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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Evolutionary Game Dynamics between Distributed Energy Resources and Microgrid Operator: Balancing Act for Power Factor Improvement

This article investigates the intricate dynamics between Distributed Energy Resources (DERs) and the Microgrid Operator (MGO) within a microgrid interconnected with the main grid. Employing an evolutionary game framework, the study scrutinizes the strategic evolution of DERs’ decision-making processes in their interactions with the MGO. Modeled as an evolutionary game, these interactions encapsulate the strategies adopted by DERs, resulting in stable equilibrium strategies over time. Motivated by direct benefits linked to increased active power production, DERs strive to sell all available power, while the MGO focuses on optimizing the microgrid’s overall performance. The study assesses the microgrid’s performance in terms of its power factor, emphasizing the strategic balance DERs must achieve in their active power generation to avoid penalization. This penalization results in decreased individual utility for DERs due to the overall power factor decrease resulting from their prioritization of active power generation. Additionally, the diminished overall power factor implies a decrease in MGO utility. The individual utility of each DER is further influenced by the strategies adopted by other DERs, impacting the penalization factor. Leveraging a modified IEEE 13-node distribution microgrid consisting of three DERs, the study presents case studies encompassing both cooperative and non-cooperative evolutionary game scenarios. These case studies illuminate the intricacies of interactions and the resulting equilibrium outcomes.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2012

Power factor improvement in hydrothermally synthesized Bi{sub 2-x}Sb{sub x}Te{sub 3} (x=1.5) - carbon sphere composites

We report fabrication of compacted Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} composites by adding 1 wt% of carbon spheres in the hydrothermal synthesis. The processing parameter of sintering temperature is investigated in order to optimize the thermoelectric power factor of pressed Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} composites. As a result, we find that the composite sintered at 360 Degree-Sign C shows the best power factor performance among the composites and has a largest power factor of 15.4 {mu}W/cm K{sup 2} at 205 K and 13.5 {mu}W/cm K{sup 2} at 290 K. When compared with the samples without addition of carbon sphere in the hydrothermal synthesis, the composites sintered at 340 Degree-Sign C and 360 Degree-Sign C both surpass the largest power factor of 12.1 {mu}W/cm K{sup 2} at 280 K and 11.9 {mu}W/cm K{sup 2} at 290 K for the 340 Degree-Sign C-sintered counterpart. - Graphical abstract: Compacted Bi{sub 0.5}Sb{sub 1.5}Te{sub 3-{delta}} composites obtained by adding 1 wt% of carbon spheres in the hydrothermal synthesis. The composites sintered at 340 Degree-Sign C and 360 Degree-Sign C both surpass the largest power factor of 12.1 {mu}W/cm K{sup 2} at 280 K and 11.9 {mu}W/cm K{sup 2} at 290 K for the 340 Degree-Sign C-sintered counterpart. Highlights: Black-Right-Pointing-Pointer Fabrication of Bi{sub 0.5}Sb{sub 1.5}Te{sub 3-{delta}} composites. Black-Right-Pointing-Pointer Addition of 1 wt% carbon spheres in the hydrothermal synthesis. Black-Right-Pointing-Pointer Investigation of sintering temperature using encapsulating-and-sintering techniques. Black-Right-Pointing-Pointer 360 Degree-Sign C-sintered composite showing the largest power factor of 15.4 {mu}W/cm K{sup 2} at 205 K. Black-Right-Pointing-Pointer 10-60% improvement over the counterpart without adding carbon spheres.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Rapid Stoichiometry Control in Cu 2 Se Thin Films for Room-Temperature Power Factor Improvement

Cu 2 Se thin films provide a promising route toward relatively safe, sustainable and solution processed thermoelectric (TE) modules in contrast to more expensive and toxic materials currently on the market such as Bi2Te3. Cu 2 Se is known in the TE community for its high performance at high temperature and has recently attracted attention from its large theoretically predicted figure of merit at room temperature. Unfortunately, one of the main limitations encountered so far in Cu 2 Se thin films is that the carrier concentrations are not optimized for TE operation after solution processing. In this work, we conduct a comprehensive study of the structural, optical, and TE properties of Cu 2 Se thin films and demonstrate that nonoptimized carrier concentrations in these films lead to observations of poor performance at room temperature. Through a simple soaking procedure in a Cu+ ion solution for only a few minutes, we demonstrate a 200-300% increase in power factor. This soaking process pushes the carrier concentration of the Cu 2 Se thin film toward its optimal value for TE operation and marks the highest TE performance for any solution processed Cu 2 Se thin film at room temperature thus far. If the performance can be further optimized at room temperature, Cu 2 Se thin films will be the material of choice to utilize in TE modules for powering miniature electronics and sensors, which has been an increasingly popular and rapidly expanding market.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The influence of non-idealities on the thermoelectric power factor of nanostructured superlattices

Cross-plane superlattices composed of nanoscale layers of alternating potential wells and barriers have attracted great attention for their potential to provide thermoelectric power factor improvements and higher ZT figure of merit. Previous theoretical works have shown that the presence of optimized potential barriers could provide improvements to the Seebeck coefficient through carrier energy filtering, which improves the power factor by up to 40%. However, experimental corroboration of this prediction has been extremely scant. In this work, we employ quantum mechanical electronic transport simulations to outline the detrimental effects of random variation, imperfections, and non-optimal barrier shapes in a superlattice geometry on these predicted power factor improvements. Thus, we aim to assess either the robustness or the fragility of these theoretical gains in the face of the types of variation one would find in real material systems. We show that these power factor improvements are relatively robust against: overly thick barriers, diffusion of barriers into the body of the wells, and random fluctuations in barrier spacing and width. However, notably, we discover that extremely thin barriers and random fluctuation in barrier heights by as little as 10% is sufficient to entirely destroy any power factor benefits of the optimized geometry. Our results could provide performance optimization routes for nanostructured thermoelectrics and elucidate the reasons why significant power factor improvements are not commonly realized in superlattices, despite theoretical predictions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Chemical Insights into PbSe– x %HgSe: High Power Factor and Improved Thermoelectric Performance by Alloying with Discordant Atoms

Thermoelectric generators can convert heat directly into usable electric power but suffer from low efficiencies and high costs, which have hindered wide-scale applications. Accordingly, an important goal in the field of thermoelectricity is to develop new high performance materials that are composed of more earth-abundant elements. The best systems for midtemperature power generation rely on heavily doped PbTe, but the Te in these materials is scarce in the Earth’s crust. PbSe is emerging as a less expensive alternative to PbTe, although it displays inferior performance due to a considerably smaller power factor S 2 σ, where S is the Seebeck coefficient and σ is electrical conductivity. In this report we present a new p-type PbSe system, Pb 0.98 Na 0.02 Se–x%HgSe, which yields a very high power factor of ~20 μW·cm –1 ·K –2 at 963 K when x = 2, a 15% improvement over the best performing PbSe–x%MSe materials. The enhancement is attributed to a combination of high carrier mobility and the early onset of band convergence in the Hg-alloyed samples (~550 K), which results in a significant increase in the Seebeck coefficient. Interestingly, we find that the Hg 2+ cations sit at an off-centered position within the PbSe lattice, and we dub the displaced Hg atoms “discordant”. DFT calculations indicate that this feature plays a role in lowering thermal conductivity, and we believe that this insight may inspire new design criteria for engineering high performance thermoelectric materials. The high power factor combined with a decrease in thermal conductivity gives a high figure of merit ZT of 1.7 at 970 K, the highest value reported for p-type PbSe to date.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Electric Power quality Analysis in research reactor: Impacts on nuclear safety assessment and electrical distribution reliability

The increased requirements on supervision, control, and performance in modern power systems make power quality monitoring a common practise for utilities. Large databases are created and automatic processing of the data is required for fast and effective use of the available information. Aim of the work presented in this paper is the development of tools for analysis of monitoring power quality data and in particular measurements of voltage and currents in various level of electrical power distribution. The study is extended to evaluate the reliability of the electrical system in nuclear plant. Power Quality is a measure of how well a system supports reliable operation of its loads. A power disturbance or event can involve voltage, current, or frequency. Power disturbances can originate in consumer power systems, consumer loads, or the utility. The effect of power quality problems is the loss power supply leading to severe damage to equipments. So, we try to track and improve system reliability. The assessment can be focused on the study of impact of short circuits on the system, harmonics distortion, power factor improvement and effects of transient disturbances on the Electrical System during motor starting and power system fault conditions. We focus also on the review of the Electrical System design against the Nuclear Directorate Safety Assessment principles, including those extended during the last Fukushima nuclear accident. The simplified configuration of the required system can be extended from this simple scheme. To achieve these studies, we have used a demo ETAP power station software for several simulations. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Recent progress in thermoelectric nanocomposites based on solution-synthesized nanoheterostructures

Thermoelectric materials, which can convert waste heat into electricity, have received increasing interest in these years. This paper describes the recent progress in thermoelectric nanocomposite based on solution-synthesized nanoheterostructures. We start our discussion with the strategies of improving power factor of a given material by using nanoheterostructures. Then we discuss the methods of decreasing thermal conductivity. Finally, we highlight one way to decouple power factor and thermal conductivity, namely, incorporating phase-transition materials into a nanowire heterostructure. We have explored the lead telluride-copper telluride thermoelectric nanowire heterostructure in our group. Future possible ways to improve figure of merit are discussed at the end of this paper.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Thermoelectric properties of CuS/Ag{sub 2}S nanocomposites synthesed by modified polyol method

This is the report on successful synthesis of Ag doped CuS nanostructures by modified polyol method. The resulting samples were characterized by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX), atomic force microscopy (AFM) and dynamic light scattering (DLS). Particle size of pure CuS nanoparticles (NPs) was 17 nm, 38 nm and 97 nm as determined from Scherrer formula, AFM and DLS, respectively. Introduction of Ag led to formation of CuS/Ag{sub 2}S composites. A transition at 55 K in thermopower is ascribed to structural transformation from hexagonal to orthorhombic structure. Further, their thermoelectric properties exhibit remarkable change owing to Ag doping in CuS nanostructures. The power factor improves with increasing Ag content. They reveal that CuS/Ag{sub 2}S nanocomposites are some of the potential candidates for generation of thermoelectricity in future.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

High Thermoelectric Performance in p-type Polycrystalline Cd-doped SnSe Achieved by a Combination of Cation Vacancies and Localized Lattice Engineering

In this paper, a high figure of merit ( ZT ) of ≈1.7 at 823 K is reported in p-type polycrystalline Cd-doped SnSe by combining cation vacancies and localized-lattice engineering. It is observed that the introduction of Cd atoms in SnSe lattice induce Sn vacancies, which act as p-type dopants. A combination of facile solvothermal synthesis and fast spark plasma sintering technique boosts the Sn vacancy to a high level of ≈2.9%, which results in an optimum hole concentration of ≈2.6 × 10 19 cm -3 and an improved power factor of ≈6.9 µW cm -1 K -2 . Simultaneously, a low thermal conductivity of ≈0.33 W m -1 K -1 is achieved by effective phonon scattering at localized crystal imperfections, as observed by detailed structural characterizations. Density functional theory calculations reveal that the role of Cd atoms in the SnSe lattice is to reduce the formation energy of Sn vacancies, which in turn lower the Fermi level down into the valence bands, generating holes. This work explores the fundamental Cd-doping mechanisms at the nanoscale in a SnSe matrix and demonstrates vacancy and localized-lattice engineering as an effective approach to boosting thermoelectric performance. The work provides an avenue in achieving high-performance thermoelectric properties of materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Electronic structure and thermoelectric properties of nanostructured EuTi{sub 1-x}Nb{sub x}O{sub 3-{delta}} (x = 0.00; 0.02)

The thermoelectric properties of polycrystalline nanostructured EuTiO{sub 3-{delta}} samples are improved by a substitution of 2% Nb for Ti. The figure of merit (ZT) was measured to reach ZT(EuTi{sub 0.98}Nb{sub 0.02}O{sub 3-{delta}}) Almost-Equal-To 0.4 at T= 1040 K while ZT(EuTiO{sub 3-{delta}}) Almost-Equal-To 0.3 at the same temperature. X-ray photoelectron spectra reveal that the in-gap states at the Fermi level are more pronounced for the Nb-substituted samples, resulting in an improved power factor. The valence band peak below the Fermi level is sharply shaped, therefore fulfilling the condition for a large Seebeck coefficient. The specific porosity of the samples reduces the lattice thermal conductivity with a minor effect on the electron transport.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Improvement in thermoelectric power factor of mechanically alloyed p-type SiGe by incorporation of TiB{sub 2}

Nearly 60% of the world’s useful energy is wasted as heat and recovering a fraction of this waste heat by converting it as useful electrical power is an important area of research{sup [1]}. Thermoelectric power generators (TEG) are solid state devices which converts heat into electricity. TEG consists of n and p-type thermoelements connected electrically in series and thermally in parallel{sup [2]}. Silicon germanium (SiGe) alloy is one of the conventional high temperature thermoelectric materials and is being used in radio-isotopes based thermoelectric power generators for deep space exploration programs.Temperature (T) dependence of thermoelectric (TE) properties of p-type SiGe and p-type SiGe-x wt.%TiB{sub 2} (x=6,8,10%) nanocomposite materials has been studied with in the temperature range of 300 K to 1100 K. It is observed that there is an improvement in the power factor (α{sup 2}/ρ) of SiGe alloy on addition of TiB{sub 2} upto 8 wt.% that is mainly due to increase in the Seebeck coefficient (α) and electrical conductivity (σ) of the alloy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Achieving high power factor and output power density in p-type half-Heuslers Nb 1-x Ti x FeSb

Significance Thermoelectric technology can boost energy consumption efficiency by converting some of the waste heat into useful electricity. Heat-to-power conversion efficiency optimization is mainly achieved by decreasing the thermal conductivity in many materials. In comparison, there has been much less success in increasing the power factor. We report successful power factor enhancement by improving the carrier mobility. Our successful approach could suggest methods to improve the power factor in other materials. Using our approach, the highest power factor reaches ∼106 μW⋅cm −1 ⋅K −2 at room temperature. Such a high power factor further yields a record output power density in a single-leg device tested between 293 K and 868 K, thus demonstrating the importance of high power factor for power generation applications.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Enhanced thermoelectric performance in zinc substituted p-type filled skutterudites CeFe{sub 4-x}Zn{sub x}Sb{sub 12}

In this study, Zn-substituted polycrystalline skutterudites CeFe{sub 4-x}Zn{sub x}Sb{sub 12} (x=0, 0.05, 0.1, 0.2, 0.3) were successfully prepared by a traditional melting-annealing method. The solubility of Zn in Fe site is {approx}1.2%, exceeding which trace amount of ZnSb phase can be detected in the XRD. This ZnSb impurity phase, with size of several hundred nanometers for the sample with x=0.2 but showing surprisingly small size of {approx}10 nm for the sample with x=0.3, selectively distributes on the grain boundaries. In particular, the introduction of Zn in Fe site effectively improves the Seebeck coefficient in a manner of enhancement in hole effective mass, but it has negligible influence on both electrical and thermal conductivities though the hole concentration is increased. Consequently the corresponding improvement in power factor leads to an improved thermoelectric figure of merit (ZT) of 0.9 at 800 K for the sample with x=0.1, which is {approx}15% higher than that of Zn-free sample. This study demonstrates a favorable effect of Zn iso-substitution and opens a new strategy to improve the thermoelectric properties of p-type Fe-based skutterudites beyond the sole phonon engineering. - Graphical abstract: (a)-(c) ZnSb nanoinclusions emerge when Zn exceeds its solubility limit. (d), (e) The introduction of Zn boosts the Seebeck coefficient and thus enhances the ZT value. Highlights: Black-Right-Pointing-Pointer Zn is successfully employed to substitute Fe atom for the first time. Black-Right-Pointing-Pointer ZnSb nanoinclusions emerge when Zn exceeds its solubility limit {approx}0.12. Black-Right-Pointing-Pointer The introduction of Zn boosts the Seebeck coefficient and enhances the ZT value.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Origins of enhanced thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films

In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} with a thickness of 6–200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materials with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bipolar effect in transport properties for the 6 nm thick film, an impressive power factor of about 2.0 mW m{sup −1} K{sup −2} is achieved at room temperature for this film. Further investigations of the electronic transport properties of TSS and interactions between TSS and the bulk band might result in a further improved thermoelectric power factor in topologically insulating Bi{sub 0.64}Sb{sub 1.36}Te{sub 3} thin films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Enhanced Thermoelectric Properties for PEDOT:PSS/Undoped Ge Thin-Film Bilayered Heterostructures

Modulation doping is one of the strategies to improve thermoelectric power factors of nanocomposites and thin-film bilayered heterostructures by effectively increasing electrical conductivity. Here, it is reported that thin-film heterostructures of heavily doped p-type organic conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and undoped thin-film Ge can enhance thermoelectric power factor by modulation doping. The maximum power factor and Seebeck coefficient of the bilayered heterostructures are 154 µW m -1 K -2 and 398 µV K -1 , respectively, corresponding to 47-fold and 41-fold increases compared to those of bulk PEDOT:PSS and 64-fold increase compared to power factor of undoped Ge. The enhancements in power factor and Seebeck coefficient are quantitatively described by the hole transfer from PEDOT:PSS to Ge, which takes into account the band alignment at the interface detected by Kraut's method. Agreement between the simulation and experiment results also implies predictability of thermoelectric performances of nanoscale bilayered heterostructures in general, when band offset, Fermi level, and individual electronic properties are available. This work can be further extended to predict performance of other nanoscale combinations of thermoelectric and other electronic materials in general.

charge transport↗
DOE OSTI2016

Quantitative analyses of enhanced thermoelectric properties of modulation-doped PEDOT:PSS/undoped Si (001) nanoscale heterostructures

Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) has high electrical conductivity (~10 3 S cm –1 ) but it demonstrates a low Seebeck coefficient (<15 μV K –1 ), resulting in a low power factor. Mixing PEDOT:PSS with nanostructured semiconductors can enhance the Seebeck coefficient and achieve an improved thermoelectric power factor. Yet, underlying mechanisms for those composite thermoelectric systems are scarcely understood so far. Here, quantitative analyses on the electrical conductivity and Seebeck coefficient for the heterostructures of nanometer-thick PEDOT:PSS on single-crystal Si (001) on sapphire (SOS) are reported. The heterostructures have larger Seebeck coefficients up to 7.3 fold and power factors up to 17.5 fold relative to PEDOT:PSS. The electrical conductivity increased with decreasing combined thicknesses of PEDOT:PSS and Si, and the Seebeck coefficient increased with decreasing PEDOT:PSS thickness, which can be attributed to modulation doping caused by diffusion of holes from PEDOT:PSS into undoped Si. This hypothesis is supported by simulation per band alignment. The valence band offset between Si and PEDOT:PSS dominantly controls the electrical conductivity and Seebeck coefficient of the heterostructures. This study not only suggests mechanistic insights to increase the power factors of PEDOT:PSS-based composites but also opens the door for new strategies to enhance the thermoelectric efficiencies of heterostructured nanocomposite materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Higher Efficiency HVAC Motors

The objective of this project was to design and build a cost competitive, more efficient heating, ventilation, and air conditioning (HVAC) motor than what is currently available on the market. Though different potential motor architectures among QMP’s primary technology platforms were investigated and evaluated, including through the building of numerous prototypes, the project ultimately focused on scaling up QM Power, Inc.’s (QMP) Q-Sync permanent magnet synchronous motors from available sub-fractional horsepower (HP) sizes for commercial refrigeration fan applications to larger fractional horsepower sizes appropriate for HVAC applications, and to add multi-speed functionality. The more specific goal became the research, design, development, and testing of a prototype 1/2 HP Q-Sync motor that has at least two operating speeds and 87% peak efficiency compared to incumbent electronically commutated motors (EC or ECM, also known as brushless direct current (DC) motors), the heretofore highest efficiency HVACR fan motor solution, at approximately 82% peak efficiency. The resulting motor prototype built achieved these goals, hitting 90% efficiency and .95 power factor at full load and speed, and 80% efficiency and .7 power factor at half speed. Q-Sync, developed in part through a DOE SBIR grant (Award # DE-SC0006311), is a novel, patented motor technology that improves on electronically commutated permanent magnet motors through an advanced electronic circuit technology. It allows a motor to “sync” with the alternating current (AC) power flow. It does so by eliminating the constant, wasteful power conversions from AC to DC and back to AC through the synthetic creation of a new AC wave on the primary circuit board (PCB) by a process called pulse width modulation (PWM; aka electronic commutation) that is incessantly required to sustain motor operation in an EC permanent magnet motor. The Q-Sync circuit improves the power factor of the motor by removing all failure prone capacitors from the power stage. Q-Sync’s simpler electronics also result in higher efficiency because it eliminates the power required by the PCB to perform the obviated power conversions and PWM processes after line synchronous operating speed is reached in the first 5 seconds of operation, after which the PWM circuits drop out and a much less energy intensive “pass through” circuit takes over, allowing the grid-supplied AC power to sustain the motor’s ongoing operation.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2014

Variations of thermoelectric properties of Mg{sub 2.2}Si{sub 1−y}Sn{sub y−0.013}Sb{sub 0.013} materials with different Si/Sn ratios

Mg{sub 2}Si–Mg{sub 2}Sn solid solutions are a promising class of thermoelectric materials. Mg{sub 2.2}Si{sub 1−y}Sn{sub y−0.013}Sb{sub 0.013} compounds with different Si/Sn ratios were prepared by B{sub 2}O{sub 3} “flux” method followed by hot-pressing. The effect of Si/Sn ratio on the thermoelectric properties of the Mg{sub 2}Si–Mg{sub 2}Sn solid solutions at a fixed Sb doping level were measured in the temperature range 300–760 K. With the increase of Sn content (0.3≤y≤0.7), power factors are improved and lattice thermal conductivity decreased. Band convergence induced by Si/Sn ratio leads to enhanced effective mass and the materials parameter β which qualifies a kind of thermoelectric material is improved evidently. A maximum ZT of ∼1.1 at ∼760 K was achieved for the Mg{sub 2.2}Si{sub 0.3}Sn{sub 0.7–0.013}Sb{sub 0.013} sample arising from a high power factor of ∼4×10{sup -3} W m{sup −1} K{sup −2} and a low lattice thermal conductivity of ∼1.6 W m{sup −1} K{sup −1} at ∼760 K. - Graphical abstract: (a)Temperature dependence of power factor of Mg{sub 2.2}Si{sub 1−y}Sn{sub y−0.13}Sb{sub 0.013} samples. (b)Temperature dependence of lattice thermal conductivity of Mg{sub 2.2}Si{sub 1−y}Sn{sub y−0.13}Sb{sub 0.013} samples. (c)Temperature dependence of dimensionless figure of merit ZT of Mg{sub 2.2}Si{sub 1−y}Sn{sub y−0.13}Sb{sub 0.013} samples. - Highlights: • Mg{sub 2.2}Si{sub 1−y}Sn{sub y−0.013}Sb{sub 0.013} was prepared by B{sub 2}O{sub 3} ''flux'' method followed by hot-pressing. • Band convergence leads to enhanced m{sup ⁎} and improved materials parameter β. • ZT{sub max} of ∼1.1 at ∼760 K was achieved for the Mg{sub 2.2}Si{sub 0.3}Sn{sub 0.7−0.013}Sb{sub 0.013} sample.

36 MATERIALS SCIENCE↗