Crystal structure and electronic and thermal properties of TbFeAsO0.85

The crystal structure and the electronic and thermal properties of a high-quality polycrystalline TbFeAsO0.85 sample made by a high-pressure technique are investigated. The crystal structure, as determined by synchrotron X-ray powder diffraction, possesses a tetragonal unit cell (space group: P4/nmm) with lattice parameters of a=b=3.8851 Å and c =8.3630 Å. In order to elucidate the electronic structure and oxidation states of corresponding elements, X-ray absorption near-edge structure (XANES) spectra are presented. The XANES spectra confirm that the oxidation states of Fe, As, and Tb in the TbFeAsO0.85 sample are ~Fe2+, ~As3−, and ~Tb3+, respectively, which are consistent with the previously reported band structure calculations. The n-type character of the charge carriers as revealed from XANES spectra is corroborated by the negative sign of the Seebeck coefficient (S) in the present study. The heat capacity (CP) measurement shows an anomaly in the vicinity of the superconducting transition temperature (Tc=42.5 K), which confirms the bulk nature of the superconductivity in this material.