Bonding and physical properties of Hume-Rothery compounds with the PtHg 4 structure
Bonding and physical properties of Hume-Rothery compounds with the PtHg 4 structure
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具有 PtHg 4 结构的 Hume-Rothery 化合物的键合和物理性质
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发表时间：
2001
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通讯作者：
S. Simak
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作者：
U. Häussermann;P. Viklund;M. Boström;R. Norrestam;S. Simak
我们对具有 ${\mathrm{PtHg}}_{4}$ 结构的金属间电子化合物的键合和结构稳定性进行了详细的实验和理论研究。由于结构简单，这些化合物代表了一个优秀的原型系统，可以更全面地了解 $d\ensuremath{-}sp$ 键合休谟-罗瑟里化合物大家族的键合和稳定性。特别是，合成了代表 ${\mathrm{CrGa}}_{4}$ 和 ${\mathrm{MnGa}}_{4}$ 并测量了它们的电阻率、磁化率和体积模量。我们发现这两种化合物都是金属导体，但在与温度无关的磁化率方面表现出显着的巨大差异。 ${\mathrm{MnGa}}_{4}$的泡利顺磁化率值比${\mathrm{CrGa}}_{4}高约$5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ ${\mathrm{m}}^{3}/\mathrm{mol}$。$ ${\mathrm{CrGa}}_{4}$ 和 ${\mathrm{MnGa}}_{4}$ 的 ${\mathrm{PtHg}}_{4}$ 结构在约 100 kbar 的压力下保持稳定。全电位线性化增强平面波计算很好地再现了 ${\mathrm{CrGa}}_{4}$ 和 ${\mathrm{MnGa}}_{4}$ 的实验结构特性，并显示了两种化合物中过渡金属原子和 Ga 原子之间的强方向（共价）键合。定向键合是由于窄 d 带与 Ga $\mathrm{sp}$ 带的大量杂化。因此，在 ${\mathrm{CrGa}}_{4}$ 的费米能级和略高于 ${\mathrm{MnGa}}_{4}$ 的费米能级处产生了大的赝能隙。这种赝能隙是具有 ${\mathrm{PtHg}}_{4}$ 结构的电子化合物的结构稳定性的特征和决定性因素。我们发现结构稳定性表现为优化赝能隙和最小化化合物平衡体积之间的竞争。因此，稳定的电子化合物仅限于$T{\mathrm{Ga}}_{4}$系统，其中T是第6族或第7族的过渡金属。Ga完全取代等价的Al或In是不可能的。
We present a detailed experimental and theoretical study concerning bonding and structural stability of intermetallic electron compounds with the ${\mathrm{PtHg}}_{4}$ structure. Due to the simplicity of the structure these compounds represent an excellent prototype system for a more general insight into bonding and stability of the large family of $d\ensuremath{-}sp$ bonded Hume-Rothery compounds. In particular, the representatives ${\mathrm{CrGa}}_{4}$ and ${\mathrm{MnGa}}_{4}$ were synthesised and their resistivity, magnetic susceptibility, and bulk modulus measured. We find that both compounds are metallic conductors but show a remarkable large difference in their temperature independent magnetic susceptibilities. The value of the Pauli paramagnetic susceptibility of ${\mathrm{MnGa}}_{4}$ is about $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ ${\mathrm{m}}^{3}/\mathrm{mol}$ higher than that of ${\mathrm{CrGa}}_{4}.$ The ${\mathrm{PtHg}}_{4}$ structure of ${\mathrm{CrGa}}_{4}$ and ${\mathrm{MnGa}}_{4}$ is stable up to pressures of about 100 kbar. Full-potential linearized augmented plane wave calculations reproduced very well the experimental structural properties of ${\mathrm{CrGa}}_{4}$ and ${\mathrm{MnGa}}_{4}$ and showed strong directional (covalent) bonding between transition metal atoms and Ga atoms in both compounds. The directional bonding is due to a large hybridization of the narrow d bands with the Ga $\mathrm{sp}$ bands. As a consequence a large pseudogap at the Fermi level for ${\mathrm{CrGa}}_{4}$ and slightly above the Fermi level for ${\mathrm{MnGa}}_{4}$ is produced. This pseudogap is characteristic and decisive for structural stability of electron compounds with the ${\mathrm{PtHg}}_{4}$ structure. We find that structural stability appears as a competition between optimizing the pseudogap and minimizing the compound equilibrium volume. Therefore, stable electron compounds are confined to systems $T{\mathrm{Ga}}_{4}$ with T being a transition metal from group 6 or 7. A complete substitution of Ga for isovalent Al or In is not possible.