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Full-Text Articles in Physical Sciences and Mathematics
Dielectric Response Spectrum Of A Damped One-Dimensional Double-Well Oscillator, J. W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer
Dielectric Response Spectrum Of A Damped One-Dimensional Double-Well Oscillator, J. W. Flocken, R. A. Guenther, John R. Hardy, L. L. Boyer
John R. Hardy Papers
The characteristic features of the dielectric response spectrum associated with the condensation of a "soft" phonon mode during a ferroelectric phase transition can be reproduced by an oscillator moving in a damped linear double-well potential. The behavior of the response function below the transition temperature Tc can be simulated by introducing a linear mean-field coupling which destroys the symmetry of the well. Potentials derived from physically realistic parameters are shown to result in dielectric responses which are in order-of-magnitude agreement with experimental values.
Calculation Of Dielectric Susceptibility For Complex Ionic Systems: Application To A Predicted Superlattice, J. L. Feldman, L. L. Boyer, P. J. Edwardson
Calculation Of Dielectric Susceptibility For Complex Ionic Systems: Application To A Predicted Superlattice, J. L. Feldman, L. L. Boyer, P. J. Edwardson
John R. Hardy Papers
The Gordon-Kim theory of interionic interactions between closed-shell ions, which has had considerable success for existing alkali halide systems, has been applied to the determination of the structure, phonon dispersion, and room-temperature dielectric properties of a proposed superlattice, RbF(NaC1)2, of alkali halides. The dielectric properties of such a hypothetical material can have an unusually strong low-frequency dependence because of the presence of Brillouin-zonefolded "infrared”-active modes. In evaluating the standard expressions for the dielectric properties, in the rigid-ion approximation, we make use of standard cubic and quartic anharmonic terms in addition to the instantaneous-phonon cubic anharmonic term, which is …
Ferroelectricity In Perovskitelike Nacaf3 Predicted Ab Initio, P. J. Edwardson, L. L. Boyer, R. L. Newman, D. H. Fox, John R. Hardy, J. W. Flocken, R. A. Guenther, Wai-Ning Mei
Ferroelectricity In Perovskitelike Nacaf3 Predicted Ab Initio, P. J. Edwardson, L. L. Boyer, R. L. Newman, D. H. Fox, John R. Hardy, J. W. Flocken, R. A. Guenther, Wai-Ning Mei
John R. Hardy Papers
The ability of zero-stress simulations, using Gordon-Kim pair potentials, to describe the structures and transformations of known fluoride-based perovskites is demonstrated for the case of KCaF3. When K+ is replaced by Na+ a new ferroelectric crystal isomorphous with LiNbO3 is predicted. The equivalent relationships of the ferroelectric lithium niobate structure with the perovskite and antiperovskite structures are examined. A polarization of 21 jµC/cm2 at room temperature and a transition temperature of 550 K are predicted for NaCaF3. Surface effects are examined in simulations of a 1080-ion cluster.
Theoretical Study Of Lattice Instabilities In Yba2Cu3O7, D. P. Billesbach, John R. Hardy, P. J. Edwardson
Theoretical Study Of Lattice Instabilities In Yba2Cu3O7, D. P. Billesbach, John R. Hardy, P. J. Edwardson
John R. Hardy Papers
We have performed a molecular dynamics simulation of the YBa2Cu3O7 structure under the constraints of the rigid-ion model. These simulations used a variety of charge states for the Cu ions and the O ions, and except for one case, the interionic potentials were obtained in an ab initio fashion. The results of these simulations showed that a lattice instability involving the Cu-O chains existed. This instability was further investigated and it was shown that simple electronic screening is probably insufficient to stabilize the lattice. An instability of this nature provides a simple explanation of some …