New representatives of the linear structure series containing empty Ga/Ge cubes in the Sm–Ga–Ge system

New ternary intermetallic compounds Sm2Ga7−xGex   (x=5.2–6.1x=5.2–6.1) and Sm4Ga11−xGex   (x=5.76–8.75x=5.76–8.75) were synthesized and their crystal structures were determined by X-ray powder diffraction at compositions Sm2Ga1.8Ge5.2 and Sm4Ga5.24Ge5.76. Sm2Ga1.8Ge5.2 crystallizes with the Ce2(Ga0.1Ge0.9)7 type of structure (space group Cmce, Pearson code oS  80–8.00, a=8.46216(13)a=8.46216(13), b=8.15343(13)b=8.15343(13), c=21.1243(3)Å, Z=8Z=8), while Sm4Ga5.24Ge5.76 exhibits a new structure (space group Cmmm, Pearson code oS  52–22.00, a=4.21038(4)a=4.21038(4), b=35.8075(3)b=35.8075(3), c=4.14023(4)Å, Z=2Z=2). Both structures are the members of the linear intergrowth structure series built up from segments of BaAl4, AlB2 and α-Po structure types. Their Ga/Ge networks contain characteristic empty cubes with one side capped by an atom subjected to an intrinsic displacive disorder. A model of Ga/Ge localization was suggested on the basis of crystal-chemical analysis.

Graphical abstractThe structures of the new ternary compounds Sm2Ga7−xGex   (x=5.2–6.1x=5.2–6.1) and Sm4Ga11–xGex   (x=5.76–8.75x=5.76–8.75) belong to the linear intergrowth structure series built up from the segments of BaAl4, AlB2 and α-Po structure types. The Ga/Ge networks in these structures contain characteristic empty cubes with one side capped by Ga atom, which display an intrinsic displacive atomic disorder.Figure optionsDownload full-size imageDownload as PowerPoint slide