An investigation of phonon scattering by chromous ions in MgO by thermal conductivity measurements

Abstract

The effects of X -irradiation, thermoluminescence and heat treatment on the thermal conductivity principally between 1 and 4 °K of nominally pure and Cr-doped MgO have been examined. It is concluded that the Cr 2+ ion produced by X -irradiation is responsible for the very strong excess phonon scattering. An analysis of the data shows that the scattering has both resonant and non-resonant components and that if the non-resonant component is proportional to concentration, the resonant component is proportional to the square root of the concentration indicating the existence of cooperative effects. The resonant scattering occurs at ca . 4 cm -1 in reasonable agreement with the calculated energy separation 5.6 cm -1 of the E and A 2 levels of Cr 2+ (Fletcher & Stevens 1968). The work also indicates that the thermal conductivity at 4.2 °K provides a useful method of determining the Cr 2+ concentration in MgO.