Technische Universität Wien

High-performance thermoelectric (TE) materials near room temperature are crucial for cooling and energy harvesting applications. This study reports the outstanding thermoelectric performance of p-type Mn-doped Fe₂VAl Heusler alloy thin films, specifically Fe₂V_0.8Mn_0.2Al, prepared using magnetron sputtering. These films were deposited on insulating oxide substrates to eliminate any spurious contributions from the substrate. Large p-type Seebeck coefficients (S) have been observed for all films, revealing a maximum power factor of 4.26 mWK^-2m^-1 at 300 K. This study revealed thickness-dependent thermoelectric properties, with the highest power factor achieved in the 500 nm film. Films with d = 300 nm and 500 nm exhibit weak ferromagnetism. Hall resistivity measurements evidence an anomalous Hall effect (AHE) for the 300 nm and 500 nm samples. The AHE is strongest for the 500 nm film, consistent with a magnetic enhancement of the Seebeck coefficient and power factor. Additionally, we synthesized Al-rich p-type Fe₂V_0.9Mn_0.1Al_1.5 thin films at room temperature, 200°C, 400°C, and 600°C. The film deposited at 600°C exhibits an exceptional figure of merit ZT _appr ~0.8 and a power factor of 6.7 mW·K^-2·m^-1 at room temperature, which are respectively, 4 times and 1.5 times larger than the best values ever reported for any bulk or thin film p-type Fe₂VAl-based material.

Fundamentally understanding lattice dynamics and thermal transport behavior in liquid‐like, partially occupied compounds remains a long‐standing challenge in condensed matter physics. Here, the microscopic mechanisms are investigated underlying the ultralow thermal conductivity in ordered/liquid‐like Cu3BiS3 by combining experimental methods with first‐principles calculations. The ordered structure and liquid‐like are first experimentally synthesized and characterized, partially Cu‐atom occupied Cu3BiS3 structure with increasing temperature. Selfconsistent phonon calculations are then combined, including bubble‐diagram corrections, with the Wigner transport equation, considering both phonon propagation and diffuson contributions, to evaluate the anharmonic lattice dynamics and thermal conductivity in phase‐change Cu3BiS3. The theoretical model predicts an ultralow thermal conductivity of 0.34 W m−1 K−1 at 400 K, dominated by diffuson contributions, which accurately reproduces and explains the experimental data. Importantly, the machine‐learning‐based molecular dynamics (MD) simulations not only reproduced the partially Cu‐atom occupied Cu3BiS3 structure with the space group Pnma but also successfully replicated the thermal conductivity obtained from experiments and Wigner transport calculations. This observation highlights the negligible impact of ionic mobility arising from partially occupied Cu sites on the thermal conductivity in diffuson‐dominated thermal transport compounds. This work sheds light on the minimal impact of ionic mobility on ultralow thermal conductivity in phase‐change materials. It demonstrates that the Wigner transport equation accurately describes thermal transport behavior in partially occupied phases with diffuson‐dominant thermal transport.

To evaluate the influence of the nature of silane coupling agents on the consistency of dental composites at various temperatures.

Silanes SI 1-4 were synthesized in one single step. They were characterized by ¹H and ¹³C NMR spectroscopy. SI 1-4, as well as 3-methacryloyloxypropyltrimethoxysilane (MPTS), 8-methacryloyloxyoctyltrimethoxysilane (MOTS) and n-dodecyltrimethoxysilane were then used to functionalize a barium aluminum borosilicate glass filler (d₅₀ = 1.0 µm). Silanizations were carried out in cyclohexane in the presence of a catalytic amount of n-propylamine. Each silane was used in an equimolar amount. Composites containing 67 wt% of silanized fillers and packable composites exhibiting a similar consistency at room temperature were subsequently formulated. The consistency of the uncured composites was determined at various temperatures (23 °C, 30 °C, 50 °C and 60 °C) using a texture analyzer. The flexural strength and modulus of the cured composites were assessed according to ISO 4049.

The structure of the silane was shown to strongly influence the consistency of composites. The spacer length between silyl and methacrylate groups, as well as the presence of a urea or a urethane moiety, were demonstrated to be key parameters. Heating of each composite resulted in a drop of the consistency. The decrease was however significantly stronger if coupling agents with long spacers were selected. Especially, the use of SI 3 provided a packable composite which exhibited a packable consistency at 30 °C and flowable consistency at 60 °C. Regarding mechanical properties, it was shown that the coupling agent must be able to copolymerize with the monomers of the organic matrix to obtain high flexural strength and modulus values. The silanization of glass fillers using silanes bearing a long spacer was shown to have an additional advantage: packable composites having a higher filler content, and consequently improved flexural modulus, can be formulated.

The use of filler particles functionalized with silanes containing long alkyl spacers between the silyl and methacrylate moiety is a promising strategy for the development of packable dental composites which exhibit good mechanical properties and a strong drop in consistency upon heating.