Crystal Structure of CaCu0.15Ga3.85—A New Variant of the BaAl4 Structure Type: Structure Analysis from X-Ray Powder Diffraction Data

Abstract

The new intermetallic compound CaCu0.15Ga3.85 was found during the investigation of the stability of the BaAl4 structure type in ternary gallium-containing systems. The crystal structure has been investigated by means of a powder diffraction technique. The experimental diffraction data set has been obtained by the use of a Ge(111) primary monochromator and a linear position sensitive detector. The sample was measured in transmission mode using CuKαI radiation in the range from 10° to 130° in 2θ with a step width of 0.02°. Unit cell parameters have been determined by means of automatic indexing and refined from the diffraction angles of 45 reflections; monoclinic system, a = 11.5741(2) Å, b = 4.2264(1) Å, c = 4.3573(1) Å, β = 110.499(1)°, V = 199.65(1) Å3, space group C 2/m. Full profile refinement of coordinate and anisotropic thermal displacement parameters led to the residual values R(I) = 0.058 and R(P) = 0.155 for all 193 reflections possible in the range measured. The final values of the atomic coordinates are as follows: 2Ca in 2(a) 0 0 0, Beq = 1.0(2) Å2 4(Ga0.962Cu0.038)1 in 4(i) x0z, x = 0.3858(1), z = 0.4099(5), Beq = 0.50(7) Å2; 4(Ga0.962Cu0.038)2 in 4(i), x = 0.2524(2), z = 0.7764(4), Beq = 0.66(7) Å2. Atomic coordination numbers are 20 for Ca, 9 for (Ga0.962Cu0.038)1, and 12 for (Ga0.962Cu0.038)2. The shortest interatomic distances are observed between gallium (copper) atoms: 2.485, 2.568, 2.605, and 2.655 Å. The structure of CaCu0.15Ga3.85 is the first representative of a new structure type and is described as a distorted variant of the BaAl4 structure type; (a, b, c )CaCu0.15Ga3.85 = (a, b, c )BaAl4 × (1, 0, 1; 1, 0, 0; 0, 1, 0). Isotypic compounds were found in the ternary systems {Ca, Yb}-{Ni, Pd, Pt, Cu, Ag, Au}-Ga.