This review is concerned with the utilization of the positron-electron annihilation phenomenon in studies of the physics of condensed matter. The theory of the annihilation process is outlined, the importance of the two-photon mode of decay is established, and it is described how the observable results depend on the initial positron and electron states of the system. A brief account of the principal experimental techniques is included. Discussion of the complex nature of positron behavior in molecular substances suggests the particular value of investigations directed at the two photon pick-off mode of decay of the orthopositronium atoms that are formed in these materials. The possibility of positronium formation in ionic and metallic materials is also considered. The many important electron aspects of positron annihilation in metals are dealt with. The independent particle approach to the analysis of two photon angular distributions is discussed and illustrated. A survey of electronic structure investigations includes studies of polycrystalline and single crystal specimens. The relevance of angular correlation measurements in investigations of the Fermi surfaces of metals and alloys is discussed. More recently developed applications to the study of defected and disordered systems are dealt with. A preliminary account of the interpretation of multicomponentmore » lifetime spectra in terms of varying numbers of distinguishable positron states provides the basis for a discussion of studies of positron trapping by defects, voids. and surfaces in ionic and metallic solids, liquids and powders. (auth)« less

Positron studies of condensed matter

The present status of our understanding of the diffusion of hydrogen in metals, both experimental and theoretical, is reviewed. Discussions are focused on the mechanism of diffusion of hydrogen isotopes H, D and T in f.c.c. and b.c.c. metals; the positive muon (μ +) is referred to where appropriate. An up-to-date compilation of diffusion data as a function of temperature and isotope mass has been made, and a clear distinction in general diffusion behaviour in f.c.c. and b.c.c. metals is noted. Subsequently, the results obtained from the Gorsky effect, nuclear magnetic resonance and quasi-elastic neutron scattering that provide information on elementary jump processes are discussed. A conceptual framework of the quantum diffusion of light interstitials in metals is given, including the recent Kondo theory that emphasizes the crucial importance of particle-conduction electron interactions in the diffusion process, especially at low temperatures. It is shown with the help of recent estimates of the ...

Diffusion of hydrogen in metals

The atomic-scale structure of amorphous solids can be determined from the X-ray, electron, or neutron scattering pattern. The atomic distribution function ϱ ( r ) or the pair correlation function g ( r ) = ϱ ( r )/ ϱ 0 , were ϱ 0 is the average atomiic density, is related to the interference function or structure factor I ( K ) by a Fourier transformation. Unfortunately, I ( K ) is not directly accessible from the scattering experiment, but can be deduced from the scattering pattern after suitable corrections for polarization, absorption, inelastic scattering, multiple scattering, and static approximation, and after normalization to absolute units. In multicomponent systems, the coherent scattering function per atom I a ( K ) is a weighted sum of the partial interference functions I ij ( K ), which represent the Fourier transforms of ϱij ( r ), the number of j -type atoms per unit volume at a distance r from an i -type atom. It is also possible to express I a ( K ) as a weighted sum of number-concentration structure factors I NC ( K ), which are associated with the number-number (density), number-concentration, and concentration-concentration correlations. The long-wavelength limit of the functions I NC ( CK ) can be expressed in terms of the various thermodynamic quantities and their variation with composition. In binary allos, three partial functions are required to describe the atomic arrangements. These functions can be obtained by varying the atomic scattering factors f i through choic of three different radiations (X-rays, electrons, and neutrons), or isotopes in neutron scattering, or anomalous dispersion in X-ray scattering. The latest developments in the experimental techniques for the determination of the interference function I ( K ) are presented, and examples of the scattering patterns of metallic glasses are given, which were obtained by the conventional, variable 2θ technique, and by the variable λ technique. Attempts are discussed to deduce the partial interference functions in binary systems from several scattering experiments, and to determine concentration fluctuations in binary alloys.

Direct methods for the determination of atomic-scale structure of amorphous solids (X-ray, electron, and neutron scattering)

Electronic structure of metallic glasses

The phase diagram of the binary Fe-Zr system was redetermined by differential thermal analysis (DTA), electron-probe microanalysis (EPMA), x-ray diffraction (XRD), and metallography in the whole range of compositions The stable intermetallic phases of the binary system are the cubic and the hexagonal polymorphs of the Fe2Zr Laves phase and the Zr-rich phases FeZr2 and FeZr3 While the cubic polymorph of the Laves phase is the stable structure at the stoichiometric Fe2Zr composition, the hexagonal C36-type polymorph of the Laves phase is a high-temperature phase that is found at Zr concentrations as low as 266 at% The Zr-rich phases FeZr2 and FeZr3 have small homogeneity ranges of about 05 at% FeZr2 is a high-temperature phase, stable between 780 and 951 °C FeZr3 decomposes peritectoidally at 851 °C The frequently reported phase Fe23Zr6 (Fe3Zr) is found not to be an equilibrium phase of the binary system

Experimental Determination of Intermetallic Phases, Phase Equilibria, and Invariant Reaction Temperatures in the Fe–Zr System

Time-of-flight pulsed neutron diffraction of liquids using an electron linac

Time-of-Flight Pulsed Neutron Diffraction of Liquids Using an Electron LINAC(Physics)

The chemical and geometrical structures of hydrogen atom sites in hydrogenated ZrNi glass have been observed by neutron total and inelastic scattering. The hydrogen atom environment available in hydrogenated ZrNi glass is exclusively the 4-coordination sites surrounded tetrahedrally by 4Zr atoms or 3Zr+1Ni atoms.

Kenzo Kai

Papers

Time-of-flight pulsed neutron diffraction of liquids using an electron linac

Time-of-Flight Pulsed Neutron Diffraction of Liquids Using an Electron LINAC(Physics)

Hydrogen atom environments in a hydrogenated ZrNi glass

Ferromagnetism in the Laves Phase Compound Fe 2+ x Hf 1− x Annealed at 1000°C

Crystal Structures and Magnetic Properties of the Intermetallic Compound Fe 2 Zr