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

作为对复合氮化物热力学性质的系统研究的一部分，研究了Li-M-N(M=Mg，Al，Ga)系在900K时的相平衡。在氮气气氛下，以LiMgN为电解液，用原电池方法测定了复合氮化物的热力学性质。测量了电池在800~1100K温度范围内的电动势。当电池在900K时的电动势为0.137 V时，数据误差为±0.03V。电动势的温度依赖性很难确定。该反应的吉布斯能变为1/3Li_3N(S)1/3 Mg_3N_2(S)=LiMgN(S)，在900K时为G^o(LiMgN)=-13.2kJ/mol。利用文献中有关二元氮化物的热力学信息，推导出在900K时LiMgN的标准吉布斯能为ΔG^Of(LiMgN)=-121kJ。通过构造等温化学势图讨论了氮化物的热力学稳定范围，从而更好地理解了LiMgN相的稳定区域。该相图与合金平衡法测定的等温相图吻合较好。虽然获得的数据包含很大的不确定性，但结果提供了对氮化物热力学稳定性的更好理解。还展示了这种复合氮化物在氮化学传感器或控制氮势的介质中的潜在应用。

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.