Klaudia Hradil

• Dipl. Min. Dr. rer. nat.
• Scattering Methods for materials investigations at TU Wien

The first photographic process was published by Louis Jacques Mandé Daguerre in 1839. Due to the insufficient sensitivity of the silver-plated copper substrates, the process could not be used for recording moving scenes. A crucial combination of new technologies had already been developed in Vienna around 1840. The breakthrough came from increas...

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....

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 electrica...

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)...

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 differe...

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-backgroun...

The Vienna Genesis: Material analysis and conservation of a Late Antique illuminated manuscript on purple parchment Abstract The Vienna Genesis (Austrian National Library, Codex Theologicus graecus 31) is a fragmentary Greek manuscript of the Book of Genesis written on purple dyed parchment with silver ink. It is assumed that the book was created i...

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...

Metal induced crystallization using aluminum (Al) as catalytic metal was applied to achieve low-temperature crystallization of amorphous silicon (a-Si) on 4H-SiC. Epitaxial crystallization of Si grains was found to occur on off-axis 4H-SiC at very low temperatures using X-ray diffractometry (XRD). In-situ heating XRD measurements revealed an onset...

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 syst...

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 co...

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 t...

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 experi...

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...

Thermochemical energy storage is considered as an auspicious method for the recycling of medium-temperature waste heat. The reaction couple Mg(OH)2–MgO is intensely investigated for this purpose, suffering so far from limited cycle stability. To overcome this issue, Mg(OH)2, MgCO3, and MgC2O4·2H2O were compared as precursor materials for MgO produc...

We report the low-temperature properties of phase-pure single crystals of the half-Heusler compound CuMnSb grown by means of optical float-zoning. The magnetization, specific heat, electrical resistivity, and Hall effect of our single crystals exhibit an antiferromagnetic transition at $T_{\mathrm{N}} = 55~\mathrm{K}$ and a second anomaly at a temp...

We report the low-temperature properties of phase-pure single crystals of the half-Heusler compound CuMnSb grown by means of optical float-zoning. The magnetization, specific heat, electrical resistivity, and Hall effect of our single crystals exhibit an antiferromagnetic transition at $T_{\mathrm{N}} = 55~\mathrm{K}$ and a second anomaly at a temp...

Criteria for a technologically relevant spin crossover (SCO) material include temperature and abruptness. A series of Fe(II) - 1,3 bis((1H tetrazol 1 yl)methyl)bicyclo[1.1.1]pentane SCO complexes with various anions (BF4-, ClO4-, PF6-) designed by a structure-property based concept is reported. All complexes feature abrupt SCO-behavior with T1/2 be...

Aiming for highly reactive and reversible thermochemical energy storage materials based on magnesium hydroxide, the impact of Ca2⁺ as dopant in magnesium hydroxide/oxide is investigated in article number 1700096 by Danny Müller and co-workers. Calcium doped magnesium oxide reveals notably increased water dissociation rates, compared to pure MgO, en...

Calcium doping of magnesium oxide results in significantly increased water dissociation rates, thus enhancing both hydration rate and reaction completeness of hydration compared to pure MgO. For a series of mixed magnesium–calcium oxides (MgxCa1−xO) with varying Ca contents between 0% and 40%, the material of a composition Mg0.9Ca0.1O shows the fas...

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,...

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 wa...

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 cann...

The low energy magnetic excitation spectrum of charge stripe ordered La(2-x)Sr(x)NiO4, x = 0.4 and x = 0.45 were studied by neutron scattering. Two excitation modes are observed in both materials, one from the ordered magnetic moments, and a second mode consistent with pseudo-one-dimensional antiferromagnetic excitations of the charge stripe electr...

We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe2TiSn we observe evidence for incipient ferromagnetic qua...

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 (Li 4.4 Si) of silicon with lithium ions...

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 e...

The Wiener Neustadt Hoard - Material Analysis and Clarification of the Excavation Site

We present a combined density-functional-perturbation-theory and inelastic neutron scattering study of the lattice dynamical properties of YNi2B2C. In general, very good agreement was found between theory and experiment for both phonon energies and line widths. Our analysis reveals that the strong coupling of certain low energy modes is linked to t...

We present a combined density functional perturbation theory and inelastic neutron scattering study of the lattice dynamical properties of YNi2B2C. In general, very good agreement was found between theory and experiment for both phonon energies and line widths. Our analysis reveals that the strong coupling of certain low energy modes is linked to t...

Im Rahmen eines vom Jubiläumsfonds der Oesterreichischen Nationalbank von Juli 2006 bis Juni 2010 geförderten Projektes (Projekt-Nr. 11990) wurde ein in der Sammlung antiker Münzen am Münzkabinett des Kunsthistorischen Museums weit verbreitetes Korrosionsproblem an antiken Bronzemünzen mit verschiede-nen Methoden zerstörungsfrei dokumentiert sowie...

Stresses in the near-surface area can form cracks which join together, propagate and combine, forming pits due to material spall-off. The stresses causing the cracks are not only influenced by external forces, residual stresses stored in the material also play an important role. Moreover, these residual stresses can vary during the lifetime of the...

Kurzfassung Die Restaustenit-Analyse mittels Röntgen-Beugungsverfahren wird häufig nach standardisierten Verfahren wie ASTM E975-03 [1] oder SAE-SP-452 [2] durchgeführt. Die Verfahren basieren auf der Analyse der integralen Intensitätsverhältnisse von wenigen Beugungsreflexen für die einzelnen Phasen. Die Anpassung erfolgt modellfrei bezüglich der...

The increasing worldwide energy consumption calls for the design of more efficient energy systems. Thermoelectrics could be used to convert waste heat back to useful electric energy if only more efficient materials were available. The ideal thermoelectric material combines high electrical conductivity and thermopower with low thermal conductivity....

Following the discovery of a universal novel magnetic order in the pseudogap phase of the cuprates [B. Fauqué et al. PRL 96, 197001 (2006); Y. Li et al., Nature 455, 372 (2008)], our inelastic neutron scattering measurements of HgBa2CuO4+δ (Hg1201) revealed two weakly-dispersive excitation branches associated with this ordered state [Y. Li et al.,...

The magnetic excitation spectrums of charge stripe ordered La(2-x)Sr(x)NiO(4) x = 0.45 and x = 0.4 were studied by inelastic neutron scattering. We found the magnetic excitation spectrum of x = 0.45 from the ordered Ni^2+ S = 1 spins to match that of checkerboard charge ordered La(1.5)Sr(0.5)NiO(4). The distinctive asymmetry in the magnetic excitat...

There exists increasing evidence that the phase diagram of the high-transition temperature (Tc) cuprate superconductors is controlled by a quantum critical point. One distinct theoretical proposal is that, with decreasing hole-carrier concentration, a transition occurs to an ordered state with two circulating orbital currents per CuO2 square. Below...

We report on the vibrational properties of the ferromagnetic shape memory alloy system Ni-Mn-Ga in its stoichiometric Ni2MnGa and off-stoichiometric Ni49Mn32Ga19 compositions. Elastic and inelastic neutron scattering measurements at different temperatures are presented with a focus on the austenite phase and compared to first-principles calculation...

We report an inelastic neutron scattering investigation of phonons with energies up to 159 meV in the conventional superconductor YNi$_2$B$_2$C. Using the SWEEP mode, a newly developed time-of-flight technique involving the continuous rotation of a single crystal specimen, allowed us to measure a four dimensional volume in (Q,E) space and, thus, de...

We present an inelastic neutron scattering study of phonon lineshapes in the vortex state of the type-II superconductor YNi$_2$B$_2$C. In a previous study [Phys. Rev. Lett. \textbf{101}, 237002 (2008)] it was shown that certain phonons exhibit a clear signature of the superconducting gap $2\Delta$ on entering the superconducting state. Our interest...

In this paper we explore the phase diagram and excitations of a distorted triangular lattice antiferromagnet. The unique two-dimensional distortion considered here is very di?erent from the 'isosceles'-type distortion that has been extensively investigated. We show that it is able to stabilize a 120{\deg} spin structure for a large range of exchang...

The dynamics of silver-alkali halide mixed single crystals (Ag(x)Na(1-x)Br, x = 0.23, 0.35, 0.40 and 0.70) were studied by inelastic neutron scattering during the process of spinodal decomposition. Using the thermal three-axes spectrometer PUMA as well as the time-of-flight spectrometer IN5, the time evolution of phonons was observed in time-resolv...

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 s...

We report on the observation of novel magnetic excitations in the pseudogap phase of the cuprate superconductor HgBa2CuO4+δ (Hg1201) using neutron scattering, and on their relationship with antiferromagnetic (AF) fluctuations. Following polarized neutron diffraction experiments that demonstrated a novel (q=0) magnetic order in the pseudogap phase [...

Motivated by predictions of a substantial contribution of the "buckling" vibration of the CuO2 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 YBa2Cu3O7. The data reveal a pronounced softening of the phonon at the in-plane wave vector q =...

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 orde...

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 itin...

Neutron scattering for Nd2-xCexCuO4+delta ( x≈0.155 , Tc=25K ) reveals two distinct magnetic energy scales in the superconducting state: omega1≈6.4meV and omega2≈4.5meV . These magnetic energies agree quantitatively with the B1g/B2g and A1g features observed in electronic Raman scattering, where the former is believed to indicate the maxim...

The elucidation of the pseudogap phenomenon of the high-transition-temperature (high-T(c)) copper oxides-a set of anomalous physical properties below the characteristic temperature T* and above T(c)-has been a major challenge in condensed matter physics for the past two decades. Following initial indications of broken time-reversal symmetry in phot...

We study the symmetry of spin excitation spectra in 122-ferropnictide superconductors by comparing the results of first-principles calculations with inelastic neutron-scattering (INS) measurements on BaFe1.85Co0.15As2 and BaFe1.91Ni0.09As2 samples that exhibit neither static magnetic phases nor structural phase transitions. In both the normal and s...

We study the symmetry of spin excitation spectra in 122-ferropnictide superconductors by comparing the results of first-principles calculations with inelastic neutron scattering (INS) measurements on BaFe1.85Co0.15As2 and BaFe1.91Ni0.09As2 samples that exhibit neither static magnetic phases nor structural phase transitions. In both the normal and s...

We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa(2)Cu(3)O(6.6), an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures a...

The elucidation of the pseudogap phenomenon of the cuprates, a set of anomalous physical properties below the characteristic temperature T* and above the superconducting transition temperature Tc, has been a major challenge in condensed matter physics for the past two decades. Following initial indications of broken time-reversal symmetry in photoe...

We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa2Cu3O6.6, an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and tri...

Below its ordering temperature at 105 K, perovskite-type SrTiO(3) exhibits a tetragonal phase with three different structural domains that are strongly influenced by the application of uniaxial mechanical stresses and electric fields. A careful neutron diffraction study of superlattice reflections provides full quantitative information about the va...

Magnetic Cooper-pairing mechanisms have been proposed for heavy-fermion and cuprate superconductors; however, strong electron correlations and complications arising from a pseudogap or competing phases have precluded commonly accepted theories. In the iron arsenides, the proximity of superconductivity and antiferromagnetism in the phase diagram, th...

CeCu2Ge2 is the counterpart of the heavy-fermion superconductor CeCu2Si2. CeCu2Ge2 is a magnetically ordering (TN= 4.1 K) Kondo lattice with a moderate Sommerfeld coefficient of 140 mJ/molK^2 [1]. Inelastic neutron measurements on a polycrystalline sample revealed a doublet ground state and a quasi-quartet at 16.5 meV [1] though a splitting of the...

Inelastic neutron-scattering measurements of single- CuO2 -layer HgBa2CuO4+delta reveal an antiferromagnetic resonance with energy omegar=56meV (≈6.8kBTc) below the superconducting transition temperature Tc≈96K . The resonance is energy-resolution limited and exhibits an intrinsic momentum width of about 0.2Å-1 , consistent with prior work on...

We present an analytical formalism investigating effects of multiple excitations with different dispersion parameters in the context of neutron resonance spin echo spectroscopy. This allows identifying conditions to obtain high resolution information on the energy split of two dispersive modes which may differ or not in their local energy gradient....

We present our latest experimental results for the pseudogap phase of the model high-Tc superconductor HgBa2CuO4+delta. Refinement of our polarized neutron diffraction experiments [Y. Li et al., Nature 455, 372 (2008)] using sizable single-crystals of this structurally simple compound consistently show a novel magnetic order below the pseudogap tem...

One of the most intriguing issues in the field of high-Tc superconductivity is the electron-hole asymmetry: the hole- or electron-doping of the parent Mott insulators leads to superconductors with differing properties. For the comparatively less-studied electron-doped materials, the antiferromagnetic phase extends much further with doping and appea...

We show that the superconducting energy gap 2Delta can be directly observed in phonon spectra, as predicted by recent theories. In addition, since each phonon probes the gap on only a small part of the Fermi surface, the gap anisotropy can be studied in detail. Our neutron scattering investigation of the anisotropic conventional superconductor YNi2...

The magnetism of charge-stripe-ordered La(1.55)Sr(0.45)NiO(4) was studied by a combination of neutron diffraction, muon-spin relaxation (mu SR), and bulk susceptibility. Long-range magnetic ordering was observed at a lower temperature by mu SR than by neutron diffraction, consistent with a glassy transition to the ordered phase. A second magnetic t...

The magnetism of charge-stripe-ordered La1.55Sr0.45NiO4 was studied by a combination of neutron diffraction, muon-spin relaxation (muSR) , and bulk susceptibility. Long-range magnetic ordering was observed at a lower temperature by muSR than by neutron diffraction, consistent with a glassy transition to the ordered phase. A second magnetic transiti...

We present an inelastic neutron scattering study of the structurally simple single-layer compound HgBa$_2$CuO$_{4+\delta}$ close to optimal doping ($T_c \approx 96$ K). A well-defined antiferromagnetic resonance with energy $\omega_r = 56$ meV ($\approx 6.8 k_BT_c$) is observed below the superconducting transition temperature $T_c$. The resonance m...

The magnetic excitations in multiferroic TbMnO3 have been investigated by inelastic scattering of polarized and unpolarized neutrons in the ferroelectric cycloidal and in the paraelectric collinear phase. The polarization analysis of the excitations at the incommensurate magnetic zone center allows one to determine the characters of three distinct...

We show that the superconducting energy gap $\Delta$ can be directly observed in phonon spectra, as predicted by recent theories. In addition, since each phonon probes the gap on only a small part of the Fermi surface, the gap anisotropy can be studied in detail. Our neutron scattering investigation of the anisotropic conventional superconductor YN...

Phonons in a metal interact with conduction electrons which give rise to a finite linewidth. In the normal state, this leads to a Lorentzian shape of the phonon line. Density functional theory is able to predict the phonon linewidths as a function of wave vector for each branch of the phonon dispersion. An experimental verification of such predicti...

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 tra...

We report on the structural instability of Ni2MnAl from calorimetry measurements and inelastic neutron scattering. The acoustic and optical phonon dispersions along the high-symmetry [ξ00], [ξξ0], and [ξξξ] directions have been interpolated from the normal modes of vibration using the Born–von Kármán model. The tendency of Ni2MnAl to undergo a mart...

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. Th...

Inelastic neutron scattering for Nd$_{2-x}$Ce$_x$CuO$_{4+\delta}$ near optimal doping reveals a change of the dynamic magnetic susceptibility at the antiferromagnetic zone center from the normal to the superconducting state consistent with the existence of two energy scales: E1 ~ 6.5 meV and E2 ~ 4.3 meV. The value of E1 agrees with the electronic...

Orbital degrees of freedom play an important role in the physics of strongly correlated electron systems. Our extensive investigation of insulating vanadates by neutron scattering has led to the discovery of an unusual magnetic ground state. YVO3 exhibits two magnetic phases, a C-type phase between 116 K and 77 K and a G-type phase below 77 K. Whil...