Search

BiCuSeO is a promising oxygen‐containing thermoelectric material due to its intrinsically low lattice thermal conductivity and excellent service stability. However, the low electrical conductivity limits its thermoelectric performance. Aliovalent element doping can significantly improve their carrier concentration, but it may also impact carrier mobility and thermal transport properties. Considering the influence of graphene on carrier‐phonon decoupling, Bi0.88Pb0.06Ca0.06CuSeO (BPCCSO)‐graphene composites are designed. For further practical application, a rapid preparation method is employed, taking less than 1 h, which combines self‐propagating high‐temperature synthesis with spark plasma sintering. The incorporation of graphene simultaneously optimizes the electrical properties and thermal conductivity, yielding a high ratio of weighted mobility to lattice thermal conductivity (144 at 300 K and 95 at 923 K). Ultimately, BPCCSO‐graphene composites achieve exceptional thermoelectric performance with a ZT value of 1.6 at 923 K, bringing a ≈40% improvement over BPCCSO without graphene. This work further promotes the practical application of BiCuSeO‐based materials and this facile and effective strategy can also be extended to other thermoelectric systems. [ABSTRACT FROM AUTHOR]

NaNbO3‐based antiferroelectric ceramics are promising candidates for high‐performance energy storage capacitors due to their environmental friendliness and low cost despite their current energy storage properties being inferior to those of their lead‐based and AgNbO3‐based counterparts. Typically, the antiferroelectric phase in NaNbO3 ceramics is not stable and the characteristic double hysteresis loops are seldom observed. In this work, the antiferroelectricity was improved by reducing the polarizability, resulting in well‐developed double hysteresis loops in 0.94NaNbO3–0.06(K0.5Bi0.5)SnO3 ceramics. To further improve the energy storage properties, defect engineering was performed for 0.94NaNbO3–0.06(K0.5Bi0.5)SnO3 by substituting Na+ with La3+ and introducing Nb vacancies. As a result, the stability of the field‐induced ferroelectric phase was reduced, and the energy storage properties were enhanced. The strategy of combining polarizability design and defect engineering can be a promising approach for optimizing NaNbO3‐based antiferroelectric ceramics. [ABSTRACT FROM AUTHOR]

Thermoelectric oxide thin films are promising in chip cooling. The issues on the orientation of thin films are essential as they are related to the structures, morphologies, and thermoelectric properties. In this regard, the orientation modulation is conducted on La‐doped SrTiO3 thin films on (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) single crystal substrates. Layer‐by‐layer growth mode is found in (001)‐ and (110)‐ oriented thin films, resulting in few grain boundaries (GBs). In (111)‐oriented films, island growth mode leads to columnar grain boundaries that build up potential barriers for electrons to be strongly scattered and filtered, suppressing electron mobility and increasing effective mass. In addition, the GBs serve as oxygen vacancy diffusion paths when annealing, causing increased carrier concentration and lattice contraction. The weighted mobility of 71.9 cm2 V−1 s−1 and electrical conductivity of ≈600 S cm−1 are realized in the (001)‐oriented film at room temperature. Ultimately, outstanding power factor values of ≈569 µW m−1 K−2 (room temperature) and ≈791 µW m−1 K−2 (573 K) are successfully achieved, outperforming those in polycrystalline ceramics and (111)‐oriented films. This study systematically investigates the influence of grain boundaries and orientations on SrTiO3‐based thermoelectric films, which lays a solid foundation for improving thermoelectric performance in other oxide thin films. [ABSTRACT FROM AUTHOR]

Layered oxychalcogenides have received extensive attention in the fields of magnetism, superconductivity, lithium battery, and luminescence due to their unique electronic, magnetic properties, and layered structure, among which layered oxyselenides have excellent and promising thermoelectric performance, such as BiCuSeO and Bi2LnO4Cu2Se2. Here, we successfully synthesized Sr2MO2Cu2Se2 (M = Co, Ni, Zn) and Sr2FeO3CuSe and investigated the thermoelectric properties at a wide temperature range (298–923 K). They have a relatively high Seebeck coefficient (>300 μV K−1) in medium to high temperature range and possess a low thermal conductivity. The power factor and ZT reach 65 μW m−1 K−1 and 0.07 at 923 K for intrinsic Sr2NiO2Cu2Se2, and a higher performance is expected to be achieved by strategies like carrier concentration optimization and band structure engineering. [ABSTRACT FROM AUTHOR]

As a transparent thermoelectric oxide, gallium‐doped zinc oxide (GZO) has the potential to power wearable or portable electronics and may be used in the integrated circuits industry for chip cooling. Constructing ZnO–GZO interfaces has been proposed as an effective strategy for improving thermoelectric performance of GZO thin films. However, without the aid of band structure calculation for multilayered films, it is hard to directly elucidate the underlying mechanisms of carrier transport. Weighted mobility is an indicator that reveals the inherent electronic transport properties like carrier scattering, electronic band structure, and so on. Thus, to further investigate the effects of ZnO–GZO interfaces on electrical properties of GZO thin films, the structures containing different numbers of ZnO–GZO interfaces were designed and the correlations among numbers of ZnO–GZO interfaces, weighted mobility, and electrical properties were explored. It was found that with more ZnO–GZO interfaces, the weighted mobility increased, and the power factor values also improved as well. Consequently, an enhanced power factor value reached 439 μW m−1 K−2 at 623 K. This work demonstrated the beneficial effects of multiple interfaces on the improvements of electrical transport performance through analyzing weighted mobility, which laid a foundation for further optimization of thermoelectric performance. [ABSTRACT FROM AUTHOR]

Polymer composite dielectrics capable of high energy density, high efficiency, and high‐temperature stability are in high demand for application in various electronic vehicles and power systems. A major challenge, however, is the reasonable design of high‐performance nanofillers that are beneficial to the polarization and breakdown strength simultaneously. Here, high‐entropy‐induced ceramic nanofibers with a stable Bi2Ti2O7‐type pyrochlore phase are developed as effective nanofillers to enhance the energy storage performance of polyetherimide (PEI) composites. Benefiting from the linear pyrochlore phase, refined grain size, and increased amorphous fraction of the high‐entropy nanofillers, the resultant PEI composites exhibit significantly improved energy storage performance over a wide temperature range of 25–150 °C. Notably, a high energy density of 6.46 J cm−3 under an electric field of 590 MV m−1 is achieved at 150 °C, which outperforms most of the reported PEI composites. This study provides a guideline for the development of dielectric fillers with tunable dielectric properties and microstructures, thus promoting the development of high‐performance polymer composites. [ABSTRACT FROM AUTHOR]

The anomalous Hall effect (AHE) is a quantum coherent transport phenomenon that conventionally vanishes at elevated temperatures because ofthermal dephasing. Therefore, it is puzzling that the AHE can survive in heavy metal (HM)/antiferromagnetic (AFM) insulator (AFMI) heterostructures at high temperatures yet disappears at low temperatures. In this paper, an unconventional high-temperature AHE in HM/AFMI is observed only around the Néel temperature of AFM, with large anomalous Hall resistivity up to 40 nQ cm is reported. This mechanism is attributed to the emergence of a noncollinear AFM spin texture with a non-zero net topological charge. Atomistic spin dynamics simulation shows that such a unique spin texture can be stabilized by the subtle interplay among the collinear AFM exchange coupling, interfacial Dyzaloshinski-Moriya interaction, thermal fluctuation, and bias magnetic field. [ABSTRACT FROM AUTHOR]

The use of water‐soluble sacrificial layer of Sr3Al2O6 has tremendously boosted the research on freestanding functional oxide thin films, especially thanks to its ultimate capability to produce high‐quality epitaxial perovskite thin films. However, the costly single‐crystalline substrates, e.g., SrTiO3, are generally discarded after obtaining the freestanding thin films. Here, it is demonstrated that the SrTiO3 substrates can be recycled to fabricate La0.7Sr0.3MnO3 films with nearly identical structural and electrical properties. After attaining freestanding thin films, the residues on SrTiO3 can be removed by 80 °C hot water soaking and rinsing treatments. Consequently, the surface of SrTiO3 reverted to its original step‐and‐terrace structure. [ABSTRACT FROM AUTHOR]

Layered oxyselenides have been widely investigated as promising thermoelectric materials due to their unique merits such as super‐lattice structural features and intrinsic complexity, which contributes to low thermal conductivity and easily controllable electrical properties. Newly developed Bi2LnO4Cu2Se2 (Ln stands for lanthanide) oxyselenides are found to be potential thermoelectric systems since they have excellent electrical conductivity over 103 S cm−1. In this work, unique energy and time‐saving method combined self‐propagating high‐temperature synthesis (SHS) with spark plasma sintering (SPS) is adopted to successfully prepare a highly pure Bi2LnO4Cu2Se2 instead of a traditional solid‐state reaction. To explore the most suitable lanthanide for Bi2LnO4Cu2Se2, thermoelectric performance in a wide temperature range (300 to 923 K) of Bi2LnO4Cu2Se2 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) is deeply evaluated and studied. Ultimately, with a relatively high electrical conductivity, moderate Seebeck coefficient, and extremely low thermal conductivity, a maximum ZT value of ≈0.27 at 923K is achieved in Bi2DyO4Cu2Se2, which is 4 times larger than that of the ever‐reported Bi2YO4Cu2Se2 and proves a potential thermoelectric system for further investigation. This work may provide some enlightenment and broaden the horizon in finding new thermoelectric materials, especially for complex layered compounds. [ABSTRACT FROM AUTHOR]

In recent years, the microstructure and physicochemical properties of high‐entropy ceramics have received much interest by the combination of multiple principal elements. Herein, (Ti0.2V0.2Cr0.2Nb0.2Ta0.2)2AlC–(Ti0.2V0.2Cr0.2Nb0.2Ta0.2)C high‐entropy ceramics (M2AlC‐MC HECs) were prepared by the spark plasma sintering (SPS) technique, attributing to the structural and chemical diversity of MAX phases. The microstructure of M2AlC‐MC HECs was characterized from micron to atomic scales, and the phase composition of M2AlC‐MC HECs was analyzed by a combination of Maud and Rietveld analysis. The results indicate the successful solid solution of Ti, V, Cr, Nb, and Ta atoms in the M‐site of the 211‐MAX configuration, and all the samples show a classic layered structure. The weight percentage of (Ti0.2V0.2Cr0.2Nb0.2Ta0.2)2AlC in the M2AlC‐MC HECs was more than 90%. Furthermore, the thermoelectric properties of M2AlC‐MC HECs were investigated for the first time in this study, and the electrical conductivity and thermal conductivity of HECs are 3278 S cm−1 and 2.78 W m−1 K−1at 298 K, respectively. [ABSTRACT FROM AUTHOR]

Ga‐doped ZnO (GZO) thin films grown on sapphire substrates have been widely investigated as a promising transparent thermoelectric (TE) material. However, due to the large lattice mismatch and thermal expansion between the sapphire substrate and GZO film, strain‐induced lattice distortion impedes the transport of electrons, leading to low carrier mobility. In this study, ZnO homo‐buffer layers with different thicknesses were inserted between sapphire substrates and GZO films, and their effect on the TE properties was investigated. A thin ZnO interlayer (10 nm) effectively reduced the lattice mismatch of the GZO film and improved the carrier mobility, which contributed to the large enhancement in the electrical conductivity. Simultaneously, energy filtering occurred at the interface between GZO and ZnO, resulting in a relatively high density of states (DOS) effective mass and maintaining a high Seebeck coefficient compared to that of the unbuffered GZO films. Consequently, the GZO film with a 10 nm thick ZnO buffer layer possessed a high power factor value of 449 μW m−1 K−2 at 623 K. This study provides a facile and effective method for optimizing the TE performance of oxide thin films by synergistically improving their carrier mobility and enhancing their effective mass. [ABSTRACT FROM AUTHOR]

Gallium (Ga) doping together with low dimensionality has been a promising approach to improve thermoelectric performance of zinc oxide (ZnO) materials, due to the increase of carrier concentration and suppression of phonon transport. So far, the highest power factor of Ga‐doped ZnO (GZO) thin films has reached 280 μW m−1 K−2, which is still limited for practical applications. In this work, we have simultaneously optimized the electrical conductivity and Seebeck coefficient of GZO thin films using the combination of oxygen defects and sandwich structure (GZO‐ZnO‐GZO). Benefiting from energy filtering effect at the interface between GZO and ZnO layers and high oxygen vacancy concentration, the density of states (DOS) effective mass has been increased together with a relatively high carrier concentration. As a result, an improved power factor value of 434 μW m−1 K−2 at 623 K has been achieved, which is comparable to the best values reported for ZnO‐based films. This method of combining defect engineering and sandwich structure design shows great potential in enhancing the thermoelectric performance of ZnO‐based thin films or other oxide materials. [ABSTRACT FROM AUTHOR]

Magnetic mixed‐phase materials with competing ground states are important from both scientific and technical points of view due to their magnetic phase transition and phase coexistence properties. Unlike artificially fabricated multi‐phase composites, it should be possible to modify their physical properties more efficiently by making use of the interphase coupling effects in mixed‐phase materials. In this study, the magneto‐transport properties are investigated to provide evidence of the existence of interphase coupling in a magnetic mixed‐phase system, specifically, Ni‐doped FeRh thin films. The rotation of the external magnetic field induces an emergent promotion effect of the antiferromagnetic (AFM)–ferromagnetic (FM) phase transition, which can be attributed to the modification of the magnetic free energy by interphase magnetic coupling across the AFM–FM phase boundary. The results shed light on the availability of an extra degree of freedom for manipulating the physical properties of material systems with mixed magnetic phases and help to further exploit their potential applications. [ABSTRACT FROM AUTHOR]

High‐performance film dielectrics are crucial for capacitive energy storage applications and electronic industries. In this work, improvements of dielectric and energy performance in BiFeO3‐based films are realized by constructing sandwich architectures, which integrates complementary features of spatially organized dielectric layers in a synergistic manner to realize concurrently high permittivity/polarization and low loss/leakage. Moreover, by rationally modifying the sandwich configuration, ie, with insulating layers on the outside, the interfacial Schottky emission is suppressed, leading to further reductions of leakage and conduction loss. Large energy density of ~44 J cm−3 (superior to that of either single layer) along with high efficiency of ~76% is thus achieved in the sandwich film. This work proves the feasibility and effectiveness of sandwich architecture in improving dielectric, leakage, and energy storage performances, providing a new paradigm for the development of high‐energy‐density dielectrics. [ABSTRACT FROM AUTHOR]

Abstract: N‐type Bi2O2Se has a bright prospect for mid‐temperature thermoelectric applications on account of the intrinsically low thermal conductivity. However, the low carrier concentration of Bi2O2Se (~1015 cm−3) severely limits its thermoelectric performance. Herein, the boosting of the carrier concentration to ~1019 cm−3 can be realized in our La‐doped Bi2O2Se ceramic samples, which could be ascribed to the formation of isoelectronic traps and the narrowing of band gap, and contribute to a marked increase in the electrical conductivity (from 0.03 S cm−1 to 182 S cm−1). Our X‐ray absorption near‐edge structure spectra results reveal that a local disordering of oxygen atoms could be an important reason for the intrinsically low thermal conductivity of Bi2O2Se, and the point defects can also suppress the lattice thermal conductivity in La‐doped Bi2O2Se. The ZT value can be enhanced by a factor of ~4.5 to 0.35 at 823 K for Bi1.98La0.02O2Se as compared to the pristine Bi2O2Se. The coordinated optimization of electrical and thermal properties demonstrates an effective method for the rational design of high‐performance thermoelectric materials. [ABSTRACT FROM AUTHOR]

Abstract: Polymer‐based dielectrics are attracting increasing attention due to their high‐density energy storage. However, mitigating the heat generation in real capacitors has been a challenge. Here an electrothermal breakdown phase‐field model is developed to fundamentally understand the thermal effects on the dielectric breakdown of polymer‐based dielectrics in real capacitor configurations including the increase in the dielectric loss and the decrease in the breakdown strength. While both enhancing the thermal conductivity and reducing the electrical conductivity of the polymer nanocomposites can reduce the thermal effects, it is found that reducing the electrical conductivity is more effective. This work is expected to not only stimulate attention to the thermal effects in polymer‐based dielectrics but also provide a fundamental guidance to mitigate the heat‐induced deterioration of breakdown strength. [ABSTRACT FROM AUTHOR]

Abstract: To make better use of solar light, a new Bi2WO6/Cu1.8Se photocatalyst active to visible and near‐infrared light has been synthesized by a facile hydrothermal method. The composites were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), UV‐vis diffuse reflectance spectroscopy (DRS), and photoluminescene (PL). The photocatalytic activities of Bi2WO6/Cu1.8Se are evaluated by degrading Congo red solution and hydrogen generation from water. It was found that the molar percentage of Cu1.8Se had great effects on the morphology and photocatalytic property of the Bi2WO6/Cu1.8Se heterojunctions, and the composite with suitable molar amount of Cu1.8Se exhibits much enhanced photocatalytic activity for Congo red degradation under visible and near‐infrared light irradiation and for hydrogen generation under visible light compared to Bi2WO6. The significant improvement photocatalytic activity of the composite could be attributed to its good light absorption, suitable band gap structure, and effective separation of photogenerated electron‐hole pairs of Bi2WO6/Cu1.8Se heterojunction. This work presents an efficient multifunction photocatalyst owning the activity both for water splitting under visible light and for organic contaminants decomposition under visible‐near‐infrared light. [ABSTRACT FROM AUTHOR]

Bi2O2Se oxyselenides, characterized with intrinsically low lattice thermal conductivity and large Seebeck coefficient, are potential n-type thermoelectric material in the mediate temperature range. Given the low carrier concentration of ~1015 cm−3 at 300 K, the intrinsically low electrical conductivity actually hinders further enhancement of their thermoelectric performance. In this work, the isovalent Te-substitution of Se plays an effective role in narrowing the band gap, which notably increases the carrier concentration to ~1018 cm−3 at 300 K and the electron conduction activation energy has been lowered significantly from 0.33 to 0.14 eV. As a consequence, the power factor has been improved from 104 μW·K−2·m−1 for pristine Bi2O2Se to 297 μW·K−2·m−1 for Bi2O2Se0.96Te0.04 at 823 K. Meanwhile, the suppressed lattice thermal conductivity derives from the introduced point defects by heavier Te atoms. The gradually decreased phonon mean free path reflects the increasingly intense phonon scattering. Ultimately, the ZT value attains 0.28 for Bi2O2Se0.96Te0.04 at 823 K, an enhancement by a factor of ~2 as compared to that of pristine Bi2O2Se. This study has demonstrated that Te-substitution of Se could synergistically optimize the electrical and thermal properties thus effectively enhancing the thermoelectric performance of Bi2O2Se. [ABSTRACT FROM AUTHOR]

The structural optimization of TiO2 materials has a significance for improving the electrochemical performance since TiO2 suffers from poor electronic conductivity. For this purpose, ultrathin N-doped carbon-coated TiO2 coaxial nanofibers have been designed and synthesized by a facile electrospinning approach. Microstructure analysis indicates that the TiO2 nanofibers can be coated by the ultrathin carbon layers. Electrochemical tests reveal that the rate performance and cycling ability of TiO2@C nanofibers have been enhanced obviously. The TiO2@C6 nanofibers carbonized at 600°C exhibit superior features with a specific discharge capacity of 284 mAh g−1 at a current density of 100 mA g−1 after 100 cycles. Besides improved rate performance of 117 mAh g−1 at a high current density of 2000 mA g−1 and excellent cycling stability with only about 0.008% capacity loss per cycle were also obtained in the sample TiO2@C6 after 500 cycles at the current density of 1000 mA g−1. Such remarkable performance may be ascribed to the unique one-dimensional nanofibers as flexible carbon matrix. [ABSTRACT FROM AUTHOR]

The n-type polycrystalline Bi2O2Se1− xCl x (0≤ x≤0.04) samples were fabricated through solid-state reaction followed by spark plasma sintering. The carrier concentration was markedly increased to 1.38×1020 cm−3 by 1.5% Cl doping. The maximum electrical conductivity is 213.0 S/cm for x=0.015 at 823 K, which is much larger than 6.2 S/cm for pristine Bi2O2Se. Furthermore, the considerable enhancement of the electrical conductivity outweighs the moderate reduction of the Seebeck coefficient by Cl doping, thus contributing to a high power factor of 244.40 μ·WK−2·m−1 at 823 K. Coupled with the intrinsically suppressed thermal conductivity originating from the low velocity of sound and Young's modulus, a ZT of 0.23 at 823 K for Bi2O2Se0.985Cl0.015 was achieved, which is almost threefold the value attained in pristine Bi2O2Se. It reveals that Se-site doping can be an effective strategy for improving the thermoelectric performance of the layered Bi2O2Se bulks. [ABSTRACT FROM AUTHOR]

The layered oxyselenide BiCuSeO system is known as one of the high-performance thermoelectric materials with intrinsically low thermal conductivity. By employing atomic, nano- to mesoscale structural optimizations, low thermal conductivity coupled with enhanced electrical transport properties can be readily achieved. Upon partial substitution of Bi3+ by Ca2+ and Pb2+, the thermal conductivity can be reduced to as low as 0.5 W m−1 K−1 at 873 K through dual-atomic point-defect scattering, while a high power factor of ≈1 × 10−3 W cm−1 K−2 is realized over a broad temperature range from 300 to 873 K. The synergistically optimized power factor and intrinsically low thermal conductivity result in a high ZT value of ≈1.5 at 873 K for Bi0.88Ca0.06Pb0.06CuSeO, a promising candidate for high-temperature thermoelectric applications. It is envisioned that the all-scale structural optimization is critical for optimizing the thermoelectricity of quaternary compounds. [ABSTRACT FROM AUTHOR]

Pure perovskite BiFeO3, sillenite Bi2 Fe4 O9, and BiFeO3/ Bi2 Fe4 O9 were synthesized facilely by controlling the precursor Bi/ Fe ion ratio through a hydrothermal method. The phase composition, morphology, optical properties, and photocatalytic activity of as-prepared samples were investigated in detail. Our results indicate that the morphology and properties of products strongly dependent on the precursor Bi/Fe ion ratio. Photocatalysis of Congo Red reveals that sillenite Bi2 Fe4 O9 shows superior activity to perovskite BiFeO3, and BiFeO3/ Bi2 Fe4 O9 exhibited higher activity with 71.45% degradation rate in 90 min. It provides an easy and efficient way to tune the composition and photocatalytic activity of Bi-based oxides. [ABSTRACT FROM AUTHOR]

Polycrystalline SmBaCuFeO5+δ/Ag composite ceramics have been synthesized by a traditional ceramic processing method. Phase composition and microstructural analyses indicate that with the introduction of Ag additives, the second phases of copper oxides and Ag appear in these composite ceramic samples. The hole concentration and molibility can be enhanced greatly by the addition of Ag particles, which results in a large increase in the electrical conductivity. The thermal conductivity behaviors show that phonons can be scattered effectively by point defects and mesoscale grain boundaries, which remain a slight change in thermal conductivity. A maximum ZT value 0.047 has been achieved at 1023 K in the SmBaCuFeO5+δ/20 vol% Ag composite ceramic, and is about 16 times than the pure SmBaCuFeO5+δ sample. Our results reveal that Ag addition is an effective way to enhance the thermoelectric properties. [ABSTRACT FROM AUTHOR]

A novel fiber-in-tube hierarchical nanostructure of SnO2@porous carbon in carbon tubes (SnO2@PC/CTs) is creatively designed and synthesized though a carbon coating on scalable electrospun hybrid nanofibers template and a post-etching technique. This 1D nanoarchitecture consists of double carbon-buffering matrixes, i.e., the external carbon tubular shell and the internal porous carbon skeleton, which can work synergistically to address the various issues of SnO2 nanoanode operation, such as pulverization, particle aggregation, and vulnerable electrical contacts between the SnO2 nanoparticles and the carbon conductors. Thus, the as-obtained SnO2@PC/CTs nanohybrids used as a lithium-ion-battery anode exhibits a higher reversible capacity of 1045 mA h g−1 at 0.5 A g−1 after 300 cycles as well as a high-rate cycling stability after 1000 cycles. The enhanced performance can be attributed to the wonderful merits of the external carbon protective shell for preserving the integrity of the overall electrode, and the internal porous carbon skeleton for inhibiting the aggregation and electrical isolation of the active particles during cycling. [ABSTRACT FROM AUTHOR]

Gd1− xLa xBaCuFeO5+δ polycrystalline ceramics have been prepared by a sol-gel method combined with the traditional ceramic processing. Analysis of the microstructure and phase composition reveals that the pure GdBaCuFeO5+δ phase can be obtained even after the substitution of 50% La at Gd-site. The band gap can be tuned from 1.47 to 1.36 eV by La substitution, resulting in a significant increase in the electrical conductivity. In addition, the total thermal conductivity can also be suppressed by the substitution of La at Gd-sites. A ZT value of 0.02 at 1023 K is achieved in the 50% La-substituted samples, which is over 20 times higher than that of the pure GdBaCuFeO5+δ sample. [ABSTRACT FROM AUTHOR]

Polycrystalline Bi2− xO2Se ceramics were synthesized by spark plasma sintering process. Their thermoelectric properties were evaluated from 300 to 773 K. All the samples are layered structure with a tetragonal phase. The introduction of Bi deficiencies will cause the orientation alignment and change of effective mass. As a result, a significant enhancement of thermoelectric performance was achieved. The maximum of Seebeck coefficient is −568.8 μV/K for Bi1.9O2Se at 773 K, much larger than −445.6 μV/K for pristine Bi2O2Se. Featured with very low thermal conductivity [~0.6 W·(m·K)−1] and an optimized electrical conductivity, ZT at 773 K is significantly increased from 0.05 for pristine Bi2O2Se to 0.12 for Bi1.9O2Se by introducing Bi deficiencies, which makes it a promising candidate for medium temperature thermoelectric applications. [ABSTRACT FROM AUTHOR]

BiFeO3 nanofibers doped with divalent barium have been fabricated using electrospinning technique. Phase transition from space group R3c to C222 can be observed by the Ba doping. Our results indicate that these BiFeO3 nanofibers show obvious room temperature ferromagnetic behaviors, which can be enhanced remarkably with the increment of Ba doping. Microstructure and composition analysis indicates that barium effectively affected the magnetism after doping content was more than 5% and optical properties. [ABSTRACT FROM AUTHOR]

A high-performance thermoelectric BiCuSeO oxyselenides has been prepared by a simple fabrication approach. Phase composition and microstructure analysis indicate that the obtained ceramic samples are almost BiCuSeO phase with plate structure. Our results show that Pb-doped BiCuSeO bulks have good electrical conductivity, large Seebeck coefficient, and low thermal conductivity. A large power factor ~672 μ/Wm/K2 at 573 K can be observed in the BiCuSeO ceramic by the 10% Pb doping, and the dimensionless figure of merit ( ZT) can reach 0.95 at 873 K, which makes them promising candidates for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Highly orientated Co-doped Zn( Mg, Cd) O thin films have been prepared on Si (001) substrate using pulsed laser deposition (PLD). Our results indicate that Mg and Cd-doping can tune the bandgap of ZnO thin film. Apparent room-temperature ferromagnetism is observed in these films, which can be modified by the bandgap of ZnO. A narrow bandgap enhances the ferromagnetism of the films through the Cd-doping, and wide bandgap does the opposite through the Mg-doping, which may be ascribed to the ferromagnetic ( FM) exchange interaction between the 3 d states of magnetic Co ions and the impurity band. These experimental results provide some new evidence that the ferromagnetism in Co: ZnO is closely related to crystal defects and improve our knowledge about ferromagnetism in dilute magnetic oxides. [ABSTRACT FROM AUTHOR]

Nanostructured Zn and Ce co-doped In2 O3-based ceramics were fabricated using co-precipitation and Spark plasma sintering. It is shown that the nanograins in Zn and Ce co-doped In2 O3-based ceramics can lead to 50% reduction in the thermal conductivity of the sample with a 50 nm grain size and meanwhile keep good electric conductivity. As a result, a reported high ZT value of 0.4 at 1050 K was achieved for n-type oxide thermoelectrics. It is expected that the ZT value could reach 0.7 when the grain size is smaller than 20 nm. Our results indicate that nanosized grain is highly desired for reducing thermal conductivity and hence a higher ZT value in oxide thermoelectrics. [ABSTRACT FROM AUTHOR]

Using the spark plasma sintering process In2 −x Ce x O3 (0 ≤ x ≤ 0.10) fine grained ceramics have been synthesized. Our results indicate that all the In2 O3-based ceramic samples show good electrical conductivity and high thermoelectric power factor. In comparison with pure In2 O3 bulks or doped samples with grain size above 1 μm, the 100-300 nm fine grain In2 O3-based ceramics exhibit much lower thermal conductivities (1.9-2.5 W·(m·K)−1 at 1173 K), demonstrating a remarkable cooperative tuning effect imposed by grain size reduction and nano-clusters formation. The maximum figure of merit ZT value is optimized up to ~0.47 at 1223 K for In1.92 Ce0.08 O3 sample, which makes them promising candidates for thermoelectric applications. [ABSTRACT FROM AUTHOR]

We present a rare-earth-doped ZnO ceramic with nonohmic electrical properties. Analysis of the microstructure and composition indicates that the ceramic is composed of the main phase of ZnO and the second phase of rare-earth oxides (e.g., Dy2O3, Pr6O11, Pr2O3). The average grain size is markedly increased from 3 to 18 μm, with an increase in the sintering temperature from 1150° to 1350°C. The corresponding varistor voltage and nonlinear coefficient decrease from 1014 to 578 V/mm, and from 15.8 to 6.8, respectively. The resistivity of grain and grain boundary evaluated by the complex impedance spectrum indicates that the resistivity of the grain is approximately constant (∼103Ω), and the resistivity of the grain boundary decreases. The relative dielectric permittivity of the sintered ceramic samples is much larger than that of pure ZnO ceramic, which should be ascribed to the internal boundary layer capacitance effect. [ABSTRACT FROM AUTHOR]

We present high-temperature electrical transport and thermoelectric power of K and/or La-doped Ca3Co4O9-based ceramics. Temperature and doping dependence of electrical transport properties indicate that both K and La substitutions can increase electrical conductivity at a high temperature, which are mainly related to an increase in carrier concentration and carrier mobility. A metallic-to-semiconducting transition temperature ( T*) can be observed and shifts to a lower temperature as the doping content increases. However, activation energy is almost independent of the doping. All of the samples show positive thermoelectric power, and the temperature dependence of the thermoelectric power exhibits a simple linear behavior at T> T*. Our experimental data indicate that all of the Ca3Co4O9-based ceramic samples exhibit large thermoelectric power (∼120 to 180 μV/K). [ABSTRACT FROM AUTHOR]

For an ideal electrostatic energy storage dielectric capacitor, the pursuit of simultaneously high energy density and efficiency presents a formidable challenge. Typically, under an applied electric field, an increase in energy density is usually accompanied with a deteriorated energy storage efficiency due to the escalated hysteretic loss, which is harmful to the reliability of the capacitor. Thus, a well‐balanced performance of improved energy density and maintained high efficiency is highly demanded. In this work, a structure with amorphous phases embedded in polycrystalline nanograins using the entropy tactic, leading to a higher transport barrier of carrier is constructed. Hence, the hysteretic loss is largely suppressed at a high electric field and the high polarization is still sustained in the high‐entropy film. Consequently, an ultrahigh energy density of 139.5 J cm−3 with a high efficiency of 87.9%, and a high figure of merit of 1153 are simultaneously achieved in the high‐entropy Ba2Bi4Ti5O18‐based relaxor ferroelectric. This work offers a promising avenue in materials structure design for advanced high‐power energy storage applications. [ABSTRACT FROM AUTHOR]

Oxygen‐containing compounds are promising thermoelectric (TE) materials for their chemical and thermal stability. As compared with the high‐performance p‐type counterparts (e.g., ZT ≈1.5 for BiCuSeO), the enhancement of the TE performance of n‐type oxygen‐containing materials remains challenging due to their mediocre electrical conductivity and high thermal conductivity. Here, n‐type layered Bi2O2Se is reported as a potential TE material, of which the thermal conductivity and electrical transport properties can be effectively tuned via carrier engineering and hierarchical microstructure. By selective modification of insulating [Bi2O2]2+ layers with Ta dopant, carrier concentration can be increased by four orders of magnitude (from 1015 to 1019 cm−3) while relatively high carrier mobility can be maintained, thus greatly enhancing the power factors (≈451.5 µW K−2 m−1). Meanwhile, the hierarchical microstructure can be induced by Ta doping, and the phonon scattering can be strengthened by atomic point defects, nanodots of 5–10 nm and grains of sub‐micrometer level, which progressively suppresses the lattice thermal conductivity. Accordingly, the ZT value of Bi1.90Ta0.10O2Se reaches 0.36 at 773 K, a ≈350% improvement in comparison with that of the pristine Bi2O2Se. The average ZT value of 0.30 from 500 to 823 K is outstanding among n‐type oxygen‐containing TE materials. This work provides a desirable way for enhancing the ZT values in oxygen‐containing compounds. [ABSTRACT FROM AUTHOR]