New Layered-Type Quaternary Chalcogenides, Tl(2)PbMQ(4) (M = Zr, Hf; Q = S, Se): Structure, Electronic Structure, and Electrical Transport Properties

作者：Sankar Cheriyedath Raj; Assoud Abdeljalil; Kleinke Holger^*

来源：Inorganic Chemistry, 2013, 52(24): 13869-13874.

DOI：10.1021/ic4025316

We have synthesized and characterized new thallium chalcogenides of the general formula Tl(2)PbMQ(4) (M = Zr, Hf; Q = S, Se) from the constituent elements via high-temperature reaction conditions. These sulfides and selenides crystallize in the monoclinic crystal system (space group C2/c). The unit cell parameters refined from single-crystal X-ray diffraction data for Tl2PbZrS4 are a = 15.455(4) angstrom, b = 8.214(2) angstrom, c = 6.751(2) angstrom, beta = 109.093(3)degrees, and V = 809.9(4) angstrom(3), with Z = 4. No corresponding tellurides were obtained from similar reaction conditions. The isostructural quaternary chalcogenides form a layered structure, composed of alternating metal and chalcogen layers. The latter are packed along the a axis as in the face-centered cubic packing (ABC), while the metal layers alternate between Tl layers and mixed Pb/Zr layers. All metal atoms are located in differently distorted Q(6) octahedra, with the TlQ(6) polyhedra being the least regular ones. Density functional theory based electronic structure calculations with inclusion of relativistic spin-orbit interactions predict (indirect) energy band gaps of 0.66 and 0.33 eV for Tl2PbZrS4 and Tl2PbHfSe4, respectively. Optical spectroscopy revealed significantly larger (direct) band gaps of 1.2 and 1.6 eV. The semiconducting character is in agreement with the charge-balanced formula (Tl+)(2)Pb2+M4+(Q(2-))(4). The electrical transport properties also show the semiconducting nature of these materials. For Tl2PbHfSe4, the Seebeck coefficient increases from +190 mu V K-1 room temperature to +420 mu V K-1 at 520 K.

• 出版日期2013-12-16