The natural chalcopyrite mineral CuFeS 2 is a semi-conductor material with potential for thermoelectric applications. This study presents the thermoelectric properties -electrical resistivity ρ, Seebeck coefficient S and thermal conductivity κ -of the substituted on the Cu site and/or sulfur deficiency CuFeS 2 chalcopyrite based series Cu 1-x M x FeS 2-y (M = Mn, Co,Ni, x ≤ 0.05 and y ≤ 0.02). All samples have been densified by Spark Plasma Sintering, allowing proper measurements of S, ρ and κ at high temperature. All compounds show n-type semi-conducting properties with large absolute values of S, from -220 to -340 µV.K -1 . Maximum ZT values up to 0.20 at 623 K were obtained for Cu 0.97 Mn 0.03 FeS 2 and Cu 0.98 Co 0.02 FeS 1.98 . The veracity of Mn for Cu substitution into the structure has been confirmed by EDS analyzes, coupled to electron diffraction within a transmission electron microscope. The latter study demonstrates the existence of twinned domains. The thermal conductivity reaches values as low as κ~1.2 W.m -1 .K -1 at 623 K. Magnetic properties of a Mn substituted sample did not show any significant modification in the magnetic behavior compared to the pristine CuFeS 2 compound. The small negative magnetoresistance observed in CuFeS 2 of about -2% at 5 K in 9 T is degraded in the Mn substituted sample. Cu 0.94 Mn 0.06 FeS 2 in terms of charge, Mn would be then 4+ charged. ZT are given in Fig. 8d, the highest ZT is found for Cu 0.98 Co 0.02 FeS 1.98 with ZT = 0.20 at 623 K. This value is similar with the previously reported Cu 0.94 Co 0.06 FeS 2 . It is found at 623 K that the resistivity and the Seebeck coefficient of Cu 0.98 Co 0.02 FeS 1.98 and Cu 0.94 Co 0.06 FeS 2 were comparable, with │S│= 247 and 240 µV.K -1 and ρ = 0.95 and 1.05 mΩ.cm, respectively.Conclusion SPS process optimization and substitution/deficiency study on the Cu 1-x M x FeS 2-y series with M = Mn, Co, Ni; x ≤ 0.05 and y ≤ 0.02 have been successfully carried out. In these substitutions ranges, the chalcopyrite is formed without significant amount of impurities.Among the three transition metals: Co, Ni and Mn, the solid solution with Mn has been more

A new ternary layered compound In2Ge2Te6, belonging to the hexatellurogermanate family has been synthesized from the reaction of appropriate amounts of the pure elements at high temperature in sealed silica tubes.

Single crystals of the new ternary selenide Ba 0.5 Cr 5 Se 8 were synthesized using a self-flux method in fused silica tubes. This new phase was first considered to crystallize in the usual monoclinic symmetry for pseudo-hollandite compounds. However, single-crystal X-ray diffraction study showed unambiguously that Ba 0.5 Cr 5 Se 8 crystallizes in the P1̅ triclinic space group with cell parameters a = 9.5084(4) Å, b = 7.1788(3) Å, and c = 8.9296(4) Å and α = 89.9979(16)°, β = 104.3958(22)°, γ = 100.8869(17)°, and Z = 2. Bulk samples were prepared by solid-state reaction and sintered using a spark-plasma sintering device. A combination of powder X-ray diffraction and transmission electron microscopy was used to perform structural analysis on spark plasma sintering prepared samples. Ba 0.5 Cr 5 Se 8 orders antiferromagnetically with T N = 58 K and shows a semiconducting behavior with ρ 300K = 0.35 Ω•cm and S 300K = 230 μV•K −1 . A maximum of the Seebeck coefficient of 315 μV•K −1 occurs at 635 K with ρ 635K = 0.14 Ω•cm, while the thermal conductivity remains low and constant at about 0.8 W•m −1 •K −1 from room temperature up to 873 K, leading to a maximum ZT of 0.12 around 800 K. A remarkably large increase of thermal conductivity is observed in the antiferromagnetic state.

The upper critical field is a fundamental measure of the strength of superconductivity in a material. It is also a cornerstone for the realization of superconducting magnet applications. The critical field arises because of the Cooper pair breaking at a limiting field, which is due to the Pauli paramagnetism of the electrons. The maximal possible magnetic field strength for this effect is commonly known as the Pauli paramagnetic limit given as μ 0 H Pauli ≈ 1.86[T/K]•T c for a weakcoupling Bardeen−Schrieffer−Cooper (BCS) superconductor. The violation of this limit is only rarely observed. Exceptions include some low-temperature heavy Fermion and some strongly anisotropic superconductors. Here, we report on the superconductivity at 9.75 K in the centrosymmetric, cubic η-carbidetype compound Nb 4 Rh 2 C 1−δ , with a normalized specific heat jump of ΔC/γT c = 1.64. We find that this material has a remarkably high upper critical field of μ 0 H c2 (0) = 28.5 T, which is exceeding by far its weak-coupling BCS Pauli paramagnetic limit of μ 0 H Pauli = 18.1 T. Determination of the origin and consequences of this effect will represent a significant new direction in the study of critical fields in superconductors.

Chalcogenide semiconducting systems are of growing interest for mid-temperature range (~500 K) thermoelectric applications. In this work, Ge20Te77Se3 glasses were intentionally crystallized by doping with Cu and Bi. These effectively-crystallized materials of composition (Ge20Te77Se3)100−xMx (M = Cu or Bi; x = 5, 10, 15), obtained by vacuum-melting and quenching techniques, were found to have multiple crystalline phases and exhibit increased electrical conductivity due to excess hole concentration. These materials also have ultra-low thermal conductivity, especially the heavily-doped (Ge20Te77Se3)100−xBix (x = 10, 15) samples, which possess lattice thermal conductivity of ~0.7 Wm−1 K−1 at 525 K due to the assumable formation of nano-precipitates rich in Bi, which are effective phonon scatterers. Owing to their high metallic behavior, Cu-doped samples did not manifest as low thermal conductivity as Bi-doped samples. The exceptionally low thermal conductivity of the Bi-doped materials did not, alone, significantly enhance the thermoelectric figure of merit, zT. The attempt to improve the thermoelectric properties by crystallizing the chalcogenide glass compositions by excess doping did not yield power factors comparable with the state of the art thermoelectric materials, as these highly electrically conductive crystallized materials could not retain the characteristic high Seebeck coefficient values of semiconducting telluride glasses.

Ammonia solution etching was carried out on thermally-oxidised cuprous oxide (TO-Cu2O) in photocathode devices for water splitting. The etched devices showed increased photoelectrochemical (PEC) performance compared to the unetched ones...

The crystal structure of single crystalline members of the solid solution series Tl(V 1Àx Cr x ) 5 Se 8 (x = 0-1 and Dx = 0.2) was determined and the magnetic and thermoelectric properties of bulk TlV 5 Se 8 were investigated. All compounds crystallize in the pseudo-hollandite-type structure (C2/m) with a nonlinear increase in the unit cell volume due to a simultaneous increase/decrease in the transition metal distances across the edge/face-sharing octahedra. A slight Tl deficiency was found for single crystalline TlV 5 Se 8 and Tl(V 0.8 Cr 0.2 ) 5 Se 8 as well as for bulk TlV 5 Se 8 according to Rietveld and single crystal structure refinements.The metallic character of bulk TlV 5 Se 8 and its low electrical resistivity compared to poly-and singlecrystalline TlCr 5 Se 8 can probably be associated with this probable Tl deficiency. In TlV 5 Se 8 , anomalies in the low temperature Seebeck coefficient, i.e. a maximum at T B 14 K and two sign changes at T B 47 K and T B 167 K, were found. Bulk TlV 5 Se 8 is a highly frustrated (f = |y|/T N E 42 K) Curie-Weiss paramagnet ordering antiferromagnetically (y = À1287 K) below T N E 31 K with an effective magnetic moment of m = 2.68 m B corresponding to V 3+ . Low-field M(H) measurements revealed the existence of a small ferromagnetic component below T N in bulk TlV 5 Se 8 and, despite the observed spin frustration, no spin glass phase was found in this compound.

The structure of Ba0.5Cr5Se8 has been recently resolved, and its thermoelectric and magnetic properties have been studied. A ZT of 0.12 was found at around 800 K. Here, we report a study on the pseudo-hollandite BaxCr5Se8 solid-solution with 0.5 ≤ x ≤ 0.55 and its thermoelectric and magnetic properties. There is no significant impact either on the cell parameters depending on the cation content or on the magnetic properties. However, thermoelectric properties are radically changed depending on x content. While the low thermal conductivity, around 0.8 W m(-1) K(-1), remains similar for all samples, a respective increase and decrease of the resistivity and the Seebeck coefficient are observed with increasing Ba content. The maximum Seebeck coefficient is found with Ba0.5Cr5Se8 at around 635 K with 315 μV K(-1), and the Seebeck coefficient then decreases and is correlated with an activation of minority charge carriers confirmed by Hall measurements. A similar but steeper behavior is observed for the Ba0.55Cr5Se8 temperature dependence plot at around 573 K. Finally, the best thermoelectric performances are found using the lowest content of Ba, unlike when x tends to 0.55, ZT approaches a tenth of the initial best value. BaxCr5Se8 compounds are antiferromagnetic with TN = 58 K. A large peak in thermal conductivity is observed around the antiferromagnetic transition for all stoichiometry.