Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, USA.
Inorg Chem. 2010 Feb 15;49(4):1433-8. doi: 10.1021/ic9016257.
The structural properties of Tc-Zr binary alloys were investigated using combined experimental and computational approaches. The Tc(2)Zr and Tc(6)Zr samples were characterized by X-ray diffraction analysis, scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy. Our XRD results show that Tc(6)Zr crystallizes in the cubic alpha-Mn-type structure (I43m space group) with a variable stoichiometry of Tc(6.25-x)Zr (0 < x < 1.45), and Tc(2)Zr has a hexagonal crystal lattice with a MgZn(2)-type structure (P6(3)/mmc space group). Rietveld analysis of the powder XRD patterns and density functional calculations of the "Tc(6)Zr" phase show a linear increase of the lattice parameter when moving from Tc(6.25)Zr to Tc(4..80)Zr compositions, similar to previous observations in the Re-Zr system. This variation of the composition of "Tc(6)Zr" is explained by the substitution of Zr for Tc atoms in the 2a site of the alpha-Mn-type structure. These results suggest that the width of the "Tc(6)Zr" phase needs to be included when constructing the Tc-Zr phase diagram. The bonding character and stability of the various Tc-Zr phases were also investigated from first principles. Calculations indicate that valence and conduction bands near the Fermi level are dominated by electrons occupying the 4d orbital. In particular, the highest-lying molecular orbitals of the valence band of Tc(2)Zr are composed of d-d sigma bonds, oriented along the normal axis of the (110) plane and linking the Zr network to the Tc framework. Strong d-d bonds stabilizing the Tc framework in the hexagonal unit cell are also in the valence band. In the cubic structures of Tc-Zr phases, only Tc 4d orbitals are found to significantly contribute near the Fermi level.
采用实验和计算相结合的方法研究了 Tc-Zr 二元合金的结构性质。用 X 射线衍射分析、扫描电子显微镜、电子探针微分析和透射电子显微镜对 Tc(2)Zr 和 Tc(6)Zr 样品进行了表征。我们的 XRD 结果表明，Tc(6)Zr 结晶为具有可变化学计量比的立方 α-Mn 型结构（I43m 空间群），Tc(6.25-x)Zr（0<x<1.45），而 Tc(2)Zr 具有六方晶格结构，属于 MgZn(2)型结构（P6(3)/mmc 空间群）。粉末 XRD 图谱的 Rietveld 分析和“Tc(6)Zr”相的密度泛函计算表明，当从 Tc(6.25)Zr 移动到 Tc(4..80)Zr 组成时，晶格参数呈线性增加，与之前在 Re-Zr 体系中的观察结果相似。“Tc(6)Zr”组成的这种变化可以通过α-Mn 型结构 2a 位的 Zr 取代 Tc 原子来解释。这些结果表明，在构建 Tc-Zr 相图时需要包含“Tc(6)Zr”相的宽度。还从第一性原理研究了各种 Tc-Zr 相的键合性质和稳定性。计算表明，费米能级附近的价带和导带主要由占据 4d 轨道的电子主导。特别是，Tc(2)Zr 的价带中最高占据分子轨道由 d-d σ 键组成，沿（110）面的法线方向取向，将 Zr 网络与 Tc 框架连接起来。在六方单元中稳定 Tc 框架的强 d-d 键也存在于价带中。在 Tc-Zr 相的立方结构中，只有 Tc 4d 轨道被发现对费米能级附近有显著贡献。
