Table of contents

It has recently become possible to use pseudopotential and total energy techniques to determine crystal structures, solid-solid phase transformations, lattice constants, bulk moduli, shear moduli, cohesive energies, phonon spectra and other static and dynamical properties of solids. The only inputs are the atomic number and mass of the constituent elements and a group of crystal structures to test, yet the results are highly accurate. Some of these results together with a description of the development of the pseudopotential approach and applications are presented.

Two recent types of application of X-ray synchrotron radiation are reviewed in the context of specific examples. Recent data on the polarization dependent K-edge X-ray absorption spectrum of plastocyanin is presented. Quantum chemistry calculations of this kind of polarization dependence in simpler molecules help with the interpretation of the spectral features. Anomalous diffraction of rare-earth labelled biological membranes form the second example. The specific case considered is of acetylcholine receptor membranes from electric fish.

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A microscopic picture of the attractive and repulsive contributions to the bonding in simple metals, transition metals, and their alloys is presented. In the light of this the recent successes of the semi-empirical approaches of Miedema to the heats of formation and St. John-Bloch and Zunger to the structural properties of binary AB alloys is examined.

In the dielectric screening theory of covalent semiconductors the phonon dispersion relations are derived from the electron density response matrix. This matrix is obtained from the polarizability using the electron energies and wavefunctions. The crystal psuedopotential is calculated starting from a local electron-ion potential with up to 150 plane waves. Exchange and correlation effects in the dielectric response are included via the local density functional formalism. The procedure ensures consistency between Hamiltonian and dielectric matrices. The dimension of the dielectric matrix is 137. Phonon frequencies of Si in the gamma and X-points are calculated using different approaches and the results are compared with experiment.

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Modern theoretical approaches and computational techniques coupled with the development of spectroscopies for probing surfaces experimentally have given a new impetus to the study of those mechanisms controlling Schottky barrier formation. It is now known that interfaces between metals and clean semiconductors are rarely abrupt and fully ordered. In this article the influence of imperfections at the interface and their role in Schottky barrier formation are considered.

Under post ion-implantation annealing treatments, semi-insulating GaAs wafers may convert to n-type or p-type. A review of the effects responsible for that conversion, and, more generally, for the influence of substrates on the properties of implanted layers is presented. These effects are related to the exodiffusion properties of shallow and deep impurities and point defects. The electrical properties of the most important of them are reminded, together with the physical phenomena which control their incorporation in Bridgman and LEC ingots. The spatial distribution of impurities and defects in these ingots is also discussed from the point of view of the quality requirements of semi-insulating wafers for the GaAs IC's technology.

An introduction is given to the physics of the many optical problems that must be solved before optical fibre waveguides can be incorporated successfully into cables. Brief mention is made of the non-linear optical problems which may arise in the future. Also, some of the many problems posed by the fracture mechanisms of elastic but brittle materials like silica are briefly examined.

Adequate solutions to all these problems must be found before cables incorporating optical fibre waveguides can be manufactured that will function and survive in the wide variety of environments now being considered.

Competing effects in real one-dimensional conductors have considerably enriched the original structural picture of the instability of a single metallic chain. Such effects include transverse as well as longitudinal polarizations of the Peierls distorsion, instabilities on different molecular chains, 2 and 4k_F instabilities, and commensurability effects. In the more recent class of organic superconductors (TMTSF)₂X, superconductivity is not only in competition with the Peierls instability but also with order-disorder phase transitions involving the non-centrosymmetric counter ions.

At an elastic phase transition, a crystal structure change takes place by a homogeneous lattice deformation, the associated soft mode being a zone centre acoustic phonon. As such a transition is approached, the mode softening is manifested as a reduction in the second order elastic constant which acts as the quadratic invariant and so the higher order terms become increasingly important: a pure elastic transition will be dominated by vibrational anharmonicity of the soft acoustic mode. For a first order, elastic transition, a quantitative understanding of this anharmonic behaviour must rest upon measurements of the third order elastic constants which constitute the cubic invariant in the order parameter (which is a strain tensor component). To obtain the forms of these physically significant invariants in the Landau free energy expansion up to third order in the strain eigenvectors, the elastic free energy is transformed from finite strain space to the irreducible strain tensor space keeping the free energy invariant. In-Tl alloys undergo a f.c.c.-f.c.t. elastic phase transition whose order has been difficult to establish experimentally, although the Landau theory suggests that the transition should be first order because there is a cubic invariant of the order parameter. These alloys provide a suitable vehicle for a quantitative asessment of the applicability of the Landau theory to a first order elastic phase transition in which the atomic displacements are small. The transition is accompanied by softening of the N[110], polarisation U[1-10] zone centre acoustic phonons: the second order invariant ½(C₁₁ - C₁₂) goes to zero at T_c. The third order invariants obtained from third order elastic constant measurements made on In-Tl alloys are discussed. The hydrostatic pressure derivative ∂(½(C₁₁ - C₁₂))/∂P is negative for those f.c.c. alloys which undergo the transition. As suggested by the Landau theory, the third order invariant (1/8)(C₁₁₁ - 3C₁₁₂ + 2C₁₂₃) of the order parameter is small, in agreement with the near second order character of the transition: there is only a slight discontinuity in the strain at T_c. The first order character of the transition is evidenced further by a marked hysteresis in ultrasonic wave velocities as crystals are taken through the transition by pressure or temperature cycles.

It is shown that fluctuations may change the order of phase transitions, in contrast to that predicted by the Landau theory. In systems in which this happens, one or two tricritical points may be observed as the result of a uniaxial symmetry breaking. These theoretical results have recently been experimentally confirmed on the structural displacive phase transitions of several perovskites.

Interest in irradiation of ion implanted semiconductors with high power Q-switched laser pulse arose initially by several possible advantages in the annealing of lattice damage and in the fully electrical activation of the implanted species. In the meantime the physical mechanisms of the annealing process were also investigated. Measurements in situ, i.e., during irradiation, indicate that the energy deposited by the laser pulse is converted "instantaneously" into heat and that the annealing process is caused by the melting of the near surface region. Heating and cooling stages are characterized by extreme large values for thermal gradients (10⁶-10⁸ K cm^-1), quenching rates (10⁶-10⁸ K s^-1) and velocity of the solid-liquid interface during solidification (∼ m s^-1). These values offer new prospects in the material science field. Crystallization of amorphous layers and impurity redistribution induced by laser irradiation are described and discussed in some detail.

Some general properties of deep impurities in semiconductors are discussed. They concern the origin of the short range potential associated with the impurity, the many electrons effects and the relaxation of the surrounding medium. Some specific examples are given to illustrate these points.

Yielding of metals can be interpreted in terms of synergetics. A set of non-linear balance equations for entropy and momentum governs the temperature and strain fields within the anharmonic solid. A critical behavior sets in as the imposed deformation reaches a threshold. This threshold is achieved when the strain dependent Grüneisen thermomechanical coupling parameter vanishes. A stability analysis identifies the amplitude of the lowest wavevector acoustic mode as the order parameter of the transition. Use of the "slaving principle" leads to a non linear differential equation for the time envelope of the order parameter, reminescent of that obtained, e.g., in the LASER theory. The experimental work supporting the above ideas will be reviewed. Finally the problems left open - more numerous than those considered so far - will be outlined.

Experimental Poincaré sections corresponding to the phase space trajectories in unsteady Rayleigh Benard convection are presented. New information about the dynamics of the system are obtained both in the quasi periodic regime and in the chaotic one where we found the presence of strange attractors.

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The current status of the ab initio crystal orbital method is reviewed. New results for cis-trans isomerism in polyacetylene and conformational stability in polyethylene are presented and a survey of ab initio results on simple hydrocarbon polymers is provided stressing those properties which can be derived from computed potential surfaces.

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The development of highly expanded He nozzle beams with velocity half widths less than 1% has made it possible to observe the annihilation and creation of single surface phonons in time of flight spectra of the scattered atoms. Measurements have been carried out for a wide range of incident angles at a beam energy of about 20 meV for the following crystals and directions: LiF ⟨100⟩, LiF ⟨110⟩, NaF ⟨100⟩, KCl ⟨100⟩, NaCl ⟨100⟩, and MgO ⟨100⟩. In all cases the spectra show up to 5 sharp well resolved maxima. From the final angle and energy of each peak the parallel surface momentum component and frequency of the phonon is determined. The results show a predominant coupling with Rayleigh surface phonons with only a weak coupling with bulk phonons. Rayleigh dispersion curves have been measured out to the zone boundary for all crystals except LiF ⟨110⟩ and MgO. There is also some evidence for excitation of modes of higher frequencies. Except for LiF ⟨100⟩ at the zone boundary the results compare well with theoretical calculations. Benedek has been able to fit the new LiF He atom and previous neutron dispersion curves with a revised breathing shell model calculation.

The use of He-diffraction as a method in surface crystallography is briefly reviewed. To illustrate the possibilities and limitations a few examples of surface structures are presented and discussed. Current problems and future needs are outlined.

The influence of the magnetic scattering contribution to electrical resistivity ρ, thermopower S and thermal conductivity λ in some REAl₂ compounds (RE = rare earth) will be discussed by comparing the experimental data of ρ(T), S(T) and λ(T) for magnetic and non-magnetic isostructural compounds.

The magnetic properties of intermetallics of the light actinides can vary from primary local moment behaviour through itinerant electron magnetism to non-magnetic behaviour. One parameter which strongly influences the magnetic character of the compound is the actinide-actinide separation which can experimentally be varied by the application of high pressure. Combining this with Mössbauer spectroscopy of the 60 keV transition in ²³⁷Np allows a detailed study of local magnetic properties of the Np ion as a function of volume. Recent measurements on three Np intermetallics will be reviewed:

(1) NpCo₂Si₂. Neutron diffraction and Mössbauer data at ambient pressure classify this material as a highly localized magnet. Under pressure the hyperfine field remains constant while the Néel-temperature T_N increases with smaller volume. The variation of T_N can be explained quantitatively within the rigid spin model of Ruderman-Kittel-Arrott.

(2) NpAl₂ and NpOs₂. These are cubic Laves phase materials, where NpAl₂ has the largest lattice parameter (a = 7.785 Å) and shows largely localized behaviour, while NpOs₂ with a = 7.459 Å is mostly itinerant. In both materials the reduction of lattice constant initiates a reduction of hyperfine field and Curie temperature, which is thought to arise from a delocalization of the magnetic 5f-electrons. In addition line broadenings are observed which show that the delocalization process is a dynamical phenomenon. It is analyzed in terms of a fluctuation between a fully localized and a fully itinerant electron state.

After a brief introduction describing the general background of the current activities performed in order to demonstrate the scientific and technological feasibility of fusion energy, an outline is presented of the major materials problems which remain to be solved. Special attention is paid to irradiation effects in candidate first wall alloys and to simulation techniques which the materials scientist has to apply in order to understand the underlying mechanisms.

We give here a brief guide to the literature concerning charge transfer and electrical conductivity of carbon based synthetic metals. In particular attention is focused on the relation between charge transfer and bond length and on the definition of the maximum conductivity for intercalated graphite and doped polyacetylene.

It is suggested that relaxation is condensed matter requires the co-operation of motions at several sites. This new approach which has been formulated in terms of a dynamic distribution of partially correlated clusters will be described in a manner illustrating the physical concepts involved. A brief comparison with experimental data and empirical expressions will be given and the potentialities of the approach summarised.

The quadratic response formalism is used to derive an expression for the photoelectron and the Auger electron currents in the spirit of the sudden approximation. We find that the centre of gravity and relative weight of the satellites in the Auger spectrum depend strongly on the life-time of the initial hole. The shape of the plasmon gain peaks in the Auger spectra of simple metals is calculated and compared with experiment. Finally, we discuss the information contained in Auger-photoelectron coincidence spectroscopy.

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Recent high-resolution measurements of the transport coefficients of the simple metals at low temperatures have yielded new data that are in striking contradiction to the generally accepted theories. We shall review these recent data and present a theory of low-temperature electron transport in metals that accounts for all the observed "anomalies" by taking into account the important couplings between the following four scattering mechanisms: (i) electron-phonon scattering, (ii) electron-electron scattering, (iii) electron-dislocation scattering and (iv) electron-impurity scattering.

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After mentioning briefly the advantages and disadvantages of amorphous alloys, examples are given of possible technological applications of such alloys. The stability of amorphous alloys is of major concern in every application. Several models dealing with the stability are discussed in the light of experimental data such as the amorphous to crystalline transformation enthalpy and the activation enthalpy of this transformation.

It is shown that the magnetic properties of amorphous alloys can be described properly only if account is taken of the presence of compositional short range ordering. The model proposed for the description of differences in magnetic properties between various types of amorphous alloys can successfully be used also to describe differences in magnetic properties between amorphous and crystalline materials.

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The analysis of the average atomic volumes (AAV) of the intermediate phases from the concentration was done in many two-component systems. It was shown that in some systems (namely transition metal with non-transition element from the IIIrd or IVth group of the periodic table) the AAV of the intermediate phases are much more less than the sum of the volumes of the pure components. It means that the formation of the intermediate phases in such systems is accompanied by a rather large decreasing of the volume in comparison with the mixture of elements. For this reason the high pressure conditions are favourable for the formation of the intermediate phases in such systems from the thermodynamical point of view. On the ground of these data the systems W-Ga, W-Ge, Re-Ga, Os-Ga, Sc-Ga, Ta-Ga, were investigated at high pressures and temperatures. It was found that many new phases are crystallised in these systems. All of them are metastable at room pressure. The composition and crystal structures of these phases were investigated at ordinary conditions.

The relevant aspects of electrical noise in metals related to the kinetic properties of lattice defects are presented. Two basic phenomena are considered: (a) resistivity fluctuations in thermal equilibrium associated with vacancy creation and annihilation processes, (b) resistivity fluctuations generated by collective dislocation rearrangements during plastic deformation. It is shown that, through the characterization of the fluctuations with a suitable statistical model, information can be obtained on the physical properties of these defects. In particular, vacancy parameters, such as the migration energy, the average life-time and the resistivity contribution of unit vacancy concentration can be experimentally determined. Moreover, the relevant features associated with dislocation rearrangement processes during plastic deformation are put in evidence.

The recent advances in the investigation of incommensurate ferroelectrics via magnetic resonance are reviewed. It is shown that the incommensurate modulation wave is generally static and pinned by defects. Only close to T_I thermal fluctuations may overcome the pinning resulting in large local phase fluctuations averaging out the incommensurate broadening of the NMR lines. Close to the "lock in" transition T_c a static narrow multisoliton lattice is formed and the phason spectrum splits into an "acoustic" and an "optic-like" branch. Spin-lattice relaxation measurements clearly show the disappearance of the acoustic phason branch on approaching T_c.

The interdisciplinary nature of the problems associated with colloids and interfaces can be understood with the help of the theory of paracrystals. Nearly all noncrystalline condensed materials are composed of microparacrystals. They unequivocally can be detected by X-ray-, neutron- or electron-diffraction and sometimes also by high precision transmission electronmicroscopy. The α*-law gives evidence that microparacrystals are in a statistical equilibrium state with a well defined polydispersity. The free enthalpy contains a third term, the so called distortion- or fragility-free volume enthalpy which makes the equilibrium state to be understood as a thermodynamical phenomenon. The conventional concepts of "liquid", "solid", "amorphous", etc., are clarified by the introduction of nine statistical parameters to crystallography. Catalysts now are no longer "crystalline", polymers no longer "semicrystalline" and melts no longer "amorphous". M. v. Laue's discovery of a nascent "new science" has been confirmed!

The conference covered the whole field of condensed matter physics, i.e., solid state physics and similar properties of liquid, polymer, etc., substances. A special effort was made to include the physics of industrial applications (but not device engineering).

The purpose of this series of Annual General Condensed Matter Division Conferences of the European Physical Society is to provide a European forum for current research in condensed matter physics and to encourage international co-operation in the field. Details of the next two conferences in the series are given below.

The format of the conference followed the first in the current series held at Antwerp 1980, with plenary talks, invited speakers grouped in symposia, individual invited talks, and contributed papers in parallel sessions and poster sessions.

A large number (fifty-seven) of invited talks formed an important aspect of the conference because they promote interchange between specialists and cross-fertilisation of ideas. In that sense the General Conference of the EPS Condensed Matter Division complemented the many topical conferences successfully run throughout Europe.

Future Conferences in this series are planned to be held annually in the spring

1983 Lausanne, Switzerland, 28-30 March 1983

Chairman: Professor E. Mooser lnstitut de Physique Appliquée EPFL-DP PHB - Ecublens CH - 101 5 Lausanne Switzerland

1984 den Haag, the Netherlands, 19-23 March 1984

Chairman: Professor F. M. Mueller, Faculteit der Wiskunde en Natuurwetenschappen Katholieke Universiteit Toernooiveld NL - 6525 ED Nijmegen The Netherlands