Crystal structure and thermoelectric properties of n-type Bi_2-xCe_xO₂Se ceramics

Full text: Bi₂O₂Se consists of the tetragonal insulating [Bi₂O₂]²⁺ and [Se]^2- layers [1]. The oxide exhibits a low thermal conductivity and a large Seebeck coefficient [2]. Thus, Bi₂O₂Se is of particular interest as a potential n-type thermoelectric material. In this work, we prepared Bi_2-xCe_xO₂Se (x = 0 – 0.15) samples by spark plasma sintering (SPS). For SPS, the prepared powders of Bi_2-xCe_xO₂Se (x = 0 – 0.15) were placed in a graphite mold, heated up to 630°C, and then kept at this temperature for 5 min under a pressure of 50 MPa in vacuum. The structural, optical, and thermoelectric properties of the Bi_2-xCe_xO₂Se as a function of Ce content were investigated by X-ray diffraction (XRD), XRD Rietveld refinement, scanning electron microscope (SEM), UV-visible spectroscopy, and thermoelectric property measurements. The major peaks of the calcined powders were matched with standard PDF⌗25-1463 of Bi₂O₂Se, indicating a tetragonal structure with I4/mmm space group. Weak XRD peaks related to CeO₂ and Bi₂O₃ in the calcined powders were detected. The sintered Bi_2-xCe_xO₂Se crystallized in a tetragonal structure. The electrical and thermal conductivities increased with increasing Ce content. The Seebeck coefficients of all the samples were negative, indicating that electrons are major carriers. The substitution of Ce for Bi is a promising approach for improving the thermoelectric properties of Bi₂O₂Se. (author)