Silver-Antimony-Telluride: From First-Principles Calculations to Thermoelectric Applications

Abstract

Silver-antimony-telluride (AgSbTe 2 ) based compounds have emerged as a promising class of materials for thermoelectric (TE) power generation at the mid-temperature range. This Chapter demonstrates utilization of irst-principles calculations for predicting TE properties of AgSbTe 2 -based compounds and experimental validations. Predictive calculations of the efects of La-doping on vibrational and electronic properties of AgSbTe 2 compounds are performed applying the density functional theory (DFT), and temperature-dependent TE transport coeicients are evaluated applying the Bolzmann transport theory (BTE). Experimentally, model ternary (AgSbTe 2 ) and quaternary (3 at. % La-AgSbTe 2 ) compounds were synthesized, for which TE transport coeicients were measured, indicating that thermal conductivity decreases due to La-alloying. The later also reduces electrical conductivity and increases Seebeck coeicients. All trends correspond with those predicted from irst-principles. Thermal stability issues are essential for TE device operation at service conditions, e.g. changes of matrix composition and second-phase precipitation, and are also addressed in this study on both computational and experimental aspects. It is shown that La-alloying afects TE igure-of-merit positively, e.g., improving from 0.35 up to 0.50 at 260 °C. We highlight the universal aspects of this approach that can be applied for other TE compounds. This enables us screening their performance prior to synthesis in laboratory.Keywords: silver-antimony-telluride, irst-principles calculations, thermoelectric transport properties, Bolzmann transport theory, latice dynamics, thermal stability IntroductionIt is of utmost technological importance to develop predictive tools that will provide us with information about design of materials' functional properties. In this context, density functional theory (DFT) irst-principle calculations ofer us such possibilities [1][2][3][4] Despite of relatively high ZT values of AgSbTe 2 phase, it is still challenging to increase them to the range of 2-3. Reaching at this limit will enable us employing this material for energy conversion at power levels >500 W [34]. Reduction in latice thermal conductivity is a conventional way to enhance TE performance and is achieved by either doping with solute elements [35] or formation of second phases to stimulate phonon scatering [36][37][38]. These latice defects afect, of course, electronic properties, mainly electrical conductivity and Seebeck coeicient. Atempts to improve TE properties of AgSbTe 2 -based alloys by doping with diferent elements [19,25,[39][40][41][42][43][44][45][46][47] Notwithstanding the aforementioned successful experimental and computational atempts, a set of experimental routines, that is initiated and directed by predictions from irst principles for complete TE performance or any other computational procedure, is missing. Thermoelectrics for Power Generation -A Look at Trends in the Technology 148A signiicant step in this direction is introduced by o...

Role of Nanostructuring and Microstructuring in Silver Antimony Telluride Compounds for Thermoelectric Applications

“…This was predicted from first-principles calculations of TE transport coefficients, applying Boltzmann transport theory, implemented for three model compounds, namely, Ag 3 SbTe 4 , AgSb 3 Te 4 , and AgSbTe 2 , exhibiting Sb/Ag ratios of 1/3, 3, and 1, respectively. It was shown that the increase in the Sb/Ag ratio results in a decrease in electrical conductivity simultaneously with an increase in the Seebeck coefficient for a wide temperature range from 50 through 1000 K . This trend is corroborated by the data recorded in Table and Figure b,c and corresponds to the results presented in the study of Jovovic and Heremans, who reported a decrease in both Seebeck coefficient and resistivity owing to the addition of 2% AgTe to a stoichiometric AgSbTe 2 -phase, that is, a reduction in the Sb/Ag ratio.…”

“…Moreover, there is a certain orientation relationship between the matrix and the precipitates as shown in Figure 7, which suggests that these precipitates are endotaxially embedded in the matrix exhibiting interfacial free-energy values as low as approximately 200 mJ m −2 . 25 Detection of such endotaxially embedded precipitates has already been demonstrated for a AgSbTe−PbTe alloy using HRTEM. 56 4.2.…”

“…It is also noteworthy that alloying additives such as La can improve thermal stability. This important aspect is thoroughly discussed …”

“…This explains why, intriguingly, AST-based alloys are suitable materials for both TE and phase-change applications. Owing to these peculiarities, these alloys have been investigated extensively, either experimentally or computationally …”

“…Owing to these peculiarities, these alloys have been investigated extensively, either experimentally or computationally. 25 In this work, we focus on the microstructure evolution of AST-based compounds upon aging heat treatments, which includes formation and coarsening of nanometer and micrometer length scale defects. To investigate the exact composition of precipitates formed after quenching and further heat treatments, we synthesize an AST TE bulk material with a composition that deviates from the stoichiometric ratio of AgSbTe 2 being referred to δ-phase in this work.…”