Polycrystalline Li0.4WO3 bronze has been synthesized by solid state reaction carried out in a silica tube at 10(-7) MPa and 973 K. The sample is characterized by temperature-dependent neutron elastic and quasielastic scatterings. The room-temperature neutron powder data Rietveld refinement confirmed the space group Im (3) over bar along with lithium occupancy found predominantly at the 6b crystallographic site. Upon increasing temperature above 300 K lithium at 6b site decreases and at 2a site increases, suggesting Li+ cation diffusion between these two sites demonstrated by quasielastic neutron scattering as well. The lattice thermal expansion anomaly is observed between 380 K and 450 K, which is explained in terms of lithium dynamic disorder (non-equilibrium) as complemented by elastic and quasielastic neutron scatterings. DFT calculations with different lithium distributions at two different crystallographic sites guide to understand the lattice expansion anomaly. The lattice thermal expansion is modeled using Gruneisen first-order approximation, where the Debye-Einstein-Anharmonicity approach provides the temperature-dependent vibrational energy. The DFT-calculated phonon density of states and bulk modulus help extract the characteristic Debye and Einstein frequencies.

While polynomial coefficients cannot explain the physical parameters associated, the Debye-Einstein-Anharmonicity (DEA) model [1, 2] adequately describes the temperature-dependent vibrational energy in the Grüneisen first-order approximation for lattice thermal expansion of a crystalline solid. In the DEA model, the Grüneisen parameter accounts for the isothermal and the anharmonicity parameter for the isochoric anharmonicity. Beside such advantages in DEA that concomitantly holds both quasi-harmonic and low-perturbed anharmonic [3] terms, this model is limited to explain metric thermal expansions close to phase transitions. For instance, framework material |Na8I2|[AlSiO4]6 sodalite [4] shows Landau-type tri-critical phase transition at 1080(6) K driven by tilt mechanism. The DEA model strikingly departs from the evolution of lattice parameters from 820(10) K up to the Tc. The kentrolite-type Pb2In2Si2O9 exhibits a second order phase transition at 778(5) K due to group-subgroup driven coordinate changes; again, the thermal expansion between 580(10) K and Tc cannot be modeled using DEA. Starting from the Landau theory for phase transitions [5-7], we propose a model that considers additional energy contributions integrated into the DEA, leading to metric parameter calculations close to phase transition. Adding the gliding (G) function to the temperature-dependent changes of internal energy essentially extends the general description as DEA+G. Thus, for the temperature-dependent metric parameter (Mi(T)) the Grüneisen first-order approximation can be expressed as:

The photocatalytic activity of titanium dioxide (TiO2) results from its crystalline phase's anatase and rutile. In this regard, plasma electrolytic oxidation (PEO) is a promising process for producing highly porous surfaces with a high proportion of crystalline phases into the oxide layer on pure titanium. PEO-coatings were produced under different conditions in various electrolytes in order to identify the crystalline fractions of the surfaces and to examine the associated photocatalytic activity. The composition of the PEO electrolyte was varied to optimize the polymorphic composition of the TiO(2 )comparable to the photocatalytic active TiO2 material AEROXIDE (R) P25. X-ray powder diffraction (XRD) was selected to identify the produced crystal structures of anatase and rutile on the surface material depending on the electrolytic system. In order to establish the expected band gap of the TiO2 on the surfaces, the samples were subjected to a diffuse reflectance measurement, which detected direct transitions for all samples using the TAUC and DASF methods. The acceptance of the photocatalytic reaction by the crystalline PEO-samples was further confirmed by the degradation of two typical dyes (methylene blue MB, rhodamine B RB) under UV-light irradiation. Both a high proportion of anatase and the presence of rutile on the PEO-layers had a targeted effect on the catalytic efficiency. However, the average crystallite sizes also played an important role in the samples produced in an optimum range of 30-40 nm. Both effects support the photocatalytic properties of PEO-surfaces.

Plasma electrolytic oxidation (PEO) is a type of high-voltage anodic oxidation process capable of producing a thick oxide layer with a wide variety of structural and chemical properties influenced by the electrolytic system. This process enables the combined adjustment of various characteristics, i.e. the morphology and chemical composition. The procedure facilitates the possibility of generating an individual structure as well as forming a crystalline surface in a single step. A highly porous surface with a high crystalline content consisting of titanium dioxide phases is ensured through the process of plasma electrolytic oxidizing pure titanium. In the present study plasma electrolytic oxidized TiO2-layers were investigated regarding their crystallinity through the layer thickness. The layers were prepared with a high applied voltage of 280 V to obtain a PEO-layer with highly crystalline anatase and rutile amounts. Raman spectroscopy and electron backscatter diffraction (EBSD) were selected to clarify the structure of the oxide layer with regard to its crystallinity and phase composition. The composition of the TiO2-phases is more or less irregularly distributed as a result of the higher energy input on the uppermost side of the layer. Scanning transmission electron microscopy (STEM) provided a deeper understanding of the structure and the effects of plasma discharges on the layer. It was observed that the plasma discharges have a strong influence on crystallite formation on top of the oxide layer and also at the boundary layer to the titanium substrate. Therefore, small crystallites of TiO2 could be detected in these regions. In addition, it was shown that amorphous TiO2 phases are formed around the characteristic pore structures, which allows the conclusion to be drawn that a rapid cooling from the gas phase had to take place in these areas. (C) 2018 Elsevier B.V. All rights reserved.

Synthesis of chlorine-free, rare earth oxide aerogels from the lanthanide series was achieved using a modified epoxide-assisted sol-gel method. An ethanolic solution of the hydrated metal nitrate, propylene oxide, and ammonium carbonate was found to gel upon heating to 333 K. Critical point drying of the wet gel in CO 2 yielded monolithic aerogels. Most of the aerogels were amorphous as-prepared, but became nano-crystalline after calcination at 923 K in air. The aerogels had high surface areas (up to 150 m 2 /g), low densities (40–225 mg/cm 3 ), and were photoluminescent.

A highly porous surface with a high crystalline content and resultant photocatalytic activity is ensured through the process of plasma electrolytic oxidation on pure titanium. In the present study the morphology, crystallinity and photocatalytic activity of plasma electrolytic oxidized TiO2-surfaces were investigated. The surfaces were prepared in acidic and alkaline electrolytes over an applied voltage range between 50V and 300V to optimize the crystalline and photocatalytic properties. Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) were selected to determine the morphologies which differ according to the type of electrolyte as well as the crystal structures of anatase and rutile on the surface material, which increase with the applied voltage. The oxide surfaces did not show morphological differences compared to typical PEO surfaces with the exception of oxide films obtained in H2SO4-solution which also exhibited an astounding amount of rutile even with low applied voltages. The increased parts of anatase and rutile on the surfaces resulted in photocatalytic activity, which was investigated under UV-light using methylene blue, while the PEO surfaces showed degradation activity. There is an indication that a high proportion of anatase and small amounts of rutile in the PEO layers positively influence photocatalytic activity.

The photocatalytic activity of titanium dioxide (TiO2) results from its crystalline phase’s anatase and rutile. In this regard, plasma electrolytic oxidation (PEO) is a promising process for producing highly porous surfaces with a high proportion of crystalline phases into the oxide layer on pure titanium. PEO-coatings were produced under different conditions in various electrolytes in order to identify the crystalline fractions of the surfaces and to examine the associated photocatalytic activity. The composition of the PEO electrolyte was varied to optimize the polymorphic composition of the TiO2 comparable to the photocatalytic active TiO2 material AEROXIDE® P25. X-ray powder diffraction (XRD) was selected to identify the produced crystal structures of anatase and rutile on the surface material depending on the electrolytic system. In order to establish the expected band gap of the titanium dioxides on the surfaces, the samples were subjected to a diffuse reflectance measurement, which detected direct transitions for all samples using the TAUC and DASF methods. The acceptance of the photocatalytic reaction by the crystalline PEO-samples was further confirmed by the degradation of two typical dyes (methylene blue MB, rhodamine B RB) under UV-light irradiation. Both a high proportion of anatase and the presence of rutile on the PEO-layers had a targeted effect on the catalytic efficiency. However, the average crystallite sizes also played an important role in the samples produced in an optimum range of 30 40 nm. Both effects support the photocatalytic properties of PEO-surfaces.

Al-rich aluminum borates were prepared by different synthesis routes using various Al/B ratios, characterized by diffraction methods, spectroscopy and prompt gamma activation analysis. The B-11 NMR data show a small amount of BO4 species in all samples. The chemical analysis indicates a trend in the Al/B ratio instead of a fixed composition. Both methods indicate a solid solution Al5-xB1+xO9 where Al is substituted by B in the range of 1-3%.The structure of B-rich Al4B2O9 (C2/m, a=1488 pm, b=553 pm, c=1502 pm,beta=90.6 degrees), was re -investigated by electron diffraction methods, showing that structural details vary within a crystallite. In most of the domains the atoms are orderly distributed, showing no signal for the postulated channel oxygen atom O5. The absence of O5 is supported by density functional theory calculations. Other domains show a probable disordered configuration of O5 and 010, indicated by diffuse scattering along the b direction.

Mullite-type Al6−xBxO9 compounds were studied by means of powder diffraction and spectroscopic methods. The backbones of this structure are chains of edge-connected AlO6 octahedra crosslinked by AlO- and BO-polyhedra. Rietveld refinements show that the a and b lattice parameters can be well resolved, thus representing an orthorhombic metric. A continuous decrease of the lattice parameters most pronounced in c-direction indicates a solid solution for Al6−xBxO9 with 1.09≤x≤2. A preference of boron in 3-fold coordination is confirmed by 11B MAS NMR spectroscopy and Fourier calculations based on neutron diffraction data collected at 4K. Distance Least Squares modeling was performed to simulate a local geometry avoiding long B-O distances linking two octahedral chains by planar BO3 groups yielding split positions for the oxygen atoms and a strong distortion in the octahedral chains. The lattice thermal expansion was calculated using the Grüneisen first-order equation of state Debye-Einstein-Anharmonicity model.

A powder sample of Li0.4WO3 was studied after exposure to air in steps up to a total exposure time of 71 days. Over this period, XPS spectra of the W 4f, O 1s and C 1s level were recorded. The spectra reveal the formation of a OH/CO3 layer rendering the powder insulating. Careful evaluation of the W 4f spectra suggests a single initial state picture in which the electron donated by Li is shared between W ions. We demonstrate how the loss of charge carriers by aging in air can be followed by the fitting parameters. Additionally, the effects of vacuum storage, inducing oxygen vacancies, and subsequent treatment with molecular oxygen are considered. (C) 2015 Elsevier B.V. All rights reserved.

We report on the structural characterization of the mullite-type PbAl1-xMnxBO4 series using neutron, synchrotron and in-house X-ray powder diffraction, Raman spectroscopy and density functional theory (DFT) calculations. The planar geometry of the BO3 group changes only slightly over the whole composition range. The rigid BO3 group plays the dominant roles in the thermal contraction in the a-direction followed by expansion in the b- and c-directions, leading to a correlation a . b/c similar to unity. The unit-cell volume at zero-pressure and 0 K was obtained, as well evaluated as the isothermal bulk-modulus from pressure dependent synchrotron X-ray diffraction using a diamond anvil cell as well as DFT calculations. Thermal expansion of the metric parameters was modeled using a first-order Griineisen approximation for the zero-pressure equation of state. We used the double-Debye-double-Einstein-Anharmonicity model to calculate the temperaturedependent internal energy of the crystalline end members. The simulation helped to understand the anisotropic thermal expansion and together with the experimental and calculated bulk moduli to approximate the thermodynamic Griineisen parameters.

The pseudo-cubic lattice parameters of rare-earth (RE) scandate, REScO3, single crystals grown by the Czochralski technique with RE = Dy to Pr lie between about 3.95 and 4.02 angstrom. These crystals are the only available perovskite substrates in this lattice constant range that can withstand virtually any thin film growth conditions. Two members of this series, PmScO3 and EuScO3, are, however, not suitable for substrate applications. Because the pseudo-cubic lattice parameters between neighbouring REScO3 compounds decrease with rising atomic number of the RE in about 0.01 angstrom steps, the unsuitability of PmScO3 (radioactivity) and EuScO3 (incompatibility with Si) causes an interruption in this lattice spacing sequence. To replace them, solid solutions of their adjacent rare-earth scandates, i.e., (Nd0.5Sm0.5)ScO3 and (Sm0.5Gd0.5)ScO3, were grown by the Czochralski method. Their average pseudo-cubic lattice parameters of 3.9979 angstrom and 3.9784 angstrom are very close to those of PmScO3 and EuScO3, respectively, and they show very low segregation. These qualities make these solid solutions excellent substitutes for PmScO3 and EuScO3.

Bi2M4O9 (M=Al, Ga, Fe) mullite-type compounds are currently being investigated with respect to their potential application as oxygen ion conductors or mixed ionic-electronic conductors. In the framework of these studies oxygen transport in (nominally) undoped and Sr-doped single crystals of Bi2Ga4O9 is of prime interest. 18O tracer diffusion in combination with secondary ion mass spectrometry (SIMS) depth profiling reveals that oxygen transport occurs via oxygen vacancies introduced by impurities of cations with lower valences in the undoped crystals grown by the top-seeded solution growth (TSSG) method. The fairly small enhancement of the oxygen diffusivity due to Sr doping leads to the conclusion that the solubility of Sr in Bi2Ga4O9 is extremely low with respect to the melt during the single crystal growing process. The measured enthalpies of activation ((163±15)kJ/mol for undoped and (140±15)kJ/mol for Sr-doped Bi2Ga4O9, respectively) must be considered as migration enthalpies.