Chemical ordering in Cr3Al and relation to semiconducting behavior

Article

关键词: DENSITY-WAVE ANTIFERROMAGNETISM;    GENERALIZED GRADIENT APPROXIMATION;    TEMPERATURE SPECIFIC-HEAT;    ELECTRICAL-PROPERTIES;    TRANSPORT-PROPERTIES;    CR;    TRANSITION;    EXCHANGE;    DEPENDENCE;    ALLOYS;   

DOI  :  10.1103/PhysRevB.86.085120

来源: SCIE

【 摘 要 】

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 Korringa-Kohn-Rostoker (KKR) formalism, we consider five possible structures with the Cr3Al stoichiometry: a bcc solid solution, two-phase C11(b) Cr2Al + Cr, off-stoichiometric C11(b) Cr3Al, D0(3) 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 D0(3) 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 mu Omega-cm) is found for films with x = 0.25, grown epitaxially on a 300 degrees C MgO substrate. At this x, a transition between nonmetallic and metallic behavior occurs at a growth temperature of about 400 degrees C, which is accompanied by a change in chemical ordering from X phase to C11(b) Cr3Al. These results clarify the range of possible structures for Cr3Al and the relationship between chemical ordering and electronic transport behavior.

【 授权许可】

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