Energetics of Substituted Pollucites Along the CsAlSi2O6–CsTiSi2O6.5 Join: A High‐Temperature Calorimetric Study

Abstract

Enthalpies of drop solution for a suite of substituted pollucites with the compositions CsTixAl1−xSi2O6+0.5x, 0 ≤x≤ 1, which are synthesized using the sol–gel method, have been measured in molten lead borate (2PbO·B2O3) at 701°C. As Ti4+ substitutes for Al3+, the enthalpies of drop solution become less endothermic and show exothermic heats of mixing within the composition range from x= 0.3 to 1. This nonideal mixing behavior is consistent with the trend seen in variation of lattice parameters, and we interpret it to be a result of the short‐range order associated with the framework cations Al3+, Si4+, and Ti4+ in the structure. Using enthalpies of drop solution of SiO2, Al2O3, TiO2, and Cs2O, standard molar enthalpies of formation of these phases from their constituent oxides and from the elements are derived for the first time.