Crystal growth and physical properties of SrCu sub(2)As sub(2), SrCu sub(2)Sb sub(2), and BaCu sub(2)Sb sub(2)

We report the growth of single crystals of SrCu[sub 2] As[sub 2], SrCu[sub 2] Sb[sub 2], SrCu[sub 2] (As[sub 0.84] Sb[sub 0.16] ) , and BaCu[sub 2] Sb[sub 2] using the self-flux technique and their structural, magnetic, thermal, and transport properties that were investigated by powder x-ray diffraction (XRD), magnetic susceptibility x, specific heat C[subp], and electrical resistivity [rho] measurements versus temperature T from 1.8 to 350 K. We present a brief review of theoretical and experimental work on the doping character of transition metals for Fe in BaFe[sub 2] As[sub 2]. The As-As covalent inter-layer bond distances in the collapsed-tetragonal (Ca,Sr,Ba)Cu[sub 2] As[sub 2] compounds are much shorter than the non-bonding As-As distances in BaFe[sub 2] As[sub 2]. 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 BaFe[sub 2] As[sub 2] and pure BaCu[sub 2] As[sub 2], perhaps via a first-order lattice instability such as a miscibility gap in the Ba(Fe[sub 1-x] Cu[subx])[sub 2] As[sub 2] system.