Structure and electrical transport properties of the misfit-layer compound (BiS)1.08TaS2
1990; Elsevier BV; Volume: 39; Issue: 1 Linguagem: Inglês
10.1016/0379-6779(90)90194-p
ISSN1879-3290
AutoresJ. Wulff, Auke Meetsma, R.J. Haange, J. L. de Boer, G.A. Wiegers,
Tópico(s)Crystal Structures and Properties
Resumo(BiS)1.08TaS2, formerly designated as ‘BiTaS3’, has been found by single-crystal X-ray diffraction to be a misfit-layer compound built of alternate TaS2 sandwiches as also present in 2H-TaS2 and modified double layers of BiS, structurally based upon (hypothetical) NaCl-type BiS. The BiS part of the structure shows a face-centered (f.c.) orthorhombic unit cell with dimensions a1=6.101(1) Å, b1=5.724(1) Å, c1=23.066(8) Åand Z=8 for reflections with h, k and l even, but for k odd of the f.c. cell a very complex pattern of satellites around the extinct main reflections is observed. The TaS2 part of the structure has unit cell dimensions: a2 = 3.300(1) Å, b2 = 5.727(3) Å, c2 = 23.12(1) Å, space group Fm2m and Z = 4. Refinements of single crystal data (RF= 0.033 for 438 reflections) confirmed the presence of TaS2 sandwiches, the TaS distances being 2.524(4) Å (×2) and 2.443(3) Å (×4). The complex structure of the BiS subsystem was not solved, but the Okl reflections (RF=0.058 for 114 reflections) showed the BiS structure to be a modulation along [100] of a double-layer structure as observed for other misfit-layer compounds. The BiS distances, calculated for an undistorted structure, indicate that Bi in the BiS part is on average Bi2+. The electrical conduction is by light holes (the Hall constant being positive) and heavy electrons (negative sign of the Seebeck coefficient) presumably in the 5dz2 conduction band of the TaS2 part. There is no substantial electron donation from the BiS to the TaS2 part, therefore Bi is Bi2+, in agreement with the BiS distances.
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