Optimization of the carrier concentration in phase-separated half-Heusler compounds

Inspired by the promising thermoelectric properties of phase-separated half-Heusler materials, we investigated the influence of electron doping in the n-type Ti_(0.3−x)Zr_(0.35)Hf_(0.35)NiSn compound. The addition of Nb to this compound led to a significant increase in its electrical conductivity, and shifted the maximum Seebeck coefficient to higher temperatures owing to the suppression of intrinsic carriers. This resulted in an enhancement of both the power factor α^2σ and figure of merit, zT. The applicability of an average effective mass model revealed the optimized electron properties for samples containing Nb. There is evidence in the literature that the average effective mass model is suitable for estimating the optimized carrier concentration of thermoelectric n-type half-Heusler compounds

Construction and validation of safe Clostridium botulinum Group II surrogate strain producing inactive botulinum neurotoxin type E toxoid

Botulinum neurotoxins (BoNTs), produced by the spore-forming bacterium Clostridium botulinum, cause botulism, a rare but fatal illness affecting humans and animals. Despite causing a life-threatening disease, BoNT is a multipurpose therapeutic. Nevertheless, as the most potent natural toxin, BoNT is classified as a Select Agent in the US, placing C. botulinum research under stringent governmental regulations. The extreme toxicity of BoNT, its impact on public safety, and its diverse therapeutic applications urge to devise safe solutions to expand C. botulinum research. Accordingly, we exploited CRISPR/Cas9-mediated genome editing to introduce inactivating point mutations into chromosomal bont/e gene of C. botulinum Beluga E. The resulting Beluga Ei strain displays unchanged physiology and produces inactive BoNT (BoNT/Ei) recognized in serological assays, but lacking biological activity detectable ex- and in vivo. Neither native single-chain, nor trypsinized di-chain form of BoNT/Ei show in vivo toxicity, even if isolated from Beluga Ei sub-cultured for 25 generations. Beluga Ei strain constitutes a safe alternative for the BoNT research necessary for public health risk management, the development of food preservation strategies, understanding toxinogenesis, and for structural BoNT studies. The example of Beluga Ei generation serves as template for future development of C. botulinum producing different inactive BoNT serotypes.Peer reviewe

Lessons from a 2-Hub Life-Science Training Course: From Heidelberg to Bangalore and Beyond

Technologies are rapidly evolving in the life sciences and other STEM areas. Advanced hands-on practical courses are key for life-science researchers to stay ahead of the game. Although the Covid-19 pandemic propelled/accelerated the transformation in remote training opportunities, it is clear that training in molecular biology methodologies requires and greatly benefits from hands-on face-to-face courses. Here we present a novel 2-hub course format, with teaching of cutting-edge technologies simultaneously in Germany (EMBL Heidelberg) and India (BLiSC in Bangalore). The format combines active-based learning on a scientific case study with collaborative exercises and networking that foster scientific exchange. We describe the digital technologies utilised in course design and delivery, and the multi-layered planning phase. Analysis of the participant and trainer feedback questionnaires demonstrates the benefits and challenges of the 2-hub format and illustrates the success of the course. The concept allows us to broaden our reach, while reducing overall CO2 emission in comparison to a 1-hub course. We show that thanks to digital tools and collaboration of dedicated organisers, we can provide conceptual design and create sophisticated active-learner training opportunities with world-wide reach

Thermoelectric properties in phase-separated half-Heusler materials

The conversion of dissipated heat into electricity is the basic principle of thermoelectricity. In this context, half-Heusler (HH) compounds are promising thermoelectric (TE) materials for waste heat recovery. They meet all the requirements for commercial TE applications, ranging from good efficiencies via environmentally friendliness to being low cost materials. This work focused on the TE properties of Ti0.3Zr0.35Hf0.35NiSn-based HH materials. This compound undergoes an intrinsic phase separation into a Ti-poor and Ti-rich HH phase during a rapid solidification process. The resulting dendritic microstructure causes a drastic reduction of the thermal conductivity, leading to higher TE efficiencies in these materials. The TE properties and temperature dependence of the phase-separated Ti0.3Zr0.35Hf0.35NiSn compound were investigated. The TE properties can be adjusted depending on the annealing treatment. The extension of annealing time for 21 days at 1000 °C revealed a reduction of the thermal conductivity and thus an enhancement of the TE performance in this sample. An increase of annealing temperature caused a change of the phase fraction ratio in favor of the Ti-rich phase, leading to an improvement of the electronic properties. rnInspired by the TE properties of the Ti0.3Zr0.35Hf0.35NiSn HH compound, the performance of different n- and p-type materials, realized via site substitution with donor and acceptor elements was examined. The fabrication of a TE n- and p-type material pair based on one starting compound can guarantee similar TE and mechanical properties and is enormous beneficial for device engineering. As donor dopants V, Nb and Sb were tested. Depending on the lattice position small doping levels were sufficient to attain distinct improvement in their TE efficiency. Acceptor-induced doping with Sc, Y and Co caused a change in the transport behavior from n- to p- type conduction, revealing the highest Seebeck coefficients obtained in the MNiSn system. rnThen, the long-term stability of an exemplary n- and p-type HH compound was proven. Surprisingly, the dendritic microstructure can be maintained even after 500 cycles (1700 h) from 373 to 873 K. The TE performance of both n- and p-type materials showed no significant change under the long-term treatment, indicating the extraordinary temperature stability of these compounds. Furthermore both HH materials revealed similar temperature-dependence of their mechanical properties. This work demonstrates the excellent suitability of phase-separated HH materials for future TE applications in the moderate temperature range.rnDas grundliegende Prinzip der Thermoelektrik ist die Umwandlung verlorener Wärmeenergie in elektrischen Strom. Hierbei sind halb-Heusler (HH) Verbindungen vielversprechende Materialien, da sie viele der erforderlichen Kriterien, wie hohe thermoelektrische (TE) Effizienz, Umweltfreundlichkeit und geringe Materialkosten, für eine kommerzielle Anwendung erfüllen. Der Fokus dieser Arbeit liegt in der Untersuchung der TE Eigenschaften in Ti0.30Zr0.35Hf0.35NiSn-basierenden HH Verbindungen. Diese Materialien separieren bei rascher Abkühlung in eine Ti-arme und Ti-reiche Phase. Die resultierende dendritische Mikrostruktur führt zu einer drastischen Reduzierung der thermischen Leitfähigkeit und ist ein entscheidender Faktor zur Erzielung hoher TE Effizienten in HH-Materialien. Die TE Eigenschaften und das Temperaturverhalten der phasenseparierten Ti0.3Zr0.35Hf0.35NiSn-Verbindung wurden untersucht. Eine Temperaturbehandlung von 21 Tage bei 1000 °C zeigte eine Reduzierung der thermischen Leitfähigkeit und damit eine Verbesserung in der TE Effizienz. Die Erhöhung der Temperatur änderte das Phasen-Verhältnis in den Proben zugunsten der Ti-reicheren HH Phase, was eine Verbesserung der elektronischen Eigenschaften zur Folge hatte. rnInspiriert durch die TE Eigenschaften der Ti0.3Zr0.35Hf0.35NiSn-Verbindung, wurde nach leistungsfähigen n- und p-typ Materialien via Substitution mit Donor- und Akzeptor-Elementen in diesem System gesucht. Die Herstellung eines TE n- und p-typ Materialpaares basierend auf einer Ausgangsverbindung ist sehr vorteilhaft für den Bau thermoelektrischer Module, da dadurch ähnliche TE und mechanische Eigenschaften gewährleistet werden können. Als Donatoren wurden V, Nb and Sb getestet, wobei bereits geringe Dotiermengen ausreichten, um eine erhebliche Steigerung der TE Leistung in den HH Proben zu erhalten. Akzeptoren wie Sc, Y und Co änderten die Transporteigenschaften von n- zu p-typ Verhalten. Dabei zeigten die p-typ Verbindungen die bisher höchsten Seebeck Koeffizienten basierenden auf dem MNiSn-System. rnDesweitern wurde die Langezeitstabilität einer exemplarischen n- und p-typ HH Verbindung untersucht. Die dendritische Mikrostruktur bleibt auch nach 500 Temperaturzyklen (1700 h) von 373 bis 873 K erhalten und die TE Effizienz beider Materialien zeigte keine signifikante Änderung nach der Langzeit-Behandlung auf. Zudem zeigten beide Materialien ähnliche mechanische Eigenschaften. Die außergewöhnliche Temperaturstabilität dieser HH-Verbindungen verdeutlicht die hervorragende Eignung phasenseparierter HH-Materialien für zukünftige TE Anwendungen im moderaten Temperaturbereich.r