RE3Co9In2 (RE = Pr, Nd, Sm) Compounds - New Members of the Homologous Series Based on CaCu5- and CsCl-type Slabs. Electronic Structure of Pr3Co9In2

The intermetallic phases RE3Co9In2 (RE = Pr, Nd, Sm) were obtained by arc-melting of the elements in an argon atmosphere followed by annealing at T = 600 degrees C for 1,500 h in evacuated and sealed quartz ampoules. All samples were characterized through their powder X-ray diffraction patterns and metallographic and quantitative phase analyses. The crystal structure of Pr3Co9In2 was refined from powder X-ray diffraction data using the Fullprof program package. The compound crystallizes in a Sm2Co9In3-related structure type (orthorhombic space group Cmmm, Z = 2; a = 23.123(4); b = 5.1003(7); c = 4.0423(5) & Aring;) and is a two-layer structure with layers perpendicular to the z direction. The crystal structure of Pr3Co9In2 is based on the intergrowth of CaCu5- and CsCl-type related slabs and is a member of the homologous series RE2m+2n+2pT2m+2nX2n+2p, where m and n are the numbers of RET5 and RET4X (CaCu5 type) slabs and p is the number of REX (CsCl type) slabs (T = Co, X = In), respectively. For Pr3Co9In2 the values are m = n = p = 2. Isostructural compounds were obtained with Nd and Sm.