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 CuK alpha(1), radiation in the range from 10
degrees to 130 degrees in 2 theta with a step width of 0.02 degrees.
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) Angstrom, b = 4.2264(1) Angstrom, c = 4.3573(1)
Angstrom, beta = 110.499(1)degrees, V = 199.65(1) Angstrom(3), space
group C2/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, B-eq = 1.0(2) Angstrom(2); 4(Ga0.962Cu0.038)1 in 4(i) x0z, x =
0.3858(1), z = 0.4099(5), B-eq = 0.50(7) Angstrom(2); 4(Ga0.962Cu0.038)2
in 4(i), x = 0.2524(2), z = 0.7764(4), B-eq = 0.66(7) Angstrom(2).
Atomic coordination numbers are 20 for Ca, 9 for (Ga0.962Cu0.038)1, and
12 for (Ga(0.96)2Cu(0.038))2. The shortest interatomic distances are
observed between gallium (copper) atoms: 2.485, 2.568, 2.605, and 2.655
Angstrom. 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) x (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. (C) 1995 Academic Press,
Inc.
