Crystal structure of the new ternary silicides Dy_(18)Pt_(50+x)Si_(16-x) (x = 0.28) and Y_(18)Pt_(50+x)Si_(16-x) (x = 0.56)

摘要

The crystal structures of the compounds Dy_(18)Pt_(50+x)Si_(16-x) (x = 0.28) (I) and Y_(18)Pt_(50+x)Si_(16-x) (x = 0.56) (II) have been investigated by means of single crystal techniques (Nonius KappaCCD diffractometer, w- and -scans, Mo Ka radiation). Both compounds belong to a new structure type (space group PAImbm, Z= 1, a = 18.7778(2) A, c = 4.0897(l) A (I) and a - 18.7777(3) A, c = 4.0891(l) A (II)) closely related to the Er_(36)Pt_(102-x)Si_(32) (x-= 2.6) type of structure (space group P4_2/mnm, Z=l, a = 18.6723 A, c = 8.1734 A). Coordination numbers for three crystallographically independent Dy and Y atoms are 18, 15 and 12 and for Pt atoms range from 9 to 12, distorted cuboctahedra being typical for most of the Pt-atom polyhedra. Triangular prisms with three additional atoms are characteristic for coordination polyhedra of silicon atoms. The peculiarity of the defects of the Pt and Si atom positions as well as the relationship with the Ei_(36)Pt_(102-x)Si_(32) structure is discussed.