Effects of Co Concentration on Structure and Thermoelectric Properties of PrBa2(Cu1-xCox)3O7-y Ceramics

This work aims to study the effects of Co-doping in Cu-site of PrBa2(Cu1-xCox)3O7-y (PrBCO) ceramics (where x = 0.05, 0.10, 0.15, 0.17 and 0.20) on thermoelectric (TE) properties at high temperature. The result of solid-state reaction synthesis of Co-doped PrBCO compounds was optimally obtained at 900 °C for 16 h. Then, the powder was compacted into pellets by uniaxial press and sintered at 920 °C for 16 h and the crystalline structure was confirmed using X-ray diffractometry (XRD). The XRD data underwent Rietveld refinement employing the GSAS II program for a detailed analysis of phase composition and crystal structure. Microstructural characteristics and chemical composition were investigated through scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The high-temperature thermoelectric properties, particularly electrical conductivity (), Seebeck coefficient () and thermal conductivity (ĸ) were also measured, and the figure of merit (ZT) was calculated to determine the thermoelectric performance of the compounds. The measured bulk density, determined through air and xylene displacement exceeded 90% of theoretical value. It was observed that Co-doping in the Cu-site of PrBCO led to an increased value of the Seebeck coefficient (), resulting in the ZT value tending to increase, particularly as the temperature rised. However, the electrical conductivity (σ) decreased, which was inversely related to  due to the reduction in carrier concentration. The power factor (PF) showed relatively high values over a broad temperature range for undoped and x=0.05 Co-doped samples. Furthermore, considering the thermal conductivity (κ), it was found that κ decreased after Co was added to PrBCO, due to the lattice structure being disturbed and causing increased phonon scattering. The sample with x = 0.05 exhibited the highest ZT value of 0.028 at 873 K, while the sample with x = 0.17 had the highest ZT value of 0.021 at 673 K.