Synthesis, Structure and Some Properties of ThCr2Si2 Type Compounds: AeCo2Ge2 (Ae=Ca,Sr) and ACo2As2(A=K,Ba)

This research was motivated by the variety of electronic and magnetic properties that ternary intermetallic compounds, AT2X2 (A= alkali/alkaline earth metals, T = transition metal and X = post-transition metal) exhibit. These polar intermetallics crystallize in the ubiquitous ThCr2Si2 structure type (space group I4/mmm) or derivatives of it. In this context, the ternary cobalt germanides: CaCo2Ge2 and SrCo2Ge2, and arsenides: KCo2As2 and BaCo2As2, were synthesized and characterized. The ternary cobalt germanides were prepared from the elements by arc melting techniques, and characterized by means of single crystal and powder X-ray diffraction. The ternary arsenides were synthesized from the high-temperature reactions of the respective active metals (K, Ba) with pre-reacted binary CoAs within welded Nb containers. The ternary arsenides were characterized by means of powder X-ray diffraction. The magnetic susceptibility of these compounds was measured. CaCo2Ge2 and KCo2As2 were found to be weakly ferromagnetic while BaCo2As2 was pauli-paramagnetic. Finally, the solid solubility of BaCo2As2 and KCo2As2, to prepare Ba(x)K(1-x)Co2As2, was investigated by the powder X-ray diffraction. The crystal chemistry and the physical properties of the ternary compounds are discussed.