We confirm that the observed piezoelectric constants can be well accounted for on the basis of the Born lattice-dynamical treatment by adding the concept of charge transfer, and we have made an estimate of the latter.

Lattice dynamics of wurtzite-type crystals—II

Abstract We evaluated, in the preceding paper, the effective ionic charge and electronic polarizability for wurtzite-type crystals on the basis of the polarizable-ion model given by Born and Huang. With use of the quantities so evaluated, we here estimated the short-range force constants from observed frequencies, elastic constants, and piezoelectric constants after simplifying Born and Huangs procedures. The resulting set of force constants can reproduce the observed data except for the piezoelectric constants. This poor reproduction of the piezoelectric constants is due to the fact that the long-range force is emphasized in the polarizable-ion model.

Molecular vibrations and force fields of alkyl sulfides—XIV. Infrared spectra of ethyl isopropyl, propyl isopropyl, butyl isopropyl and diisopropyl sulfides☆

Abstract Infrared spectra of ethyl isopropyl and propyl isopropyl sulfides were examined in the liquid and glassy states, and those of butyl isopropyl and diisopropyl sulfides were observed in the liquid and crystalline solid states. The spectra observed were assigned. Normal coordinates were treated. We have then discussed on the rotational isomers and molecular conformations for these sulfides.

Lattice dynamics of wurtzite-type crystals including the effect of the electronic extension

Abstract Birman has given a physical meaning to the Ewald method and has given a potential including the effect of the electronic extension with the use of this method. Thus we can easily take into account the effect of the electronic extension with the use of the Birman method without considering any other new procedures. On the basis of the polarizable-ion model, after applying the Birman method we have calculated macroscopic quantities (wave number, elastic constant, and piezoelectric constant), and examined the contribution of this effect to them. The result is that the effect is not so small that it can be neglected, and enables better agreement with the observed macroscopic quantities to be obtained.

Optically-active vibrations and effective charges of dolomite

Abstract A rigid-ion model analysis was made for the optically-active crystal vibrations of dolomite (CaMg(CO 3 ) 2 ) with reference to that of calcite (CaCO 3 ) and magnesite (MgCO 3 ). Effects of the effective charge distribution on the TO—LO splitting were examined on the proposed distribution model, and the best set of the effective charges has been found by the use of the least-squares technique: Z C = 0·21, Z O = −0·48 and Z Ca and Z Mg = 1·24 respectively in electron units. Force field and effective charges determined in the present study reproduce satisfactorily well the observed transverse and longitudinal frequencies of the optically-active vibrations.

Molecular vibrations and force fields of alkyl sulfides: Part XV. C-S stretching vibrations of aliphatic alkyl sulfides

Abstract The C-S stretching vibrations of 28 aliphatic sulfides including one thiol are summarized, and all of the C-S stretching bands are classified into several groups. An extraordinarily low frequency associated with the ethyl group is discussed briefly.

Lattice dynamics of α-quartz including the effect of the width of the atomic electron distribution

On the basis of the polarizable-ion model (PIM) the effect of the width of the atomic electron distribution on the lattice dynamics of α-quartz was taken into account using the Birman method. The frequencies of optical mode, elastic constants and piezoelectric constants were reproduced using the parameters of this model (an effective charge z, a width parameter w, an electronic polarizability α, and force constants). The width parameter of oxygen atom was found to be about 0.59 Å, and the effective charge of the silicon atom 1.42 electron charges.