Active research in the field of condensed matter and nanotechnology not only led to significant progress in understanding the mechanisms of formation of electrical polarization and magnetoelectric phenomena, but also showed the possibilities of creating new classes of devices based on a combination of magnetoelectric and piezoelectric properties. Meanwhile, macroscopic properties, such as multiferroism and piezoelectricity, are associated with local structural changes that occur under the influence of external perturbations. In a first step chosen crystal structures are analyzed by means of density functional theory (DFT) to validate the connection of external stress and internal change of lattice symmetry as well as atomic displacements. Among them are TeO 2 , Li 2 B4O 7 , ZnO and SrTiO 3 . Also in focus is the influence of oxygen vacancies on our structures. The research is currently accompanied by experiments in which standing acoustic waves are encoupled in crystal samples to change the structure parameters and particularly the structures' symmetry locally. Because the displacements are expected to be on the picometer scale, X-ray diffraction on forbidden reflections is applied to observe the induced effects. The obtained switching results can significantly widen the range of functional materials and can be directly used in modern technological applications.

To gain an overview of the various structure reports on RSi2 and R2TSi3 compounds (R is a member of the Sc group, an alkaline earth, lanthanide or actinide metal, T is a transition metal), compositions, lattice parameters a and c, ratios c/a, formula units per unit cell, and structure types are summarized in extensive tables and the variations of these properties when varying the R or T elements are analyzed. Following the structural systematization given in Part I, Part II focuses on revealing the driving factors for certain structure types, in particular, the electronic structure. Here, concepts of different complexity are presented, including molecular orbital theory, the principle of hard and soft acids and bases, and a Bader analysis based on Density Functional Theory calculations for representatives of the reported structure types. The potential Si/T ordering in different structures is discussed. Additionally, the influences from intrinsic and extrinsic properties (e.g. elemental size and electronics as well as lattice parameters and structure type) are investigated on each other using correlation plots. Thermal treatment is identified as an important factor for the ordering of Si/T atoms.

Here, structural parameters of various structure reports on RSi2 and R2TSi3 compounds [where R is an alkaline earth metal, a rare earth metal (i.e. an element of the Sc group or a lathanide), or an actinide and T is a transition metal] are summarized. The parameters comprising composition, lattice parameters a and c, ratio c/a, formula unit per unit cell and structure type are tabulated. The relationships between the underlying structure types are presented within a group-subgroup scheme (Bärnighausen diagram). Additionally, unexpectedly missing compounds within the R2TSi3 compounds were examined with density functional theory and compounds that are promising candidates for synthesis are listed. Furthermore, a correlation was detected between the orthorhombic AlB2-like lattices of, for example, Ca2AgSi3 and the divalence of R and the monovalence of T. Finally, a potential tetragonal structure with ordered Si/T sites is proposed.

Crystallography is a powerful descriptor of the atomic structure of solid-state matter and can be applied to analyse the phenomena present in functional materials. Especially for ion diffusion - one of the main processes found in electrochemical energy storage materials - crystallography can describe and evaluate the elementary steps for the hopping of mobile species from one crystallographic site to another. By translating this knowledge into parameters and search for similar numbers in other materials, promising compounds for future energy storage materials can be identified. Large crystal structure databases like the ICSD, CSD, and PCD have accumulated millions of measured crystal structures and thus represent valuable sources for future data mining and big-data approaches. In this work we want to present, on the one hand, crystallographic approaches based on geometric and crystal-chemical descriptors that can be easily applied to very large databases. On the other hand, we want to show methodologies based on ab initio and electronic modelling which can simulate the structure features more realistically, incorporating also dynamic processes. Their theoretical background, applicability, and selected examples are presented.

Monoatomic ion sputtering is a common concept for surface sensitive analysis methods to clean surfaces prior investigation or to obtain information from deeper regions. However, severe damage of the materials - linked to preferential sputtering, ion implantation, atomic mixing and in worst case chemical degradation - can affect the validity of the analysis. Hence, the impact of C-60 cluster etching, furthermore, of Ar+ ion bombardment with and without azimuthal sample rotation and also the application of heavy projectiles (Xe+ ions) was investigated to find a concept, which is less destructive or with less critical influence on the chemical nature of the investigated materials. In this work the focus is set on hydrozincite and zinc oxide, two common corrosion products of Zn-based coatings. As a main point, all the obtained results from (i)Ar+ ion, (ii) Ar cluster, and (iii) C-60 cluster etching on the degradation kinetics of hydrozincite were compared with respect to the reached sputter depth. In addition, the sputter rate of all three methods was experimentally determined for ZnO. In total, fully non-destructive conditions could not be found, but valuable knowledge on the type and rate of degradation, which is essential to choose the most suited sputter concept. (C) 2017 Elsevier B.V. All rights reserved.

13C-enriched fine-grained graphitic material has been studied towards its potential for chemical and electrochemical applications. The structural and morphological modification of the material as results of pressure-assisted thermal treatment and gaseous BrF3 and/or Br2 room-temperature treatments has been investigated using a combination of the characterization tools: electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy, solid state nuclear magnetic resonance (NMR) spectroscopy and magnetic susceptibility measurements. It has been found that the starting material represents graphitized carbon with oxygen containing defects. The evidence of distorted sp2 hybridization of carbon was found in the Raman and the 13C NMR spectra. Under high pressure and temperature, some initially open graphitic edges are coupled that causes decreasing specific surface area and mean in-plane size of crystallites, and, generally, a higher degree of disorder. The Br2 treatment improves the material structure due to removal of tiny graphitic flakes and oxygenated carbon groups. The use of BrF3 results, in addition, in partial fluorination of graphitic material. Electrochemical characteristics along with a high degree of 13C isotope enrichment enable the application of these graphitic materials in operando studies using methods sensitive to 13C isotope, such as NMR.

In this work, we determine the dielectric functions of multi-target, reactively sputtered Ba(Zr0·2Ti0.8)O3 by spectroscopic ellipsometry in the photon energy range from 0.8 to 8.7eV. Based on this data, we discuss the interband transition energies and the spectral dependencies of the refractive index and the absorption coefficient.

Defect engineering is an effective and powerful tool to control the existing material properties and produce completely new ones, which are symmetry-forbidden in a defect-free crystal. For example, the application of a static electric field to a single crystal of SrTiO3 forms a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. While it was previously shown that this near-surface phase holds pyroelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO3, this paper reports that the same phase is strongly piezoelectric. We demonstrate the piezoelectricity of this phase through stroboscopic time-resolved X-ray diffraction under alternating electric field and show that the effective piezoelectric coefficient d33 ranges between 60 and 100 pC/N. The possible atomistic origins of the piezoelectric activity are discussed as a coupling between the electrostrictive effect and spontaneous polarization of this near-surface phase.

Hydrogen incorporation into lithium niobate and lithium tantalate during crystal growth has attracted research interest for a long time, but the diffusion paths and defect sites within the materials are only partially understood. In the present study, the hydrogen defect is investigated by crystal orientation and light polarization resolved FT-IR spectroscopy. The OH− absorption band is splitting in two sub-bands, which are significantly affected by intrinsic defects. We attribute the line broadening of both band components to the antisite defect cluster, which is decorated by hydrogen. LiNbO3 and LiTaO3 although, isomorphic in crystal and defect structure, differ significantly in their antisite defect cluster concentration and, as we show, also in the occupation of hydrogen bonding sites in the structure.

Impedance spectroscopy and Li-7 NMR have been applied to characterize the lithium conducting glass-ceramics membranes of the Li1.5Al0.5Ge1.5(PO4)(3) composition with the NASICON-type structure. The Li-7 NMR spectra and T-1 relaxation times have been compared for the precursor glass and two glass-ceramics annealed for 2 and 6 hours, and analysed with respect to the ionic conductivity in these materials. The Li-7 static NMR spectra reveal two components in the glass-ceramics samples: A quadrupole pattern with C-Q of 38.7 kHz and 32.5 kHz, and a narrow signal of the Lorentzian or Gaussian lineshape for the samples annealed for 2 and 6 hours, respectively. Variation of the lineshape and the deconvolution parameters point out to the modification of the NASICON framework in the former, which affects the conductivity channels towards improved movement of lithium ions. The NMR data correlate with the conductivity measurements demonstrating enhanced ionic mobility in the glass-ceramics annealed for 2 hours. The Li-7 NMR relaxation data seem to be very sensitive to the species with different mobility and reveal the presence of an additional minor component, which can be responsible for decrease of conductivity at longer thermal treatment.

Defect engineering is an effective and powerful tool to control existing material properties and create completely new ones, which are symmetry-forbidden in a defect-free crystal. This letter reports on the creation of piezoelectrically active near-surface layer of centrosymmetric SrTiO3, modified by the electric field-induced migration of oxygen vacancies. We provide the unequivocal proof of piezoelectricity through the stroboscopic time-resolved X-ray diffraction under alternating electric field. The magnitude of the discovered piezoelectric effect is comparable with the bulk piezoelectric effect in commercial ferroelectric materials. Such artificially formed defect-mediated piezoelectricity can be important as an alternative road for smart materials design.

Monoatomic ion guns mounted on X-ray photoelectron spectrometers are frequently used for depth profiling to determine the depth distribution of various chemical compounds, or for surface cleaning. Sputtering with single ions may cause severe damage to some materials. Hence, in this study the influence of different sputter parameters on the degradation kinetics was examined. For comparison, the potential of Ar cluster sputtering was tested with the same materials, namely hydrozincite and FeO two representatives of corrosion products that are susceptible to degradation. Chemical damage could only be minimized by cooling or cluster sputtering within a narrow cluster energy window. (C) 2015 Elsevier Ltd. All rights reserved.

Thin films of pure Ge and ZrO2, composite Ge-ZrO2 layers and [Ge-ZrO2/ZrO2]40 multilayers were fabricated by confocal radio frequency magnetron sputtering. The structural and optical properties of these samples were studied by spectroscopic ellipsometry, Raman scattering and Fourier transform infrared spectroscopy in dependence of the chemical composition and the annealing treatment. It could be shown that rapid thermal annealing stimulates a phase separation process within the Ge-ZrO2 composite films leading to a formation of Ge nanocrystals and tetragonal ZrO2. The starting point of this process depends significantly on the Ge content: the higher the Ge content, the lower is the crystallization temperature. Compared to the monoclinic phase, the tetragonal ZrO2 phase offers an enhanced permittivity.

The atomic layer deposition (ALD) of stoichiometric SrTiO3 as well as layers with either Sr or Ti excess from the commercial precursors Bis(tri-isopropylcyclopentadienyl)-strontium Sr(iPr3Cp)2, Tetrakis-(dimethylamido)titanium(IV) Ti[N(CH3)2]4 and H2O on a commercial ALD system is demonstrated. The influence of the stoichiometry on the optical layer properties was investigated. Spectroscopic ellipsometry shows that all SrxTiyOz layers are transparent up to the optical gap energy, which amounts to 3.87eV for stoichiometric SrTiO3. A direct correlation between the Sr content, optical properties, layer density and the growth per cycle value was determined. X-ray photoelectron spectroscopy after Ar ion cluster sputtering indicates that the layers are free of carbon. After ex situ annealing under atmospheric conditions we observed a change in microstructure from amorphous to polycrystalline starting at 545°C by atomic force microscopy and grazing incidence X-ray diffraction. Electrical I–V measurements show very small leakage currents confirming the insulating character of the SrxTiyOz layers.

The dielectric properties of atomic layer deposited pure Al2O3 and Si doped Al2O3 thin films were characterized by various measurement techniques. By the use of capacitance voltage and conductance measurements charged defects within the oxide and at the silicon interface were detected. It was shown that the passivation quality of Al2O3 is strongly related to the density of fixed oxide charges Qf and the interface trap density Dit. The fixed charge density could be adjusted from -6.2∙1012 cm-2 for samples annealed at 500°C to +2.1∙1012 cm-2 for as deposited Si doped layers. Additionally current voltage characteristics were performed in a temperature range from 25°C to 125°C. The leakage current was found to increase with higher temperature. A barrier height of 0.4 eV was extracted from the data by assuming a Pool-Frenkel mechanism.

Nitrogen ion implantation into strontium titanate single crystals causes a slight shift of the Ti-K edge position compared to pristine SrTiO3 and a strong increase of the second pre-edge peak in X-ray absorption near-edge spectroscopy (XANES) using grazing incidence geometry. Calculations by a finite difference method demonstrate that the strong increase of the second pre-edge feature in the defect distorted phase can be attributed to a static displacement of the Ti atom relative to the surrounding oxygen octahedron. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.