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Ta-doped Ti1-xTaxCoSb (0≤x≤0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900 K. The Ti1-xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1-xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900 K. This value is about ten times larger than that of the undoped TiCoSb compound. [ABSTRACT FROM AUTHOR]

Single phases of SrBi2-χNdχNb2O9 (χ=0, 0.1, 0.2, and 0.4) ceramics were prepared by the solid-state reaction method and studied by dielectric and Raman spectroscopy. The substitution of Nd3+ for Bi3+ induced a dielectric relaxation behavior for SrBi2-χNdχNb2O9 (χ=0.1, 0.2, and 0.4). When χ=0.4, the dielectric response of SrBi1.6Nd0.4Nb2O9 is characteristic of typical relaxor ferroelectrics, which could be attributed to the disorder induced by the Nd3+ substituting for Bi3+ in Bi2O2 layers. The dielectric relaxation of SrBi1.6Nd0.4Nb2O9 was fitted using the Vögel-Fulcher relationship, which indicates that SrBi1.6Nd0.4Nb2O9 is analogous to a spin glass with thermally activated polarization fluctuations above a static freezing temperature. Raman spectra of SrBi2-χNdχNb2O9 ceramics could indicate that the structural distortion of NbO6 octahedron decreases with the increase in Nd content, which results in the decrease in Tm for SrBi2-χNdχNb2O9 ceramics. [ABSTRACT FROM AUTHOR]

Recently, defective three-quarter Heusler compounds MCo1.5Sn (M = Ti, Zr, and Hf) have been reported with interesting crystal structure differing from the traditional half-Heusler and full-Heusler compounds. These defective compounds are metallic ferromagnets, but the detailed correlation between magnetic and electrical transport properties is still unclear. In this study, we dope Cu in ZrCo1.5Sn to dilute the magnetic Co atoms with the purpose of clarifying how the magnetism influences the electrical transport properties in the defective three-quarter Heusler compounds. Significantly lowered ferromagnetic transition temperature and decreased saturated magnetic moment are observed in Cu-doped ZrCo1.5Sn due to the diluted Co atoms. Likewise, in the ferromagnetic phase, the dominant carrier scattering mechanism is changed from spin fluctuation scattering to magnetic impurity scattering. The doped Cu atoms introduce non-bonding states below the valence band maximum, resulting in the appearance of a narrow bandgap around 0.1 eV. Correspondingly, the electric transport behavior in the paramagnetic phase shows a semiconducting character with a negative temperature dependence of resistivity. This study provides further understanding to the correlation between magnetic properties and electrical transport properties in defective Heusler-based compounds. [ABSTRACT FROM AUTHOR]

Diamondlike compound Cu2SnS3 has attracted great attention recently due to its excellent thermoelectric performance and the features of being eco-friendly and low cost. However, the underlying mechanism for its good electrical transports under high carrier concentration range is still not clear. In this work, we synthesized a series of Cu2+xSn1−xS3 (x = 0–0.08) samples. These nonstoichiometric Cu2+xSn1−xS3 samples are polymorph simultaneously crystalizing in the monoclinic, tetragonal, and cubic structures. The characterization on the electrical transports and the analysis on the band structure reveal that the large density-of-states effective mass, high Seebeck coefficient, and high mobility under a high carrier concentration in the Cu2+xSn1−xS3 system are originated from the existence of multiple bands near the edge of the valence band. Likewise, the polymorphic structure has little influence on the electrical transports. A maximum power factor of 12.6 μW cm−1 K−2 at 700 K has been obtained for the nonstoichiometric Cu2.08Sn0.92S3. Combining the low lattice thermal conductivity of these samples, Cu2.08Sn0.92S3 shows a peak dimensionless figure of merit of 0.5 at 700 K. This work is helpful for guiding the future optimization of thermoelectric performance on Cu2SnS3. [ABSTRACT FROM AUTHOR]

TiCoSb-based half-Heusler compounds have been prepared and their thermoelectric properties are studied. By isoelectronic alloying on the Ti site with Zr, although both the thermal conductivity and electrical conductivity are suppressed, the Seebeck coefficient is improved remarkably with a highest value of -420 μV/K for Ti0.5Zr0.5CoSb at 600 K, which provides a larger space to optimize the thermoelectric performance. To further improve the performance of the TiCoSb-based isoelectronic alloy, doping Ni on the Co site was explored. It is found that small amount of Ni doping results in a great increase in the electrical conductivity, still with a relative large Seebeck coefficient. Ti0.6Hf0.4Co0.87Ni0.13Sb sample exhibits a peak power factor of 23.4 μW/cm K2, which is the highest value for n-type TiCoSb-based half-Heusler compounds reported so far. As a result, a maximum dimensionless figure of merit of 0.70 has been achieved at 900 K for Ti0.6Hf0.4Co0.87Ni0.13Sb. [ABSTRACT FROM AUTHOR]

The reproducible forming-free resistive switching (RS) behavior in rare-earth-oxide Gd2O3 polycrystalline thin film was demonstrated. The characteristic of this forming-free RS was similar to that of other forming-necessary binary RS materials except that its initial resistance starts from not the high resistance state (HRS) but the low resistance state (LRS). An ultrahigh resistance switching ratio from HRS to LRS of about six to seven orders of magnitude was achieved at a bias voltage of 0.6 V. Mechanism analysis indicated that the existence of metallic Gd in the Gd2O3 films plays an important role in the forming-free RS performance. Our work provides a novel material with interesting RS behavior, which is beneficial to deepen our understanding of the origin of RS phenomenon. [ABSTRACT FROM AUTHOR]

TiFexCo1-xSb half-Heusler materials with randomly distributed TiO2 particles have been synthesized by arc melting and annealing. Thermoelectric properties were measured in the temperature range of ∼300–850 K. TiCoSb shows n-type conduction, while TiFexCo1-xSb transfers to p-type conduction when x≥0.01. The electrical conductivity of p-type TiFexCo1-xSb increased with increasing Fe content. The maximum Seebeck coefficient reached about 300 μV/K at 850 K for x=0.15. Since Fe powder contained a trace of Fe2O3, a small amount of TiO2 particles formed during the synthesis process. The lattice thermal conductivity dramatically decreased with increasing Fe content, which was mostly caused by the introduction of in situ formed TiO2 particles, as well as the effects of mass fluctuation and strain field fluctuation due to the substitution of Fe to the Co site. The dimensionless figure of merit (ZT=S2σT/κ) was significantly improved over the whole temperature region, and a maximum ZT value of 0.45 has been obtained for the composition of TiFe0.15Co0.85Sb at 850 K. [ABSTRACT FROM AUTHOR]

Synthesis and electrical and thermal transport properties are reported for several filled skutterudite compounds doped with Ni: Ba[sub 0.3]Ni[sub x]Co[sub 4-x]Sb[sub 12] with 0