Intrinsic Planar Defects in Germanium and Their Contribution to the Excess Specific Heat at High Temperatures

Excessively high specific heat is usually observed in solids at comparatively high temperatures. It was believed to be associated with the anharmonic effects. Using the simple case of elemental germanium with archetypical  diamond structure we demonstrate that anharmonicity effect can not fully describe its excess specific heat. Instead we propose the two type of extended planar defects with the record low formation energy (ΔE = 1900-1950 K) which can account for the discrepancy between theoretical and observed specific heat. By comparison of experimental and theoretical specific heat it was found that germanium sample is subdivided into domains where intrinsic planar defects are aligned along the single crystallographic direction.