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首页> 外文期刊>Physical review >First-principles study of phase stability of stoichiometric vanadium nitrides
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First-principles study of phase stability of stoichiometric vanadium nitrides

机译：化学计量的氮化钒的相稳定性的第一性原理研究

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First-principles pseudopotential total-energy and phonon-spectrum calculations of various phases of stoichiometric vanadium nitrides with a small number of vanadium and nitrogen vacancies, as well as with small carbon and oxygen admixtures, were carried out. It was found that the stoichiometric hexagonal and tetragonal vanadium nitrides (VN) were dynamically stable. The NaCl-type VN exhibited lattice instability. The total energy for the computed ground-state phases of VN increased in the sequence hexagonal (WC type, P6m2)-hexagonal (AsNi type, .P6_3/mmc)-tetragonal (P4_2/mcm)-cubic (NaCl type, Fm3m)-cubic (ZnS type, F43m)-cubic (CsCl type, Pm3m). At low temperatures, the vacancies in both sublattices stabilize the triclinic phases of V_xN_x for x < 0.94, which is consistent with tetragonal symmetry. At high temperatures, the stability of the NaCl- and WC-type VN structures was estimated using an approach based on band-energy smearing. The results obtained indicate that the cubic structure of VN with the fully occupied sublattices will be stable only at high temperatures. The small carbon and oxygen admixtures do not stabilize the cubic phase compared to the hexagonal one. The phase stability of the cubic and hexagonal structures of V_xN_x was explained on the basis of the peculiarities of their electronic densities of states near the Fermi level. The predicted structural transformations in stoichiometric vanadium nitrides are compatible with those observed experimentally.
机译：进行了第一性原理的具有少量钒和氮空位以及具有少量碳和氧混合物的化学计量的氮化钒各相的伪势全能和声子谱计算。发现化学计量的六方氮化钒和四方氮化钒是动态稳定的。 NaCl型VN表现出晶格不稳定性。 VN的计算基态相的总能量按六边形（WC型，P6m2）-六边形（AsNi型，.P6_3 / mmc）-四边形（P4_2 / mcm）-立方（NaCl型，Fm3m）-的顺序增加立方（ZnS型，F43m）-立方（CsCl型，Pm3m）。在低温下，两个亚晶格中的空位都稳定了x≤0.94的V_xN_x的三斜晶相，这与四方对称性是一致的。在高温下，使用基于能带拖尾的方法评估了NaCl和WC型VN结构的稳定性。获得的结果表明，具有完全占据的子晶格的VN立方结构只有在高温下才会稳定。与六方相相比，小的碳和氧混合物不能稳定立方相。 V_xN_x的立方和六边形结构的相稳定性是根据费米能级附近的电子态的特殊性来解释的。化学计量的氮化钒中的预测结构转变与实验观察到的相容。

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