Acoustic relaxation due to Ni3+ions in Al2O3

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Abstract
The authors have obtained an expression for the acoustic relaxation loss due to the ion Ni3+ in Al2O3 including the effects of lattice strains. In the absence of a magnetic field the six lowest-lying levels of this system reduce to two uncoupled three-level systems which can be treated exactly using the current dynamic Jahn-Teller model to obtain both the relaxation loss and the associated relaxation times. It is predicted that there is no loss in the absence of lattice strains, but that in the presence of a distribution of lattice strains the loss is given by the classical expression for a two-level system reduced by a number of strain-dependent factors. Their expression has the correct dependence on acoustic model and greatly improves agreement with the experimentally observed magnitudes. Comparisons between the calculated and observed relaxation times enable an estimate of the second moment of the lattice strain distribution and a value for the Jahn-Teller reduction factor r to be obtained.

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