Thermal Conductivity of MgO,Al2O3, MgAl2O4, andFe3O4Crystals from 3° to 300°K

Abstract

The thermal conductivity from 3\ifmmode^\circ\else\textdegree\fi{} to 300\ifmmode^\circ\else\textdegree\fi{}K of single crystals of the two spinels, diamagnetic Mg${\mathrm{Al}}_{2}$${\mathrm{O}}_{4}$ and paramagnetic ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$, has been measured and analyzed. The heat is transported by phonons in both cases. The phonon scattering processes in the two crystals are quite similar except that the phonons in ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ are also scattered by the magnetic lattice in its disordered state. The thermal conductivity of ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ falls abruptly with increasing temperature at the 121\ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}K transition.Comparison of results on the double oxide Mg${\mathrm{Al}}_{2}$${\mathrm{O}}_{4}$ with those on the single oxides MgO and $\ensuremath{\alpha}$---${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ indicates the double oxide has an intermediate thermal conductivity. Measurements on crystals of MgO\ifmmode\cdot\else\textperiodcentered\fi{}3.5${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and ${\mathrm{Mg}}_{x}{\mathrm{Fe}}_{y}{\mathrm{Al}}_{z}{\mathrm{O}}_{4}$ from 3\ifmmode^\circ\else\textdegree\fi{} to 300\ifmmode^\circ\else\textdegree\fi{}K indicate that vacancies and certain impurities can noticeably lower the thermal conductivity of Mg${\mathrm{Al}}_{2}$${\mathrm{O}}_{4}$. The effect of vacancies and impurities on ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ is also noticeable, particularly below 30\ifmmode^\circ\else\textdegree\fi{}K.