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Abstract Bi 1- x Pb x Cu 1- x Ni x SeO (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) BiCuSeO based ceramics have been prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process. The effects of Pb/Ni doping and 3D modulation doping on the thermoelectric properties have been investigated systematically. For Pb doping, it can tune the Fermi level and promote the band convergence, decreasing the band gap and significantly enhancing the carrier concentration. Besides, it contributes to higher effective mass and Seebeck coefficient due to the delocalized 6s orbitals from the lone pair electrons. For Ni doping, Ni ions could enhance Seebeck coefficient. The results indicates that the substitution of Pb at Bi site and Ni at Cu site resulted in the significantly increase of electrical conductivity and power factor. Based on this, 3D modulation doping led to the simultaneous increase of the electrical conductivity and power factor. The maximum power factor of the modulation doped sample (Bi 0.90 Pb 0.10 Cu 0.90 Ni 0.10 SeO) reached 0.64 mW m−1 K−2, and the maximum ZT value reached 1.08, which is 1.3 and 1.0 times higher than those of the undoped sample, respectively. Graphical abstract Pb/Ni doping combined with modulation doping led to the great increase of BiCuSeO based ceramics(Bi 1- x Pb x Cu 1- x Ni x SeO, x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) fx1 Highlights • Pb/Ni doping led to the great increase of carrier concentration and electrical conductivity. • Modulation doping based on Pb/Ni doping increases the electrical conductivity further. • The highest ZT is 1.08 for the modulation doped sample at 873 K. [ABSTRACT FROM AUTHOR]

Here, Bi 1- x Ba x CuSe 1- x Te x O ( x  = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics have been prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process. The effects of Ba/Te doping on the thermoelectric properties have been investigated systematically. For Ba doping, it can tune the Fermi level and promote the band convergence, decreasing the band gap and significantly enhancing the carrier concentration; for the Te doping based on Ba doping, it can profoundly reduce the difference of electronegativity in (Cu 2 Se 2 ) 2- layer, increase bond covalency, and then increase the electrical conductivity. The results indicate that the substitution of Ba/Te resulted in significant increases of electrical conductivity and power factor. Based on this, modulation doping leads to the simultaneous increase of the electrical conductivity and Seebeck coefficient. Finally, the maximum power factor of 0.98 mW m −1 K −2 and ZT value of 1.17 were obtained for the modulation doped Bi 0.90 Ba 0.10 CuSe 0.90 Te 0.10 O bulk, which were ~ 3.5 and ~ 2.2 times respectively as those of the pristine BiCuSeO ceramic. [ABSTRACT FROM AUTHOR]

Abstract The layered oxyselenide BiCuSeO thermoelectric ceramics are attracting much scientific attention for its excellent thermoelectric properties. Herein, Bi 1- x Sb x CuSe 1- x Te x O ( x = 0, 0.01, 0.02, 0.04, 0.06, 0.08) ceramics have been prepared by ball milling (BM) and resistance pressing sintering (RPS) process. The effects of Sb/Te doping and grain size on the thermoelectric/mechanical properties are investigated systematically. For the former, it can tune the Fermi level and promote the band convergence, decreasing the band gap and concurrently enhancing the carrier concentration; for the latter, it can profoundly modify microstructure into an all-scale hierarchical architecture to scatter phonons with broad range of mean free paths, effectively reducing the lattice thermal conductivity. The results indicates that the substitution of Sb/Te resulted in the significantly increase of electrical conductivity and power factor, and BM effectively reduces the grain size to ~ 387 nm in the sample after sintering, which leads to a decrease in the thermal conductivity and an increase in the electrical conductivity. The maximum power factor of 0.72 m Wm−1 K−2 and ZT value of 1.19 were obtained for Bi 0.92 Sb 0.08 CuSe 0.92 Te 0.08 O with BM time = 16 h at 873 K, which was ~ 2.7 and ~ 2.2 times as that of the pristine BiCuSeO ceramic. Graphical abstract Sb/Te doping combined with grain refining led to the great increase of BiCuSeO based ceramics(sample 0–3 stand for ball milling time=5 h, 8 h, 12 h 16 h, respectively) fx1 [ABSTRACT FROM AUTHOR]

The diffusion of Ni and Sn is undesirable in thermoelectric (TE) device. However, the quantitative effect on TE properties is unknown. In this work, the effect of Ni/Sn doping on the TE properties of p-type Bi 2 Te 3 based alloys and the corresponding mechanism are investigated to provide beneficial reference for device designers and researchers. The results show that nickel doping in Bi 0.4 Sb 1.6 Te 3 can make the intrinsic excitation temperature shift to lower temperature region due to the formation of the second phase NiTe, which greatly reduces the carrier concentration and increases the electrical resistivity. Ultimately, the thermoelectric figure of merit (ZT value) deteriorates rapidly with the increase of Ni content, and only 7 wt ‰ Ni results in a 32% drop in ZT value. Tin doping moves the intrinsic excitation temperature to higher temperature region due to the promotion of Sn' Bi to the generation of anti-sites (Bi' Te and Sb' Te), which significantly increases the carrier concentration and deteriorates the Seebeck coefficient. At last, the ZT value also declines sharply with the increase of Sn content, and just 7 wt ‰ Sn doping results in a 52% drop in ZT value. The temperature dependence of figure of merit (ZT) of BiSbTe bulks doped with different contents of Ni (a) and Sn (b). BiSbTe without doping Ni/Sn obtained the maximum ZT value of 1.08 at 383 K. The ZT value of BiSbTe bulks decreases more and more seriously with the increasing Ni/Sn content. Only 7 wt ‰ Ni/Sn could result in a 32%/52% declination to the maximum ZT value (ZT max). Image 1 • Quantitative characterization of the effect of Ni/Sn on TE properties of BiSbTe polycrystalline bulks. • Revelation of the mechanism of the influence of Ni/Sn on TE properties of BiSbTe polycrystalline bulks. • Providing beneficial reference related to Ni/Sn diffusion into TE legs for device designers and researchers. [ABSTRACT FROM AUTHOR]

Fe 3 Si 0.7 Al 0.3 @SiO 2 core–shell particles and Fe 3 Si/Al 2 O 3 soft magnetic composite core have been synthesized via a modified stöber method combined with following high temperature sintering process. Most of conductive Fe 3 Si 0.7 Al 0.3 particles could be uniformly coated by insulating SiO 2 using the modified stöber method. The Fe 3 Si 0.7 Al 0.3 @SiO 2 core–shell particles exhibited good soft magnetic properties with low coercivity and high saturation magnetization. The reaction 4Al+3SiO 2 =2α-Al 2 O 3 +3Si took place during the sintering process. As a result the new Fe 3 Si/Al 2 O 3 composite was formed. The Fe 3 Si/Al 2 O 3 composite core displayed more excellent soft magnetic properties, better frequency stability at high frequencies, much higher electrical resistivity and lower core loss than the pure Fe 3 Si 0.7 Al 0.3 core. The method of introducing insulating layers surrounding magnetic particles provides a promising route to develop new and high compact soft magnetic materials with good magnetic and electric properties. [ABSTRACT FROM AUTHOR]

Introduction of porous structure is a feasible and promising method for improving thermoelectric performances for thermoelectric materials. Meanwhile, the uniformity of pores distribution plays a decisive role in the objective evaluation of thermoelectric properties for porous structures. In this work, extremely uniform porous structures in p-type Bi 0.4 Sb 1.6 Te 3 bulks were obtained by pre-mixing with NH 4 HCO 3 combined with resistance pressing sintering (RPS) process. The thermoelectric performance was obviously affected by the porous structure. The increasing porosity resulted in a significant decrease in electrical and thermal conductivity. It was inspiring that the reduction of thermal conductivity could compensate for the deterioration of electrical conductivity, leading to the enhancement in ZT value. The maximum ZT value of 1.11 was obtained for the sample prepared by pre-mixing with 5 ​wt % NH 4 HCO 3 at 343 ​K, which was 20% higher than that of the fully dense sample. Finally, the advantages on the homogeneity of pores, thermoelectric properties and mechanical properties of the sample prepared by this method are confirmed through comparing with the sample prepared without NH 4 HCO 3 , when their relative densities both are 90%. The NH 4 HCO 3 content dependence of thermoelectric figure of merit (ZT) of the Bi 0.4 Sb 1.6 Te 3 bulks (a); The NH 4 HCO 3 content dependence of the Vickers Hardness of the Bi 0.4 Sb 1.6 Te 3 bulks(b).The maximum ZT value of 1.11 can be obtained for the sample pre-mixed with 5 ​wt % NH 4 HCO 3 at 343 ​K, which is 20% higher than that of 0.92 of the sample without pre-mixing with NH 4 HCO 3. Though the Vickers Hardness of bulks decreases from 51.71 to 40.8 HV continuously with the increase of NH 4 HCO 3 content from 0 to 13 ​wt %, it is still far higher than that of 21.35 HV of the zone melting sample. Image 1 • Extremely uniform porous structures in p-type Bi 0.4 Sb 1.6 Te 3 bulks were obtained by pre-mixing with NH 4 HCO 3. • The homogeneity of the sample was confirmed by simulation and experiment. • The maximum ZT value was 20% higher than that of the fully dense one. [ABSTRACT FROM AUTHOR]