ZT Enhancement in Solution-Grown Sb_(2−x)Bi_xTe₃ Nanoplatelets

Abstract

We report a solution-processed, ligand supported synthesis of 15-20 nm thick Sb (2−x) BixTe3 nanoplatelets. After complete ligand removal by a facile NH3-based etching procedure, the platelets are spark plasma sintered to a p-type nanostructured bulk material with preserved crystal grain sizes. Due to this nanostructure, the total thermal conductivity is reduced by 60 % in combination with a reduction in electric conductivity of as low as 20 % as compared to the bulk material demonstrating the feasibility of the phonon-glass electron-crystal concept. An enhancement in the dimensionless thermoelectric figure of merit of up to 15 % over state-of-the-art bulk materials is achieved meanwhile shifting the maximum to significantly higher temperatures.Recently, Bi 2 Te 3 based nanostructured materials have received great attention due to their outstanding thermoelectric properties. From the first reports in the 1950s until today, the dimensionless thermoelectric figure of merit (ZT) of such materials at room temperature has been improved threefold. ZT is estimated to require a value of 3 to be competitive with conventional cooling devices and to open up novel pathways for efficient and greener power generation.The record high efficiency of 2.4 was reported for molecular beam epitaxy engineered thin films of Bi 2 Te 3 /Sb 2 Te 3 layers, which may be difficult to use in large-scale applications but convincingly demonstrated the potential for further improvements to come from nanostructured Bi 2 Te 3 based materials [5].In order to fabricate such materials on a macroscopic scale, one conventionally applies high pressure and suitable temperatures to sinter a Bi 2 Te 3 based nanopowder to a dense nanocomposite with preserved crystal grain boundaries. Such nanocomposites have been studied by the means of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) [6] and scanning electron microscopy (SEM) [7]. It is believed that the unique structural details in these materials such as laminated structure, coherent interfaces, nanoprecipitates with defect concentrations and broad size distribution of crystalline domains effect all three parameters of ZT, namely the thermopower, electric and * Electronic address: scheele@chemie.uni-hamburg.de thermal conductivity and can lead to an overall improvement of thermoelectric efficiency.Synthetic strategies to Bi 2 Te 3 based nanopowders can be divided into two approaches: (a) ligandless or (b) ligand supported nanograin growth. Advantages of the former are the absence of organic impurities and the good alloying possibilities by standard semiconductor manipulations. As a matter of this, the ligandless approach was more successful recently and all of the mile stone achievements in enhancing zT as cited above were due this strategy. An instructive summary has been provided recently by Ren and coworkers [8]. However, it is found almost impossible to achieve a good size control and narrow size distribution of nanoparticles by this strategy. This is the major advan...

Optimizations of Pulsed Plated p and n‐type Bi2Te3‐Based Ternary Compounds by Annealing in Different Ambient Atmospheres

“…[ 11 ] Hence, the fabrication of (Bi x Sb 1−x ) 2 Te 3 is of high interest and several works report on the fabrication of (Bi x Sb 1−x ) 2 Te 3 using several deposition methods such as pulsed laser deposition (PLD) [ 16 ] or solution-growth. [ 17 ] It exhibits the same crystal structure as Bi 2 Te 3 with Sb atoms randomly occupying the Bi lattice sites, forming a different type of doping causing higher thermoelectrical performances. [ 11 ] Many previous works also report on the electrodeposition of (Bi x Sb 1−x ) 2 Te 3 , although the deposition process is more challenging compared to binary compounds due to signifi cantly poorer control of the fi lm composition by the deposition potential or -current density.…”

“…The uncertainties of D and C p are of the order of ± 10% each and the density´s accuracy is assumed to be ± 15% due to the possibility of signifi cant porosity of the deposited fi lms. [ 17 ] Thus, the experimental uncertainty on ZT can easily reach ± 50%.…”

Synthesis and Characterization of Nanocrystalline FeSb2 for Thermoelectric Applications

“…Chemical syntheses allow for processing the nanocrystals in a size-controlled and scalable manner, most useful in investigations of size-dependent TE properties. [12,13,[16][17][18][19] Herein we report on a simple, lowtemperature solvothermal approach for the synthesis of FeSb 2 nanocrystals with space group Pnnm (no. 58), the FeSb 2 prepared by a solid-state synthesis process.…”

Chemical Trends of Electronic Properties of Two-Dimensional Halide Perovskites and Their Potential Applications for Electronics and Optoelectronics

“…One is to enhance the Seebeck coefficient or the PF using band structure engineering methods, [5] such as modifying the electronic density of states and Fermi energy through doping heteroatoms, reducing crystal symmetry to achieve high band edge degeneracy, [6][7][8] etc. The other is to reduce thermal conductivity using methods such as nanostructuring, [9][10][11][12][13][14][15][16][17][18][19][20][21] alloying, [14,[22][23][24][25][26] etc. These strategies have achieved significant progress in the past decade.…”