Thermal conductivity of additively colored MgO

The thermal conductivity of MgO additively colored in magnesium vapor has been measured in the temperature range 1–55 K. These measurements have been compared to the pure crystal thermal conductivity data. There is a “dip” in the thermal conductivity vs. temperature curve of the additively colored specimen near 20 K, where the thermal conductivity is depressed to one-fifth of the pure crystal value. The “dip” is attributed to resonant phonon scattering associated with quasilocalized modes of theF center. After UV irradiation, resulting in partialF →F ⁺ conversion, the thermal conductivity “dip” was found to be much weaker. The increase in thermal conductivity of the bleached sample is attributed to a relaxation of neighboring ions due to the different charge state of the defect. A successful fit to the thermal conductivity data has been made using the Debye model of solids and a defect scattering rate consisting of a resonance expression plus Rayleigh scattering term. A good fit can be made to the data of the bleached specimen by varying only the parameter associated with concentration ofF centers.