No abstract

Strong pressure-induced effects in the thermal equilibrium properties of semiconducting glasses are revealed and theoretically analysed. The basic property under consideration is the concentration of the negative-U centres which determine the mobilitygap spectral structure and the related electron phenomena in the materials. For accessible high pressures, 10 4 p 10 5 bar, a rapid increase of the concentration with growing pressure is predicted. This holds for ('weak') negative-U centres formed in typical, 'rigid', configurations for the vast majority of atoms, as both the mobility-gap width and the related effective magnitude of the negative pair-correlation energy decrease with pressure. However, at ambient (and low) pressure another type of centre, 'strong' negative-U centres formed in glassy atomic soft configurations, predominate, whose concentration decreases with increasing pressure. The resulting concentration of negative-U centres and some related characteristics are shown to exhibit a non-monotonic pressure dependence with a minimum. Future experimental tests of the corresponding theoretical relationships might determine the basic parameters of the phenomenon for the materials under consideration. 10 −4 c 2e (0) ≈ g 0 (E * c )wc a (0) 10 −3 (1.3)

The reaction of argon ions with hydrogen and deuterium molecules by crossed beams: Low energy resonances and role of vibronic levels of the intermediate complex Some new experimental results concerning the magnetic resonance in PrH-doped YIG are presented and discussed, together with the results for Tb H and HOH in YIG already published, in terms of existing theories. It is shown that the magnetization directions corresponding to the near crossings of energy levels in the case of Hos+ can lie within a certain local plane and, in the case of Pr H , can coincide with a local axis of the dodecahedral site (for Tb H , as Huber has found, these directions form a conical surface). The angle and temperature dependences of AH for Tb H and HOH are very similar and can be explained completely in terms of slow relaxation. For Pr s + these dependences in the directions of near crossings resemble the "anomalous'.' behavior for Yb H in octahedral sites. A contribution from transverse relaxation is probable in the case of PrH.

No abstract

No abstract