Yaniv Gelbstein

Half-Heusler TiCoSb is a promising thermoelectric material due to its mechanical robustness and thermal stability, but its efficiency is constrained by high lattice thermal conductivity. This study investigates single and double alloying at the Co site. Samples of TiFe0.2Co0.8Sb and TiCo0.8Ni0.2Sb were produced by arc melting and hot pressing with additional prolonged heat treatments at 873 K. Additionally, double-alloyed TiFexCo1−2xNixSb were produced with x = 0, 0.1, 0.2, 0.3, and 0.4. All samples were tested for their microstructure and thermoelectric properties. Single-alloyed samples with 20 at % Fe or Ni showed significant enhancement in thermoelectric properties, especially electrical conductivity—an order of magnitude higher than pristine TiCoSb—while reducing thermal conductivity by nearly 50%. After prolonged heat treatments at 873 K, these samples tended to oxidize. The CoSb metallic phase was formed in both alloys, indicating that CoSb plays a key role in limiting performance, highlighting the need for a controlled low-oxygen environment. Fe-alloyed samples exhibited stable lamellar structures that preserved low thermal conductivity. With further optimization of the doping strategy, these samples can achieve higher thermoelectric efficiency. Double-alloyed samples, Ti(FexCo1−2xNix)Sb, (0 ≤ x ≤ 0.4), formed a primary single-phase half-Heusler structure with a lattice parameter that increased with the alloying content and secondary phases such as Co, CoSb, and (Ti, Fe)Sb. Double alloying effectively reduced thermal conductivity due to enhanced phonon scattering. The TiFe0.4Co0.2Ni0.4Sb sample provides a promising baseline for advanced doping strategies, with strong potential for substantial ZT enhancement.

Optimizing the electronic transport properties of thermoelectric compounds is commonly achieved by either donor or acceptor atom doping to increase the conduction of the appropriate carrier type, electrons or holes, respectively. Enhancing carrier mobility and carrier concentration will both lead to optimized electronic properties. In this work the effect of various dopants on the electronic properties of TiNiSn was explored, by modeling the doping of an ideal compound on the Ti-sublattice with acceptor or donor elements. Using ab initio DFT calculations and a set of analytical expressions of transport properties, the temperature dependencies of the electronic properties were calculated, to examine possible n-type or p-type dopants to be used in further experimental studies.

Solid oxide fuel cells are characterized by a high efficiency for converting chemical energy into electricity and fuel flexibility. This research work focuses on developing durable and efficient anodes for solid oxide fuel cells (SOFCs) based on exsolving nickel from the perovskite structure. A-site-deficient La- and Ni-doped strontium titanates (La_0.2Sr_0.7Ti_0.95Ni_0.05O_3−δ, LSTN) were synthesized using four different techniques and mixed with Ce_0.8Gd_0.2O_2−δ (GDC) to form the SOFC anode. The synthesis routes of interest for comparison included solid-state, sol-gel, hydrothermal, and co-precipitation methods. LSTN powders were characterized via XRD, SEM, TPR, BET and XPS. In situ XRD during reduction was measured and the reduced powders were analyzed using TEM. The impact of synthesis route on SOFC performance was investigated. All samples were highly durable when kept at 0.5 V for 48 h at 800 °C with H₂ fuel. Interestingly, the best performance was observed for the cell with the LSTN anode prepared via co-precipitation, while the conventional solid-state synthesis method only achieved the second-best results.

Most high-performance thermoelectric materials require either expensive, rare, or toxic elements. By doping TiNiSn, a low-cost, abundant thermoelectric compound, with copper as an n-type donor, some optimization can be performed for such materials. Ti(Ni_1-xCu_x)Sn was synthesized by arc melting followed by heat treatment and hot pressing. The resulting material was analyzed for its phases using XRD and SEM and its transport properties. Cu undoped and 0.05/0.1% doped samples showed no additional phases in addition to the matrix half-Heusler phase, while the 1% copper doping initiated some Ti₆Sn₅ and Ti₅Sn₃ precipitation. The transport properties showed that copper acts as an n-type donor while also lowing the lattice thermal conductivity of the materials. the sample containing 0.1% copper showed the best figure of merit, ZT, with a maximal value of 0.75 and an average value of 0.5 through 325–750 K showing a 125% improvement over the undoped sample of TiNiSn.

Diamond offers great promise as a solution to some of the limitations of current state of the art semiconductor technologies. Yet, significant challenges associated with the doping process remain a primary impediment to the development of diamond-based electronic devices. At present, it is unclear which simple measurement methods are needed to evaluate the diamond doping process. We propose non-destructive inspection methods for evaluating the polycrystalline chemical vapor deposition (CVD) diamond doping process, by analyzing the wettability, optical absorption, photoluminescence emission spectroscopy and atmospheric scanning electron microscope (Air-SEM) tests. Our results show that the properties of the measured samples are distinctly changed due to the presence of the doping elements, thereby confirming the effectiveness of these non-destructive methods for the diamond production industry.