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SrTiO 3 (STO)-based perovskite oxide is regarded as a promising high-temperature n-type thermoelectric material. However, its intrinsic high thermal conductivity leads to poor thermoelectric properties. Using entropy engineering, lower thermal conductivity can be obtained. However, the high configuration entropy can also lead to poor carrier mobility, which inhibits electron transport and consequently reduces the electrical conductivity. Along these lines, in this work, an ultra-low thermal conductivity was obtained, which is significantly lower than the majority of the values reported in the literature, and the concept of phononic glass electronic crystal was attained at the same time. The enhanced effective scattering of phonons through the multi-scale defects gives rise to a low thermal conductivity of 1.8 W m−1 K−1 at 973K. Optimization of electrical properties due to in situ reduction at high temperature and pressure，the high-entropy ceramics possess the maximum power factor of 7.03 μW cm−1 K−2 at 973K. The application of high pressure is considered an important approach for the development of new materials with special properties. A new strategy for the composition design and in-situ reduction of oxide thermoelectric materials was provided in this work, which paves the way for the optimization and application of both the electrical and thermal properties of perovskite-based materials. [ABSTRACT FROM AUTHOR]

Electronegative S-filled skutterudite compounds have attracted considerable attention due to scattering of low-frequency phonons (35–50 cm − 1 ), but there are few reports on S-filled double-substituted skutterudite. In this work, a series of S-filled Te-Sn double-substituted skutterudite compounds were synthesized using high pressure and high temperature (HPHT) method. The phase composition, microstructure, and thermoelectric properties of SxCo4Sb 1 1 Te 0. 7 Sn 0. 3 (x = 0 , 0.05, 0.10, 0.20) samples were systematically determined. The results show that the introduction of S increases the substitution limit of Te in the Sb site. Under the combined effect of the sample synthesis pressure and S filling, the nucleation density of the sample grains increases and the grain size decreases. At the same time, there are numerous special microstructures in the samples synthesized in a high-pressure environment. Thermoelectric performance studies show that a small amount of S filling optimizes the Seebeck coefficient of the sample and increases the power factor (PF). With an increase of the amount of S introduced, the thermal conductivity of the samples decreases significantly. Therefore, the maximum zT value of an S 0. 0 5 Co4Sb 1 1 Te 0. 7 Sn 0. 3 sample synthesized at 2.5 GPa pressure is 0.17 at room temperature. The maximum zT value of the sample is 1.26 at 773 K. [ABSTRACT FROM AUTHOR]

Introducing the nanosecond phase into thermoelectric materials is an effective strategy to improve their thermoelectric properties. In this study, the influence of nano Y2O3 dispersion on the resistivity, Seebeck coefficient and thermal conductivity of Cu2Se + x mol% Y2O3 (x = 0, 0.5, 1.0, 2.0, 3.0) was investigated. Their resistivity and Seebeck coefficient have no obvious change under the combined effects of the microstructure and the energy filtering. Especially, Y2O3 dispersion can inhibit the recrystallization of Cu2Se and make the lamellar grains thinner, thus scattering phonon and reducing the thermal conductivity effectively. When x = 1.0, the thermal conductivity reaches a minimum of 0.65 W/K·m at 923 K. The dimensionless thermoelectric figure of merit (ZT) value of the Cu2Se + 1.0 mol% Y2O3 sample reaches 1.81 at 923 K. The study indicates that nano rare earth oxides are relatively effective second-phase that can reduce thermal conductivity, which may be further promoted for other thermoelectric materials. [ABSTRACT FROM AUTHOR]

SrTiO 3 (STO) is a thermoelectric (TE) material with a wide band gap. It is usually either sintered or annealed in a reducing atmosphere to obtain semiconducting behavior. In this work, non-stoichiometric SrTiO 2.8 was synthesized by the high temperature and high pressure (HPHT) method in a reducing environment to obtain improved electrical and thermal properties. The reducing environment was obtained by the application of high pressure and due to the strong ability of Ti to capture oxygen at high temperatures. The thermoelectric properties of the samples synthesized at high temperature and pressure were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV spectroscopy. The results show that with increasing of synthesis pressure, the band gap of the samples decreases, improving their electrical properties; at the same time, the high pressure also changes the micro-morphology of the samples and improves their thermal properties. The zT value of the sample synthesized at 5 GPa reached the maximum value of 0.20 at 973 K. It was found that the mechanical strength of the synthesized samples is superior to that of the traditional alloy-based thermoelectric materials. Our work shows that HPHT provides a new variable of pressure for the optimization of the synthesis process of TE materials and provides a new approach for the synthesis and performance optimization of thermoelectric materials. [ABSTRACT FROM AUTHOR]

The temperature in the high-pressure high-temperature (HPHT) synthesis is optimized to enhance the thermoelectric properties of high-density ZnO ceramic, Zn0.98Al0.02O. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that HPHT can be utilized to control the crystal structure and relative density of the material. High pressure can be utilized to change the energy band structure of the samples via changing the lattice constant of samples, which decreases the thermal conductivity due to the formation of a multi-scale hierarchical structure and defects. The electrical conductivity of the material reaches 6 × 104 S/m at 373 K, and all doped samples behave as n-type semiconductors. The highest power factor (6.42 μW ⋅ cm−1⋅K−2) and dimensionless figure of merit (zT = 0.09) are obtained when Zn0.98Al0.02O is produced at 973 K using HPHT, which is superior to previously reported power factors for similar materials at the same temperature. Hall measurements indicate a high carrier concentration, which is the reason for the enhanced electrical performance. [ABSTRACT FROM AUTHOR]

PbS synthesized at the same condition with PbSe exhibits an opposite electrical conduction type from it. Via the solid solution of PbS into PbSe, we attempt to change the major carries kind of PbSe-base materials and improve the thermoelectric (TE) property of synthesis samples in corresponding temperature areas. Introduction of high pressure into the synthesis stage could reduce the reactive activation energy and improve the synthesis efficiency. Characterizations via the electron microscopes demonstrate that synthesis samples are made of multiscale grains. Finally, characterizations on the thermoelectrical properties of PbSe 1 − x S x demonstrate that the solid solution treatment could modulate the electrical conduction type and the figure of merit effectively. [ABSTRACT FROM AUTHOR]

SrTiO 3 (STO) is considered a promising high-temperature N-type thermoelectric material. However, its intrinsic insulating properties and high thermal conductivity limit the dimensionless quality factor (zT) due to its simple crystal structure and the existence of light elements. Along these lines, in this work, the optimization of the thermoelectric properties of STO-based materials was achieved by using the high temperature and high pressure (HPHT) method and adjusting the doping ratios of the La and Nb heavy elements. To enhance the doping effect, oxygen vacancies need to be formed within the sample. For this reason, titanium powder was added to the sample. Due to the confined environment induced by the high pressure, which can be attributed to the application of the HPHT method and the strong oxygen trapping ability of Ti at high temperatures, a reducing environment was attained for the samples, the latter, promoted the formation of oxygen vacancies in the synthesized samples, and semiconducting properties were achieved. The thermoelectric properties and microscopic morphology of the synthesized samples with different doping ratios of La and Nb were also thoroughly investigated. Finally, the maximum zT value obtained for the samples was 0.28@973 K. A fast, simple, and effective method for the preparation of oxygen-deficient packet-crystalline oxide materials was developed in this work, which paves the way for significantly improving their thermoelectric properties. [ABSTRACT FROM AUTHOR]

As an oxide thermoelectric material, the adjustment of oxygen vacancy plays an important role in strontium titanate (SrTiO 3). Traditional synthesis methods typically necessitate post-synthesis reduction annealing to optimize its electrical properties. However, the oxygen vacancy concentration of samples synthesized by this approach may be distributed in a gradient manner. In this study, a high-temperature and high-pressure (HPHT) synthesis treatment was adopted, incorporating titanium powder into the raw material. This novel approach leverages the closed environment created by high pressure and the robust oxygen-trapping capabilities of titanium powder at elevated temperatures. It resulted in enhanced electrical properties in synthesized samples without the need for reduction annealing. Building upon this achievement, we successfully synthesized SrTiO 3 samples doped with lanthanum (La) at different pressures. The sample synthesized at 5GPa demonstrated an optimal zT value of 0.22 at 973 K. This work provides a novel approach to the effective synthesis and improved electrical properties of strontium-based thermoelectric materials. • The grain size and band gaps of SrTiO 3 were effective optimized. • Partial high pressure features of SrTiO 3 have been captured to the ordinary pressure. • The whole synthesis procedure last only for 40 min • Ubiquitous lattice defect engineering was realized in our samples by HPHT. [ABSTRACT FROM AUTHOR]

Ceramic materials with low thermal conductivity are critically important in applications such as thermoelectric conversion and thermal barrier coatings. Introducing the concept of entropy and its singular physical properties permits attainment of low thermal conductivity in ceramics, and the high-pressure synthesis conditions can also reduce the thermal conductivity of the synthesized samples by adjusting the micro-morphology. In this work, high-entropy (Sr 0.2 La 0.2 Nd 0.2 Sm 0.2 Eu 0.2)TiO 3 ceramics were synthesized by solid-state reaction at high temperature and high pressure, which significantly shortened the synthesis time. X-ray diffraction (XRD) results affirmed that high-entropy cubic perovskite ceramics can be synthesized using high temperature and high pressure. High-resolution transmission electron microscopy (HRTEM) results show that the multi-component cations are uniformly distributed at the A-site. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results show that the pressure provided by the synthesis method can effectively adjust the microstructure of the synthesized samples. Ultra-low thermal conductivity was obtained by synthesizing high-entropy samples under high pressure; the lowest thermal conductivity of resulting high-entropy (Sr 0.2 La 0.2 Nd 0.2 Sm 0.2 Eu 0.2)TiO 3 perovskite ceramics was 0.82 Wm−1 K−1 at the test temperature of 973 K, which is the lower value of perovskite strontium-titanate-based ceramics reported in the literature at present. The high-entropy perovskite ceramics prepared by this new high-temperature and high-pressure method also have good mechanical properties, with Vickers hardness of 10.05 GPa. This study provides a new synthesis strategy for the rapid and effective synthesis of perovskite ceramics with low thermal conductivity, which is a new method for the synthesis of high-entropy materials. • The high-entropy perovskite material synthesized by the high-pressure method has ultra-low lattice thermal conductivity. • High pressure-induced micromorphological changes reduce thermal conductivity. • The whole synthesis procedure last only for 60 min. • Introducing high-pressure synthesis conditions and incorporating high entropy enhances the scattering of all phonon spectra. [ABSTRACT FROM AUTHOR]

The electrical properties of the perovskite oxide thermoelectric material SrTiO 3 (STO) should be improved in order to realize its thermoelectric application due to its intrinsic insulation characteristics. The bulk STO materials usually optimize their electrical properties by annealing in reducing environment after synthesis. However, this method inevitably leads to the gradient distribution of oxygen defect concentration in materials. In this study, the combination of High Temperature and High Pressure (HPHT) method is used, and Ti powder is added to optimize the electrical properties of STO materials. HPHT provides a closed synthesis environment. In addition, with the strong oxygen-capturing ability of Ti at high temperature, the semi-conductivity of materials is performed. The thermoelectric properties of the synthesized materials under HPHT are studied using XRD, XPS, SEM, and TEM. The properties and micro-morphology of the synthesized samples with different Ti contents are investigated. The results show that, with the increase of the Ti content, the oxygen defect concentration increases and the electrical properties are significantly improved. Simultaneously, the sample synthesized using the HPHT method changes its micro-morphology and reduces the thermal conductivity of the material. The increase of oxygen vacancy concentration can also effectively reduce the thermal conductivity. Under the collaborative optimization of HPHT while adding Ti, the maximum obtained zT value at 20 wt% addition is 0.19 @ 973 K. The density functional theory calculation also shows that, compared with pure STO, the band gap of STO with oxygen vacancy decreases, which increases the conductivity. Therefore, a high pressure and the addition of Ti powder provide a fast, simple and efficient method for preparing oxygen-deficient perovskite oxide materials, which is of great significance for improving its thermoelectric properties. • The introduction of oxygen vacancies effectively improves the electrical properties. • High pressure-induced micromorphological changes and generated oxygen vacancies reduce thermal conductivity. • The whole synthesis procedure last only for 30 min • Theoretical calculations show that oxygen vacancies can significantly improve the electrothermal transport properties of perovskite-structured materials. [ABSTRACT FROM AUTHOR]

• High pressure increases the solid solubility of Al 2 O 3 in ZnO. • The thermoelectric properties of the sample are explained by the given band gap model under high pressure. • The whole synthesis procedure last only for 30 min. • High pressure can induce rich defects. ZnO has excellent electrical properties such as high conductivity (σ) and Seebeck coefficient (S) that are important for its thermoelectric properties and have provided the basis for obtaining improved ZnO-based thermoelectric materials by doping. In particular, the most representative Al-doped ZnO (AZO) has excellent thermoelectric performance. Although the Al doping is beneficial for reducing the lattice thermal conductivity of ZnO, the solubility of Al 2 O 3 in ZnO is limited and excessive doping of Al gives rise to the generation of a large amount of the ZnAl 2 O 4 secondary phase that limits the further improvement of the electrical properties. Thus, it is crucial to develop approaches to reduce thermal conductivity while still maintaining high electrical properties. In this work, high pressure and high temperature (HPHT) synthesis was used to adjust the ZnO optical band gap by modifying the lattice parameters of ZnO, and thereby improving the electrical properties of the sample. It was found that the optimal doping content for the samples synthesized at high pressure is different from that of the samples synthesized at normal pressure, providing a new approach for the further improvement of the thermoelectric properties of ZnO. Additionally, high pressure can promote grain refinement that is conducive to the generation of the multi-scale hierarchical structure of the sample that introduces a variety of phonon scattering mechanisms to reduce the thermal conductivity while maintaining a high power factor. The Zn 0.96 Al 0.04 O material obtained by sintering at a pressure of 3 GPa and a temperature of 1053 K for 30 min reached the highest power factor (7.8 µW cm−1 K−2) and the highest zT (0.16) at 973 K. [ABSTRACT FROM AUTHOR]

Bi 2 Te 3 -based crystal ingots produced by zone melting (ZM) are the most widely used materials to manufacture commercial thermoelectric (TE) devices. However, the poor mechanical properties of such crystalline materials limit the production of small-scale devices. While processability can be improved by powder metallurgy (PM), it also leads to the deterioration of the TE properties due to the donor-like effect of the introduced defects and grain boundaries. Thus, additional efforts towards re-optimizing doping are required. Here, we report a PM method to improve the mechanical properties of Bi 2 Te 3 -based TE materials through the crushing and hot pressing of Bi 2 Te 3 ingots obtained by ZM. Besides, we demonstrate the TE properties of n-type Bi 2 Te 2.7 Se 0.3 (BTS) to be remarkably improved by Cu doping, which enables optimization of the carrier concentration and enhances phonon scattering at heterointerphases thus increasing the Seebeck coefficient and reducing thermal conductivity. Overall, optimized materials reach dimensionless TE figures of merit (ZT) up to 1.16 at 408 K, i.e. 45% higher than that of state-of-the-art BTS, and an average ZT value of 1.08 in the temperature range of 300–473 K. [ABSTRACT FROM AUTHOR]

The high stability and low cost are considered comparative advantages of the SrTiO 3 chalcogenide oxide thermoelectric material. However, the pure SrTiO 3 material is characterized by low electrical conductivity and high thermal conductivity, which could eventually lead to poor overall thermoelectric performance, and limit its application in the field of high temperature thermoelectricity. The development of composite-based metal materials with SrTiO 3 by using suitable methods is arising as the most promising approach to improve their electrical properties. Along these lines, in this work, xNb: (1-x) SrTiO 3 composite ceramics were successfully synthesized by using the high temperature and high-pressure (HPHT) method. The Nb powder was oxidized into various niobium oxides exhibiting their own thermoelectric properties under HPHT conditions to optimize the thermoelectric properties of the Nb/SrTiO 3 composites. From our analysis, it was demonstrated that with the increase of the Nb powder content, the electrical properties were significantly improved. In addition, the fabricated Nb/SrTiO 3 composite ceramics possessed a special "pore" microstructure, which significantly reduced the thermal conductivity of the material. In this work, the physical phase, microscopic morphology, and thermoelectric properties of the synthesized samples were also systematically tested and analyzed, and the maximum zT value of 0.28@973 K was obtained for the final sample with x = 0.4. The implementation of the HPHT method for the preparation of chalcogenide oxide composite ceramics provides valuable insights for the improvement of their thermoelectric properties. [ABSTRACT FROM AUTHOR]

Using high pressure and high temperature (HPHT) technology to improve the thermoelectric properties of oxides is a feasible solution. To further understand the micro-physical mechanism improving the thermoelectric performance of ZnO in a higher pressure environment, the effects of α and γ lattice structure Al 2 O 3 (α -Al 2 O 3 , γ -Al 2 O 3) on doped ZnO were systematically studied. ZnO samples with different Al doping ratios (α -x, γ -x; x = 0.02, 0.04, 0.06, 0.08) were prepared by HPHT. Test results show that the high pressure and high temperature synthesis method effectively improves the solid solubility of α -Al 2 O 3 and γ -Al 2 O 3 in ZnO, among which γ -Al 2 O 3 is more easily dissolved into the zinc oxide crystal lattice. Under the same doping ratio, the electronic conductivity of the sample synthesized with γ -Al 2 O 3 is higher than that of the sample synthesized with α -Al 2 O 3. In addition, the ZnAl 2 O 4 phase precipitated out of the sample with increased Al doping. Although the ZnAl 2 O 4 phase decreases the electrical properties of the sample, a small amount of ZnAl 2 O 4 is uniformly dispersed in the ZnO sample, which can inhibit the growth of crystal grains, and assist grain refinement. The optimized high pressure sintering temperature was 1123 K, and the zT value of γ -0.04 was 0.17 at 973 K. [ABSTRACT FROM AUTHOR]

Bi 2 S 3 -based materials without containing expensive, toxic, and rare components are considered more attractive for the realization of large-scale practical applications. Under this perspective, in this work, nickel was employed to enhance the thermoelectric properties of polycrystalline Bi 2 S 3 , which was fabricated by using the mechanical alloying (MA) method combined with the high pressure and high temperature (HPHT) technology. By increasing the Ni doping content, the electrical conductivity was significantly enhanced, whereas the absolute value of the Seebeck coefficient was gradually reduced, which was mainly derived from the increased carrier concentration. Moreover, numerous lattice and distortions were introduced in the stucture of the Bi 2 S 3 samples that were synthesized by the HPHT technology. At the same time, Ni doping contributed to the strong impedance for phonon propagation and suppressed thermal conductivity. As a consequence, a peak zT value of 0.23 at 543 K was achieved in the Ni 0.005 Bi 2 S 3 sample, being about three times than that of pure Bi 2 S 3. • Ni-doped Bi 2 S 3 samples were fabricated by combining mechanical alloying and high-pressure and high-temperature technology. • Ni doping improves electrical transport properties by tuning carrier concentration. • The microstructural changes induced by the incorporation of Ni and HPHT method enhanced phonon scattering. • The maximum zT value of 0.23 is obtained in Ni 0.005 Bi 2 S 3 at 543 K. [ABSTRACT FROM AUTHOR]

A series of graphene-S 0.05 Co 4 Sb 11.6 Te 0.4 (C x -S 0.05 Co 4 Sb 11.6 Te 0.4) composite polycrystalline skutterudite materials with graphene stoichiometric ratio of x = 0, 0.05, 0.10, 0.20 have been successfully prepared by high pressure and high temperature (HPHT) technology. Graphene is a two-dimensional material with large carrier mobility and large specific surface area. Through microscopic observation, it is found that graphene is attached to the grains in the sample. At the same time, with the increase of graphene content, grain growth is inhibited. Graphene addition reduces the thermal conductivity of skutterudite by increasing grain boundaries and achieves the purpose of optimizing its thermoelectric properties. At the same time, there are numerous lattice defects and distortions introduced in skutterudite synthesized by HPHT technology. Finally, the samples were synthesized under the conditions of 1.5 GPa and 900 K. The lattice thermal conductivity of the graphene composite sample C x -S 0.05 Co 4 Sb 11.6 Te 0.4 with x = 0.10 reaches a minimum of 0.99 at 773 K, and the zT value of this sample is 1.25 at 773 K, which is greater than pure S 0. 05 Co 4 Sb 11.6 Te 0.4 , its zT value is 1.00 at 773 K. Compared with the method of synthesizing skutterudite under normal pressure, the HPHT technology can dramatically reduce the reaction time from several days to less than 30 min, while forming a high-pressure airtight reaction environment, which can effectively prevent the volatilization and oxidation of samples during the reaction process, thus providing a convenient method for synthesizing thermoelectric materials quickly and efficiently. [ABSTRACT FROM AUTHOR]

The primary purpose of this work is to introduce the second phase of graphene (G) into non-stoichiometric TiO 1.80 successfully and optimize the thermoelectric properties of this composite material through high pressure and high temperature (HPHT) technology. The purpose of doping Ti powder under high pressure is to create a closed reducing atmosphere to change the ratio of titanium to oxygen in the titanium oxide base. The addition of graphene can considerably improve the electrical properties of the material and reduce its resistivity. An X-ray diffractometer, X-ray photoelectron spectrometer, scanning electron microscope, and transmission electron microscope were used to analyze and characterize the phase structure, chemical bond, micro morphology and crystal morphology of the samples. An abundance of grain boundaries and lattice dislocation defects can inhibit the lattice thermal conductivity. We also tested and analyzed the thermoelectric performance of the high-temperature and high-pressure synthetic samples through a variable temperature system. The variation of the absorption intensity of the ultraviolet UV spectrum with wavelength shows that high pressure can reduce the band gap, which is beneficial to the carrier transition and improves the conductivity of semiconductors. HPHT optimizes both the electrical and the thermal parameters of the sample. At a final sintering pressure of 5.0 GPa, the dimensionless figure of merit (zT) of the bulk composite material G/TiO 1.80 was found to be 0.23 at 700 °C. [ABSTRACT FROM AUTHOR]

Bi 2 S 3 is considered a promising n-type thermoelectric (TE) material due to its inherent extremely low thermal conductivity and earth-abundant elements. Herein, we have successfully synthesized a series of Nb-doped Bi 2 S 3 (Bi 2-x Nb x S 3 , x = 0, 0.01, 0.02, 0.03) bulk materials by combining mechanical alloying (MA) method and high pressure and high temperature (HPHT) technology. The enhanced electrical transport properties of the Nb-doped Bi 2 S 3 samples is derived from the collaborative optimization of carrier concentration and effective mass, which indicated that the Nb dopants acted as donors. In addition, differences in the direction of the lattice fringes were observed in the samples, and a large number of lattice distortions and dislocation defects occurred, which significantly reduced the lattice thermal conductivity of the Bi 2 S 3 material. Consequently, a peak zT of 0.22 was achieved for the Bi 1.98 Nb 0.02 S 3 sample at 543 K, which is 120% higher than that of pure Bi 2 S 3. • Nb-doped Bi 2 S 3 samples were fabricated via mechanical alloying method followed by high-pressure and high-temperature. • The carrier concentration, carrier mobility, and effective mass of Bi 2 S 3 can be synergistically optimized via Nb doping. • The high synthetic pressure and Nb-doping introduce defects to enhance phonon scattering. • The maximum zT value for Bi 1.98 Nb 0.02 S 3 reached 0.22 at 543 K. [ABSTRACT FROM AUTHOR]

Here, the thermal and electrical properties of Al doped ZnO were synergistically improved by using high temperature and high pressure (HPHT) technology. HPHT treatment to modulate its crystal structure and microstructure. We simulated this process using first-principles calculations and finite element analysis. Increasing the synthesis pressure improved the electrical and thermal properties. As the synthesis pressure increased, the band gap decreased, and the electrical properties were improved. HPHT also changed the microstructure, and full-spectrum phonon scattering provided the sample with a relatively low thermal conductivity. The sample synthesized at 4.5 GPa achieved a dimensionless figure of merit (zT) of 0.165 at 973 K. Compared to related literature, the synthesized Al doped ZnO showed better thermoelectric properties than previous achievements at the same temperature, showing that HPHT provides a promising method for improving its thermoelectric performance. • The grain size and band gaps of ZnO were effective optimized. • Partial high pressure features of ZnO have been captured to the ordinary pressure. • The whole synthesis procedure last only for 30 min. • High pressure can induce rich defects which are beneficial for thermal properties. [ABSTRACT FROM AUTHOR]

Lutetium-doped Lu x Bi 2- x Te 2.7 Se 0.3 ( x = 0–0.3) nanopowders were synthesized by the hydrothermal method, and then they were hot-pressed into bulk pellets at 773 K under a pressure of 60 MPa in vacuum. The doping effects of Lutetium on the thermoelectric properties were investigated. Compared with the undoped sample, the electrical resistivities of Lu doped samples increased, and the Seebeck coefficients increased slightly. The lower carrier mobility caused by scattering may be the reason for the increase of the electrical resistivities of the doped samples. The thermal conductivities were significantly reduced because the Lu doping introduces a number of point defects into the crystals, which can effectively enhance phonon scattering, and because smaller grain size caused by Lu doping can enhance interface scattering. As a result, all the Lu doped Lu x Bi 2- x Te 2.7 Se 0.3 samples show higher ZT values compared with the undoped samples, indicating that Lu doping is an efficacious way to improve the thermoelectric properties of the n-type Bi 2 Te 2.7 Se 0.3 alloys. [ABSTRACT FROM AUTHOR]

Bismuth sulfide (Bi 2 S 3) is a promising non-tellurium candidate for thermoelectric application due to its low thermal conductivity and abundance of low-toxicity elements. In this work, Bi 2 S 3 -based materials are fabricated by combining mechanical alloying, high-pressure and high-temperature treatment, and spark plasma sintering (MA ​+ ​HPHT ​+ ​SPS). Cation and anion doping (copper and chlorine) are then employed to enhance the thermoelectric properties. While chlorine doping can effectively improve the electrical transport properties of Bi 2 S 3 , it results in a corresponding increase in thermal conductivity. Upon copper doping, the electrical properties show a moderate and steady improvement, which also plays a role in reducing thermal conductivity. Thus, the collaborative optimization of electrical and thermal properties is achieved, whereby a maximum zT value of 0.45 is finally obtained for the Bi 2 S 3 -0.25 ​mol% Cu sample at 573 ​K. [Display omitted] • The Bi 2 S 3 materials were fabricated by a MA + HPHT + SPS route. • Chlorine doping can optimize carrier concentration, it results in a corresponding increase in thermal conductivity. • Copper doping significantly suppress lattice thermal conductivity. • A high zT value of 0.45 is achieved in Bi 2 S 3 -0.25 ​mol% Cu at 573 ​K. [ABSTRACT FROM AUTHOR]

Preparation of TiAl x O 1.80-x (x = 0.06, 0.04, 0.02) under high temperature and high pressure (HPHT) can adjust the energy band gap and modify the resistivity of the material, and gives rise to special microstructure and morphology that reduce the phonon thermal conductivity. In this work, we sought to obtain improved the thermoelectric performance of oxide materials by adjusting the doping ratio of Al and Ti in TiAl x O 1.80-x. The phase structures of different samples were studied by X-ray diffraction. The morphology characteristics generated by HPHT synthesis were studied by electron microscopy （FSEM, HRTEM）and the thermoelectric properties of TiAl x O 1.80-x (x = 0.06, 0.04, 0.02) were evaluated. It was found that an appropriate Al and Ti doping ratio combined with the use of HPHT synthesis can reduce the resistivity of the sample and inhibit the rapid increase of thermal conductivity with increasing temperature. The best zT value (0.22) was obtained at the temperature of 973 K for the TiAl 0 · 04 O 1.76 sample. • Prepare samples with different Al and Ti doping ratios under high temperature and high pressure. • The typical non-stoichiometric titanium oxide structure obtained at high temperature improves the thermoelectric performance of the sample. • Adjust the doping ratio of different Al and Ti to obtain the best thermoelectric performance of the sample, which is 10% higher than that of the sample prepared under the same conditions. • The effect of the ratio of doping with Al and Ti on the performance of the samples was studied. [ABSTRACT FROM AUTHOR]