Chemical ordering in Cr3Al and relation to semiconducting behavior
Chemical ordering in Cr3Al and relation to semiconducting behavior
复制标题
Cr3Al 中的化学排序及其与半导体行为的关系
DOI：
10.1103/physrevb.86.085120
复制
发表时间：
2012
影响因子：
3.7
通讯作者：
F. Hellman
中科院分区：
文献类型：
--
作者：
Z. Boekelheide;D. Stewart;F. Hellman
Cr3Al 表现出类似半导体的行为，这归因于反铁磁性和 bcc 亚晶格上 Cr 和 Al 原子的化学排序的结合。本文对 Cr3Al 中的化学有序性进行了详细的理论和实验研究。使用 KorringaKohn-Rostoker (KKR) 形式体系内的密度泛函理论，我们考虑了 Cr3Al 化学计量的五种可能结构：bcc 固溶体、两相 C11b Cr2Al+ Cr、非化学计量 C11b Cr3Al、D03 Cr3Al 和 X 相 Cr3Al。计算表明，化学有序、菱形扭曲的 X 相结构具有所考虑的最低能量，因此应该是自然界中发现的基态，而 D03 结构具有最高能量，不应出现。虽然 X 相的 KKR 计算表明态密度中存在赝能隙，但使用全势线性松饼罐轨道方法和平面波技术进行的额外计算显示出窄带隙。实验上，生长了 Cr1−xAlx 薄膜，并系统地改变了浓度、生长温度和基材。 x = 0.25 的薄膜的峰值电阻率 (2400 μ -cm) 是在 300 ℃ MgO 衬底上外延生长的。在该 x 处，非金属行为和金属行为之间的转变发生在约 400°C 的生长温度下，同时伴随着化学顺序从 X 相到 C11b Cr3Al 的变化。这些结果阐明了 Cr3Al 可能结构的范围以及化学排序和电子传输行为之间的关系。
Cr3Al shows semiconductor-like behavior which has been attributed to a combination of antiferromagnetism and chemical ordering of the Cr and Al atoms on the bcc sublattice. This article presents a detailed theoretical and experimental study of the chemical ordering in Cr3Al. Using density functional theory within the KorringaKohn-Rostoker (KKR) formalism, we consider five possible structures with the Cr3Al stoichiometry: a bcc solid solution, two-phase C11b Cr2Al+ Cr, off-stoichiometric C11b Cr3Al, D03 Cr3Al, and X-phase Cr3Al. The calculations show that the chemically ordered, rhombohedrally distorted X-phase structure has the lowest energy of those considered and should, therefore, be the ground state found in nature, while the D03 structure has the highest energy and should not occur. While KKR calculations of the X phase indicate a pseudogap in the density of states, additional calculations using a full potential linear muffin-tin orbital approach and a plane-wave technique show a narrow band gap. Experimentally, thin films of Cr1−xAlx were grown and the concentration, growth temperature, and substrate were varied systematically. The peak resistivity (2400 μ -cm) is found for films with x = 0.25, grown epitaxially on a 300 ◦C MgO substrate. At this x, a transition between nonmetallic and metallic behavior occurs at a growth temperature of about 400 ◦C, which is accompanied by a change in chemical ordering from X phase to C11b Cr3Al. These results clarify the range of possible structures for Cr3Al and the relationship between chemical ordering and electronic transport behavior.