Crystal growth and physical properties of SrCu₂As₂, SrCu ₂Sb₂, and BaCu₂Sb₂

Journal Article · Mon Jun 25 00:00:00 EDT 2012 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.85.214523· OSTI ID:1047720

Anand, V. K. ^[1]; Perera, P. Kanchana ^[1]; Pandey, Abhishek ^[1]; Goetsch, R. J. ^[1]; Kreyssig, A. ^[1]; Johnston, D. C. ^[1]

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1. Ames Laboratory, and Iowa State University, Ames, IA (United States)

Here we report the growth of single crystals of SrCu₂As₂, SrCu₂Sb₂, SrCu₂(As_0.84Sb_0.16)₂, and BaCu₂Sb₂ using the self-flux technique and their structural, magnetic, thermal, and transport properties that were investigated by powder x-ray diffraction (XRD), magnetic susceptibility χ, specific heat Cp, and electrical resistivity ρ measurements versus temperature T from 1.8 to 350 K. Rietveld refinements of XRD patterns for crushed crystals confirm that SrCu₂As₂ crystallizes in the ThCr₂Si₂-type body-centered tetragonal structure (space group I4/mmm) and SrCu₂Sb₂ crystallizes in the CaBe₂Ge₂-type primitive tetragonal structure (space group P4/nmm). However, as reported previously, BaCu₂Sb₂ is found to have a large unit cell consisting of three blocks. Here a ThCr₂Si₂-type block is sandwiched between two CaBe₂Ge₂-type blocks along the c axis with an overall symmetry of I4/mmm, as reported, but likely with a monoclinic distortion. The χ data of all these compounds are diamagnetic and reveal nearly T-independent anisotropic behavior. The χ of SrCu₂As₂ is found to be larger in the ab plane than along the c axis, as also previously reported for pure and doped BaFe₂As₂, whereas the χ values of SrCu₂Sb₂ and BaCu₂Sb₂ are larger along the c axis. This difference in anisotropy appears to arise from the differences between the crystal structures. The finite values of the Sommerfeld linear specific heat coefficients γ and the T dependences of ρ reveal metallic character of all four compounds. The electronic and magnetic properties indicate that these compounds are sp metals with Cu in the nonmagnetic 3d¹⁰ electronic configuration corresponding to the oxidation state Cu⁺¹, as previously predicted theoretically for SrCu₂As₂ by Singh. We present a brief review of theoretical and experimental work on the doping character of transition metals for Fe in BaFe₂As₂. The As–As covalent interlayer bond distances in the collapsed-tetragonal (Ca,Sr,Ba)Cu₂As₂ compounds are much shorter than the nonbonding As–As distances in BaFe₂As₂. Thus, the electronic character of the Cu and the strength of the As–As interlayer bonding are both expected to drastically change between weakly Cu-substituted BaFe₂As₂ and pure BaCu₂As₂, perhaps via a first-order lattice instability such as a miscibility gap in the Ba(Fe_1-xCu_x)₂As₂ system.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE)
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1047720
• Alternate ID(s): OSTI ID: 1103647
• Report Number(s): IS-J--7728
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 21 Vol. 85; ISSN 1098-0121; ISSN PRBMDO
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE