Phase separation has become a fascinating subject in the discussion of cuprate superconductors. All these materials have layered structures containing CU02 planes as the most important building blocks. They are coupled only weakly so that the electronic properties show a nearly two-dimensional behaviour. Due to correlations the undoped compounds are insulators of the Mott Hubbard type exhibiting long-range antiferromagnetic order. Upon doping a rich scenario of physical phenomena appears: Even at low hole concentra tions the antiferromagnetic ordering temperature is reduced drastically and spin-glass behaviour as well as a hopping type conductivity can be observed. Further doping leads to metallic-like conductivity and below Tc to super conductivity. In this doping regime antiferromagnetic fluctuations are still observed. At very high charge carrier densities superconductivity is lost and the systems show pure metallic conduction without ,magnetic correlations. One of the most interesting phenomena in high-T c research is the interplay between magnetism and conductivity or superconductivity. Especially the behaviour of charge carriers in the antiferromagnetic background raises a number of open questions. Two scenarios become possible: the carriers tend to delocalize over the whole crystal forming a homogeneous state with band-like structure or they separate into hole-rich (conducting, superconducting) and hole-poor (insulating, antiferromagnetic) phases leading to an inhomogeneous structure.

Structural Phase Transitions II, like its predecessor (Topics in Current Physics, Vol. 23), presents selected methods and recent advances in the experimental investigation of phase transitions in solids. The two chapters in this volume deal with electron paramagnetic resonance (EPR), and with nuclear magnetic and nuclear quadrupole resonance (NMR-NQR). Both techniques are particularly sensitive to local properties. The chapter on EPR concentrates largely on the investigation of static properties, including mean-field behaviour, critical and multicritical phenomena, whilst NMR is shown to be a powerful tool for studying nonlinear dynamics, incommensurate transitions, and disordered systems. This book will serve as an excellent introduction to the methodology and applications of EPR and NMR-NQR for all those wishing to become acquainted with these important tools for studying structural phase transitions.

This volume contains the lectures of "Earlier and Recent Aspects of Super conductivity," the 18th course of the International School of Materials Science and Technology, which was held at the Ettore Majorana Centre for Scientific Culture in Erice (Sicily), Italy, July 4-16, 1989. In the wake of the discovery of high-Tc oxides many international confer ences have been held on the subject, mainly intended for those already working in high-Tc research. Hence, the idea evolved of organizing a school dedicated to students and young scientists entering the field of superconductivity. The intention was to give a broad perspective of the field with its eight decades of research history and thus to link existing fields of knowledge and gain con tinuity. The new high-Tc cuprates were integrated, both historically and by subject, into the field of classical superconductivity, as well as into its newer branches of heavy-fermion, organic and chalcogenide superconductors. Even the organizers and the lecturers were surprised how many cross-links became apparent between the different branches of superconductivity. The lectures have been grouped into four parts, namely: - Fundamental properties of superconductors - Coherence-length-related properties - Electronic and magnetic properties - Theoretical models The number of applications from potential participants greatly exceeded the capacity of the facilities available. Ultimately, 100 students from 25 coun tries were selected to attend the course. The remarkable surroundings of the medieval town of Erice promoted a most stimulating but nevertheless relaxed atmosphere."