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The flexoelectric effect describes the electromechanical coupling of a strain gradient to a polarization and vice versa. This effect scales linearly with permittivity and strain gradients can get very high for dimensions on the micro and nanoscale. Even though the flexoelectric effect can be best exploited within micro or nanoelectromechanical systems (M/NEMS) applications, it has not been established in today`s M/NEMS device architectures as other transducer principles, like piezoelectricity. In this work, values of the converse flexoelectric coefficient for one of the most promising flexoelectric materials, titanium dioxide (TiO2) are provided. The experimental results are based on a carefull characterization of IrO2/TiO2/IrO2 cantilevers. Besides CMOS compatiblity TiO2 is selected as functional thin film material as it offers a very high permittivity and shows no hysteresis or saturation effects as it is neither ferro- nor paraelectric. Additionally, it guarantees a low cost, lead-free realization and can be directly integrated in a standard silicon MEMS fabrication process by sputter deposition. In order to correctly determine the flexoelectric coefficient, other electromechanical coupling effects are considered and assessed. The flexoelectric coefficient is shown to be µeff = 1.78 ± 0.16 nC m−1 at 10 kHz. The flexoelectric coupling constant with a value of 2.75 V is in good agreement with that theoretically predicted by Kogan`s estimate of 3.14 V.

The flexoelectric effect describes the electromechanical coupling of a strain gradient to a polarization and vice versa. This effect scales linearly with permittivity and strain gradients can get very high for dimensions on the micro and nanoscale. Even though the flexoelectric effect can be best exploited within micro or nanoelectromechanical systems (M/NEMS) applications, it has not been established in today`s M/NEMS device architectures as other transducer principles, like piezoelectricity. In this work, values of the converse flexoelectric coefficient for one of the most promising flexoelectric materials, titanium dioxide (TiO2) are provided. The experimental results are based on a carefull characterization of IrO2/TiO2/IrO2 cantilevers. Besides CMOS compatiblity TiO2 is selected as functional thin film material as it offers a very high permittivity and shows no hysteresis or saturation effects as it is neither ferro- nor paraelectric. Additionally, it guarantees a low cost, lead-free realization and can be directly integrated in a standard silicon MEMS fabrication process by sputter deposition. In order to correctly determine the flexoelectric coefficient, other electromechanical coupling effects are considered and assessed. The flexoelectric coefficient is shown to be μ eff= 1.78 ± 0.16 nC m-1 at 10 kHz. The flexoelectric coupling constant with a value of 2.75 V is in good agreement with that theoretically predicted by Kogan`s estimate of 3.14 V.

Aluminum nitride (AlN) on sapphire has been investigated with two different pretreatments prior to sputter deposition of the AlN layer to improve the orientation and homogeneity of the thin film. An inverse sputter etching of the substrate in argon atmosphere results in an improvement of the uniformity of the alignment of the AlN grains and hence, in enhanced electro-mechanical AlN film properties. This effect is demonstrated in the raw measurements of SAW test devices. Additionally, the impulse response of several devices shows that a poor AlN thin film layer quality leads to a higher signal damping during the transduction of energy in the inter-digital transducers. As a result, the triple-transit signal cannot be detected at the receiver.

Hardfacing by laser provides a cost-effective option for protecting components against mechanical wear and corrosion. In the present work, high speed steel hardfacings were deposited using a high-power direct diode laser with the aim of investigating the role of niobium content on their mechanical and corrosion properties. The content of niobium was varied between 0.1 and 3 wt%. The results show that niobium content has a high impact on the hardfacing microstructure and its resulting mechanical properties. In particular, niobium is able to significantly enhance the abrasive wear resistance of high speed steel laser hardfacings. This improvement is accompanied by a superior corrosion resistance. The impact of niobium content on slurry erosion resistance is less remarkable and a clear benefit can only be achieved by microalloying. These results are correlated with the microstructural changes induced by the varying niobium content. An increase in niobium content reduces the amount of carbides found along the grain boundaries, raises the amount of chromium dissolved in the iron matrix and increases the elastic strain to failure of the hardfacing. This results as a consequence in high speed steel laser hardfacings with superior toughness and enhanced corrosion resistance. acceptedVersion submittedVersion

With the porosification of sintered Low Temperature Co-fired Ceramic (LTCC) surfaces areas with alternating dielectric properties can be created by embedding air. The method, including a wet-chemical treatment with phosphoric acid, is also investigated in detail for several commercial celsian forming tapes. Since the results of these materials cannot provide the required selectivity, in this work the analysis is extended to anorthite forming tapes. Furthermore, the investigations include a LTCC based on lanthanum borate. The results show that the porosification with phosphoric acid is not applicable to the latter material. In contrast, the silicate based, corundum containing tapes feature the most satisfying porosification results. Thereby, the stability of the glass, the size of the grains, the exclusivity of the crystallized phase and its degree of crystallization are identified as the tape features which directly influence the porosification results.

The wet chemical porosification of low temperature co-fired ceramics (LTCC) applying ortho-phosphoric acid enables the implementation of areas with low permittivity directly into the as-fired substrate surface. Currently, the corresponding chemical reaction is only investigated for the widely used anorthite forming tape DuPont 951. In this paper the research is extended to cover celsian forming tapes with different ceramic particles. As the investigations show, the residual glass after porosification together with the grains should provide stable phases or components and ensure a bearing surface for further metallization. In the LTCC investigated here, the necessary selective etching to the containing celsian phase is given. However, the locality of the pores suffers from the presence of willemite, which is a second predominantly dissolved phase. The high amount of modifier oxides and the agglomeration of the dispersed corundum grains further weaken the stability of the LTCC substantially with respect to this treatment.

Systematic variation of the dehydration temperature and time enables the preparation of highly reactive magnesium oxide for thermochemical energy storage purposes. The reactivity of the MgO, resulting from varying dehydration conditions has been studied by a comparative approach, including reactive surface area, particle morphology and reactivity towards rehydration. For the rehydration an in-situ powder X-Ray diffraction setup is used, allowing for continuous monitoring of Mg(OH) 2 formation. The outcome of this investigation was subsequently applied to MgO from natural magnesites to assess the impact of impurities in the material on rehydration reactivity.

Metal carbonates are attractive materials for combining carbon capture and thermochemical energy storage. Carbonate materials feature high decomposition and formation temperatures and may be considered in applications in combination with concentrating solar power. In the present study in-situ P-XRD carbonation (1–8 bar CO2) and reactor-based experiments (1–55 bar CO2) are combined focusing on the effect of elevated CO2 pressures on carbonation of metal oxides. Carbonation of MnO and PbO at CO2 pressures between 8 and 50 bar in the presence of moisture resulted in reaction with CO2, forming the corresponding carbonates at notably lower temperatures than under dry CO2 atmosphere of 1 bar. This enables the application of metal oxide/metal carbonate reaction couples for energy storage at temperatures between 25 and 500 °C. Based on the reversible carbonation/decarbonation of PbO under varying CO2 pressures, an isothermal storage cycle between PbO/PbCO3·2PbO, triggered by changing the CO2 pressure between 2 and 8 bar, was developed.

Normal modes of vibration of a Ni–Mn–Al single crystal have been measured by inelastic neutron scattering. The force constants have been fitted to the Born–von Karman model using axially symmetric forces. Dispersion curves of both acoustical and optical phonons have been determined along the high symmetry [1 0 0], [1 1 0] and [1 1 1] directions. The temperature dependence of the normal modes revealed an anomalous softening of the TA 2 [1 1 0] phonons observed in the range of 0.1–0.25 reciprocal lattice units in good agreement with recent ab initio calculations. Contrary to the acoustical TA 2 [1 1 0] modes. The optical TO 2 [1 1 0] modes with the same polarisation showed a normal behaviour with temperature, namely a decrease in frequency upon heating due to increasing anharmonicity. Elastic scattering performed along the [1 1 ¯ 0] direction did not reveal any significant elastic or diffuse scattering.