Search

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]

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]

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]

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]

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: 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]

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]

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]