Enhancement of thermoelectric power factor in boron and graphene-doped strontium cobalt oxide nanoceramics via sol-gel synthesis

Abstract

In this study, boron and graphene-doped cobalt oxide-based thermoelectric nanoceramic materials were produced and characterized using the sol–gel method. The samples, designated as NC-1, NC-2, and NC-3, were composed of Sr₃Co₄O_α, Sr_2.9B_0.1Co₄O_α, and 1% graphene-doped Sr_2.9B_0.1Co₄O_α, respectively. The aim of the study was to investigate the effects of boron and graphene doping on the crystal structure, degradation temperature, and thermoelectric properties of the materials. Advanced characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and differential scanning calorimetry-thermogravimetric analysis (DSC-TGA), were employed. Additionally, thermoelectric properties were measured using a physical property measurement system (PPMS). XRD analysis identified orthorhombic (SrCO₃) and hexagonal (Sr₅Co₄O₁₂) structures, with NC-2 exhibiting only Sr₅Co₄O₁₂ peaks, indicating enhanced phase purity due to boron doping. SEM revealed predominantly spherical structures, with a noticeable reduction in particle diameter for NC-2 and NC-3, attributed to the synergistic effects of boron and graphene. TG analysis showed that boron doping increased the thermal degradation temperature, while graphene further improved thermal stability. NC-3 achieved the highest thermoelectric power factor, demonstrating the synergistic effect of boron and graphene co-doping. Although NC-2 outperformed NC-1, NC-3 exhibited superior performance, indicating that combined doping significantly enhances structural strength and thermoelectric properties.