Microstructure and thermoelectric properties of the medium-entropy block-textured BiSbTe1.5Se1.5 alloy

Abstract

Medium-entropy BiSbTe1.5Se1.5 alloy has been prepared by self-propagating high-temperature synthesis (to prepare a starting powder with desired composition and structure) and spark plasma sintering (to prepare block-textured samples). Under texturing, a partial ordering of grains, which is typical for Bi2Te3-based alloys, takes place resulting in forming a lamellar grain structure. Lamellar sheets are not continuous for whole volume of the textured sample. There are blocks with continuous lamellar sheets of some definite orientation, but the orientations of the sheets in neighboring blocks are different from each other. Forming the block-textured structure can be related to specific features of the starting powder, applied to sinter the bulk samples. The starting powder was strongly inhomogeneous and particles in the starting powder were rather big and shape-isotropic. As result, the texturing can be initiated in local domains of volume independently from each other resulting in forming the blocks with different preferential grains orientation. Due to the block texturing, the thermoelectric properties of the BiSbTe1.5Se1.5 alloy, measured perpendicularly or parallel to a texturing axis, are different. Many features, found in these properties, are typical for textured Bi2Te3-based alloys. The thermoelectric properties of the medium-entropy block-textured BiSbTe1.5Se1.5 alloy can be believed to be promising enough. The highest thermoelectric figure-of-merit equal to ~0.43 was observed for the perpendicular measuring orientation. This alloy can be next applied as a precursor for developing five- or six-element high-entropy alloys with enhanced thermoelectric efficiency.