A Comparative Study on the Thermoelectric Properties of Bismuth Chalcogenide Alloys Synthesized through Mechanochemical Alloying and Microwave-Assisted Solution Synthesis Routes

Abstract

The way a material is synthesized and processed has an immense effect on its microstructure, which in turn has a big impact on its transport properties. Here, we compare the thermoelectric (TE) properties of n-and p-type Bi 2−x Sb x Te 3 (x: 0 and 1.5) materials synthesized through two different routes, specifically mechanochemical alloying (MA)-as a solid-state synthesis route-and microwave(MW)-assisted polyol synthesis-as a solution synthesis route. Reaction time is significantly reduced in the MW synthesis, leading to significantly lower energy consumption (i.e., higher energy efficiency) per batch than using the MA route. The resultant materials are compared for their crystallinity, phase purity, morphology, and microstructure. Spark plasma sintering was used to prepare pellets, and the resultant consolidates were evaluated for their transport properties. TE properties and microstructure of the specimens were investigated in relation to processing conditions and composition. MA samples formed fused structures (from 200 nm to several micrometers in size) composed of smaller particles. MWsynthesized materials exhibited hexagonal platelet morphology, high crystallinity, and phase purity. They also showed lower thermal conductivity, leading to a higher resultant TE figure-of-merit ZT. TE properties of Bi 2−x Sb x Te 3 samples were studied on sintered cylindrical pellet samples, where the highest ZT values achieved were 1.04 (at 440 K) for MW-Bi 2 Te 3 and 0.76 (at 523 K) for MW-Bi 0.5 Sb 1.5 Te 3 samples, while MA-Bi 2 Te 3 and MA-Bi 0.5 Sb 1.5 Te 3 samples showed maximum ZT values of 0.74 (at 460 K) and 0.27 (at 300 K), respectively, as n-and p-type TE materials. The observed trend is much higher ZT values for MW samples, ascribed to their higher degree of texturing and nanostructured grains reducing the thermal conductivity, thus achieving a better overall performance, verifying the prospect to enhance ZT using MW-assisted solution synthesis approach.

Thermoelectric Inks and Power Factor Tunability in Hybrid Films through All Solution Process

“…The efficiency of TE energy conversion increases with an increasing figure of merit −ZT, defined as S 2 σ T /κ, where S is the Seebeck coefficient (=−Δ V /Δ T , the voltage (−Δ V ) induced by a temperature gradient (Δ T )), σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. It is an exciting scientific challenge to find materials that optimize the strongly negatively correlated material properties such as S , σ, and κ. Nanostructuring has become an important approach in the field of TEs for reducing the thermal conductivity κ independently from the electrical conductivity σ. − For the widespread application of TE materials, it is equally important that the structural integrity and chemical stability of the materials are preserved under operating conditions.…”

Minute-Made, High-Efficiency Nanostructured Bi2Te3 via High-Throughput Green Solution Chemical Synthesis

“…Bottom up chemical methods are commonly used because of their low cost, low investment need and possibility of scale-up of the synthesis process [ 26 ]. Different morphologies of Bi 2−x Sb x Te 3 including nanoparticles, nanoplates, nanocrystalline films, nanorods, nanotubes, nanowires and nanoflowers have been synthesized by reverse micelle [ 27 ], metal-organic chemical vapor deposition (MOCVD) [ 28 , 29 , 30 ], vapor–liquid–solid (VLS) [ 31 , 32 ], refluxing [ 33 , 34 , 35 , 36 ], electrodeposition [ 37 , 38 ], chemical reduction [ 39 , 40 ], solvothermal [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ], hydrothermal [ 26 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 ], ultrasonic-assisted [ 59 , 60 , 61 ], and microwave (MW)-assisted [ 62 , 63 , 64 , 65 , 66 ] routes, to name a few. Among all these chemical syntheses methods, solvothermal/hydrothermal routes are the preferred methods to prepare nanostructures with different morphologies.…”

“…MW technology is emerging as an alternative energy source for chemical synthesis with the aim to reduce the reaction time from hours or even days to a few minutes [ 64 , 65 , 67 , 68 , 69 , 70 ]. The dielectric constant of the solvent may significantly influence the outcome of the MW-assisted reaction.…”

A Review on Doped/Composite Bismuth Chalcogenide Compounds for Thermoelectric Device Applications: Various Synthesis Techniques and Challenges

“…Microwave-synthesized samples showed thermal conductivity less than that obtained by the alloying method, with ZT values of 1.0 and 0.6 obtained at 440 K for the microwave route and mechanochemical alloying, respectively. 174 The microwave technique was also adopted to synthesize thermoelectric nanopowders of a Bi 2−x Sb x Te 3 system. A unique transition was observed from p-to n-type semiconducting with ZT values of 1.04 and 0.4, respectively, for the n and p types at 448 K. 175 Ahmed et al 176 used spark plasma sintering for the preparation of n-type (Bi 0.95 Sb 0.05 ) 2 (Se 0.05 Te 0.95 ).…”