Rare-earth manganese germanides RE2+xMnGe2+y (RE=La, Ce) built from four-membered rings and stellae quadrangulae of Mn-centred tetrahedra

Reactions of the elements through arc-melting and annealing at 800 degrees C have led to the ternary rare-earth manganese germanides RE2+xMnGe2+y (RE=La, Ce). The approximate composition is RE2.1MnGe2.2, as determined by single-crystal X-ray diffraction studies on the La member (space group P4/nmm, a=16.0491(4) angstrom, c=8.1587(2) angstrom, z=16). Although this composition is close to other germanides RE2MGe2 (Sc2CoSi2-type), the structure is completely unrelated. Rather, La2.1MnGe2.2 contains layers built up of Mn-centred tetrahedra in two types of arrangements, four-membered rings and stellae quadrangulae, with La and additional Ge atoms in the intervening spaces. Disorder of La atoms, isolated Ge atoms, and Ge-2 dimers takes place within tunnels in the structure. Electrical and magnetic measurements on La2.1MnGe2.2 indicate metallic behaviour and likely ferromagnetic ordering with a transition temperature above 300 K. (C) 2013 Elsevier Inc. All rights reserved.