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Planar Symmetry Incompatibility in Ru−Sn−Zn Pseudo-Decagonal Approximants Composed of Novel Pentagonal Antiprisms

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posted on 07.02.2011 by Ding-Bang Xiong, Norihiko L. Okamoto, Haruyuki Inui
Two new ternary compounds in the Ru−Sn−Zn system were synthesized by conventional high-temperature reactions, and their crystal structures were analyzed by means of the single crystal X-ray diffraction: Ru2Sn2Zn3 (orthorhombic, Pnma, Pearson symbol oP28, a = 8.2219(16), b = 4.1925(8), c = 13.625(3) Å, V = 469.66(16) Å3, Z = 4) and Ru4.15Sn4.96Zn5.85 (orthorhombic, Pnma, Pearson symbol oP60-δ, a = 8.3394(17), b = 4.2914(9), c = 28.864(6) Å, V = 1032.98(40) Å3, Z = 4). With the increase in the Sn content, the half-decagon structure unit with a triangle center in Ru2Sn2Zn3 grows up to a symmetry incompatible decagonal unit with a central triangle in the common plane in Ru4.15Sn4.96Zn5.85. Both structures can be described by hexagonal arrays of Sn-centered novel pentagonal antiprisms. In light of their pseudodecagonal diffraction in the h0l section and point group mmm, both phases are considered as new quasicrystal approximants in the Ru−Zn−Sn ternary system. The temperature dependences of the electrical resistivity for both compounds exhibit metallic behavior, but their Seebeck coefficients are of opposite sign.