钍基碳化物ThC的高压结构稳定性研究

Structural stability of ThC under high pressure

钍基碳化物ThC是重要的核材料,基于第一性原理计算,我们研究了ThC的结构稳定性及相变.声子色散曲线表明基态结构的晶格能够稳定到42 GPa附近,当压力继续升高时虚频的出现表明了动力学的不稳定.经比较基态Fm-3m及高压相Pnma结构的自由能,发现零温下,相变压力为22.4 GPa,符合声子色散曲线的结果,同时预测了两种结构的相变边界.

The phase transition and structure stability of binary compounds of actinide metal ThC have always at- tracted much attention of the experimental and theoretical investigators. The stable phase of ThC at room condi- tion is rock salt structure, but the high pressure phase transitions may be possible. Under compression, we cap- tured a large softening around the X point. When the pressure is raised to 42 GPa, the frequencies around the T point in transverse acoustical branches become imaginary, indicating a structural instability. Within the quasi - harmonic approximation, we predicted the high pressure phase boundary.