State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, People's Republic of China.
J Chem Phys. 2013 Dec 21;139(23):234504. doi: 10.1063/1.4846995.
The structural evolution of tetragonal Zr2Cu has been investigated under high pressures up to 70 GPa by means of density functional theory. Our calculations predict a pressure-induced isosymmetric transition where the tetragonal symmetry (I4/mmm) is retained during the entire compression as well as decompression process while its axial ratio (c/a) undergoes a transition from ~3.5 to ~4.2 at around 35 GPa with a hysteresis width of about 4 GPa accompanied by an obvious volume collapse of 1.8% and anomalous elastic properties such as weak mechanical stability, dramatically high elastic anisotropy, and low Young's modulus. Crystallographically, the tetragonal axial ratio shift renders this transition analogous to a simple bcc-to-fcc structural transition, which implies it might be densification-driven. Electronically, the ambient Zr2Cu is uncovered with an intriguing pseudo BaFe2As2-type structure, which upon the phase transition undergoes an electron density topological change and collapses to an atomic-sandwich-like structure. The pseudo BaFe2As2-type structure is demonstrated to be shaped by hybridized dxz + yz electronic states below Fermi level, while the high pressure straight Zr-Zr bonding is accommodated by electronic states near Fermi level with dx(2) - y(2) dominant features.
采用密度泛函理论研究了四方相 Zr2Cu 在高达 70 GPa 压力下的结构演化。我们的计算预测了一种等对称相变，其中四方对称（I4/mmm）在整个压缩和减压过程中保持不变，而其轴比（c/a）在约 35 GPa 时从3.5 转变到4.2，滞后宽度约为 4 GPa，同时伴有~1.8%的明显体积收缩和异常弹性性质，如弱力学稳定性、极高的弹性各向异性和低的杨氏模量。从晶体学上看，四方相轴比的变化使得这种转变类似于简单的 bcc 到 fcc 结构转变，这意味着它可能是由致密化驱动的。从电子学角度看，环境中的 Zr2Cu 揭示了一种有趣的伪 BaFe2As2 型结构，该结构在相变过程中经历了电子密度拓扑变化，并塌缩成原子夹层状结构。证明了伪 BaFe2As2 型结构是由费米能级以下的杂化 dxz + yz 电子态形成的，而高压直线 Zr-Zr 键则由具有 dx(2) - y(2)主导特征的费米能级附近的电子态来容纳。
