Crystal growth and physical properties of SrCu2As2, SrCu2Sb2, and BaCu2Sb2

TitleCrystal growth and physical properties of SrCu2As2, SrCu2Sb2, and BaCu2Sb2
Publication TypeJournal Article
Year of Publication2012
AuthorsAnand VK, Perera PK, Pandey A, Goetsch RJ, Kreyssig A, Johnston DC
Journal TitlePhysical Review B
Date Published06
Type of ArticleArticle
ISBN Number1098-0121
Accession NumberWOS:000305604600004
Keywords1ST-ORDER PHASE-TRANSITIONS, arh(2)p(2), high-temperature superconductivity, iron-pnictides, layered quaternary compound, magnetic-properties, MOSSBAUER, phosphides caco2p2, ternary arsenides, thcr2si2 type-structure

We report the growth of single crystals of SrCu2As2, SrCu2Sb2, SrCu2(As0.84Sb0.16)(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 chi, specific heat C-p, and electrical resistivity rho 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-entered tetragonal structure (space group I4/mmm) andSrCu(2)Sb(2) crystallizes in theCaBe(2)Ge(2)-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 chi data of all these compounds are diamagnetic and reveal nearly T-independent anisotropic behavior. The chi 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 chi 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 gamma and the T dependences of rho reveal metallic character of all four compounds. The electronic and magnetic properties indicate that these compounds are sp metals with Cu in the nonmagnetic 3d(10) electronic configuration corresponding to the oxidation state Cu+1, as previously predicted theoretically for SrCu2As2 by Singh [Phys. Rev. B 79, 153102 (2009)]. 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(Fe1-xCux)(2)As-2 system.

URL<Go to ISI>://WOS:000305604600004
Alternate JournalPhys. Rev. B