Debye temperature and stiffness of carbon and boron nitride polymorphs from first principles calculations
Debye temperature and stiffness of carbon and boron nitride polymorphs from first principles calculations
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DOI：
10.1103/physrevb.73.064304
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发表时间：
2006-02
影响因子：
3.7
通讯作者：
T. Tohei;A. Kuwabara;F. Oba;I. Tanaka
中科院分区：
文献类型：
--
作者：
T. Tohei;A. Kuwabara;F. Oba;I. Tanaka
本文从理论上研究了碳和氮化硼多晶型体的声子谱和热容，特别是德拜温度和刚度随温度的变化。石墨的部分光学声子支的频率比金刚石的高。因此，在1000 K的交叉温度以上，石墨显示出比金刚石更小的热容和更高的德拜温度。这支持了热容量的实验报告，尽管可用的实验数据广泛分散。石墨在1000 K以上具有较高的德拜刚度，这与金刚石的常规刚度远大于石墨的德拜刚度这一事实并不矛盾，因为德拜刚度是由声学声子和光学声子共同决定的，而只有声学声子对常规刚度有贡献。在六方氮化硼和立方氮化硼之间发现了相同的趋势，交叉温度为600 K。
A theoretical investigation has been made on the phonon spectrum and heat capacity of polymorphs of carbon and boron nitride with special interests on the variation of Debye temperature and stiffness with temperature. A part of optical phonon branches of graphite exhibits higher frequencies than those of diamond. As a consequence, graphite shows smaller heat capacity and higher Debye temperature than diamond above a crossover temperature of 1000 K. This supports experimental reports of heat capacity although available experimental data are widely scattered. The higher Debye stiffness of graphite at above 1000 K is not contra-dictory to the fact that conventional stiffness of diamond is much larger than that of graphite, since the Debye stiffness is determined by both acoustic and optical phonons, whereas only acoustic phonons contribute to the conventional stiffness. The same trend was found between hexagonal and cubic boron nitrides with a crossover temperature of 600 K.