(1) Institut für Festkörperphysik, Universität Hannover, Appelstr. 2, 30167 Hannover, Germany;(2) Theoretische Chemie, Universität Hannover, Am Kleinen Felde 30, 30167 Hannover, Germany
Abstract:
The results of calculations of the phonon dispersion,the vibrational density of states and the heat capacity of lithiumtetraborate and lithium triborate crystals are presented. They areobtained in the framework of a potential model that takes intoaccount the non-equivalence of boron atoms in different structuralpositions (BO3 and BO4 units). A symmetry analysisof the phonon modes at point was performed, and calculatedfrequencies are compared to experimental spectra.Analysis of Li contributions to the vibrational density of states reveals thatthe Li-O bonds in both crystals are relatively weak. This is in linewith the experimentally observed high mobilityof lithium ions at high temperatures. A good agreement between calculated and measured heat capacities from the literature was obtained.
point was performed, and calculatedfrequencies are compared to experimental spectra.Analysis of Li contributions to the vibrational density of states reveals thatthe Li-O bonds in both crystals are relatively weak. This is in linewith the experimentally observed high mobilityof lithium ions at high temperatures. A good agreement between calculated and measured heat capacities from the literature was obtained.