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The meaning of the oxygen second-electron affinity and oxide potential models

机译:氧二次电子亲和力和氧化物电势模型的含义

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The second-electron affinity of the oxygen atom is often required in modelling the behaviour of ceramics. It is usually taken to be about 8 eV, independent of the structure of the oxide being modelled. We show that this is not so. Quantum-mechanical calculations show that the true second-electron affinity of an in-crystal O2- ion depends on both the chemical composition and the nuclear geometry. Moreover, for a binary oxide at its equilibrium geometry, this true second-electron affinity is about 40% greater than 8eV. This discrepancy between the true second-electron affinity and the value of 8 eV derived from semi-empirical potentials determined by fitting to experimental crystal data arises from the structural dependence of the true value. In a semi-empirical treatment, this dependence becomes absorbed into the quantity regarded as the short-range cation-oxide interaction with the consequence that the resulting second-electron affinity is smaller than the true value. A further consequence is that these short-range cation-oxide interactions are dependent on the crystal structure. Thus, for example, a semi-empirical potential determined from a binary oxide with the rock salt structure cannot be transferred to a polymorph with the eightfold-coordinated CsCl structure.
机译:在对陶瓷的行为进行建模时,经常需要氧原子的第二电子亲和力。通常取值为约8 eV,与要建模的氧化物的结构无关。我们证明事实并非如此。量子力学计算表明,晶内O2-离子的真实第二电子亲和力取决于化学成分和核几何形状。此外,对于处于平衡几何形状的二元氧化物,该真正的第二电子亲和力比8eV高约40%。真实的第二电子亲和力与通过拟合实验晶体数据确定的半经验电势得出的8 eV值之间的差异是由真实值的结构依赖性引起的。在半经验处理中,这种依赖性被吸收到被认为是短程阳离子-氧化物相互作用的量中,结果是所得到的第二电子亲和力小于真实值。进一步的结果是这些短程阳离子-氧化物相互作用取决于晶体结构。因此,例如,由具有岩盐结构的二元氧化物确定的半经验电势不能转移至具有八倍配位的CsCl结构的多晶型物。

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