NEW PHASES RCU5SN (R = LA, CE, PR, ND, SM, GD) AND CE2CU9SN2.65

Two new phases were identified in the copper-rich region of the Ce-Cu- Sn system with composition CeCu5Sn and Ce2Cu9Sn2.65 and their crystal structures were determined by single crystal diffractometric data. CeC u5Sn, orthorhombic, space group Pnma, Pearson symbol oP28, a = 8.323(1 ) Angstrom, b = 5.064(1) Angstrom, c = 10.597(1) Angstrom, Z = 4, R = 0.042 for 352 reflections with F-o > 4 sigma(F-o), is isotypic with Ce Cu5Au, a ternary derivative of the CeCu6 structure. Ce2Cu9Sn2.65, orth orhombic, space group Pnnm, Pearson symbol oP56-1.4, a = 10.669(1) Ang strom, b = 16.734(2) Angstrom, c = 5.066(1) Angstrom, Z = 4, R = 0.040 for 906 reflections with F-o > 4 sigma(F-o), can be derived from the Ce2Cu9In3 type. Different from the parent structure, the copper and ti n atoms occupy all the atomic sites in an ordered way, but a Sn positi on is only partially filled. The crystal structures of CeCu5Sn and Ce2 Cu9Sn2.65 are closely related and show very similar coordination polyh edra. Isotypic phases were found in the series RCu5Sn with R = La, Pr, Nd, Sm, Gd. The crystal structure of the already known Ce3Cu4Sn4 (Gd3 Cu4Ge4-type) was also refined from single crystal data.