Possible Origins of High-Tc, Superconductivity

A new mechanism is proposed to explain high-T, superconductivity in copper-oxide-based, open perovskitelike systems. It is shown that, should the oxygen ions be moving in a double-well potential, an order-of-magnitude enhancement of the electron-lattice coupling follows automatically from a consistent treatment of this motion. Both theoretical and experimental evidence for the presence of such double wells is cited

Arnold M. Karo

Arnold M. Karo died on 16 June 1991 at age 63, after a yearlong battle with leukemia. He was a theoretical chemist and solid-state physicist with the chemistry and materials science department at Lawrence Livermore National Laboratory

Lattice Dynamics and Second-Order Raman Spectrum of CsF

Results are presented for a precise calculation, based on the deformation dipole model with short-range repulsive interactions between second-neighbor negative ions, of the normal-mode frequency distribution of CsF. The extreme properties of this crystal are reflected in the unusual appearance of the distribution. From these results, we can also predict the form of the second-order Raman spectrum of CsF for two alternative assumptions regarding the Raman polarizability tensor. Both spectra are unusual in that they consist almost entirely of very sharp, clearly separated lines. Furthermore, the spectra corresponding to these two assumptions are very different and should be easily distinguishable experimentally

Reply to “Comments on ‘Theoretical study of impurity-induced first-order Raman spectra for the alkali halides’”

This is a reply to the preceding comment by Page on the relative merits of the breathing-shell and deformation-dipole models for predicting defect-activated first-order Raman spectra. We show that when both models are parametrized in the same fashion the agreement between theory and experiment is comparable

Lattice Dynamics and Second-Order Raman Spectrum of CsF

Results are presented for a precise calculation, based on the deformation dipole model with short-range repulsive interactions between second-neighbor negative ions, of the normal-mode frequency distribution of CsF. The extreme properties of this crystal are reflected in the unusual appearance of the distribution. From these results, we can also predict the form of the second-order Raman spectrum of CsF for two alternative assumptions regarding the Raman polarizability tensor. Both spectra are unusual in that they consist almost entirely of very sharp, clearly separated lines. Furthermore, the spectra corresponding to these two assumptions are very different and should be easily distinguishable experimentally

Possible Origins of High-\u3ci\u3eT\u3csub\u3ec\u3c/sub\u3e\u3c/i\u3e, Superconductivity

A new mechanism is proposed to explain high-Tc superconductivity in copper-oxide-based, open perovskitelike systems. It is shown that, should the oxygen ions be moving in a double-well potential, an order-of-magnitude enhancement of the electron-lattice coupling follows automatically from a consistent treatment of this motion. Both theoretical and experimental evidence for the presence of such double wells is cited

Theoretical Study of the Structural Phase Transition in RbCaF\u3csub\u3e3\u3c/sub\u3e

We have made a first-principles study of the structural phase transition at Tc = 193 K in RbCaF3, using interionic potentials derived by the Gordon-Kim approach, and a new extension of the quasiharmonic approximation for the free energy. The transition is caused by instability of a triply degenerate R-point vibration which leads to a coordinated rotation of the CaF6 octahedra. We find that, as the lattice contracts, the quasiharmonic frequency of the R-point vibrations becomes imaginary at approximately 1280 K: Below this temperature the static lattice energy, as a function of CaF6 rotation, has a double minimum. However, the quasiharmonic free energy has no minimum for finite rotations until T ≤ 125 K. Thus the present theory predicts that Tc = 125 K (cf Tc = 193 K. experimental). In the region between 125 and about 1280 K nests of modes about the zone edges have imaginary quasiharmonic frequencies. By a simple extension of the quasiharmonic theory their contribution to the free energy has also been included. We also predict that the melting temperature is approximately 1350 K, which agrees very well with the measured value of 1382 K. However, the predicted thermal expansion of the perovskite phase at room temperature is ~17% lower than the observed value. This leads us to argue that the good agreement between theoretical and experimental melting temperatures is, in part, due to a cancellation between neglected anharmonic effects and certain deficiencies in the interionic potentials. We also find that, for the tetragonal phase, the calculated c / a ratio and rotation angle for the CaF6 octahedra which minimize the static energy are in good agreement with measured values at low temperature. We also discuss certain more general implications of the present work. Specifically, we suggest that our results indicate that it may be more natural to regard the structural phase transition as arising from the unfreezing of the distortion associated with the lower-symmetry phase. Our results also provide a natural explanation for the apparently universal tendency of transition temperatures for zone-boundary instabilities to be raised by hydrostatic stress

Infrared Absorption Properties of LiH, LiD Mixed Crystals

The normal modes of pure LiH and LiD, required in impurity mode calculations, have been computed on the basis of the deformation-dipole model. Neutron-scattering results of Verble, Warren, and Yarnell for Li7D, along with some other experimental quantities, have been used to determine the various parameters involved. It is found that the frequency spectrum of LiH has a gap and that a substitutional D- ion produces a local mode in this gap whose frequency has been computed, together with its amplitude at the impurity. The infrared absorption frequency associated with this local mode and its integrated absorption have been computed as functions of D- content in the limit of low D- concentration. Also, we find an in-band resonance in the amplitude of the substitutional D- ion. Similar calculations have been carried out for H- impurities in LiD. The present results are compared with those of other calculations and with experiment

Raman Scattering and Lattice-Dynamical Calculations of Crystalline KNO\u3csub\u3e3\u3c/sub\u3e

The Raman spectrum of a KNO3 single crystal was measured at both room and liquid-nitrogen temperatures. Lattice-dynamical calculations, based on the rigid-ion approximation and empirical potentials, were performed. The possibility of a phase transition at 217 K was investigated by measuring the temperature dependence of the Raman spectrum

Attitude of the church and state in Scotland to sex and marriage: 1560-1707

The thesis examines the attitudes which lay behind the different laws relating to marriage and sexual offences enacted between 1560 and 1707 by the Scottish Parliament, the Privy Council and the General Assemblies of the Church of Scotland. The Canon Law as it was taught in Scotland in Scotland in the 1530's is considered as it is necessary to identify both the changes between and the continuity of pre- and post-Reformation law. The particular topics included under 'marriage' are the regulations on the celebration of marriage, the penalties for irregular or clandestine marriages, the legal proofs for the existence of a marriage, and the introduction of divorce 'a vinculo' on the grounds of adultery and desertion. The sexual offences are incest, adultery, and fornication (including ante-nuptial fornication). The legislation passed by the central authorities represents the 'official' attitudes to sex and marriage but it does not necessarily reflect the attitudes of every section of society nor of actual behaviour. This material is therefore supplemented by examples derived from other published sources - kirk sessions, burgh councils, Court of Justiciary - local regulations and of the application of the law in particular cases. The evidence suggests that it is possible to outline a general moral code but that there were conflicting views on the definition of particular offences and the appropriate penalties. The thesis confirms the importance of undisputed paternity and the system of inheritance in discussing attitudes to sex and marriage, and shows that 'moral' legislation was as much a product of political events as other Acts of Parliament