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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]

In this work, the competitive relationship between the double amorphous phases is systematically investigated to increase the high-temperature wear resistance of the self-lubricating TiAlSiCN coating. These double amorphous phases combine the SiN x phase with high-temperature resistance and the C-related phase with a low friction coefficient. An increase in the Si content facilitates the change in the phase composition. The resultant coating exhibits an adhesion strength of 153 N, a friction coefficient of 0.24 and a hardness of 25.24 GPa upon generation of the TiAlN(C), the SiN x and the C-related phase. In this case, the TiAlSiCN coating achieves long-term self-lubrication at high temperatures with the titanium alloy friction pair. This mechanism stems from the SiN x phase replacing the portion of the easily oxidized amorphous C-related phase, which yields an enhanced high-temperature wear resistance. The cutting distance of this TiAlSiCN is 120% higher than that of the TiAlCN during the high-speed cutting of the titanium alloy. This outcome provides an effective solution for high-temperature applications of self-lubricating coatings. • Long-term self-lubricating is remained in TiAlSiCN coating by optimal Si content. • Synergistic effect of amorphous SiN x and C-related phase is solved in TiAlSiCN. • Tool life of TiAlSiCN improved 225% by comparing with that of TiAlN. [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]

Cu 2 Se is one kind of popular thermoelectric materials due to its performance of the phonon glass-electron crystal. However, the poor thermal stability limits its application. Regulating the distribution of the Cu+ by elemental dopant is a general method to solve the stability and to improve the thermoelectric performance. In this study, the Ag-doped β-Cu 2−x Se films were prepared by vacuum thermal evaporation method. The Cu+ distribution on the octahedral 32(f) sites in the Cu 2 Se crystal is tuned by the Ag content. It found that when the Ag content is 1.0%, the Cu+ and Ag+ contents in the 32(f) sites reach the maximum. In this case, the power factor of the film is 1750 μW·m−1·K−2 at 530 K. As the Ag content rises, the second phase of CuAgSe appears. This results in the decrease of the power factor. It shows that controlling the distribution of the Cu+ by the Ag dopant is conducive to improve the thermoelectric properties of the β-Cu 2−x Se films. • Occupancy increase of Cu+ and Ag+ in 32(f) sites decreases resistivity. • CuAgSe second phase increases carrier concentration and effective mass. • Power factor of Ag-1.0% film is maximum and 300% higher than that of Ag-0.0% film. [ABSTRACT FROM AUTHOR]

Three kinds of high entropy (Y 0.25 Sc 0.25 Er 0.25 Yb 0.25) 2 Si 2 O 7 , (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Lu 0.2) 2 Si 2 O 7 and (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Gd 0.2) 2 Si 2 O 7 were designed and synthesized in order to investigate the relation of microstructures and CMAS corrosion resistance. At low temperature of 1300 °C, lattice distortion played a crucial role in resistance to CMAS corrosion, and larger lattice distortion contributed to CMAS corrosion resistance. However, the corrosion behavior at 1500 °C was related to the equivalent ionic radius and RE species. The smaller equivalent ionic radius tended to promote the re-precipitation of high entropy RE disilicate in residual CMAS glass rather than apatite. The results will provide theoretical guidance for the microstructural design of high entropy RE disilicate and selection of RE elements in future. • High entropy ceramics were synthesized by solid state reaction method. • (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Gd 0.2) 2 Si 2 O 7 ceramics had a maximum lattice distortion. • (Y 0.2 Sc 0.2 Er 0.2 Yb 0.2 Gd 0.2) 2 Si 2 O 7 presented a best CMAS corrosion resistance. [ABSTRACT FROM AUTHOR]

The self-lubricating TiAlTaCN coating with high-temperature resistance above 800 °C is developed using magnetron sputtering. This mechanism stems from the TaN phase is easily oxidized to form a protective Ta 2 O 5 that compensates for the insufficient antioxidant capacity of Al 2 O 3. Moreover, the TaC phase, being resistant to oxidation, contributes to achieving the self-lubrication effect with amorphous C-related phases. The cutting distance of the TiAlTaCN is 250% greater than that of the TiAlCN during the high-speed cutting of titanium alloy. These results reveal the oxidation mechanism of different carbon nitrides and provide a new solution for the self-lubricating coatings applied at high temperatures. • A new high-temperature resistant (800 °C) self-lubricating (COF=0.27) TiAlTaCN nanocomposite coating was prepared. • The Ta addition inhibits the phase transition and increases the high thermal stability from 600 °C to 1000 °C. • The wear rate of the TiAlTaCN is 38.7% lower than that of the TiAlCN at 600 °C. • The cutting distance of the TiAlTaCN is 250% higher than the TiAlCN during the high-speed cutting of titanium alloy. [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]