0000000000538299
AUTHOR
Elisabeth Rausch
showing 6 related works from this author
Enhanced thermoelectric performance in the p-type half-Heusler (Ti/Zr/Hf)CoSb0.8Sn0.2 system via phase separation
2014
A novel approach for optimization of the thermoelectric properties of p-type Heusler compounds with a C1b structure was investigated. A successful recipe for achieving intrinsic phase separation in the n-type material based on the TiNiSn system is isoelectronic partial substitution of Ti with its heavier homologues Zr and Hf. We applied this concept to the p-type system MCoSb0.8Sn0.2 by a systematic investigation of samples with different compositions at the Ti position (M = Ti, Zr, Hf, Ti0.5Zr0.5, Zr0.5Hf0.5, and Ti0.5Hf0.5). We thus achieved an approximately 40% reduction of the thermal conductivity and a maximum figure of merit ZT of 0.9 at 700 °C. This is a 80% improvement in peak ZT fr…
Fine tuning of thermoelectric performance in phase-separated half-Heusler compounds
2015
Two successful recipes to enhance the thermoelectric performance, namely carrier concentration optimization and reduction of thermal conductivity, have been combined and applied to the p-type (Ti/Zr/Hf)CoSb1−xSnx system. An intrinsic micrometer-scale phase separation increases the phonon scattering and reduces the lattice thermal conductivity. A substitution of 15% Sb by Sn optimizes the electronic properties. Starting from this, further improvement of the thermoelectric properties has been achieved by a fine tuning of the Ti to Hf ratio. The microstructuring of the samples was studied in detail with high-resolution synchrotron powder X-ray diffraction and element mapping electron microscop…
Charge carrier concentration optimization of thermoelectric p-type half-Heusler compounds
2015
The carrier concentration in the p-type half-Heusler compound Ti0.3Zr0.35Hf0.35CoSb1−xSnx was optimized, which is a fundamental approach to enhance the performance of thermoelectric materials. The optimum carrier concentration is reached with a substitution level x = 0.15 of Sn, which yields the maximum power factor, 2.69 × 10−3 W m−1 K−2, and the maximum ZT = 0.8. This is an enhancement of about 40% in the power factor and the figure of merit compared to samples with x = 0.2. To achieve low thermal conductivities in half-Heusler compounds, intrinsic phase separation is an important key point. The present work addresses the influence of different preparation procedures on the quality and re…
Short and long range order of Half-Heusler phases in (Ti,Zr,Hf)CoSb thermoelectric compounds
2016
Abstract The structural properties of (Ti,Zr,Hf)CoSb thermoelectric Half-Heusler compounds were investigated by synchrotron radiation based techniques. The short-range order, in particular the environment of the Co atoms, was studied by extended X-Ray absorption fine structure spectroscopy and the long range order by powder X-Ray diffraction. Structural models were obtained for the single phase materials TiCoSb0.85Sn0.15, ZrCoSb0.85Sn0.15, and HfCoSb0.85Sn0.15. These models were transferred for the phase-separated material Ti0.5Hf0.5CoSb0.85Sn0.15. As a result, proving that each Half-Heusler phase was well ordered, apart from the intermixing of Ti and Hf on its designated crystallographic l…
Half-Heusler materials as model systems for phase-separated thermoelectrics
2015
Semiconducting half-Heusler compounds based on NiSn and CoSb have attracted attention because of their good performance as thermoelectric materials. Nanostructuring of the materials was experimentally established through phase separation in (T1−x′Tx″)T(M1−yMy′) alloys when mixing different transition metals (T, T′, T″) or main group elements (M, M′). The electric transport properties of such alloys depend not only on their micro- or nanostructure but also on the atomic-scale electronic structure. In the present work, the influence of the band structure and density of states on the electronic transport and thermoelectric properties is investigated in detail for the constituents of phase-sepa…
Long-Term Stability of (Ti/Zr/Hf)CoSb1−xSnxThermoelectric p-Type Half-Heusler Compounds Upon Thermal Cycling
2015
The effect of thermal cycling upon the thermoelectric performance of state-of-the-art p-type half-Heusler materials was investigated and correlated with the impact on the structural properties. We simulated a heat treatment of the material similar to actual applications in the mid-temperature range, such as occurs during the energy conversion from an automotive exhaust pipe. We compared three different compositions based on the (Ti/Zr/Hf)CoSb1−xSnx system. The best and most reliable performance was achieved using Ti0.5Hf0.5CoSb0.85Sn0.15, which reached a maximum figure of merit ZT of 1.1 at 700 °C. The intrinsic phase separation and resulting microstructuring, which are responsible for the …