α-SrZn5-Type solid solution, BaZn2.6Cu2.4

BaCu2.6Zn2.4 has an α-SrZn5-type structure. Although the Ba atom is larger than the Sr atom, the cell volume of title compound is smaller than that of α-SrZn5. This can be attributed to the partial substitution of Cu atoms with Zn atoms, and the average Ba—Zn/Cu distance becomes shorter than the Sr—Zn distance.

The Ba1 sites are staggered along the array of the triangular prisms in the tunnel extending in the b-axis direction.

Synthesis and crystallization
The title compound was prepared from pieces of Ba (Aldrich Chemicals, 99.9%), Cu (Kojundo Chemical Laboratory Co., Ltd., 99.99%), and Zn (Strem Chemicals Inc., 99.99%) metals with molar ratio of Ba:Cu:Zn = 1:1:1. The metals were placed in a BN crucible (Showa Denko Co., Ltd., purity 99.95%, outer diameter 8.5 mm, inner diameter 6.5 mm, depth 18 mm), which was then put inside a stainless-steel tube (SUS 316: outer diameter 12.7 mm, inner diameter 10.7 mm, height 80 mm) and sealed with a stainless-steel cap in an Ar-filled glove box (MBRAUN; O 2 and H 2 O < 1 ppm). The tube was heated to 933 K at a rate of 330 Kh À1 for 10 h, then slowly cooled at a rate of 10 Kh À1 to below 573 K. Finally, the sample was cooled to room temperature by shutting off the electric power to the heater of the furnace. The stainless-steel tube was cut in the Ar-filled glove box. The resulting product contained silver metallic single crystals of the title compound with size of several hundred mm. The surface color of the single crystals changed to metallic gold in air, but crystal decomposition did not occur. A thin layer formed by oxidation may have prevented the further oxidation of the sample. Single crystal XRD data collection was carried out in air. Another single crystal grain obtained from the same sample was buried in resin and polished with a SiC polishing sheet to verify the composition of the crystal by electron probe microanalysis (EPMA, JEOL JXA-8200). A Ba:Cu:Zn atomic ratio of 1.01 AE 0.01:2.62 AE 0.10:2.37 AE 0.09 was obtained by measurements at seven points with the total weight percent of 94-98%. From the EPMA measurement, the chemical composition of the single crystal was determined to be BaCu 2.6 Zn 2.4 .

Refinement
Crystal data, data collection, and structural refinement details are summarized in Table 3. The initial structural model was constructed from the -SrZn 5 model by substituting the Ba1 site with the Sr1 site, and the Zn/Cu mixed sites with the four Zn sites. In the first stage of refinement, the sum of the occupancies for Cu and Zn atoms in each Zn/Cu site was constrained to be 1. After several refinement iterations, the Cu occupancy for the Zn/Cu1 site became 0.98 (6), and then this site was set to be fully occupied by Cu only. The substitutional occupations of the other three Zn/Cu mixed sites were refined under the restriction that the total chemical composition should be Zn:Cu = 0.48:0.52, which was determined by EPMA.

barium zinc copper
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )