Eur. Phys. J. B 42, 461-466 (2004)
https://doi.org/10.1140/epjb/e2005-00003-1

Phonon spectra and heat capacity of Li₂B₄O₇ and LiB₃O₅ crystals

¹ Institut für Festkörperphysik, Universität Hannover, Appelstr. 2, 30167 Hannover, Germany
² Theoretische Chemie, Universität Hannover, Am Kleinen Felde 30, 30167 Hannover, Germany

Corresponding author: ^a maslyuk@mail.ru

Received: 15 July 2004
Published online: 18 January 2005

Abstract

The results of calculations of the phonon dispersion, the vibrational density of states and the heat capacity of lithium tetraborate and lithium triborate crystals are presented. They are obtained in the framework of a potential model that takes into account the non-equivalence of boron atoms in different structural positions (BO₃ and BO₄ units). A symmetry analysis of the phonon modes at Γ point was performed, and calculated frequencies are compared to experimental spectra. Analysis of Li contributions to the vibrational density of states reveals that the Li-O bonds in both crystals are relatively weak. This is in line with the experimentally observed high mobility of lithium ions at high temperatures. A good agreement between calculated and measured heat capacities from the literature was obtained.