Thermodynamics and phase stability in the Ga-N system
Thermodynamics and phase stability in the Ga-N system
复制标题
DOI：
10.1016/s0022-0248(03)01352-6
复制
发表时间：
2003-08-01
影响因子：
1.8
通讯作者：
Schmid-Fetzer, R
中科院分区：
文献类型：
--
作者：
Unland, J;Onderka, B;Schmid-Fetzer, R
采用两种不同的定制热重法——动态振荡热重法和等温步进热重法，对氮化镓粉末的分解进行了实验研究。在较低温度下可重现的质量增益表明，在1bar氮气下，平衡温度为1110+/- 10k。对所有可用的相平衡和热力学数据进行了CALPHAD型热力学分析。这包括确定氮化镓的绝对熵，30+/-4 J/mol K，基于德拜和爱因斯坦对热容实验数据的分析。建立了氮的逸度-压力关系的显式方程f(P)，该方程可用于复相图计算输出的转换。这是至关重要的，因为对于GaN分解过程中遇到的高压，f可能比P高几个数量级。基于为Ga-N体系开发的一致热力学描述，计算了所有热力学数据和各种相图。它们表明不同类型的实验数据（量热、蒸气压、相平衡）之间有很好的总体一致性。根据热力学模型预测了氮化镓分解压力的高压部分，与实验数据吻合较好。(C) 2003 Elsevier B.V.版权所有
The decomposition of GaN powder was studied experimentally using two different customized thermogravimetric methods, dynamic oscillation TGA, and isothermal stepping TGA for a higher resolution of the decomposition start. A reproducible mass gain at slightly lower temperature suggests the equilibrium temperature to be at 1110+/-10 K under 1 bar of nitrogen. A CALPHAD type thermodynamic analysis of all available phase equilibrium and thermodynamic data is performed. This includes the determination of the absolute entropy of GaN, 30+/-4 J/mol K, based on a Debye- and Einstein-analysis of the experimental data on the heat capacity. An explicit equation for the fugacity-pressure relation of nitrogen, f(P), is developed, which is useful for the conversion of complex phase diagram calculation output. This is crucial because f can be several orders of magnitude higher than P for the high pressures encountered during GaN decomposition. Based on the consistent thermodynamic description, developed for the Ga-N system, all thermodynamic data and various phase diagrams are calculated. They indicate a good overall agreement between the different types of experimental data (calorimetric, vapor pressure, phase equilibrium). The high pressure part of the decomposition pressure of GaN is actually predicted from the thermodynamic model in good agreement with the experimental data. (C) 2003 Elsevier B.V. All rights reserved.