The present Supplement Volume Beryllium A 3 continues and completes the description of the physical properties of the element, begun in Supplement Volume A 2, 1991, and also treats the electrochemical behavior of the metal. The unique combination of the Be properties, which was pointed out in Supplement Volume A 2, is also demonstrated in the following chapters of this Volume A 3: 13. Electrical Properties 14. Electronic Properties 15. Optical Properties. Emission and Impact Phenomena 16. Electrochemical Behavior Starting with the electrical properties, Be isarather good electrical conductor in centrast to what might be expected. Superconductivity was studied, especially on films. Quantum effects, which are more pronounced in Be than in most other metals, are the reason for numerous in vestigations of the magnetoresistance and the magnetic-breakdown effect. The basis for many of the characteristic properties is the unique nature of bonding in Be as a consequence of its peculiar electronic structure and the special shape of its Fermi surface which also gave rise to further numerous studies. Detailed cluster calculations were per formed to better understand the bonding in the metal. Regarding the optical properties, the high reflectivity of Be, particularly in the infrared region, makes it attractive for the fabrication of precision optical surfaces (mirrors); it is also useful for solar-collector surfaces in spacecraft applications. Emission and electron-and ion impact phenomena as well as neutron optics are also discussed.

The volume Rare Earth Elements C 11 deals with the compounds and systems of the rare earth elements with boron, i.e. borides, borates, and associated alkali double compounds. As in all earlier volumes of "Rare Earth Elements" Series C (Seltenerdelemente Reihe C) comparative data are presented in sections preceding treatment of the individual compounds and systems. Topics of the present volume C 11 a are the comparative data on the borides and the individual sections on the systems and borides containing Sc, Y, and La. The individual sections for the systems and borides with Ce to Lu can be found in the following volume C 11 b together with the borates, its alkali double compounds and other compounds containing Ce to Lu, boron and elements related by the Gmelin system. The most extensively studied borides treated in the comparative sections are of the type MB6. These rare earth hexaborides are refractory compounds and some of them, especially LaB6, are good thermionic emissive materials or exhibit other interesting physical properties. The most comprehensive chapter in the individual sections of volume C 11 a deals with LaB6, which is a well-known thermionic material of great practical importance with high electron emission efficiency and an excellent stability in the surface composition at high temperatures. The effects of preparation conditions, composition, temperature, surface structures, surface treatment, and of the atmosphere on the thermionic emission are studied thoroughly. Another important item of the LaB6 chapter is the electronic structure, which often serves as an example for the other rare earth hexaborides.

This voLume continues the description of the physicaL properties of tungsten metaL and covers specificaLLy surface properties, eLectron emission, and fieLd evaporation. Tungsten surfaces are probabLy the most extensiveLy studied metaL surfaces. RecentLy, experimentaLists and theorists have focused their interest on the atomic structure, Lattice dynamics, and eLectronic properties of the W(100) surface. WhiLe the structure of the recon- structed Low-temperature surface is weLL estabLished, there are still unresoLved probLems concerning the structure at and above room temperature, the nature of the phase transition, and the driving force for the reconstruction. Other Low-index tungsten surfaces have been studied in much Less detail. There are numerous and partLy confLicting data on the surface energy, the seit-diffusion parameters, and the work function of singLe-crystaL and poLycrystaL tungsten surfaces. ELec- tron emission, which is of fundamentaL importance for many appLications, comprises therm- ionic, fieLd, photofieLd, and photoeLectric emission as weLL as emission induced by impinging eLectrons, atoms, or ions. Pioneering work in areas Like thermionic or fieLd emission is comprehensiveLy discussed. Very recent studies of vaLence-band and core-LeveL spectra moreover provide detaiLed information on intrinsic surface properties. FieLd evaporation phenomena are treated at the end of this voLume. Frankfurt am Main Woltgang HuisL November 1993 fable of Contents Page 1 Atomic Structure, LaHice Dynamies, and Electronic Structure of Tungsten Surfaces 1 1.1 W(100) ...1.1.1 Atomic Structure. Reconstruction and Relaxation Survey ...