Nitride Metallurgy: Thermodynamics of Nitrides and Development of New Synthesis Methods

作为复合氮化物热力学性质系统研究的一部分，研究了Li-M-N（M=Mg，Al，Ga）体系在900 K时的相平衡。采用原电池法，在氮气气氛下，以LiMgN为电解质，对复合氮化物的热力学性质进行了测定。在800和1100 K之间的温度下的电池的电动势（EMF）进行了测量。在900 K时测得电池的电动势为0.137 V，但测量数据的误差为± 0.03 V，很难确定电动势的温度依赖性。测得900 K时1/3 Li_3N（s）+1/3Mg_3N_2（s）=LiMgN（s）反应的吉布斯能变化为△G^o_r（LiMgN）= -13.2（±2.9）kJ/mol。利用文献中有关二元氮化物的热力学信息，推导出LiMgN的标准吉布斯自由能为ΔG^o_f（LiMgN）= -121 kJ（900 K）。通过构造等温化学势图，更好地理解LiMgN相的稳定区域，讨论了氮化物的热力学稳定范围。该相图与合金平衡法测定的等温相图符合得很好。虽然获得的数据包括很大的不确定性，结果提供了一个更好的理解氮化物的热力学稳定性。这种复合氮化物的潜在应用氮化学传感器或用于控制氮势的介质也被示出。

As part of a systematic study on the thermodynamic properties of complex nitrides, phase equilibria of the system Li-M-N (M=Mg, Al, Ga) at 900 K were investigated. An attempt to determine the thermodynamic properties of complex nitrides was made by using the galvanic cell method, which utilizes LiMgN as an electrolyte under nitrogen atmosphere. The electromotive force (Emf) of the cell at temperatures between 800 and 1100 K was measured. While the Emf of the cell at 900 K was measured to be 0.137 V, data discrepancies of ±0.03V were found. It was difficult to determine temperature dependence of the Emf. The Gibbs energy change for the reaction, 1/3 Li_3N(s)+1/3Mg_3N_2(s)=LiMgN (s), at 900 K was determined to be △G^o_r (LiMgN) = -13.2 (±2.9) kJ/mol. Using thermodynamic information on the binary nitride from literature, the standard Gibbs energy of LiMgN was derived to be ΔG^o_f (LiMgN) = -121 kJ at 900 K. The thermodynamic stability range of nitride was discussed by constructing isothermal chemical potential diagrams that provide a better understanding of the stability region of the LiMgN phase. The diagram was found to be in good agreement with the isothermal phase diagram determined by the alloy equilibration method. Although the obtained data includes large uncertainties, the results provide a better understanding of the thermodynamic stability of nitrides. The potential application of this complex nitride to nitrogen chemical sensors or a medium for controlling nitrogen potential is also shown.