Thermoelectric figure of merit, ZT, exceeding 2.6 at 850 K and copper electromigration inhibition have been demonstrated in indium modified Cu2Se.

PbBiSe, the selenium analogue of heyrovsyite, crystallizes in the orthorhombic space group Cmcm (#63) with a = 4.257(1) Å, b = 14.105(3) Å, and c = 32.412(7) Å at 300 K. Its crystal structure consists of two NaCl-type layers, A and B, with equal thickness, N = N = 7, where N is the number of edge-sharing [Pb/Bi]Se octahedra along the central diagonal. In the crystal structure, adjacent layers are arranged along the c-axis such that bridging bicapped trigonal prisms, PbSe, are located on a pseudomirror plane parallel to (001). Therefore, PbBiSe corresponds to a L member of the lillianite homologous series. Electronic transport measurements indicate that the compound is a heavily doped narrow band gap n-type semiconductor, with electrical conductivity and thermopower values of 350 S/cm and -53 μV/K at 300 K. Interestingly, the compound exhibits a moderately low thermal conductivity, ∼1.1 W/mK, in the whole temperature range, owing to its complex crystal structure, which enables strong phonon scattering at the twin boundaries between adjacent NaCl-type layers A and B. The dimensionless figure of merit, ZT, increases with temperature to 0.25 at 673 K.

Single-phase polycrystalline powders of SrSb HfSe ( x = 0, 0.005, 0.01), a new member of the chalcogenide perovskites, were synthesized using a combination of high temperature solid-state reaction and mechanical alloying approaches. Structural analysis using single-crystal as well as powder X-ray diffraction revealed that the synthesized materials are isostructural with SrZrSe, crystallizing in the orthorhombic space group Pnma (#62) with lattice parameters a = 8.901(2) Å; b = 3.943(1) Å; c = 14.480(3) Å; and Z = 4 for the x = 0 composition. Thermal conductivity data of SrHfSe revealed low values ranging from 0.9 to 1.3 W m K from 300 to 700 K, which is further lowered to 0.77 W m K by doping with 1 mol % Sb for Sr. Electronic property measurements indicate that the compound is quite insulating with an electrical conductivity of 2.9 S/cm at 873 K, which was improved to 6.7 S/cm by 0.5 mol % Sb doping. Thermopower data revealed that SrHfSe is a p-type semiconductor with thermopower values reaching a maximum of 287 μV/K at 873 K for the 1.0 mol % Sb sample. The optical band gap of SrSb HfSe samples, as determined by density functional theory calculations and the diffuse reflectance method, is ∼1.00 eV and increases with Sb concentration to 1.15 eV. Careful analysis of the partial densities of states (PDOS) indicates that the band gap in SrHfSe is essentially determined by the Se-4p and Hf-5d orbitals with little to no contribution from Sr atoms. Typically, band edges of p- and d-character are a good indication of potentially strong absorption coefficient due to the high density of states of the localized p and d orbitals. This points to potential application of SrHfSe as absorbing layer in photovoltaic devices.

The use of template nanostructures for the creation of photovoltaic and thermoelectric semiconductors is becoming a quickly expanding synthesis strategy. In this work we report a simple two-step process enabling the formation of ternary CuAgSe nanoplatelets with a great degree of control over the composition and shape. Starting with hexagonal nanoplatelets of cubic Cu2-xSe, ternary CuAgSe nanoplatelets were generated through a rapid ion exchange reaction at 300 K using AgNO3 solution. The Cu2-xSe nanoplatelet template and the final CuAgSe nanoplatelets were analyzed by electron microscopy and X-ray diffraction (XRD). It was found that both the low temperature pseudotetragonal and the high temperature cubic forms of CuAgSe phase were created while maintaining the morphology of the Cu2-xSe nanoplatelet template. Thermal and electronic transport measurements of hot-pressed pellets of the synthesized CuAgSe nanoplatelets showed a drastic reduction in the thermal conductivity and a sharp transition from n-type (S = -45 μV K(-1)) to p-type (S = +200 μV K(-1)) semiconducting behavior upon heating above the structural transition from the low temperature orthorhombic to the high temperature super-ionic cubic phase. This simple reaction process utilizing a template nanostructure matrix represents an energy efficient, cost-efficient, and versatile strategy to create interesting materials with lower defect density and superior thermoelectric performance.

Single-phase samples of the solid-solution series FeSb2–x In x Se4 (0 ≤ x ≤ 0.25) were synthesized using solid-state reaction of the elements to probe the effect of electronic structure engineering on the magnetic behavior of the p-type semiconductor, FeSb2Se4. Powder X-ray diffraction data suggest that all samples are isostructural with FeSb2Se4. Rietveld refinements of the distribution of In atoms at various metal positions indicate a preferential substitution of Sb at the M1­(4i) position within the magnetic layer A for In concentration up to x = 0.1. FeSb2–x In x Se4 compositions with higher In content show the distribution of In atoms at all metal positions, except for the M3­(2d), which is fully occupied by Fe atoms. Interestingly, the ordering of Fe atoms within the crystal structure of FeSb2–x In x Se4 remains essentially unaffected by the degree of substitution (x values) and is comparable to the distribution of Fe atoms reported in FeSb2Se4. X-ray photoelectron spectroscopy confirms the oxidation states of various metal atoms In­(+3), Sb­(+3), Fe­(+2) in the structure. Electronic transport properties indicate p-type semiconducting behavior for all samples. The electrical conductivity above 300 K first increases with In content, reaches the maximum value for x = 0.1, then decreases with further increase in In content. A reverse trend is observed for the thermopower. All samples show drastically low thermal conductivity with room temperature values ranging from 0.45 Wm–1 K–1 for x = 0 to 0.27 Wm–1 K–1 for the sample with x = 0.25. Magnetic susceptibility data suggest ferromagnetic-like behavior from 2–300 K for all samples. The magnitude of the magnetic susceptibility rapidly increases with In content, reaches a maximum for x = 0.1, and marginally decreases with further increase in In concentration. The observed surprising change in the magnetic and electronic behavior of samples with high In content (x > 0.1) is rationalized using the concept of antiferromagnetic scattering of charge carriers at the interfaces between overlapping bound magnetic polarons from adjacent layers A and B.

The Anatase phase of Titania (TiO 2 ) in nanocrystalline form is a well known photocatalyst. Photocatalysts are commercially used to accelerate photoreactions and increase photovoltaic efficiency such as in solar cells. This study investigates the in-flight synthesis of Titania and its doping into a Silicon matrix resulting in a catalyst-dispersed coating. A liquid precursor of Titanium Isopropoxide and ethanol was coaxially fed into the plasma gun to form Titania nanoparticles, while Silicon powder was externally injected downstream. Coatings of 75-150 lm thick were deposited onto flat coupons. Further, Silicon powder was alloyed with aluminum to promote crystallization and reduce the amorphous phase in the Silicon matrix. Dense coatings containing nano-Titania particles were observed under electron microscope. X-ray diffraction showed that both the Rutile and Anatase phases of the Titania exist. The influence of process parameters and aluminum alloying on the microstructure evolution of the doped coatings is analyzed and presented.

The electrochemical behavior of composite electrodes used in Li ion batteries is influenced by factors such as microstructural characteristics (e.g. particle size, crystallinity, porosity etc.) and composition. For optimal performance of electrodes these factors are of utmost concern and serve as motivation for research in this field. In this report, we investigated LiFePO4 films synthesized by a novel plasma spray deposition method, which has capability for direct deposition of LiFePO4 films with carbon. This enables electrode characterizations to be carried out at the film level, without recourse to steps involving powder material handling. In this report microstructure and electrochemical properties of LiFePO4 films were investigated to elucidate their unique characteristics. Our studies show that factors such as porosity and microstructure of the films affect the electrochemical properties. The mechanical compression and thermal annealing experiments are shown to affect the electrochemical characteristics of LiFePO4 films. We show that annealing treatment leads to a drastic improvement in impedance and charge-discharge capacities for the LiFePO4 films. These treatments could serve to improve the electrode properties of porous film based materials for Li ion batteries and help us develop new film based materials for energy storage applications.

This study investigates the in-flight synthesis of titania and its doping into a silicon matrix resulting in a catalyst dispersed coating. In the experiments, a liquid precursor of titanium isopropoxide and ethanol is fed into a plasma gun forming a stream of titania nanoparticles into which a silicon-aluminum powder mixture is injected. The influence of process parameters and aluminum alloying on the microstructure and phase composition of the titania-doped silicon coatings is analyzed and presented.