Temperature Dependence Of Thermoelectric Properties Research Articles

Thermoelectric properties of monolayer and bilayer di boron nitride (di BN)

Motivated by the diverse uses of 2D materials in the modern technologies, we explore the temperature dependent thermoelectric properties of monolayer and bilayer di boron nitride. These materials are not still synthesized therefore the formation energy for monolayer and binding energy for bilayer is computed indicating the thermodynamical stability of both systems. The monolayer has a moderate direct band gap of 1.71 eV, while the bilayer possesses a band gap of 0.99 eV. The Seebeck coefficient has no substantial thickness and directional dependency. The Seebeck coefficient for bilayer decreases more as compare to monolayer with increasing temperature and at 600 K it decreases more than 1.7 times as compared to monolayer. However, the bilayer system has a longer carrier relaxation time than the monolayer system. Besides, the p-type relaxation in the ZZ-direction is longer than the n-type for both monolayer and bilayer systems. Consequently, the electrical and electronic thermal conductivities are two times larger in bilayer system. Here, p-type doping system have higher magnitude of electrical and electronic thermal conductivities than n-type doping system. The bilayer system has a greater lattice thermal conductivity than the monolayer. As results, we obtain that the maximum ZT of 0.8 in the bilayer system while the monolayer has a maximum ZT of 0.36 at 600 K with hole doping.

First-principles investigation of structural, electronic and thermoelectric properties of SmMg2X2 (X = P, As, Sb, Bi) zintl compounds

Structure complexity, adequate electronic character and congenital lower thermal conductivity of zintl phases result in designing thermoelectrics of tremendous efficiency. Such qualities of zintl phases embolden us to present a detailed study of SmMg2X2 (X = P, As, Sb, Bi) zintl compounds by first principles. The structural characteristics fit well with the existing data. Electronic properties of titled compounds are scrutinized by adopting PBE-GGA, TB-mBJ and hybrid (YS-PBE0) potentials. The band structure calculations through TB-mBJ and hybrid (YS-PBE0) proclaim the semiconducting behavior of compounds and there is a shrinkage of band gap by changing X anion from P to Bi. The density of states (DOS) calculation reveals that there is a major contribution of Sm-f states and Mg atom in valence band while in conduction band, the prominent role is offered by Sm-d states and p states of X anion. Similarly, the temperature-dependent thermoelectric properties are scrutinized by using BoltzTraP2 code embedded within WIEN2k software for with and without spin–orbit coupling (SOC) and also through hybrid (YS-PBE0) functional. SOC, but even more hybrid functional, has been shown to have a significant effect on the transport behavior. Optimized values of carriers’ concentration are achieved which subsidize thermoelectric parameters like power factor (PF), Seebeck coefficient ([Formula: see text] and thermoelectric figure of merit (ZT) at elevated temperature. The compounds show excellent thermoelectric performance in the studied temperature range.

Unveiling the temperature-dependent thermoelectric properties of the undoped and Na-doped monolayer SnSe allotropes: a comparative study

Motivated by the excellent thermoelectric (TE) performance of bulk SnSe, extensive attention has been drawn to the TE properties of the monolayer SnSe. To uncover the fundamental mechanism of manipulating the TE performance of the SnSe monolayer, we perform a systematic study on the TE properties of five monolayer SnSe allotropes such as α-, β-, γ-, δ-, and ε-SnSe based on the density functional theory and the non-equilibrium Green’s functions. By comparing the TE properties of the Na-doped SnSe allotropes with the undoped ones, the influences of the Na doping and the temperature on the TE properties are deeply investigated. It is shown that the figure of merit ZT will increase as the temperature increases, which is the same for almost all the Na-doped and undoped cases. The Na doping can enhance or suppress the ZT in different SnSe allotropes at different temperatures, implying the presence of the anomalous suppression of the ZT. The Na doping induced ZT suppression may be caused basically by the sharp decrease of the power factor and the weak decrease of the electronic thermal conductance, rather than by the decrease of the phononic thermal conductance. We hope this work will be able to enrich the understanding of the manipulation of TE properties by means of dimensions, structurization, doping, and temperature.

High figure-of-merit of single-walled carbon nanotubes films with metallic type conduction

Carbon nanotubes are promising candidates for thermoelectric power generation because of their one-dimensionality mediated high Seebeck coefficient, high electrical conductivity with added advantages of flexibility, light weight, and scalability. We report the temperature-dependent thermoelectric properties of single-walled carbon nanotube (SWCNTs) films. The SWCNTs films exhibit p-type metallic conduction with high Seebeck coefficient (∼69.5 μVK−1) and moderate electrical conductivity (∼76 Scm−1). The films exhibit low thermal conductivity (∼0.1 Wm−1 K−1) due to phonon scattering at the interjunction region. The synergetic combination of thermoelectric properties resulted in a high figure-of-merit of ∼0.11 at 305 K. A flexible thermoelectric generator based on SWCNTs films mounted on a curved hot surface exhibited an output of 17 mV and 54 μA under a small temperature gradient of 10 K. The present work provides possible avenues for developing wearable SWCNTs based thermoelectric power generation modules for harvesting body heat.

Thermally processed phase change behavior on the stoichiometric efficacy of quaternary Se77.5-X Te20 Sn2.5 AgX (X = 2.5, 5, 7.5) thin films

Thin films of the quaternary metal chalcogenide have recently gained attention due to their improved electrical, optical, thermal, and structural properties. The structural, thermal, morphological, optical, and electrical properties of Ag-modified novel quaternary Se–Te–Sn–Ag thin film systems are investigated in this paper. Temperature-dependent structural, electrical, and thermoelectric properties are given special attention. From Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA), the Ag content in this composition induces thermal stability and crystalline phase as well as glass phase transitions. High-temperature X-ray diffraction (HTXRD) patterns were used to investigate the temperature-dependent structural phase transition, grain size, lattice strain, and dislocation density. The morphological observations show that Ag concentration promotes the nucleation and growth processes of nanorod structures in as-deposited thin films. Optical characteristics reveal higher IR transparency in thin films and high refractive indexes in the range of 3.22–3.29. The as-deposited thin films resistivity decreases with increasing temperature and silver content. The Hall measurement corroborates the results obtained from the Seebeck measurements, indicating that the samples are n-type. The phase change switching mechanism of phase change devices is still unclear; there are two possible mechanisms: thermal and electronic models. This work proposes thermally processed phase transition behaviors in structural and electrical studies. The result of the above analyses shows that the quaternary Se–Te–Sn–Ag thin film will be a potential candidate for phase change device applications.

First-principles calculations to investigate Structural, mechanical, electronic, magnetic and thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) spinel oxides

Structural, mechanical, magnetic, electronic and thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) spinel oxides are studied through first-principles calculations. Calculations of structural and elastic stiffness constants (Cij’s) show that the MRh2O4 oxides are stable structurally and mechanically. Elastomechanical results show that the CdRh2O4 is ductile, MnRh2O4 is brittle, while MgRh2O4 lies on the borderline differentiating the ductile and brittle character. MnRh2O4 has high bulk modulus and high Young’s modulus which indicate its ability to resist plastic deformation. MnRh2O4 spinel oxide bears the highest values of Debye temperature (TD = 634.4 K) and melting temperature (Tm = 3530.4 K) among the MRh2O4 (M = Mg, Mn, Cd) oxides. Band structure calculations and density of states spectra indicate the p-type semiconducting nature of MRh2O4 (M = Mg, Mn, Cd) oxides. Spin-polarized electronic structure of CdRh2O4 show 100 % spin-polarized behavior, while MgRh2O4 and MnRh2O4 oxides show 0.12 % and 0.29 % spin-polarization, respectively. MnRh2O4 exhibits saturation magnetization Ms = 172 emu/g and total magnetic moment mtot = 9.99 µB/f.u. Temperature dependent thermoelectric properties (thermal conductivity, electrical conductivity, Seebeck coefficient, Hall coefficient, power factor and figure of merit) are also studied for MRh2O4 oxides. Calculated thermoelectric properties of MRh2O4 (M = Mg, Mn, Cd) oxides show that these oxides are promising for applications as novel thermoelectric materials.

First-principles calculations to investigate structural, electronic, mechanical, optical and thermoelectric properties of Sr-based fluoride perovskites SrXF3 (X = Nb, Ti, Zr)

In the present study, we elaborated a group of SrXF3 (i.e., SrNbF3, SrTiF3 and SrZrF3) fluoride materials using the computational approach and calculated their structural, electronic, thermal, mechanical, and optical properties with the help of WIEN2K. Amongst the three presently studied SrNbF3, SrTiF3 and SrZrF3 materials, the material with Nb at the X site showed the least value of energy at the ground state than the SrTiF3 and SrZrF3 materials. Furthermore, the SrNbF3 material also showed superior value of bulk modulus which certifies its extensive opposition to the compressibility amidst the three studied materials. IRelast package is used to find the elastic constants from which mechanical stability and other mechanical parameters are calculated. Analysis of elastic properties reveals that all compounds have ductile nature. Temperature dependent thermoelectric properties such as Seebeck coefficient (S), electronic thermal conductivity (κe), and figure of merit (ZT) were calculated with Boltztrap. Our results revealed that among the investigated perovskites, SrTiF3 exhibited ZT∼0.19 and suitable for thermoelectric applications at higher temperature. For optoelectronic response, the optical properties of the given compounds were calculated for the photon energy 0–20 eV. The response of the understudy compounds over a wide range of electromagnetic radiations, indicating their potential usage for optoelectronic devices.

Design of Thermoelectric Generators and Maximum Electrical Power Using Reduced Variables and Machine Learning Approaches

This work aims to contribute to studies on the geometric optimization of thermoelectric generators (TEGs) through a combination of the reduced variables technique and supervised machine learning. The architecture of the thermoelectric generators studied, one conventional and the other segmented, was determined by calculating the cross-sectional area and length of the legs, and applying reduced variables approximation. With the help of a supervised machine learning algorithm, the values of the thermoelectric properties were predicted, as were those of the maximum electrical power for the other temperature values. This characteristic was an advantage that allowed us to obtain approximate results for the electrical power, adjusting the design of the TEGs when experimental values were not known. The proposed method also made it possible to determine the optimal values of various parameters of the legs, which were the ratio of the cross-sectional areas (Ap/An), the length of the legs (l), and the space between the legs (H). Aspects such as temperature-dependent thermoelectric properties (Seebeck coefficient, electrical resistivity, and thermal conductivity) and the metallic bridge that connects the legs were considered in the calculations for the design of the TEGs, obtaining more realistic models. In the training phase, the algorithm received the parameter (H) and an operating temperature value as input data, to predict the corresponding value of the maximum power produced. This calculation was performed for conventional and segmented systems. Recent advances have opened up the possibility of applying an algorithm for designing conventional and segmented thermocouples based on the reduced variables approach and incorporating a supervised machine learning computational technique.

A computational insight into the Zintl SZr2N2 and BaAg2S2 phases for optoelectronic thermoelectric applications

The physical characteristics of SZr2N2 and BaAg2S2 Zintl phases have been explored by utilizing the full-potential augmented plane wave (FP-LAPW) method with the combination of modified Becke-Johnson (mBJ) approximation. The negative formation energies and phonon modes with positive frequencies endorsed the stability of both compounds. The electronic band profile reveals a bandgap of 1.18 eV for SZr2N2 and 2.15 eV for BaAg2S2. The optical characteristics are also calculated. The absorption of light for the studied compounds falls in the ultra-violet region, which shows their possibility to be employed as UV-rays absorbers. A large optical conductivity and low energy loss is also seen for both materials on UV region. The efficiency of temperature-dependent thermoelectric properties increases with the temperature rise, as calculated with the BoltzTraP code. The high electrical with low thermal conductivities and maximum Seebeck coefficient is witnessed for both materials. The large ZT values of 0.75 and 0.80 are achieved for SZr2N2 and BaAg2S2, respectively. All calculated transport parameters indicate the opportunity of using the studied compounds for thermoelectric applications.

Tuning the Radius Ratio to Enhance Thermoelectric Properties in the Zintl Compounds AM2Sb2 (A = Ba, Sr; M = Zn, Cd)

Five novel Zintl phase solid solutions in the Ba1–xSrxZn2–yCdySb2 (0 ≤ x ≤ 0.13(1); 0 ≤ y ≤ 0.32(2)) system were successfully synthesized by the molten Pb metal-flux method, and the powder X-ray diffraction and single-crystal X-ray diffraction analyses proved that all five title compounds adopted the BaCu2S2-type phase having the orthorhombic Pnma space group (Z = 4, Pearson code oP20) with five crystallographically independent atomic sites. The previously studied BaCu2S2-type antimonides demonstrated a limited tolerance for doping in contrast to the CaAl2Si2-type antimonides. To understand the relatively narrower phase width and limited dopability of the title BaCu2S2-type phase than the CaAl2Si2-type phase in the overall Ba1–xSrxZn2–yCdySb2 system, the radius ratio of cations and anionic elements r+/r– for two structure types were thoroughly investigated. For the first time, the r+/r– ratio was identified as a critical factor for the phase selectivity: (1) r+/r– > 1 favored the BaCu2S2-type phase, and (2) r+/r– < 1 favored the CaAl2Si2-type phase. We also revealed the structural transformation mechanism from the more widely observed CaAl2Si2-type phase to the title BaCu2S2-type phase as the relatively larger cationic elements were introduced to the system. A series of DFT calculations using the three hypothetical models indicated that a resonance peak near EF in the density of states curves was descended from the relatively flat band structure at several special symmetry points rationalizing the enhanced Seebeck coefficients of Ba0.94(1)Sr0.06Zn1.86(3)Cd0.14Sb2 and Ba0.96(1)Sr0.04Zn1.68(2)Cd0.32Sb2. Electron localization function analysis rationalized the correlation between the polarity change of anionic Zn/Cd–Sb bonds and the charge carrier mobility on the anionic frameworks. Temperature-dependent thermoelectric properties were studied for the four title compounds, and the results proved that the Sr and Cd doping in the title Ba1–xSrxZn2–yCdySb2 system successfully enhanced the ZT values through the increased Seebeck coefficients and the reduced total thermal conductivities.

Temperature dependences of thermoelectric properties of bulk SiGeAu composites

Recently, we have demonstrated thermoelectric power factor enhancement of bulk SiGeAu composites at room temperature by thermal management with resonant level effect. In terms of the application to the thermoelectric generation from low temperature wasted heat, the thermoelectric properties in the low temperature range should be investigated. In this study, we evaluate the temperature dependences of thermoelectric properties of P- and B-doped SiGeAu samples. Accompanying the thermoelectric power factor enhancement of P-doped SiGeAu sample by thermal management with resonant level effect, ZT was higher than practically-used SiGe in the range from room temperature to 200 ºC. This study indicates that SiGeAu composites can be used for reusing low temperature wasted heat.

First-principles investigation on the novel half-Heusler VXTe (X=Cr, Mn, Fe, and Co) alloys for spintronic and thermoelectric applications

Half-Heusler (HH) alloys are a well-known and extensively researched family of thermoelectric (TE), magnetic, and spintronic materials. Doping may significantly increase the thermoelectric conversion efficiency of these materials; nevertheless, practical applications remain far. As a result, the hunt for superior parent TE alloys is critical. Using extensive first-principles density functional calculations, we predicted a novel class of vanadium-based four HH VXTe alloys, where X is one of the four elements: Cr, Mn, Fe, and Co. Their TE properties, as well as their mechanical, magnetic, electrical, and structural stability, have been studied in depth. Their mechanical and thermodynamic stability is confirmed using the predicted elastic constants, formation and cohesive energies, and phonon spectra. A comprehensive analysis of elastic constants and moduli demonstrates that HH VXTe alloys possess elastic anisotropy with reasonably good machinability, higher melting and Debye temperatures, mixed bonding characteristics with ionic and covalent contributions, and brittle nature, except for VCoTe, which is ductile. We find that the ground state of HH VCrTe and VFeTe is ferrimagnetic, while HH VCoTe is ferromagnetic and HH VMnTe is non-magnetic. Three VXTe (X = Cr, Fe, & Co) alloys demonstrated half-metallicity with 100% spin-polarization, whereas HH VMnTe is an 18-electron indirect semiconductor. In the studied HH VXTe alloys, most of the heat flow is caused by the phonon-group velocity of the acoustic phonons. Further studies on the relationship between carrier concentration and temperature dependence of TE properties reveal that the high ZT ∼1.2 at 1000 K of the pristine HH VMnTe alloy is obtained due to its high-power factor of 249.4×1012Wm−1K−2 and this value is greater than the values of some known pristine and doped HH TE materials. Our findings pave the way for further investigation into the HH VXTe alloys in the quest for improved TE and spintronic materials for use in domains that necessitate high thermoelectricity and spintronic performance.

Geometric conditions for minimizing entropy production in thermocouple design

This work shows a methodology for designing thermocouples of thermoelectric modules. The main quantities for design calculations are the geometric parameters: Cross-sectional area and leg length. Furthermore, the thickness of the ceramic material and the thickness of the metal bridge are considered. In addition, temperature-dependent thermoelectric properties are included in the analysis: Seebeck coefficient, thermal conductivity, electrical resistivity. An analysis of the entropy production is performed for two thermocouple geometries: Quadrangular and cylindrical. The proposed methodology allows determining the geometric conditions that the thermocouple must meet to minimize the entropy production and maximize efficiency. A conclusive result of this work is that the geometric conditions that minimize entropy production are the same that maximize the efficiency.

Iso efficiency in nanostructured thermoelectric materials

A study is carried out for the efficiency of segmented thermoelectric microgenerators (μSTEGs). The study includes a) n-type and p-type double or triple segmentation and b) geometry shape factor of the thermoelements. The temperature-dependent thermoelectric properties of nanostructured materials are determined from experimental data. In addition, the impact of internal resistance, as a function of the thermoelement-geometric shape factor, on the efficiency surfaces of the μSTEGs is studied based on non-equilibrium thermodynamics. Results show that the efficiency surfaces of different μSTEGs intersect under different working conditions. The curve formed by the intersection points of the efficiency surfaces of the two thermoelectric systems is called the iso-efficiency curve. Thus, segmented thermoelectric systems with different efficiencies can reach a common efficiency for a given segmentation and geometric shape form of their thermoelements under different working conditions. The common efficiency that reaches (corresponds to) these thermoelectric systems is called Iso efficiency. The iso efficiency is reached due to the n-type and p-type material segmentation and geometric shape, which affect each thermoelement’s internal resistance. Furthermore, the efficiency of a μSTEG system can be improved due to the combination of effects such as the relationship between load resistance and internal resistance when it is affected by the geometric shape, temperature difference, and segmentation. Our results allow determinate the new iso efficiency parameters with a good selection of the thermodynamic, electrical, and geometric parameters and establish guidance for other materials engineering investigations, to improve the efficiency of μSTEGs.

Enhancing transparent thermoelectric properties of Sb-doped ZnO thin films via controlled deposition temperature

ZnO is known as a wide-bandgap transparent thermoelectric material. Herein, the electronic transport and temperature-dependent thermoelectric properties of transparent Sb-doped ZnO (SZO) films are reported. The sputtered SZO films prepared at the optimum deposition temperature of 673 K show an n-type semiconducting behavior with the highest thermoelectric power factor of 406 μW/mK2 at 773 K, and a good transmittance ∼82% in the wavelength region of 400–1100 nm. It can well meet the requirements for transparent thermoelectric thin films. Through X-ray diffraction, UV–Vis, and photoluminescence analyses, the Zn2+ substitution by Sb5+ can be elucidated for significantly enhancing the Seebeck coefficient and thermoelectric power factor due to the increase of density-of-state effective mass.

Experimental validation and development of an advanced computational model of a transcritical carbon dioxide vapour compression cycle with a thermoelectric subcooling system

The inclusion of a thermoelectric subcooler as an alternative to increment the performance of a vapour compression cycle has been proved promising when properly designed and operated for low-medium power units. In this work, a computational model that simulates the behaviour of a carbon dioxide transcritical vapour compression cycle in conjunction with a thermoelectric subcooler system is presented. The computational tool is coded in Matlab and uses Refprop V9.1 to calculate the properties of the refrigerant at each point of the refrigeration cycle. Working conditions, effect of the heat exchangers of the subcooling system, temperature dependent thermoelectric properties, thermal contact resistances and the four thermoelectric effects are taken into account to increment its accuracy. The model has been validated using experimental data to prove the reliability and accuracy of the results obtained and shows deviations between the ± 7% for the most relevant outputs. Using the validated computational tool a 13.6 % COP improvement is predicted when optimizing the total number of thermoelectric modules of the subcooling system. The computational experimentally validated tool is properly fit to aid in the design and operation of thermoelectric subcooling systems, being able to predict the optimal configuration and operation settings for the whole refrigeration plant. • Transcritical CO2 vapour compression cycle with thermoelectric subcooling. • Advanced computational model to predict optimal operation settings of the system. • Validation of the model using experimental data with deviations between the ±7%. • Computational optimization of the number of modules in a thermoelectric subcooler. • 13.6% COP improvement using the hybrid solution and optimum number of modules.

Strongly Coupled Tin(IV) Sulfide–MultiWalled Carbon Nanotube Hybrid Composites and Their Enhanced Thermoelectric Properties

Herein, tin(IV) sulfide (SnS2) and multiwalled carbon nanotube (MWCNT) composites are fabricated via a simple solution-mixing method in a hydrothermal reactor. SnS2 is closely coupled to the MWCNT surface, thus forming a coaxial nanostructure. Examination by X-ray photoelectron spectroscopy and scanning transmission electron microscopy indicates that the strong interface between SnS2 and the MWCNTs in the composite material is due to the formation of Sn-O and Sn-S bonds. In addition, an examination of the temperature-dependent thermoelectric (TE) properties demonstrates that the SnS2-MWCNT hybrid composite with 3 wt % MWCNTs exhibits the maximum power factor of ∼91.34 μW/(m·K2) at 500 K, which is ∼50 times larger than that of the pristine SnS2. These results highlight the fabrication and enhanced TE properties of hybrid composites via the coupling of SnS2 and MWCNTs.

Elaboration of the Calculation Algorithm for the Load Diagram of a Thermoelectric Generator that Applies the Temperature Dependent Thermoelectric Layer Properties

The aim of the work is the development of the algorithm for the working parameters calculation of a marine waste heat thermoelectric generator, where the thermoelectric layer properties are considered as temperature dependent. The marine thermoelectric generator must have an extensive operational profile that includes a number of modes with a different power demand and different magnitudes of the waste heat parameters. The working mode alteration involves the change in the thermoelectric properties. To achieve the goal a mathematical model was offered for a load diagram calculation. The load diagram represents the generator parameters alteration with respect to the load current change. The most important result was the proposed new order of calculation that differs from the present models with offered variables, an approach to constructional thermal resistances application and a specific electrical power implementation. Mean temperature and load factor are taken as variables with the load factor being accepted as a relation between the electrical resistances of a load and a generator. Constructional thermal resistances were combined into two complex parameters – the thermal resistances of a hot and cold sides. The significance of the obtained results is determined by shaping a versatile approach to the generator`s working parameters calculation. The methodology is independent of the scheme of the calculated generator`s thermal resistances, which could be transformed into the complex parameters. The specific power calculation allows defining the performance per a cross-sectional unit area. The optimal selection of variables reduces the computational time.

The phonon scattering mechanism and its effect on the temperature dependent thermal and thermoelectric properties of a silver nanowire.

In this work, the electron-phonon, phonon-phonon, and phonon structure scattering mechanisms and their effect on the thermal and thermoelectric properties of a silver nanowire (AgNW) is investigated in the temperature range of 10 to 300 K. The electron-phonon scattering rate decreases with the increase of temperature. The phonon-phonon scattering rate increases with temperature and becomes greater than the electron-phonon scattering rate when the temperature is higher than the Debye temperature (223 K). The rate of phonon structure scattering is constant. The total phonon scattering rate decreases with temperature when the temperature is lower than about 150 K, and increases when the temperature is higher than 150 K. Correspondingly, the temperature dependent variation trend of the lattice thermal conductivity is opposite diametrically to that of the total phonon scattering rate. The thermoelectric properties of the AgNW are strongly coupled with the thermal conductivity via the phonon and electron transition. The thermoelectric properties of the material are quantified by the figure of merit (ZT). The ZT value of the AgNW is greater than that of bulk silver in the corresponding temperature range, and this difference increases with temperature. The order of the ZT of the AgNW is about 13 times greater than that of bulk silver at room temperature. The large increase of the ZT value of the AgNW is mainly due to the enhanced electron scattering and phonon scattering mechanisms in the AgNW.

Combined effect of donor doping and RGO (reduced graphene oxide) coating in La/Nb-doped SrTiO3 thermoelectrics

SrTiO3 (STO) is one of the most promising oxide thermoelectric (TE) materials with high thermopower, but the low electrical conductivity and high thermal conductivity are still issues to be solved. Recently, grain boundary engineering using reduced graphene oxide (RGO) has been demonstrated to have capable of simultaneously improving both the electrical and thermal properties of STO. In this study, we investigated the combined effect of La/Nb doping and RGO coating in STO to improve further the electrical conductivity and the TE efficiency of STO materials. Two series of La- and Nb-doped Sr1-xLaxTi1-yNbyO3 (x, y = 0–0.02) samples incorporated with RGO were prepared by a combinatorial procedure of solid-state reaction, RGO coating, and the spark plasma sintering (SPS) process. The structural, morphological and temperature-dependent thermoelectric properties of the Sr1-xLaxTi1-yNbyO3/RGO were studied and as a result, the figure of merit was enhanced ∼6.5 times by the combined effect of donor doping and lowering the double Schottky barrier height due to RGO at grain boundaries.