Very recent report 1 on observation of superconductivity in Bi 4 O 4 S 3 could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here synthesis of Bi 4 O 4 S 3 at 500 0 C by vacuum encapsulation technique and its basic characterizations. Bi 4 O 4 S 3 is contaminated by small amounts of Bi 2 S 3 and Bi impurities. The majority phase is tetragonal I4/mmm space group with lattice parameters a = 3.9697(2)Å, c = 41.3520(1)Å. Both AC and DC magnetization measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (T c ) of 4.4K. Isothermal magnetization (MH) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H c1 ) at 2K, of the new superconductor is found to be ~15 Oe. The magneto-transport R(T, H) measurements showed a resistive broadening and decrease in T c (ρ=0) to lower temperatures with increasing magnetic field. The extrapolated upper critical field H c2 (0) is ~ 31kOe with a corresponding Ginzburg-Landau coherence length of ~100Å . In the normal state the ρ ~ T 2 is not indicated. Hall resistivity data show non-linear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi 4 O 4 S 3 . On the other hand same temperature heat treated Bi is not superconducting, thus excluding possibility of impurity driven superconductivity in the newly discovered Bi 4 O 4 S 3 superconductor.

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Compositional tailoring enables fine-tuning of thermoelectric (TE) transport parameters by synergistic modulation of electronic and vibrational properties. In the present work, the aspects of compositionally tailored defects have been explored in ZrNiSn-based half-Heusler (HH) TE materials to achieve high TE performance and cost effectiveness in n-type Hffree HH alloys. In off-stoichiometric Ni-rich ZrNi 1+x Sn alloys in a low Ni doping limit (x < 0.1), excess Ni induces defects (Ni/vacancy antisite + interstitials), which tend to cause band structure modification. In addition, the structural similarity of HH and full-Heusler (FH) compounds and formation energetics lead to an intrinsic phase segregation of FH nanoscale precipitates that are coherently dispersed within the ZrNiSn HH matrix as nanoclusters. A consonance was achieved experimentally between these two competing mechanisms for optimal HH composition having both FH precipitates and Ni/vacancy antisite defects in the HH matrix by elevating the sintering temperature up to the solubility limit range of the ZrNiSn system. Defect-mediated optimization of electrical and thermal transport via carrier concentration tuning, energy filtering, and possibly all scale-hierarchical architecture resulted in a maximum ZT ≈ 1.1 at 873 K for the optimized ZrNi 1.03 Sn composition. Our findings highlight the realistic prospect of enhancing TE performance via compositional engineering approach for wide applications of TE.

We report the synthesis, characterization and evaluation of the thermoelectric properties of Cu 3 SbSe 3 with a view to explore its utility as an useful thermoelectric material due to its intrinsically low thermal conductivity. Cu 3 SbSe 3 was synthesized employing a solid state reaction process followed by spark plasma sintering, and the synthesized material was extensively characterized for its phase, composition and structure, which suggested formation of a single-phase. The measured electrical transport properties of Cu 3 SbSe 3 indicated p-type conduction in this material. The electrical transport behavior agrees well with that predicted theoretically using first-principle density-functional theory calculations, employing generalized gradient approximation. The measured thermal conductivity was found to be 0.26 W m À1 K À1 at 550 K, which is the lowest reported thus far for Cu 3 SbSe 3 and is among the lowest for state-of-the-art thermoelectric materials. Despite its ultralow thermal conductivity coupled with a moderate Seebeck coefficient, the calculated value of its thermoelectric figure-of-merit was found to be exceptionally low (<0.1), which was primarily attributed to its low electrical conductivity. Nevertheless, it is argued that Cu 3 SbSe 3 , due its environmentally-friendly constituent elements, ultralow thermal conductivity and moderate thermopower, could be a potentially useful thermoelectric material as the power factor can be favorably tailored by tuning the carrier concentration using suitable metallic dopants.

Despite Hf-free half-Heusler (HH) alloys being currently explored as an important class of cost-effective thermoelectric materials for power generation, owing to their thermal stability coupled with high cost of Hf, their figure-of-merit (ZT) still remains far below unity. We report a state-of-the-art figure-of-merit (ZT) ∼ 1 at 873 K in Hf-free n-type V-doped Zr1–x V x NiSn HH alloy, synthesized employing arc-melting followed by spark plasma sintering. The efficacy of V as a dopant on the Zr-site is evidenced by the enhanced thermoelectric properties realized in this alloy, compared to other reported dopants. This enhancement of ZT is due to the synergistic enhancement in electrical conductivity with a simultaneous decrease in the thermal conductivity, which yields ZT ∼ 1 at 873 K at an optimized composition of Zr0.9V0.1NiSn, which is ∼70% higher than its pristine counterpart and ∼25% higher than the best reported thus far in Hf-free n-type HH alloys. The enhancement of the electrical conductivity is due to the modification of the band structure by suitable tuning of the electronic band gap near the Fermi level, through optimized V-doping in ZrNiSn HH alloys. The reduction in the thermal conductivity has been attributed to the mass fluctuation effects and the substitutional defects caused by V-doping, which results in an abundant scattering of the heat-carrying phonons. The optimized V-doped ZrNiSn HH composition, therefore, strikes a favorable balance between cost and thermoelectric performance, which would go a far way in the realization of a cost-effective (Hf-free) HH based thermoelectric generator for power generation through waste heat recovery.

We report the electrical, magneto transport and specific heat of the layered polycrystalline RECoPO (RE = La, Nd and Sm) samples. These compounds are iso-structural to recently discovered superconductor LaFeAs(O/F). Bulk polycrystalline samples are synthesized by solid state reaction route in an evacuated sealed quartz tube. All these compounds are crystallized in a tetragonal structure with space group P4/nmm. The Cobalt in these compounds is in itinerant state with its paramagnetic moment above 1.

We report the synthesis of thermoelectric compounds, Cu3SbSe3 and Cu3SbSe4, employing the conventional fusion method followed by spark plasma sintering. Their thermoelectric properties indicated that despite its higher thermal conductivity, Cu3SbSe4 exhibited a much larger value of thermoelectric figure-of-merit as compared to Cu3SbSe3, which is primarily due to its higher electrical conductivity. The thermoelectric compatibility factor of Cu3SbSe4 was found to be ∼1.2 as compared to 0.2 V−1 for Cu3SbSe3 at 550 K. The results of the mechanical properties of these two compounds indicated that their microhardness and fracture toughness values were far superior to the other competing state-of-the-art thermoelectric materials.