Crystal Growth and Physical Properties of SrCu2As2, SrCu2Sb2 and BaCu2Sb2

TL;DR

This study reports the synthesis and detailed structural, magnetic, thermal, and transport characterization of SrCu2As2, SrCu2Sb2, and BaCu2Sb2 single crystals, revealing their metallic, diamagnetic, and layered structures with novel features.

Contribution

It provides new insights into the crystal structures and physical properties of these Cu-based compounds, including the discovery of a complex layered structure in BaCu2Sb2.

Findings

SrCu2As2 has a collapsed-tetragonal structure.

All compounds exhibit metallic behavior and are diamagnetic.

BaCu2Sb2 has a large, possibly monoclinic unit cell with layered blocks.

Abstract

We report the growth of single crystals of SrCu2As2, SrCu2Sb2, SrCu2(As{0.84}Sb{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 chi, specific heat Cp 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 structure and SrCu2Sb2 crystallizes in the CaBe2Ge2-type structure. However, 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, 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 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 3d^{10} electronic configuration corresponding to the oxidation state Cu^{+1}, as previously predicted theoretically for (Sr,Ba)Cu2As2 by D. J. Singh. We find that SrCu2As2 has a collapsed-tetragonal structure. 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 BaFe2As and pure BaCu2As2.