In the past two decades, many studies have focused on the effects of electropositive guest fillers on the electrical and thermal transport properties in CoSb3-based skutterudites. Recently, some electronegative elements such as S, Se, Cl, and Br have been filled into the voids in CoSb3 with a small amount of n-type dopant Te on the Sb sites. In this report, self-charge compensated skutterudites SeyCo4Sb12–xSex (0 < x + y < 0.9) with Se occupying two different atomic sites have been fabricated by a traditional melting–annealing process combined with a spark plasma sintering method. Phase purity was determined by X-ray diffraction, and the microstructures were examined by scanning electron microscopy. The temperature dependencies of the electrical and thermal transport properties were characterized. Se could enter both the void and Sb sites in CoSb3 with a solubility limit around 0.6. The Se content has little effect on bandgap. Similar to Ga dual-site occupied GayCo4Sb12–xGax (y = 2x), a typical semiconducting electrical property with a low carrier concentration as well as a large Seebeck coefficient is observed. A correlation between the large Seebeck coefficient and the carrier scattering mechanism has been proposed. In addition, a largely reduced room temperature lattice thermal conductivity is obtained with a minimum value of 2.1 Wm–1 K–1 for Se0.2Co4Sb11.6Se0.4. The effects of Se on lattice thermal conductivity and filler resonant frequency are discussed.Keywords: compound defects; electronegative filler; lattice thermal conductivity; Se; skutterudite; thermoelectric;

•We developed Ni material as the electrode for skutterudite thermoelement.•The Ni electrode had a good adhesion with the Ti barrier layer and skutterudites.•For Ni/Skutterudite interface there was no inter-diffusion below 200 °C.•For Ti/Ni interface there were three intermetallic compounds above 500 °C.•The Ti/Ni and Ni/SKD interfaces showed satisfied stability after aging and thermal shock.Ni/Ti/SKD/Ni (SKD: skutterudite) thermoelements were fabricated by spark plasma sintering and electroplating procedures. The interfacial stability was evaluated by long-term isothermal aging and multi-round thermal shock tests. The interfacial diffusion at Ni/SKD and Ni/Ti in the thermoelements during high temperature aging up to 15 days was systematically studied by scanning electron microscopy with elemental distribution. The growth kinetics of the intermetallic compounds was analyzed, and the coefficients of the intermetallic compound growth rate were calculated. For the Ni/SKD interface, there was no inter-diffusion at temperatures below 200 °C. However, three intermetallic compound layers for the Ti/Ni interface were confirmed to be TiNi3, TiNi and Ti2Ni sequentially from the Ni side to the Ti side at temperatures above 500 °C, leading to an interfacial structure of Ti/Ti2Ni/TiNi/TiNi3/Ni. All interfaces maintained good bonding strength after long-term isothermal aging and multi-round thermal shock tests. The experimental data demonstrated that Ni is an ideal candidate as the electrode of skutterudite thermoelements at both the hot and cold sides.

Sr0.29CoO2 crystals have been successfully prepared by a low temperature ion exchange from layered NaxCoO2, and it is isomorphic to its precursor NaxCoO2 with a layered triangular structure. The thermoelectric properties of Sr0.29CoO2 crystal were measured in the temperature of 2.5–773 K. A transition has been exhibited in the resistivity, Seebeck coefficient and carrier concentration at approximately 75 K. The resistivity, Seebeck coefficient and power factor increase with increasing temperature, and reach the values of 2.78 mΩ cm, 171 μV/K and 7.1 × 10−4 W m−1 K−2 at 773 K, respectively.

Highly dense n-type Bi2Te3-based thermoelectric materials dispersed with x vol.% γ-Al2O3 nanoparticles (x = 0, 0.4, 1.0, 1.5) were fabricated by spark plasma sintering method. The effects of γ-Al2O3 addition on microstructure and the thermoelectric properties were studied. It was found that γ-Al2O3 nanoparticles locate both at grain boundaries and inside Bi2Se0.3Te2.7 grains. The nanoparticles induce both potential barrier scattering effect and additional phonon scattering effect, which simultaneously enhance the Seebeck coefficient and reduce the lattice thermal conductivity of the nanocomposites in the measured temperature range of 300–500 K, respectively. The maximum dimensionless figure of merit (ZTmax) reaches up to 0.99 for the sample with x = 1.0 at 400 K, which is 35% improvement over the Bi2Te3-based matrix. More importantly, the average ZT value of the sample increases from 0.65 to 0.91 in the temperature range 300–500 K, making the nanocomposites much more applicable in cooling and power generation.Research highlights► n-Type γ-Al2O3-dispersed Bi2Se0.3Te2.7 nanocomposites were fabricated by spark plasma sintering. ► The nanophase distribute at grain boundary and inside the matrix. ► The introduction of γ-Al2O3 nanoparticles simultaneously enhances the Seebeck coefficient and reduces the thermal conductivity. ► The ZTmax reaches up to 0.99 for the sample with x = 1.0, being 35% improvement over the matrix.

A novel process has been introduced to synthesize an alternately stacked Ca3Co4O9/γ-Na0.66CoO2 composite with nanostructured layers and high c-axis orientation. The thickness of each layer is about 60–100 nm. The maximum power factor at 1000 K is 6.3 × 10−4 W m−1 K2, which is about 50% higher than that of conventional Ca3Co4O9 ceramics.

The effects of ZrO2 nano particles addition to the ZrNiSn matrix on the thermoelectric properties were investigated. Thermal conductivity, Seebeck coefficient and electrical resistivity were measured. The X-ray powder diffraction, EPMA and FESEM were adopted for the microstructure characterization of the composites. The transport properties are mainly discussed with regard to the microstructures. The lattice contribution to thermal conductivity can be reduced by addition of small amount of ZrO2 nano particles, which serve as additional phonon-scattering centers. The dimensionless figure of merit ZT of ZrNiSn half-Heusler thermoelectric material was improved by introducing ZrO2 nano particles.

A layered cobaltite BaxCoO2 (x = 0.19, 0.28, 0.30, 0.33) was synthesized by an ion exchange technique from the layered NaxCoO2 precursors. The phase composition and physical properties were investigated. BaxCoO2 is isomorphic to the precursor NaxCoO2. The magnetic susceptibility of BaxCoO2 decreases with increasing barium content and shows a Curie–Weiss-like behavior at temperatures above 50 K. The resistivity is sensitive to the barium content. As the barium content increases from 0.19 to 0.33, a crossover from a semiconducting behavior to a metallic behavior was observed. The Seebeck coefficient of BaxCoO2 is insensitive to the barium content due to the tradeoff effect between the carrier concentration and the Co4+ content, while the thermal conductivity increases with the increasing barium content from 0.19 to 0.33 owing to the ordered state of Ba ions between the CoO2 layers.