Crystal structure and physical properties of EPCo4.7Ge9 (EP = Sr, Ba, Eu)

BaCo4.7Ge9 (BaCo5−xGe9, x = 0.29) is a novel ternary compound which forms incongruently from the melt and crystallizes in a unique structure type (space group Pnma; a = 1.39910(2), b = 0.40218(2), c = 1.69882(2) nm, Z = 4). Isotypic compounds were found with SrCo4.7Ge9 (a = 1.39389(8), b = 0.39665(1), c = 1.67860(9) nm) and EuCo4.7Ge9 (a = 1.3910(1), b = 0.39425(2), c = 1.6741(2) nm). Physical properties (electrical resistivity, specific heat, magnetic susceptibility) were studied for BaCo4.7Ge9 and EuCo4.7Ge9. BaCo4.7Ge9 shows metallic behaviour but neither a superconducting nor a magnetic phase transition was observed for temperatures as low as T = 2 K. Magnetic susceptibility and specific heat data of EuCo4.7Ge9, evidence the onset of antiferromagnetic order at 18.5 K. Both magnetic ordering and the effective magnetic moment derived verify the Eu2+ state with a total angular momentum j = 7/2.