Conferences on the Physics of Selenium and Tellurium were held in 1964 in London, 1967 in Montreal, and eight years ago, 1971, in Pont-a-Mousson. The last conference was noteworthy because of two facts: For crystalline Te and Se a high level of results was achieved and, further, it was possible to outline the focal points for continuing research work. These points were mainly to explore. the electronic structure of trigonal Se and Te and of the hypothetic~l cubic limit of these materials. To im plement such study, progress in band structure calculations was necessary. In addition, a consistent analytical description of the bands near the va lence band conduction band gap was required with the aim to understand the semiconducting properties, mainly magnetotransport and magnetooptical ef fects of band electrons and of impurities. Further questions concerned the influence of defects, such as dislocations, on transport properties and, finally, a concluding description of lattice dynamics of trigonal Se and Te, based on theoretical and experimental work, such as neutron diffraction and optical measurements. Besides the listing of this future research program it became obvious that more detailed work on the amorphous state of solids and liquids was necessary in order to improve our knowledge about their crystalline proper ties, growing conditions. and all problems of chemical bonds.

Inhalt
I. Bands and Bonds in Se and Te.- The Electronic Structure of Crystalline Phases of Se and Te.- Charge and Momentum Density, and Compton Profile of Se and Te.- Self-consistent Ground State of Trigonal Tellurium.- Mössbauer Study of Tellurium at High Pressure.- Electronic Structure of Trigonal and Amorphous Se and Te and the Non-Empirical Calculation of Structural Properties..- Dielectric Matrix Calculations in Helical Chain Semiconductors.- II. Lattice Dynamics of Trigonal Se and Te.- Homology of Phonons in Se and Te.- Lattice Dynamics of Trigonal Selenium and Tellurium State of the Art..- Phonon Dispersion Calculations for Trigonal Selenium..- Comparison of the Phonon Density of States of Trigonal, Vitreous, and Red Amorphous Selenium..- Specific Heat and Thermal Conductivity of Trigonal and Vitreous Selenium in the Temperature Range 3300 K..- Low Temperature Specific Heat and Elastic Constants of Trigonal Selenium..- Surface Lattice Dynamics of Trigonal Se and Te: Mean Square Displacement Spectra in the Long-Wavelength Limit..- III. Bandstrueture in the Neighbourhood of the Gap of Trigonal Se and Te.- Optical Activity, De Haas-Van Alphen-Oscillations and Conduction Band Parameters of Tellurium..- Optical Properties of Tellurium Under High Pressure.- Electron Cyclotron Resonance in Te at Very High Magnetic Fields.- Pressure Influence on the Intervalence Band Absorption in Te.- Circular Photogalvanic Effect in Optically Active Crystals.- Submillimeter Cyclotron Resonance in Uniaxially Stressed Tellurium.- Identification of the Indirect Transition in Trigonal Selenium.- IV. Imperfections and Impurities in Te.- Dislocations in Te-Influence on Galvanomagnetic Properties.- Pressure Effect on the Impurity State and Impurity Conduction in Tellurium..- SecondHarmonic Generation and Propagation of CO2 Laser Radiation in Strained and Unstrained Tellurium Crystals..- Impurity Spectroscopy on Tellurium..- V. Transport Phenomena in Trigonal Se and Te.- Two Types of Carriers in Tellurium..- Acoustoelectric Current Saturation on Trigonal Se and SexTe1-x Single Crystals..- Magnetoresistance of Trigonal Selenium..- Low-Frequency Coupled Photocurrent and Temperature Oscillation in Polycrystalline Selenium Samples..- VI. The Amorphous, Glassy, and Liquid State.- Selenium, the Amorphous and Liquid States.- Localized Electronic States in Glassy Se.- Bonding Coordination Defects in Selenium.- Raman Spectral Studies on the Crystallization Processes of Amorphous and Liquid States in Se and Te.- VII. Photoelectric and Transport Phenomena in Amorphous Systems.- Photoelectronic Behavior of a-Se and some a-Se:As Alloys in Their Glass Transition Regions..- Localized States in the Gap of Amorphous Selenium..- Influence of Wavelength on the Optical Quenching of Photoconductivity in Amorphous Selenium Films.- Electronic Transport Properties and Equation of State of Selenium at Temperatures up to 1900 K and Pressures up to 1800 bars.- VIII. Crystalline and Amorphous As2Se3.- Chemical Bonds and Electronic States in Monoclinic As2Se3.- Transient Electrical Transport in a-As2Se3, a-Se, a-Si, and a-SiO2.- IX. Preparation and Application.- Fabrication and Characteristics of Te-Se-Cd Structures.- The Application of Selenium and Its Alloys to Xerography..- Growth of Tellurium and Selenium-Tellurium Crystals by the Czochralski Method.- Photo-Crystallization of Amorphous Se1-xTex Films..- Time Evolution of Photovoltaic Effect at Tellurium-Metal Thin Film Contacts..- On Stress-Relief Appearance Conditions in Te-Ag and Te-Bi Thin Film Systems..- Index of Contributors.