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In this study, we explored the role of the intrinsic defects on the tuning thermoelectric (TE) performance of Al-doped ZnO (ZnO:Al) films. The intrinsic defects of the Zn interstitial (Zn i) and the oxygen vacancy (V O) were controlled by varying the Zn content by using the radio frequency atomic source vacuum evaporation method. In the Zn-rich case, the excessive Zn formed Zn i to provide most of the carriers. V O became the main origin of the carriers with a decreasing Zn content. When the Zn content was 55.2% and 52.5%, the segregation of Zn i decreased the carrier concentration and subsequently, enhanced the resistivity and the Seebeck coefficient. The ZnO:Al film with a Zn content of 52.5% had the highest power factor of 274.03 μW·m−1·K−2 at 819 K. In addition, the higher Zn i concentration had a more prominent effect on thermal conductivity. The thermal conductivity increased to 1.756 W·m−1·K−1 from 0.608 W·m−1·K−1 with the Zn content decreasing from 55.2% to 50.6%. The ZT value reached the highest of 0.121 when the film had the optimum Zn concentration of 51.5%. This study concluded that the tuning of the intrinsic defects was an effective method to enhance the TE performance. [ABSTRACT FROM AUTHOR]

Electrical and thermal transport controlled by growth mode can be used to optimize thermoelectric properties of ZnO:Al films, which was adjusted by the re‐evaporation of Zn and Al via substrate temperatures. The growth modes include equiaxed crystal, columnar crystal and coexistence of both crystals. In the ZnO:Al film, equiaxed crystals improve the carrier mobility and reduce the lattice thermal conductivity. Thus, the carrier mobility and thermal conductivity are tuned by the ratio of equiaxed crystals to columnar crystals. The carrier mobility is dependent on the growth‐mode‐related defects of oxygen vacancies, zinc interstitials and the substitutional dopant of Al. Improved thermoelectric properties with a power factor of 198.45 µW m−1 K−2 at 510 K were achieved. This study presents a film with the structure of an equiaxed‐crystal buffer layer to enhance its thermoelectric properties. [ABSTRACT FROM AUTHOR]

Multi-nanocomposite is an effective method to achieve high thermoelectric (TE) performance by breaking the tradeoff among three TE parameters. This paper presents a comparative study of incorporated carbon nanotube (CNT)/Au in evaporated porous Al-doped ZnO (AZO) films. The effect of the nanocomposite interface on scattering of carriers and phonons is used to independently tune thermal conductivity and power factor in the multi-nanocomposite AZO films. This breaks the tradeoff and improves the figure of merit (ZT) of the film. Moreover, the temperature gradient retains in the out-of-plane of the films. These make the AZO film composited CNT and porosity have higher output power than that of the non-porous films. This provides a simple method for the low-dimension film to increase the TE properties through breaking the tradeoff and makes the TE materials suitable for efficient harvesting in low-grade waste heat. [Display omitted] • This study presents a simple method to prepare multi-nanocomposite film. • Multi-nanocomposite breaks the tradeoff among thermoelectric parameters. • Film with CNT and porosity has higher ZT value and output power. [ABSTRACT FROM AUTHOR]

Bi 2 Te 3 is a successful and commercial thermoelectric material. However, Bi 2 Te 3 is easily generates point defects, which limits its thermoelectric (TE) properties. This study presents a novel method to tune point defects by using short-range atomic diffusion via pulsed electric field (PEF) treatment in C-doped Bi 2 Te 3 films. The C atoms migrate from the interstitial position in the Bi layer (C i) and the Van der Waals gap (C vdw) to the Bi vacancy after the PEF treatment. For this case, it increases the content of the Te–C bonds for the PEF films, resulting in increased electron concentration. And the PEF can eliminate amorphous regions of the C-doped Bi 2 Te 3 films. In addition, the shorter bond length of the Te–C improves the compressive stress of the film and increases the effective mass of carriers. Thus, the conductivity and the Seebeck coefficient are improved simultaneously. In this study, the power factor was 2450.32 μW m−1·K−2 at 513 K after the PEF treatment. Therefore, the PEF is an effective method to improve TE properties by short-range atomic diffusion. [ABSTRACT FROM AUTHOR]

The order-disorder transition (ODT) of RE zirconate (RE 2 Zr 2 O 7) has received much attention due to its potential applications in the design of thermal barrier coatings (TBCs). A series of high entropy RE zirconates (RE = La, Sm, Gd, Er and Lu) were designed and synthesized in order to regulate the fluorite-pyrochlore phases, and to investigate the effect of phase composition on the microstructures and performances. The results showed that the sintering temperature, as well as equivalent ion radius, played an important role in regulating the phase transformation of fluorite-pyrochlore. The coexistence of pyrochlore-fluorite phases not only can result in the decrease in grain size but also increased the lattice strain of each phase, thereby enhancing the phonon scattering and contributing to the reduction in the thermal conductivity. The CMAS corrosion resistance was mainly related to phase compositions, and the thicknesses of reaction layer decreased gradually with the increasing fluorite phase content. The results will provide theoretical guidance for the microstructural design of high entropy RE zirconates as next generation TBC materials in future. [ABSTRACT FROM AUTHOR]

• Angle of grain boundaries converts to low from high by electrostatic force. • Low energy of low-angle grain boundary scatters carrier but not phonon. • Pulse current treatment provides a method to get high power factor and power density. Current applications of thermoelectric (TE) materials are limited by their low conversion efficiency. Interfacial engineering is a common way to improve TE properties. This study employed a pulsed electric field to tune the grain interfacial structure of Bi 2 Te 3 films and thereby improve their power factor. The high-angle grain boundaries of the as-deposited films were transformed into low-angle grain boundaries (LAGBs) by the electrostatic force of a high pulse current density. The low interfacial energy of LAGBs maintains high carrier mobility while their reduced defects result in a low carrier concentration. These effects improve the Seebeck coefficient and conductivity simultaneously, with the power factor reaching 5394.77 μW·m−1·K−2 at 513 K. In addition, the compression stress generated by LAGBs enhances phonon scattering, creating a film with the highest power density yet reported (1.31 W·m−2). This provides a method for using PEF to improve the performance of TE materials. [ABSTRACT FROM AUTHOR]

The novel rare earth monosilicates (xRE 1/x) 2 SiO 5 (RE=Yb, Tm, Er, Y, Dy and Tb, x = 2–6) were prepared in order to establish the relationship between configurational entropy and lattice distortion, and the effect of configurational entropy on their properties was investigated. The results showed that the lattice distortion of (xRE 1/x) 2 SiO 5 increased gradually with the increase of configurational entropy, but the multi-principal component solid solution tended to form a highly symmetrical crystal structure when the configurational entropy was large enough, thus inhibiting the lattice distortion. (5RE 1/5) 2 SiO 5 had a maximum lattice distortion, which leaded to a relatively low thermal conductivity and coefficient of thermal expansion, and good CMAS corrosion resistance. • The effect of configurational entropy on microstructure and properties was investigated. • (5RE 0.2) 2 SiO 5 ceramic had a maximum lattice distortion. • (5RE 0.2) 2 SiO 5 ceramic presented the relatively good thermal properties and CMAS corrosion resistance. [ABSTRACT FROM AUTHOR]

• Different dimensions of carbon have different effects on thermoelectric performance. • The lower the dimension of carbon, the higher the carrier concentration of the film. • The CNT composite makes ZnO: Al films have the best performance. The low-dimensional carbon composite is expected to improve electrical conductivity and reduce the thermal conductivity of thermoelectric (TE) materials, which is considered an effective method to improve the TE properties of materials. However, the different dimensions of carbon have various effects on the properties of TE film composite. This study investigated the effects of zero-dimensional fullerene, one-dimensional carbon nanotubes (CNT), and two-dimensional graphene on the TE properties of vacuum evaporated ZnO: Al films. The results demonstrated that these three types of composites influenced the carrier concentration and mobility of the films, which in turn affected the TE properties and output power. The lower the dimension of carbon, the higher the carrier concentration of the film. The CNT composite did not affect the microstructure and preferred orientation. However, it increased the particle size and surface roughness. The interface between CNT and ZnO: Al provided more carriers and improved effective mass, thereby increasing the Seebeck coefficient. In addition, the CNT can be used as a carrier transport channel to improve carrier mobility because of its unique tubular structure. Therefore, the CNT composited ZnO: Al films demonstrated the best TE performance and output power. Its power factor reached 136.5 μWm−1K−2 at room temperature. [ABSTRACT FROM AUTHOR]