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

Abstract

Excessively high specific heat is usually observed in solids at comparatively high temperatures. It is believed to be associated with anharmonic effects. Using the simple case of elemental germanium with archetypical diamond structure, it is demonstrated that the anharmonicity effect can not fully describe the excess specific heat in germanium. Instead, two types of extended planar defects with a record low formation energy () are proposed, which can account for the discrepancy between theoretical and observed specific heat. These planar defects can be considered as finite distortion of crystal lattice produced by shear phonon modes accompanied by specific reconstruction of interatomic bonds on certain atomic planes. By comparison of experimental and theoretical specific heat, it is found that the germanium sample is subdivided into domains with intrinsic planar defects aligned along a single crystallographic direction.