Thermodynamic properties of solid electrolyte Li7La3Zr2O12

The heat capacity temperature dependence of the high-potential solid electrolyte Li7La3Zr2O12 was experimentally determined using differential scanning calorimetry. Besides, the heat capacity in the temperature range 298-800 K was calculated according to the additive Neumann-Kopp rule. The experimental and calculated values of heat capacities are close to each other. The correctness of the Neumann-Kopp assumption for zirconates was also confirmed by comparing the available literature for other similar systems. The molar heat capacity of Li7La3Zr2O12 at constant pressure in the temperature range 298-800 K should be calculated as C-p,C-m = 533.725 + 0.128 x T - 9.537.10(6) x T-2, where T is absolute temperature. Other thermodynamic characteristics of tetragonal Li7La3Zr2O12 were determined: entropy (S degrees(298) = 424.0 J mol(-1) K-1), the standard Gibbs free energy of formation (Delta(f)G degrees(298) = -6777.3 kJ mol(-1)), the enthalpy increment from 0 to 298 K (H degrees 298-H degrees(0) = 72.64 kJ mol(-1)), the enthalpy of formation at 0 K (Delta H-f degrees(0) = -7109.7 kJ mol(-1)). The performed thermodynamic calculations confirm that solid electrolyte Li7La3Zr2O12 is stable against metallic lithium at room temperature. (C) 2018 Elsevier Ltd.