Above room temperature heat capacity and phase transition of lithium tetrahydroborate

New calorimetric determinations of molar heat capacity C-p,C-m of lithium tetrahydroborate (LiBH4) were performed in order to analyze the origin of the previously observed anomaly before the polymorphous transition at 386 K. The above room temperature dependence of LiBH4 C-p,C-m was measured until approaching the melting point of the compound at 553 K and the abnormal behaviour was attributed to lattice defects independent of the main crystalline phase transition. As a result, lower entropy of the transition Delta S-trs = 13.11 +/- 0.23J K-1 mol(-1) than that proposed in literature was obtained, which is in agreement with the observed anisotropy and crystal density decrease before the transition from recent X-ray diffraction indexing. An estimate of the liquid C-p,C-m of LiBH4 molten salt is proposed. (C) 2011 Elsevier B.V. All rights reserved.