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

The thermopower (S) and electrical conductivity (σ) in conventional semiconductors are coupled adversely through the carriers' density (n) making it difficult to achieve meaningful simultaneous improvements in both electronic properties through doping and/or substitutional chemistry. Here, we demonstrate the effectiveness of coherently embedded full-Heusler (FH) quantum dots (QDs) in tailoring the density, mobility, and effective mass of charge carriers in the n-type Ti(0.1)Zr(0.9)NiSn half-Heusler matrix. We propose that the embedded FH QD forms a potential barrier at the interface with the matrix due to the offset of their conduction band minima. This potential barrier discriminates existing charge carriers from the conduction band of the matrix with respect to their relative energy leading to simultaneous large enhancements of the thermopower (up to 200%) and carrier mobility (up to 43%) of the resulting Ti(0.1)Zr(0.9)Ni(1+x)Sn nanocomposites. The improvement in S with increasing mole fraction of the FH-QDs arises from a drastic reduction (up to 250%) in the effective carrier density coupled with an increase in the carrier's effective mass (m*), whereas the surprising enhancement in the mobility (μ) is attributed to an increase in the carrier's relaxation time (τ). This strategy to manipulate the transport behavior of existing ensembles of charge carriers within a bulk semiconductor using QDs is very promising and could pave the way to a new generation of high figure of merit thermoelectric materials.

Surfactant-free Co 3 O 4 nanostructures with various particle size ranges were synthesized via the solution combustion method using cobalt nitrate solution as a cobalt precursor and urea as a combustion fuel.Control over average particles size range was achieved by tuning the reaction ignition temperature between 300 C and 800 C. X-ray diffraction (XRD) and helium gas pycnometry indicated the formation of single phase Co 3 O 4 nanoparticles with a spinel structure. Transmission electron microscopy (TEM) studies revealed an increase of the size range from 5-8 nm to 200-400 nm for Co 3 O 4 nanoparticles synthesized at 300 C and 800 C, respectively. The corresponding decrease in the specific surface area from 39 m 2 g À1 to $2 m 2 g À1 was confirmed by gas adsorption analysis using BET techniques. Magnetic susceptibility measurements revealed a dominant antiferromagnetic (AFM) ordering and the Néel temperature decreases with a decreasing average particle size range from 31 K (200-400 nm) to 25 K (5-18 nm). Interestingly, effective magnetic moments (ranging from 4.12 m B to 6.16 m B ) substantially larger than the value of 3.9 m B expected for Co 2+ ions in the normal spinel structure of Co 3 O 4 were extracted from the inverse susceptibility data. This finding was rationalized by taking into account the disordered distribution of Co 2+ and Co 3+ ions in the Co 3 O 4 inverse spinel structures ([(Co 2+ ) 1Àx (Co 3+ ) x ] tet [(Co 2+ ) x (Co 3+ ) 2Àx ] oct O 4 ) where the inversion degree (x) depends on the synthesis temperature. Transport measurements using hot pressed pellets of Co 3 O 4 nanoparticles indicated p-type semiconducting behavior and drastic reductions in the thermal conductivity with decreasing average particle size.