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The investigation and conservation of the Vienna Genesis, a Late Antique manuscript on purple parchment, included the study of parchment production and purple dyeing in the sixth century. The process of parchment making and of purple dyeing was recreated and compared with the Vienna Genesis and other manuscripts from the sixth and eighth centuries. Parchment made from the hides of young lambs and dyed with orchil resembled the folios of the Vienna Genesis. The results of material analysis and the study of parchment technology influenced decisions for the conservation and storage of the manuscript. Fragile areas of ink and parchment were stabilised with strips of adhesive coated Japanese tissue paper. The single folios are stored in folders of Japanese paper and museum matboard within a sink mat.Die Untersuchung und Konservierung der Wiener Genesis, einer spätantiken Purpurhandschrift, beinhaltete eine Studie zur Herstellung von Pergament und zur Purpurfärbung im sechsten Jahrhundert. Der Prozess des Pergamentmachens und des Färbens mit Purpurfarbstoffen wurde in Experimenten rekonstruiert und die Ergebnisse mit der Wiener Genesis und anderen Handschriften des sechsten und achten Jahrhunderts verglichen. Aus den Häuten junger Lämmer hergestelltes und mit Flechtenfarbstoff gefärbtes Pergament ist den Folios der Wiener Genesis ähnlich. Die Erkenntnisse aus Materialanalyse und technologischen Studien beeinflussten Entscheidungen zur Konservierung und Aufbewahrung der Handschrift. Fragile Stellen in Tinte und Pergament wurden mit Brücken von beschichtetem Japanpapier stabilisiert. Die einzelnen Folios werden in Umschlägen aus Japanpapier und Museumskarton in versenkten Passepartouts aufbewahrt.

How is hydrogen distributed among minerals and how is it bonded in their crystal structures? These are important questions, because the amount of hydrogen and the bonding configuration of hydrogen in crystalline materials governs many of that material’s properties: its thermal and compressional behavior, P–T phase stability, rheology, and electrical conductivity. A reliable reconstruction of the Earth’s interior, or the prediction of mineral transformations in complex industrial processes, must account for these parameters. Neutron diffraction can locate hydrogen sites in mineral structures, reveal any static or dynamic hydrogen disorder, help define the libration regime of hydrogen, and elucidate hydrogen-bonding configurations. Thus, that most elusive element for X-ray probes is perfectly detectable using neutrons.

A commercial Empyrean X-ray diffractometer was adapted for combined grazing incidence X-ray fluorescence analysis (GIXRF) measurements with X-ray reflectivity (XRR) measurements. An energy-dispersive silicon drift detector was mounted and integrated in the angle-dependent data acquisition of the Empyrean. Different monochromator/X-ray optics units have been compared with the values obtained by the Atominstitut GIXRF + XRR spectrometer. Data evaluation was performed by JGIXA, a special software for combined GIXRF + XRR data fitting, developed at Atominstitut. A sample consisting of a ~50 nm nickel layer on a silicon substrate was used to compare the performance criteria (i.e. divergence and intensity) of the incident beam optics. An Empyrean X-ray diffractometer was successfully refitted to measure both GIXRF and XRR data.

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.

[EN] Ferroelectric materials exhibit a phase transition to a paraelectric state driven by temperature - called the Curie transition. In conventional ferroelectrics, the Curie transition is caused by a change in crystal symmetry, while the material itself remains a continuous three-dimensional solid crystal. However, ferroelectric polymers behave differently. Polymeric materials are typically of semi-crystalline nature, meaning that they are an intermixture of crystalline and amorphous regions. Here, we demonstrate that the semi-crystalline morphology of the ferroelectric copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) strongly affects its Curie transition, as not only a change in crystal symmetry but also in morphology occurs. We demonstrate, by high-resolution nanomechanical measurements, that the semicrystalline microstructure in the paraelectric state is formed by crystalline domains embedded into a softer amorphous phase. Using in situ X-ray diffraction measurements, we show that the local electromechanical response of the crystalline domains is counterbalanced by the amorphous phase, effectively masking its macroscopic effect. Our quantitative multiscale characterisations unite the nano- and macroscopic material properties of the ferroelectric polymer P(VDF-TrFE) through its semi-crystalline nature., European Union’s Horizon 2020 research and Innovation programme under the Marie Skłodowska-Curie grant agreement number 721874 (SPM2.0). RG acknowledges funding from the European Research Council ERC–AdG–340177 (3DNanoMech). This work was supported by the UK government’s Department for Business, Energy and Industrial Strategy. The dynamic mechanical analysis was supported by T. Koch from the Institute of Materials Science and Technology, TU Wien. We gratefully thank A. Muhamedagić for the contribution of artworks to the figures (armindesign.li).

The present study analyses transformation pathways of pristine and thermally treated porous limestone and dense marble surfaces by means of time-resolved streaming current and potential measurements coupled with scanning electron microscopy and in-situ X-ray diffraction. The results reveal that under nonequilibrium conditions the zeta potential (ζ) of natural carbonates may exhibit positive and negative signs and ζ drifts in opposite directions. Sample surface roughness influences ζ because it contributes to dissolution, as observed particularly in the initial period of time-resolved measurements. Thermal treatment causes a temporary charge reversal from negative to positive. The reactivity of calcium hydroxide on calcite surfaces governs the net electrokinetic potential and isoelectric point (IEPpH), even at low surface coverage, as cross-validated by in-situ XRD. It was also found that pore conductivity may lead to ~90% underestimation of ζ when assessed by streaming potential. SEM studies revealed micro cracks inducement on marble after thermal treatment, which can result in underestimation of ζ up to the same extent as for the porous limestone. When an asymmetric cell configuration involving calcite and polypropylene surfaces is used, the fractional contribution of polypropylene to the IEPpH is 0.3 and to the overall determined ζ up to 0.5. Our findings contribute to the understanding of nonequilibrium and time-dependent electrokinetic potential modifications associated with the reactivity of porous surfaces. This study highlights the effectiveness of the streaming potential technique for monitoring such changes further supported by the use of ancillary techniques to analyze the extend of chemo-mineralogical and physical alterations.

Confocal micro-x-ray fluorescence (μXRF) is a powerful tool to analyze the spatial distribution of major, minor, and trace elements in three dimensions. Typical (confocal) μXRF measurements in the lab use polychromatic excitation, complicating quantification and fundamental parameter-based corrections and furthermore deteriorating peak-to-background ratios due to scattered bremsstrahlung. The goal for the new setup was to remedy these problems, without sacrificing spatial resolution, and keep it flexible for different excitation energies and transportation to other sources. The source assembly consists of a water-cooled fine-focus x-ray diffraction tube and a parallel beam-mirror, which produces a quasi-parallel, monochromatic beam. The presented results were obtained using a 2 kW molybdenum tube and a mirror for Mo-Kα. The confocal setup itself consists of two polycapillary half-lenses, one for the source side and the other for the detector side, where a 50 mm2 silicon drift detector is mounted. Both polycapillaries have a focus size of ∼15 μm for Mo-Kα. The second polycapillary can also be exchanged for a custom-designed collimator in order to perform non-confocal μXRF. Details of the technical setup and results from technical and biological samples are presented. Detection limits for selected elements from Ca to Pb in the confocal and non-confocal mode were established (e.g., 1 μg/g non-confocal and 20 μg/g confocal for As) using the NIST standard reference materials (SRMs) 621 and 1412. Furthermore, the results of the measurements of SRM 621 were evaluated using the fundamental parameter based quantification software ATI-QUANT. The results are compared with the certified values and generally are in good agreement.

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.

Thiolate protected metal nanoclusters are emerging materials for the preparation of atomically defined heterogeneous catalysts. Recently it was revealed that the ligands migrated to the support upon cluster deposition, which influences the catalytic behaviour. Here we examined the role of the protecting thiolate ligands on the cyclohexane oxidation for Au38(SR)24 supported on CeO2 and Al2O3. Sulfur containing products were detected. XANES S K-edge measurements revealed SOx species on the support during the reaction. The results indicate (i) an active and complex role of the thiolate ligand and (ii) changes of cluster (surface) structure, depending on support material and reaction conditions.

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.

Thermochemical energy storage is considered as an auspicious method for the recycling of medium-temperature waste heat. The reaction couple Mg(OH)2&ndash, MgO is intensely investigated for this purpose, suffering so far from limited cycle stability. To overcome this issue, Mg(OH)2, MgCO3, and MgC2O4&middot, 2H2O were compared as precursor materials for MgO production. Depending on the precursor, the particle morphology of the resulting MgO changes, resulting in different hydration behavior and cycle stability. Agglomeration of the material during cyclization was identified as main reason for the decreased reactivity. Immersion of the spent material in liquid H2O decomposes the agglomerates restoring the initial reactivity of the material, thus serving as a regeneration step.

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.

In this paper, we report on the surface evolution of focused ion beam treated single crystalline Bi(001) with respect to different beam incidence angles and channeling effects. ?Erosive? sputtering appears to be the dominant mechanism at room temperature (RT) and diffusion processes during sputtering seem to play only a minor role for the surface evolution of Bi. The sputtering yield of Bi(001) shows anomalous behavior when increasing the beam incidence angle along particular azimuthal angles of the specimen. The behavior of the sputtering yield could be related to channeling effects and the relevant channeling directions are identified. Dynamic annealing processes during ion irradiation retain the crystalline quality of the Bi specimen allowing ion channeling at RT. Lowering the specimen temperature to T?=??188 ?C reduces dynamic annealing processes and thereby disables channeling effects. Furthermore unexpected features are observed at normal beam incidence angle. Spike-like features appear during the ion beam induced erosion, whose growth directions are not determined by the ion beam but by the channeling directions of the Bi specimen.

Motivated by predictions of a substantial contribution of the ``buckling'' vibration of the ${\mathrm{CuO}}_{2}$ layers to $d$-wave superconductivity in the cuprates, we have performed an inelastic neutron scattering study of this phonon in an array of untwinned crystals of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$. The data reveal a pronounced softening of the phonon at the in-plane wave vector $\mathbf{q}=(0,0.3)$ upon cooling below $\ensuremath{\sim}105\text{ }\text{ }\mathrm{K}$, but no corresponding anomaly at $\mathbf{q}=(0.3,0)$. Based on the observed in-plane anisotropy, we argue that the electron-phonon interaction responsible for this anomaly supports an electronic instability associated with a uniaxial charge-density modulation and does not mediate $d$-wave superconductivity.

We report on the structural instability of ${\text{Ni}}_{2}\text{MnAl}$ from calorimetry measurements and inelastic neutron scattering. The acoustic and optical phonon dispersions along the high-symmetry $[\ensuremath{\xi}00]$, $[\ensuremath{\xi}\ensuremath{\xi}0]$, and $[\ensuremath{\xi}\ensuremath{\xi}\ensuremath{\xi}]$ directions have been interpolated from the normal modes of vibration using the Born--von K\'arm\'an model. The tendency of ${\text{Ni}}_{2}\text{MnAl}$ to undergo a martensitic transformation shows up in the anomalous phonon softening of the particular ${\text{TA}}_{2}[\ensuremath{\xi}\ensuremath{\xi}0]$ phonons in the $\ensuremath{\xi}$ range 0.1--0.25 rlu of two different crystals. The phonon frequencies of this branch scale inversely with the valence electron concentration in good agreement with ab initio calculations. Contrary to the prediction of first-principles calculations in the Heusler $\text{L}{2}_{1}{\text{-Ni}}_{2}\text{MnAl}$, no anomaly is seen in the optical phonons measured in $\text{B}2{\text{-Ni}}_{2}\text{MnAl}$. The anomalous ${\text{TA}}_{2}[\ensuremath{\xi}\ensuremath{\xi}0]$ phonon softening is not enhanced below room temperature when ${\text{Ni}}_{2}\text{MnAl}$ orders in the antiferromagnetic state.

Silicon has been considered as one of the most promising anode materials for LIBs in order to replace the conventional anode material (graphite). Investigations of the Li-Si binary system indicated at least theoretically, the highest specific capacity (4200 mAh/g), during the electrochemical lithium alloying (Li4.4Si) of silicon with lithium ions. Unfortunately, Si shows a very low mechanical elasticity during the battery cycling (lithiation/delithiation), which causes a contact loss in the electrode and subsequently lead to a shorter cycle life and finally fast capacity fading. This is the major drawback of Si as an anode material and the reason why a general distribution within the lithium ion battery market couldn´t be established up to now. The first idea proposed to overcome this shortcoming, is a new approach concerning the binder materials. In the research of energy storage materials, a new technology named biomimetics has been adapted to breakthrough the serious technical problem. The use of bioinspired binders for the silicon anode materials represents one basic approach of our present study. Namely, potato starch, gelatine and alginic acid from brown algae were studied as a binder. It was found that the potato starch was the best binder, exhibiting 1500 mAh/g at the 20thcycle. This is due to the fact that amylopectin polysaccharides suppress the volume change of silicon and form a beneficial SEI film on the electrode during cycling. The second idea proposed in this work is based on the formation of a nanoscale, 3D-connected mesoporous silicon by a magnesiothermic reduction process, providing short diffusion pathways for the lithium ions during lithiation / delithiation. The silicon-based cells were characterized by electrochemical investigations and the first results show that the mesoporous silicon-based cell exhibits a discharge capacity of 1200 mAh/g and a coulombic efficiency of 84% after the cycling precondition with 0.05C. The improvement of the electrical conductivity and the modification of the surface´s electrochemical properties is achieved by an adaption of a coating method, known as substrate-induced coagulation. The coating materials are distinguished between lithium reactive and nonreactive. Further, they can be subdivided, i.e. carbonaceous materials (nano-graphite, graphene), nano metals (Cu, Ni) and nano metal oxides [TiO2, In(OH)3, ITO(indium tin oxide)].

Neutron spectroscopy is a powerful tool to examine the fundamental properties of condensed matter, mostly using a so called triple axis spectrometer. A critical problem of this measurement procedure is the collision free and time optimized physical positioning of the instruments axes to the desired coordinates in momentum and energy space. This work shows the concept and the implementation of the library “paprika”, which is a control tool for neutron spectrometers, avoiding collisions and calculating a time optimized path. The tool was created for the PUMA, a triple axis spectrometer located at the new research reactor FRM-II in Garching near Munich. Furthermore it can be easily adopted to other applications.

The intermetallic compound, CeCu2Ge2, is the counterpart of the heavy-fermion superconductor CeCu2Si2. CeCu2Ge2 is a magnetically ordering (TN = 4.1K) Kondo lattice with a moderate Sommerfeld coefficient of 140 mJ/ molK2. Earlier inelastic neutron measurements on a polycrystalline sample revealed a doublet ground state and a quasi-quartet excited state at 16.5 meV, although a splitting of the 4f1 (J = 5/2) ground state multiplet into 3 doublets is expected from the point symmetry of the Ce3+ ions. We performed detailed inelastic neutron scattering experiments on a single crystal at the thermal triple-axis spectrometer PUMA at FRM II for different crystallographic directions. From our results we infer that the quasi-quartet, in fact, consists of two doublets at 17.0 and 18.3 meV which exhibit a strong directional dependence of their transition matrix elements to the ground state doublet. Finally, we will present a new set of crystal field parameters.

The field induced switching process across the ferroelectric lock-in transition in K2SeO4 has been studied on a millisecond timescale using stroboscopic neutron diffraction. The time evolution of both the first and the third order satellites was examined. The time constants are found to vary with temperature between 0.2 and 1.2?ms. This is an order of magnitude faster than in the isostructural Rb2ZnCl4. Moreover, the time dependence of the satellite's linewidth provides information about the evolution of the coherence of the modulated structure.

Neutrons and X-rays are powerful probes for studying magnetic and lattice excitations in strongly correlated materials over very wide ranges of momentum and energy transfers. In the focus of the present work are the incommensurate magnetic systems MnSi and Cr. Under application of a magnetic field, helically ordered MnSi transforms into a weak itinerant ferromagnet. Using polarized neutrons we demonstrate that the Stoner excitations are spin flip excitations. The amplitude (longitudinal) fluctuations associated with the magnon modes are already strong far away from T_C. Interestingly, even the non spin flip excitations associated with the Stoner modes are observable. In Cr, we have observed Kohn anomalies in the phonon spectrum at those incommensurate positions in reciprocal space, where the spin density wave is observed. The corresponding phonon and magnon modes are not coupled. In addition, an anomalous softening of a transverse phonon branch along the N-H zone boundary line is observed that is caused by strong electron phonon coupling. High resolution neutron scattering indicate that the low energy Fincher-Burke excitations may rather correspond to localized modes in momentum and energy and not to propagating collective modes. Finally, we demonstrate that in the near future it may become feasible to investigate excitations in very small samples thus allowing to measure the dynamics of strongly correlated materials under extreme conditions and in the vicinity of quantum phase transitions.

The lock-in transition of K2SeO4 at 93.2 K was studied using high-resolution γ-ray diffraction, in situ dielectric measurements and neutron scattering. The phase transition shows a coexistence regime of 1.0 K with clearly resolved incommensurate and commensurate satellite reflections. Within a temperature interval of several K above the lock-in transition, strong third order satellites are observed, indicating a pronounced squaring of the modulation wave. Under the influence of high electric fields an intermediate phase is observed, which is characterized by a diffuse intensity distribution. In addition, the dielectric permittivity exhibits two maxima, indicating the existence of two separate phase transitions. This behaviour is attributed to distortions of the discommensuration lattice and pinning of the discommensurations by accumulated charged defects. It seems to be characteristic for modulated ferroelectrics of the A2BX4 group, since a similar behaviour is also found in isostructural Rb2ZnCl4 and K2ZnCl4. The soft-mode dynamics close to Tc is found to be essentially independent of the electric field and not affected by the discommensuration lattice.

We obtain phonon lifetimes in aluminium by inelastic neutron scattering experiments, by ab initio molecular dynamics, and by perturbation theory. At elevated temperatures significant discrepancies are found between experiment and perturbation theory, which disappear when using molecular dynamics due to the inclusion of full anharmonicity and the correct treatment of the multiphonon background. We show that multiple-site interactions are small and that local pairwise anharmonicity dominates phonon-phonon interactions, which permits an efficient computation of phonon lifetimes.

International audience; The Chair of Mineralogy of The Sorbonne, created in 1809 for René-Just Haüy, evolved to the present Institute of Mineralogy, Materials Physics and Cosmochemistry (IMPMC) of Sorbonne Université. Brilliant women crystallographers have been working or still work in this laboratory, which also is the headquarter of the two French societies of crystallography (AFC and SFMC). The research activities of these women scientists range from experimental to theoretical diffraction, and concern the exploration of extraterrestrial samples as well as the development of synchrotron beamlines. In this talk, we will examine the careers of some women researchers of our laboratory, who had striking contributions in the French crystallography from the 60s to nowadays. This presentation will be set in a more general context of women crystallographers in Paris in the twentieth century.