C/N比对Cr_(2)(C,N)晶体结构的影响研究

Effect of C/N ratio on crystal structure of Cr_(2)(C,N)

基于第一性原理计算,研究了不同C/N比Cr_(2)(C,N)的晶格常数、形成能等的变化规律,结果表明,随着C/N比的增大,属正交结构的Pbcn型Cr_(2)(C,N)的晶格常数a不断减小、c不断增大,与之相反,属三方晶系的P-31m型Cr_(2)(C,N)的晶格常数a则不断增大,c不断减小;Cr_(2)(C,N)发生晶体结构转变的临界点约为C/N比1/5,低于这一比值时P-31m型Cr_(2)(C,N)更稳定,高于这一比值时Pbcn型Cr_(2)(C,N)更稳定。通过碳热还原氮化法合成了不同C/N比的Cr_(2)(C,N),其晶体结构转变的C/N比临界点与理论计算结果吻合。

Based on the first principles calculation,the lattice constant,formation energy,etc.of different C/N ratio Cr_(2)(C,N)were studied,and the results show that with the increase of C/N ratio,the lattice constant a of Pbcn type Cr_(2)(C,N)of the orthogonal structure decreases and c continues to increase,on the contrary,the lattice constant a of P-31 m type Cr_(2)(C,N)of the tripartite crystal system is continuously increasing,and the critical point of crystal structure transformation of Cr_(2)(C,N)is about C/N ratio 1/5,below this ratio P-31 m type Cr_(2)(C,N)is more stable,above this ratio Pbcn type Cr_(2)(C,N)is more stable.Cr_(2)(C,N)with different C/N ratios was synthesized by carbon thermal reduction nitriding,and the C/N ratio critical point of the crystal structure transformation was consistent with the theoretical calculation results.