Table of contents

The relationship of the glass transition temperature T_g to transport properties has been established. Simple arguments relating transport to distributions of barrier heights, barrier heights to random potential reliefs, and typical potential fluctuations to crystalline potentials allows the establishment of a relationship between T_g and the melting temperature, T_m, by application of the Lindemann criterion for melting.

The authors numerically solve the time-dependent Ginzburg-Landau equation for a homogeneous, isotropic type-II superconducting film in the presence of an external magnetic field. They study the dynamical processes of the magnetization by stepwise change of the external field. It is demonstrated that the magnetic vortices penetrate and are expelled from the system boundary in accord with the change of the field, and the dynamical instability of magnetic flux wall near the boundary leads to the formation of a vortex at low fields. The hysteresis loop of magnetization versus the external field is also obtained.

The assumptions of conventional effective-mass theory, especially the one of continuity of the envelope function at an abrupt interface, are reviewed critically so that the need for a fresh approach becomes apparent. A new envelope-function method, developed by the author over the past few years, is reviewed. This new method is based on both a generalization and a novel application to microstructures of the Luttinger-Kohn envelope-function expansion. The differences between this new method and the conventional envelope-function method are emphasized. An alternative derivation of the new envelope-function equations, which are exact, to that already published is provided. A new and improved derivation of the author's effective-mass equation is given, in which the differences in the zone-centre eigenstates of the constituent crystals are taken into account. The cause of the kinks in the conventional effective-mass envelope function, at abrupt effective-mass changes, is identified.

The difference between the vapour pressures of HCl and DCl has been measured over the temperature range 170-203 K by a differential manometric technique in a precision cryostat. In this range the vapour pressure of HCl is higher than that of DCl by 3.2% at 170 K, decreasing to 0.9% at 200 K. The reduced partition function ratios f_l/f_g derived from the vapour pressure data can be described by the equation ln(f_l/f_g)=(3914.57+or-10)T²-(17.730+or-0.055)/T. The experimentally observed H-D vapour pressure isotope effect, together with the values on the ³⁵Cl-³⁷Cl isotope effect available in the literature, is interpreted in the light of the statistical theory of isotope effects in condensed systems by using spectroscopic data of the vapour and liquid phases. The results indicate that the rotation in liquid hydrogen chloride is hindered. Temperature-dependent force constants for the hindered translational and rotational motions were invoked in order to obtain better agreement between the model calculation and experiment.

A neutron diffraction study has been performed on AgBr at a series of temperatures from 293 K to 706 K (melting point, T_m=701 K), including measurements as close as 0.3+or-0.05 degrees from T_m. Analysis of the structure factors using the reverse Monte Carlo modelling technique indicates that the motion of the Ag⁺ ions about their rocksalt lattice sites is anisotropic, with increasing occupancy of the (1/4 1/4 1/4) tetrahedral interstitial site as the melting point is approached. It is concluded that the silver sub-lattice is undergoing a second-order transition to a fast-ion phase in which both tetrahedral and octahedral sites are occupied (possibly similar to the fast-ion transition in the high pressure FCC phase of AgI) although melting prevents complete transition. There is a clear discontinuity in Bragg scattering at T_m, suggesting that the first-order nature of the melting transition is unaffected.

The dynamics of phase separation in binary systems containing surfactants is investigated by means of a time-dependent Ginzburg-Landau model. The Langevin equations for two scalar fields are solved numerically in two spatial dimensions. One of these fields is the order parameter representing the local difference in the concentrations of the two phase-separating components and the second is the local surfactant concentration. Different conservation laws of the fields, which represent different models for the dynamics of phase separation, are investigated. In all models, the average domain size for intermediate to late times is characterized by anomalously slow dynamics caused by the accumulation of surfactants at the interfaces and by the concomitant decrease in the driving force. Although all models exhibit similar slow growth, the domain structure is found to depend strongly on the nature of the conservation law. Indeed, the structure factor exhibits a peak at k>0 when the order parameter is conserved, whereas the peak is found to lie at k=0 if the order parameter is not conserved. Finally, dynamical scaling in both real- and Fourier-space correlation functions for the order parameter is found during the intermediate time regime.

A molecular dynamics simulation on the phase transitions of a reheated Al_0.86V_0.14 glass is presented. The results obtained demonstrate a number of aspects of the transitions involved, leading to the suggestion that such solids as the experimentally reported amorphized icosahedral quasicrystals in the literature may be considered as highly perturbed quasicrystals, in which the orientational order is lost through the random orientation of icosahedra.

In this paper, the ab initio calculations of optical-phonon deformation potentials (ODPS) d₃₀, d₁₀(val) and d₁₀(con) on the Lambda axis in the Brillouin zone for 12 elemental and compound semiconductors are reported. This work is based upon the density-functional theory LMTO ASA band-structure method with a frozen-phonon model. The ODP values as functions of the k-points and their material dependences have been investigated.

Measurements of the specific heat from 0.4 to 7 K have been made on two polycrystalline specimens of samarium of different purity. There are differences in the specific heat of the two specimens between 2 and 7 K which are attributed to differing magnetic contributions. Below 2 K, both specimens show a small specific heat anomaly that is most likely due to samarium oxide. For samarium, a value for the electronic specific heat of 9+or-2 mJ mol^-1 K^-2 is obtained. Magnetization measurements on the two specimens between 2 and 40 K show a large peak at 13.7 K. A smaller peak in the magnetization, corresponding to that in the specific heat, is observed at 20.4 K in the purer specimen.

An average cluster Bethe lattice method is developed for the calculation of the electronic density of states of an infinite system of atoms. The correctness and efficiency of the method are tested by two examples of calculating the electronic structure for square and honeycomb lattices.

The muffin-tin multiple-scattering theory is employed to evaluate the interatomic forces in simple and transitional metals. In the framework of this theory the pair interatomic potentials have been calculated for K, Ni and Cu. The vacancy formation energy, the elastic constants and the phonon spectra have been obtained on the basis of the calculated potentials.

The band structure of lead sulphide has been investigated using angle-resolved photoemission, with synchrotron radiation in the photon energy range 25-95 eV as the excitation source. Many spectral features originate from direct transitions, while others are due to 'density of state' features, i.e. they arise from electrons scattered into the observation direction. Good agreement was found between the experimental spectra and transitions expected on the basis of the calculated linearized muffin-tin-orbital (LMTO) band structure and free electron final states. Partial yield spectra at the Pb O_4,5 edge are also reported, from which it is concluded that the exciton energy in lead chalcogenides is not anomalously large, in contradiction to previous work.

The author proposes a Su-Schrieffer-Heeger-type electron-phonon model for C₆₀ with O defects and solve it by using the adiabatic approximation. Two new properties are obtained: (i) the dimerization becomes weaker around the oxygen, two localized states appear deep in the gap, and optical transition between them is allowed-this accords with the recent optical absorption data; (ii) oxygens are predicted to cluster on the surface of C₆₀.

A complete set of symmetry-adapted vibronic states for strongly coupled orthorhombic T(X)(e+t₂) JT systems are derived analytically using projection operator techniques from the exact infinite-coupling states. Details are given for the case of a T₁ orbital state at a site of tetrahedral symmetry T_d. The purpose of this calculation is to provide a complete set of basis states from which it is possible to calculate analytically the second-order reduction factors for this JT system as shown in the companion paper. The states are used here to obtain the energy level diagrams for the first few excited states using appropriate choices for the parameter values. The results compare favourably with numerical results obtained elsewhere for similar systems.

Second-order vibronic reduction factors for spin-orbit coupling are derived for the strongly coupled orthorhombic T(X)(e+t₂) Jahn-Teller system. The method adopted is based on symmetry arguments as described by the authors in earlier papers. The symmetry-adapted cubic vibronic states, which are derived analytically in the companion paper, are used in the calculations. This approach gives a significant improvement in the accuracy compared to earlier calculations. The relevance of such calculations in the modelling of impurity T₁ ions occupying substitutional sites of T_d symmetry in III-V semiconductors is also discussed, with the orthorhombic GaAs:Cr³⁺ Jahn-Teller system considered as an example.

The authors study the Kronig-Penney model with incommensurate potentials in the presence of an electric field. Both localization and delocalization by electric fields are observed, which are results intermediate between those obtained in periodic and disordered systems under electric fields. By performing a multifractal analysis, they show that the wave functions for large fields are multifractal.

In this paper, the authors discuss a class of quasi-one-dimensional models containing both spins and charge, which share the same generic solutions. In particular, they concentrate on a Heisenberg model of a topologically frustrated antiferromagnet, and a d-p model for oxygen hole hopping in a subgeometry of the copper-oxygen plane of the perovskite superconductors. The outstanding feature of these models lies in the simplicity of their solutions: their ground states are exact and contain uncorrelated, short-ranged singlet pairs. Excitations in these models fall into two distinct classes, namely, spin-1/2 chargeless domain-wall excitations or 'spinons', together with their conjugate excitations, which take the form of spin-1/2 chargeless 'antispinon' domain walls in the Heisenberg model, and spinless charge+e hole excitations or 'holons' in the d-p model. In the case of the Heisenberg model, the authors have successfully constructed a sufficiently simple representation for the 'spinon' excitation which allows them to calculate its dispersion using elementary methods. This is therefore a concrete example of a 'spinon' excitation for which explicit representation has been possible.

Nuclear magnetic resonance of thallium impurities has been detected by monitoring the magnetic circular dichroism of the absorption of F centres produced by room temperature X-irradiation under optical pumping conditions in Tl-doped KCl and RbCl crystals. In addition, electron nuclear double resonance signals of the F centre ligands were detected without microwaves. The observed effects are caused by hyperfine coupling of the F centres to the surrounding nuclei. F centres are probably produced with a spatial correlation to the thallium impurities.

The birefringence, rotation of the optical indicatrix and optical activity of triglicine sulphate (TGS) have been measured in the paraelectric and ferroelectric phases using a high-accuracy universal polarimeter (HAUP). The present measurements are compared with results already published in the literature and, surprisingly, many of them have been found to be in clear disagreement. Possible sources of systematic error are pointed out in the case of the optical activity measurements. The spontaneous parts of the different optical properties in the ferroelectric phase have been studied. These parts can be considered to develop under the exclusive influence of the spontaneous polarization. Simple relationships between the spontaneous optical quantities and the spontaneous polarization (quadratic for birefringence and indicatrix angle, and linear for gyration) are observed. Several electro-optic and electrogyration coefficients referred to the polarization are evaluated.

The Curie-Weiss temperature dependence of the paramagnetic susceptibility of polycrystalline SmCu₂ that has recently been measured by Gratz et al allows the exchange interaction between the 4f shell and the itinerant electrons to be estimated to be+0.061+or-0.003 eV.