High-ZT Due to the Influence of Copper in Ti(NiCu)Sn.

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(NiCu)Sn was synthesized by arc melting followed by heat treatment and hot pressing.

Alloying effect on the lattice thermal conductivity of MNiSn half-Heusler alloys.

The lattice thermal conductivity of MNiSn (M = Ti, Zr, Hf) half-Heusler (HH) alloys was studied. DFT calculations were used for the calculation of the material physical properties. A combination of the Slack model and Klemens analytical alloying model was used to simulate the lattice thermal conductivity as a function of composition and temperature.

The Thermo-Mechanical Response of GeTe under Compression.

Thermoelectric generators (TEGs) are devices capable of transforming heat energy into electricity and vice versa. Although TEGs are known and have been in use for around five decades, they are implemented in only a limited range of applications, mainly extraterrestrial applications. This is due to their low technical readiness level (TRL) for widespread use, which is only at levels of 3-5 approaching laboratory prototypes.

Phase separation in bismuth doped MgSiGe thermoelectric alloy.

Phase separation by the spinodal decomposition or nucleation and growth mechanisms is an established method for the generation of thermodynamically stable sub-micron features, capable of both reducing the lattice thermal conductivity, , and stabilizing its value, while obtaining high and stable thermoelectric (TE) figure of merit values during practical applications. In the Mg(Si,Sn,Ge) class of TE materials, a miscibility gap and a thermodynamic tendency of phase separation were reported in the MgSi-MgSn quasi-binary section of the ternary phase diagram, capable of enhancing and stabilizing the TE performance, by minimization. Yet, no such tendency was ever reported for the MgSi-MgGe quasi-binary system, prohibiting the fulfillment of its TE potential.

The Initial Oxidation of HfNiSn Half-Heusler Alloy by Oxygen and Water Vapor.

The MNiSn (M = Ti, Zr, Hf) -type semiconductor half-Heusler alloys are leading candidates for the use as highly efficient waste heat recovery devices at elevated temperatures. For practical applications, it is crucial to consider also the environmental stability of the alloys at working conditions, and therefore it is required to characterize and understand their oxidation behavior. This work is focused on studying the surface composition and the initial oxidation of HfNiSn alloy by oxygen and water vapor at room temperature and at 1000 K by utilizing X-ray photoelectron spectroscopy.

Phase Stability of Nanocrystalline Grains of Rare-Earth Oxides (SmO and EuO) Confined in Magnesia (MgO) Matrix.

Rare-earth (RE) oxides are important in myriad fields, including metallurgy, catalysis, and ceramics. However, the phase diagram of RE oxides in the nanoscale might differ from the phase diagrams for bulk, thus attracting attention nowadays. We suggest that grain size in the nanoscale also determines the obtained crystallographic phase along with temperature and pressure.

Thermoelectric transport properties of (TiAl)NiSn half-Heusler alloy.

The influence of Al on the thermoelectric properties of the half-Heusler (HH) TiNiSn compound is reported. The research combined ab initio Density Functional Theory (DFT) calculations with experimental microstructure evaluation and measurements of the transport properties up to 750 K. It is shown that Al addition to the Ti sub-lattice results in an increase of the absolute value of the Seebeck coefficient and electrical resistivity in polycrystalline TiNiSn, while preserving the n-type behavior of the ternary compound, in addition to a significant reduction of the thermal conductivity.

The Initial Stage in Oxidation of ZrNiSn (Half Heusler) Alloy by Oxygen.

The MNiSn (M = Ti; Zr; Hf); half-Heusler semiconducting alloys have a high potential for use as -type thermoelectric materials at elevated temperatures (~1000 K). The alloys' durability is crucial for their commercial handling and use, and therefore it is required to characterize their surface oxidation behavior and stability at the working temperature. X-ray photoelectron spectroscopy was utilized to study the surface composition and oxidation of the ZrNiSn alloy at room and elevated temperatures.

Al solubility in (TiAl)NiSn half-Heusler alloy.

Half-Heusler, HH, alloys are widely used n-type materials in thermoelectric applications. Today, there is a shortage in p-type HH based materials, which may have an inherent compatibility with the HH n-type pair. Al is a good candidate as an acceptor doping element for this purpose, and the results on alloying of TiNiSn-based HH with Al are reported in details.

Surface Oxidation of TiNiSn (Half-Heusler) Alloy by Oxygen and Water Vapor.

TiNiSn-based half-Heusler semiconducting compounds have the highest potential as -type thermoelectric materials for the use at elevated temperatures. In order to use these compounds in a thermoelectric module, it is crucial to examine their behaviour at a working temperature (approximately 1000 K) under oxygen and a humid atmosphere. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were utilized to study the surface composition and oxidation of the TiNiSn alloy at elevated temperatures.

Metallurgical and Hydrogen Effects on the Small Punch Tested Mechanical Properties of PH-13-8Mo Stainless Steel.

PH13-8Mo is a precipitation hardened martensitic stainless steel, known for its high strength but also for its high sensitivity to hydrogen embrittlement. Small punch test, SPT (also referred to as the ball punch test, BPT), is a relatively simple and new technique to assess the mechanical properties of samples under biaxial loading conditions. The current study utilizes the unique loading conditions of SPT to investigate the mechanical behavior and fracture prior to and after the hydrogen charging of PH13-8Mo steel.

Applying the general effective media (GEM) approach for analyzing the thermal conductivity of ZrO-8YSZ composites.

Zirconia (ZrO2) and yttria-stabilized-zirconia (YSZ) are known as advanced oxides, widely applied in gas-turbine engines, fuel cells and other applications, requiring controlled thermal conductivity values. In the current research hot-pressed ZrO2-8YSZ composites, were synthesized. The effect of the three apparent phases, 8YSZ, ZrO2 and the pores on the thermal conductivity was analyzed using the general effective media (GEM) approach, while considering their relative amounts and morphology.

Thermoelectric BiTeSe alloys for efficient thermal to electrical energy conversion.

Eco-friendly renewable energy conversion methods are constantly investigated. Thermoelectric devices, directly converting thermal into electrical energy, show high potential for utilizing waste heat into useful electricity. Yet enhancing their efficiency is a challenging task.

Compatibility between Co-Metallized PbTe Thermoelectric Legs and an Ag-Cu-In Brazing Alloy.

In thermoelectric (TE) generators, maximizing the efficiency of conversion of direct heat to electricity requires the reduction of any thermal and electrical contact resistances between the TE legs and the metallic contacts. This requirement is especially challenging in the development of intermediate to high-temperature TE generators. PbTe-based TE materials are known to be highly efficient up to temperatures of around 500 °C; however, only a few practical TE generators based on these materials are currently commercially available.

Internal Nano Voids in Yttria-Stabilised Zirconia (YSZ) Powder.

Porous yttria-stabilised zirconia ceramics have been gaining popularity throughout the years in various fields, such as energy, environment, medicine, etc. Although yttria-stabilised zirconia is a well-studied material, voided yttria-stabilised zirconia powder particles have not been demonstrated yet, and might play an important role in future technology developments. A sol-gel synthesis accompanied by a freeze-drying process is currently being proposed as a method of obtaining sponge-like nano morphology of embedded faceted voids inside yttria-stabilised zirconia particles.

The Mechanical Behavior of HAVAR Foils Using the Small Punch Technique.

Prediction of the mechanical behavior of thin foils (~25 µm) requires special characterization techniques. The current work is focused on the mechanical and microstructural characterization of 25 µm alloy foils following annealing, cold rolling, and subsequent heat treatments, using small punch testing (SPT), X-ray diffraction (XRD), and transmission-scanning electron microscopy (TEM). The SPT technique revealed that the annealed specimens exhibited the largest maximal load to failure and deformation (more than two-fold), compared to the cold rolled and heat treated conditions.

Evaporation-condensation effects on the thermoelectric performance of PbTe-based couples.

In thermoelectric (TE) generators, Carnot efficiency maximization, by increasing the hot side temperature, is required for maximizing the heat to electricity energy conversion. Yet, volatile species sublimation, apparent in many TE material classes including tellurides, selenides, sulfides, silicides and more, limits the hot side temperature to a certain level, depending on the specific composition. In the current research, the TE performance of a PbTe-based couple subjected to a large temperature difference of an extreme hot side temperature of 600 °C and cold side temperature of 60 °C for 456 h was investigated both experimentally and theoretically and was correlated to evaporation-condensation effects in the vicinity of the hot-side temperature.

Highly efficient functional GexPb1-xTe based thermoelectric alloys.

Methods for enhancement of the direct thermal to electrical energy conversion efficiency, upon development of advanced thermoelectric materials, are constantly investigated mainly for efficient implementation of thermoelectric devices in automotive vehicles, for converting the waste heat generated in such engines into useful electrical power and thereby reduction of the fuel consumption and CO2 emission levels. It was recently shown that GeTe based compounds and specifically GeTe-PbTe rich alloys are efficient p-type thermoelectric compositions. In the current research, Bi2Te3 doping and PbTe alloying effects in GexPb1-xTe alloys, subjected to phase separation reactions, were investigated for identifying the phase separation potential for enhancement of the thermoelectric properties beyond a pure alloying effect.