The recent discovery of stable FeO₂ under high pressures has aroused great interest in materials science, suggesting the existence of the 4+ oxidation state of late transition metals in their binary oxides. Compared with other cobalt and nickel compounds, reports on CoO₂ and NiO₂ are limited, and even the oxidation states of Co and Ni in CoO₂ and NiO₂ are the subject of debate in theoretical works. Herein, PbO₂-type CoO₂ and pyrite-type NiO₂ are predicted using density functional theory calculations. The equations of state and relative enthalpies with known compounds are determined, showing that the PbO₂-type CoO₂ and pyrite-type NiO₂ can be synthesized above 40 and 43 GPa, respectively. The calculations of elasticity and phonon spectra have confirmed their mechanical and dynamical stabilities at 0 GPa. The band structures and densities of states show that PbO₂-CoO₂ is half metallic and pyrite-NiO₂ is semiconducting.

中文翻译：

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高压下的半金属 CoO2 和半导体 NiO2

最近在高压下发现稳定的 FeO ₂引起了材料科学的极大兴趣，这表明后期过渡金属在其二元氧化物中存在 4+ 氧化态。与其他钴和镍化合物相比，CoO ₂和NiO _{2 的}报道有限，甚至CoO ₂和NiO ₂中Co和Ni的氧化态也是理论工作中争论的主题。在此，使用密度泛函理论计算来预测PbO ₂型CoO ₂和黄铁矿型NiO ₂。确定了已知化合物的状态方程和相对焓，表明 PbO ₂-型CoO ₂和黄铁矿型NiO ₂可以分别在40和43 GPa以上合成。弹性和声子谱的计算证实了它们在 0 GPa 下的机械和动力学稳定性。能带结构和态密度表明PbO ₂ -CoO ₂是半金属的，而黄铁矿-NiO ₂是半导体的。