Synthesis, structure and properties of TiCoSb-based half-Heusler thermoelectrics

Half-Heusler compounds have gained significant attention due to their potential as thermoelectric materials for high temperature waste heat recovery. They are characterised by a favourable combination of large Seebeck coefficients and low electrical resistivities, leading to large power factors but also have relatively large thermal conductivities, which limit the thermoelectric figure of merit ZT to values near one. TiCoSb-based half Heusler compounds are considered as promising p-type thermoelectric materials, however, studies on these compounds are fewer in number as compared to other half Heusler systems. For this reason, three novel series of TiCoSb-based half Heuslers were prepared and studied in this thesis. A detailed investigation of the Ti1-xVxCoSb1-xSnx half Heusler alloys is provided in Chapter 3. This study revealed that V and Sn co-substitution improves the high-temperature thermal stability of these materials. Thereafter, in Chapter 4, attempts were made to p-type dope these materials by substitution of Fe on the Co site. Surprisingly, electrical property measurements revealed n-type conduction for a number of the investigated samples. Thus, this study provides the first experimental observation of an unexpected change in carrier type in half Heusler compounds. The last results chapter of this thesis explores TiCoSb-based nanocomposites. Five series of compositions (TiCoSb)1-x(TiM2Sn)x (M2 = Fe2, FeCo, Co2, CoNi, Ni2) were prepared. In which, these compounds are expected to segregate into half Heusler and full Heusler phases. All samples were prepared using solid-state reactions. The synthesised materials were structurally characterised using X-ray and neutron powder diffraction. Complementary scanning and transmission electron microscopy was performed to probe the microstructure and compositional homogeneity of the investigated samples. This has allowed, coupled with measuring the thermoelectric properties, the structure-property relations to be established

Thermoelectric properties and high-temperature stability of the Ti_1-xV_xCoSb_1-xSn_x half-Heusler alloys

The thermoelectric properties and high-temperature stability of the Ti1−xVxCoSb1−xSnx solid solution have been investigated.</p

Ordered arrays of gold nanoparticles crosslinked by dithioacetate linkers for molecular devices

The final performance of a molecular electronic device is determined by the chemical structure of the molecular wires used in its assembly. Molecular place-exchange was used to incorporate di-thioacetate terminated molecules into ordered arrays of dodecanethiol capped gold nanoparticles. X-Ray photoelectron spectroscopy confirmed successful molecular replacement. Room-temperature molecular conductance of a statistically large number of devices reveals that conductance is enhanced by up to two orders of magnitude for the di-thioacetate terminated molecules. Density functional theory transport calculations were performed on five different configurations of the di-thioacetate molecules between gold electrodes, and the calculated average conductance values are in good agreement with the experimentally-observed conductance trend. Our findings highlight important cooperative effects of bridging neighboring gold nanoparticles and choice of appropriate molecular wires when designing devices for efficient transport

Ordered arrays of gold nanoparticles crosslinked by dithioacetate linkers for molecular devices

Enhanced electrical conductance of the self-assembled monolayers upon molecular exchange with dithioacetate-terminating molecules.</jats:p

Chlorosulfuric acid-assisted production of functional 2D materials

10.1038/s41699-021-00215-2npj 2D Materials and Applications513