Syntheses and crystal structures of three copper tellurides:: BaDyCuTe3, K1.5Dy2Cu2.5Te5, and acentric K0.5Ba0.5DyCu1.5Te3

Three compounds, BaDyCuTe3, K1.5Dy2Cu2.5Te5, and K0.5Ba0.5DyCu1.5Te3, were synthesized from the reaction at 850 degrees C of the pure elements with fluxes such as BaCl2 or a eutectic mixture of LiCl/KCl. The crystal structures of the three compounds were determined by the single-crystal X-ray method. The final R-values for the three crystals were, respectively, 4.34%, 3.95%, and 3.46%. All three structures can be viewed as tetrahedral structures based on CuTe4 units. BaDyCuTe3 crystallizes in the orthorhombic space group Cmcm (no. 63) with cell dimensions of a = 4.4286(3) Angstrom, b = 14.7895(10) Angstrom, c = 11.3454(8) Angstrom, and Z = 4. BaDyCuTe3 is isotypic with the known structure of KZrCuS3. The other compounds, K0.5Ba0.5DyCu1.5Te3 and K1.5Dy2Cu2.5Te5, belong to new structure types. The structure of the former compound is a filled version of the BaDyCuTe3 compound noted above. However, unlike BaDyCuTe3, K0.5Ba0.5DyCu1.5Te3 crystallizes in the noncentrosymmetric orthorhombic space group Cmc2(1) (no. 36) with cell dimensions of a = 4.3877(3) Angstrom, b = 14.9001(12) Angstrom, c = 11.4847(9) Angstrom, and Z = 4. While BaDyCuTe3 contains infinite one-dimensional chains of tetrahedra with stoichiometry [CuTe35-](infinity), the new phase K0.5Ba0.5DyCu1.5Te3 forms a three-dimesional framework of tetrahedra. The compound K1.5Dy2Cu2.5Te5 crystallizes in another orthorhombic space group, Pmnn (No.58) with cell axes of a = 4.3307(1) Angstrom, b = 16.6766(2) Angstrom, c = 17.6945(2) Angstrom, and Z = 4. This final structure can also be related to that of K0.5Ba0.5DyCu1.5Te3.