热力学
焓
固溶体
化学
标准摩尔熵
快离子导体
混合熵
电解质
电化学
混溶性
旋节分解
物理化学
相(物质)
电极
有机化学
物理
聚合物
作者
U. Warhus,Joachim Maier,A. Rabenau
标识
DOI:10.1016/0022-4596(88)90014-x
摘要
It is shown that Hong's NASICON solid solution range is intrinsically stable for T > 600 K. With the help of electrochemical and calorimetric experiments, complete thermochemical information of Na1+xZr2SixP3−xO12 (0 ≦ x ≦ 3) compositions has been elucidated, i.e., formation enthalpies, standard entropies, and molar volume (1.5–1000 K). For the purpose of a precise evaluation of the electrochemical values the specific heats of ZrP2O7 and Na2ZrSi2O7 have also been determined. A thermodynamic mixture model is constructed showing that the solid solution is entropy stabilized. The energetic interaction has a destabilizing influence. The zero-point entropy and the excess entropy at higher temperatures suggest a partial ordering (SiP) at higher temperatures. A miscibility gap, however, which is predicted for T ≤ 600 K by the model, could not be found due to the slow kinetics or because of a simultaneous phase transformation. The obtained values clearly show that NASICON is thermodynamically unstable with respect to a reaction with elementary sodium. The instability increases with increasing P content.
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