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Paraelastic Alignment and Electric Dipole Relaxation Behavior of Off‐Center Ag + Defects in RbI
Author(s) -
Jimenez R. V.,
Lüty F.,
Siu Li M.,
De Souza M.
Publication year - 1981
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221060234
Subject(s) - dipole , condensed matter physics , relaxation (psychology) , transition dipole moment , electric dipole moment , absorption (acoustics) , electric dipole transition , materials science , moment (physics) , molecular physics , nuclear magnetic resonance , chemistry , crystallography , magnetic dipole , optics , physics , psychology , social psychology , organic chemistry , classical mechanics
Substitutional Ag + defects are investigated for the first time in RbI host material. The absorption spectrum of isolated defects – obtainable only after quenching and rapid cooling of the crystals – consists of three UV absorption bands at 4.81, 4.94, and 5.13 eV. Uniaxial stress application produces characteristic increases or decreases of these absorptions for 〈111〉 and 〈110〉 stress, due to elastic dipole alignment following a Curie (1/ T ) law, while dichroism is absent under 〈100〉 stress. This stress alignment is possible only above 27 K demonstrating freezing‐in of dipole reorientation below this temperature. In agreement with this, ITC measurements show a peak of the depolarization current at 23.4 K, yielding an activation energy for reorientation of 53 meV and an electric dipole moment of 0.64 e Å. For interpretation of the elasto‐optical data, two models involving pure T 2g elastic dipole reorientation are dipole reorientation are discussed: the normal 〈111〉 dipole model, and a restricted 〈110〉 dipole model, in which strong and immobile E g distortions allow dipole reorientation only among four orientational states in a (100) plane. It is shown that both models cannot be distinguished in the linear range of the elasto‐optical effect and that both can be fitted well to the observed data. Several arguments, however, favor the 〈111〉 model with deep off‐center wells of Ag + in RbI.