Effect of cold and hot compactions on corrosion behavior of p- and n-type bismuth telluride-based alloys developed through microwave sintering process

Abstract

Bismuth Telluride (BiTe) based p-type and n-type alloys exhibit superior thermoelectric (TE) performance covering energy requirements for specialized and home utilization. The main challenge nowadays is the sustainability of their adequate TE performance in corrosive environments, which might activate the corrosion reactions, leading to the degradation of p/n semiconductors, and then failure of the TE device. This study investigates the electrochemical responses of cold and hot compacted, microwave-sintered p- and n-type BiTe alloys in a saline medium (3.5 wt% NaCl solution). XRD analysis of microwave-sintered cold- and hot-compacted BiTe pellets confirmed their phase purity and uniform crystal structure. Potentiodynamic polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) data showed enhancements in the corrosion behavior of hot-compacted p-type and cold-compacted n-type BiTe pellets. The study also proposes a corrosion resistance mechanism with an equivalent electrical circuit (EEC) to fit the experimental EIS data of both BiTe pellets. FE-SEM analysis showed visible microstructural evolutions of the BiTe pellets and their passive films. It revealed a remarkable improvement in the microstructure and blocking effect caused by the formed passive films coating the surfaces of the pellets and acting as a physical barrier preventing the passing of destructive Cl- ions. EDX spectra have proved the presence of p-type and n-type BiTe alloys, each with the corresponding dopant element of Antimony (Sb) or Selenium (Se), respectively, and in the same weight compositions for either hot or cold compacted pellets. AFM analysis examined the surface topography of developed pellets. It showed an increment in the surface roughness-mean-square (RMS) values with the development of passive films on p- and n-type BiTe alloys.