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The output power (30–150 W) and the periodicity (20–100%) of ultrasound emission were varied in a wide range to regulate and improve the crystallization process in the commonly used co-precipitation technique of chloride-intercalated CaFe-layered double hydroxides. The influence of ultrasound irradiation on the as-prepared materials was studied by X-ray diffractometry, dynamic light scattering, UV–Vis–NIR diffuse reflectance spectroscopy, specific surface area measurement, pore size analysis, ion-selective electrode potentiometric investigations and thermogravimetry. Additionally, structural alterations due to heat treatment at various temperatures were followed in detail by Fourier-transform infrared and X-ray absorption spectroscopies as well as scanning electron microscopy. The ultrasonic treatment was capable of controlling the sizes of primarily formed (from 19 nm to 30 nm) as well as the aggregated (secondary) particles (between 450 nm and 700 nm), and thus modifying their textural parameters and enhancing the incorporation of chloride anions into the interlamellar space. For the first time, the optical energy gap of CaFe-LDH was reported here depending on the nature of applied stirring (4.18–4.34 eV). The heat-treatment investigations revealed that the layered structure was stabile until 200 °C, even at the atomic level.

An ultrasonically-enhanced mechanochemical method was developed to synthesize CaFe-layered double hydroxides (LDHs) with various interlayer anions (CO32−, NO3−, ClO4−, N3−, F−, Cl−, Br− and I−). The duration of pre-milling and ultrasonic irradiation and the variation of synthesis temperature in the wet chemical step were investigated to obtain the optimal parameters of preparation. The main method to characterize the products was X-ray diffractometry, but infrared and synchrotron-based X-ray absorption spectroscopies as well as thermogravimetric measurements were also used to learn about fine structural details. The synthesis method afforded successful intercalation of the anions, among others the azide anion, a rarely used counter ion providing a system, which enables safe handling the otherwise highly reactive anion. The X-ray absorption spectroscopic measurements revealed that the quality of the interlayered anions could modulate the spatial arrangement of the calcium ions around the iron(III) ions, but only in the second coordination sphere.

Intercalated composite materials were prepared with CaAl-layered double hydroxide as host and Cu(II)-amino acid (L-cysteine, L-histidine and L-tyrosine) complex anions as guests. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the synthesis conditions were performed to obtain composites having the complex exclusively among the layers. The composite materials were structurally characterized by powder X-ray diffractometry, mid infrared (IR) spectroscopy with ATR (attenuated total reflectance) or photoacoustic detections, transmission and scanning electron microscopies and X-ray photoelectron spectroscopy. Structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR (electron paramagnetic spectroscopy), X-ray absorption and far IR spectroscopies. Structural models based on these methods are also given. Catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants in the liquid phase. The catalysts were active in the Ullmann coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities. (Less)

The combination of mechanochemical and ultrasonic treatment was applied to synthesize CaAlFe-layered triple hydroxides with carbonate or chloride anions in the interlamellar space. The optimal parameters of the preparation were explored by altering the initial ratio of the metal ions and the temperature of ultrasonic irradiation. The resulting triple hydroxides were characterized by X-ray diffractometry, infrared and X-ray absorption spectroscopies, thermogravimetric analysis and scanning electron microscopy. The products were close-to-phase-pure CaAlFe-layered triple hydroxides. Elevation of the temperature transformed the CaAlFe-Cl(-)-layered triple hydroxide to rare oxyhalides (Ca2FeO3Cl and Ca12Al14O32Cl2).

Intercalated composite materials were prepared with CaAl-layered double hydroxide as the host and Mn(II)-amino acid (l-cysteine, l-histidine and l-tyrosine) complex anions as the guest. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the auxiliary conditions were performed to arrive at composites having the complex exclusively among the layers. The obtained substances were structurally characterized by powder X-ray diffractometry, mid IR spectroscopy in diffuse reflectance mode and with ATR or photoacoustic detections, and scanning electron microscopy. The structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR, X-ray absorption and far IR spectroscopies. Structural models are also given. The catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants and allylic alcohol with peracetic acid, in the liquid phase. The intercalated substances proved to be efficient and highly selective (with peracetic acid: outstanding epoxide, with iodosylbenzene superior diol selectivities) catalysts with very good recycling abilities. (Less)

A mechanochemical method (grinding the components without added water – dry grinding, followed by further grinding in the presence of minute amount of water or NaOH solution – wet grinding) was used in this work for the preparation and intercalation of CaFe-layered double hydroxides (LDHs). Both the pristine LDHs and the amino acid anion (cystinate and tyrosinate) intercalated varieties were prepared by the two-step grinding procedure in a mixer mill. By systematically changing the conditions of the preparation method, a set of parameters could be determined, which led to the formation of close to phase-pure LDH. The optimisation procedure was also applied for the intercalation processes of the amino acid anions. The resulting materials were structurally characterised by a range of methods (X-ray diffractometry, scanning electron microscopy, energy dispersive analysis, thermogravimetry, X-ray absorption and infra-red spectroscopies). It was proven that this simple mechanochemical procedure was able to produce complex organic–inorganic nanocomposites: LDHs intercalated with amino acid anions.

Structural, elastic and electronic properties of zircon-type and scheelite-type EuVO4 are investigated experimentally, by in-situ X-ray diffraction using synchrotron radiation, and theoretically within the framework of the density functional theory (DFT) and using the PBE prescription of the exchange-correlation energy. This study was motivated by the fact that the previous knowledge of the equation of state (EOS) was inconclusive due to a large scatter of the experimental and theoretical data, and by the lack of information on the dependence of the electronic structure with pressure. Under the applied experimental conditions, the zircon-type structure transforms to a scheelite-type one at 7.4(2) GPa, whereas the calculations yield a lower zircon-scheelite-coexistence pressure of 4.8 GPa. The experimental part of the study shows that the bulk modulus of the zircon-type phase is 119(3) GPa, perfectly supported by the DFT-calculated value, 119.1 GPa. The bulk modulus for the scheelite-type polymorph is higher, with an experimental value of 135(7) GPa and a theoretical one of 137.4 GPa. Compared to those reported in previous experimental and DFT or semiempirical works, the present values for the zircon-type phase are comparable or slightly lower, whereas those for the scheelite-type phase are markedly lower. Discrepancies between the present results and earlier reported ones are attributed to differences in details of the experimental method such as the pressure transmitting medium and the pressure calibration method. The calculated band structure confirms that zircon-type EuVO4 is a direct-gap semiconductor, with a bandgap energy at zero pressure of 2.88 eV. Under compression, the bandgap of the zircon phase increases with a coefficient of 10.3 meV/GPa up to the transition pressure, at which point the present calculations show a small drop of the bandgap energy. Above the transition pressure, the bandgap energy of the scheelite phase becomes almost constant, with a small pressure coefficient of just 1.5 meV/GPa. (C) 2015 Elsevier B.V. All rights reserved. (Less)

Co-C-protected amino acid (C-protected L-histidine, L-tyrosine, L-cysteine and L-cystine) complexes were covalently grafted onto chloropropylated silica gel, and the materials thus obtained were structurally characterised by mid/far IR and X-ray absorption spectroscopies. The superoxide dismutase-like activities of the substances were determined via the Beauchamp-Fridovich test reaction. It was found that covalent grafting and the preparation of the anchored complexes were successful in most cases. The coordinating groups varied upon changing the conditions of the syntheses. All materials displayed catalytic activity, although catalytic activities differed widely. (C) 2014 Elsevier B.V. All rights reserved.

In this work the syntheses, structure, superoxide dismutase (SOD) activity and the catalytic use in the oxidative transformations of cyclohexene of covalently grafted Mn(II)–complexes formed with various C-protected amino acid ( l -histidine, l -cysteine and l -cystine) ligands are presented. The structural features of the surface complexes were studied by EPR, X-ray absorption, and mid/far IR spectroscopies. The superoxide dismutase activities of the materials were determined in a biochemical test reaction. The obtained materials were used as catalysts for the oxidation of cyclohexene with peracetic acid in acetone. Covalent grafting and building the complex onto the surface of the chloropropylated silica gel were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Mn(II)–complexes displayed superoxide dismutase activity and could catalyse the oxidation of cyclohexene.

Covalently anchored Ni(II)–C-protected amino acid ( l -histidine, l -cysteine, and l -cystine) complexes inspired by the active site of the Ni-superoxide dismutase enzyme were synthesised using chloropropylated silica gel as support. The structural features of the surface complexes were studied by the Kjeldahl method and ICP-MS, mid/far IR, UV–vis diffuse reflectance, and X-ray absorption spectroscopies. The enzyme-like activities of the materials were determined in a biochemical test reaction. Covalent grafting and building the complex onto the surface of the support were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Ni(II)-complexes displayed enzyme-like activity. They also were active in the liquid-phase oxidation of cyclohexene, providing the epoxide with high selectivity.

We have investigated the oxidation of inorganic As(III) with H2O2 catalysed by Al2O3, using X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopy. The effects of different reaction conditions (pH, time and initial H2O2 concentration) were also studied as were the kinetics of the oxidation reaction. We demonstrated that As(III) was oxidized to As(V) in the presence of H2O2 and Al2O3. Furthermore, all arsenic species found on the Al2O3 surface were in the As(V) state. The presence of both Al2O3 and H2O2 was necessary for oxidation of As(III) to take place within the period of time studied. The oxidation kinetics indicate a mechanism where reversible As(III) binding to the alumina surface is followed by irreversible oxidation by H2O2 leading to strongly bound As(V). Results from this study indicate that there is a surface-catalysed oxidation of As(III) on Al2O3 by H2O2, a reaction that can take place in nature and can be of help in the development of novel treatment systems for As(III) removal.

The up-converting ZrO2:Yb3+,E3+ nanomaterials were prepared with the combustion and sal-gel methods. The structure of the materials was cubic except for the minor monoclinic and tetragonal impurities associated with the use of the sal-gel method. The XANES results revealed only the trivalent form for both the Yb and Er dopants. The distance distributions calculated from EXAFS confirm that Er3+ and Yb3+ occupy the Zr-IV site in the structure. The nanomaterials show red (650-700 nm) and very weak green (520-560 nm) up-conversion luminescence due to the F-4(9/2) -> I-4(15/2) and (H-2(11/2),S-4(3/2)) -> I-4(15/2) transitions of Er3+, respectively. The nanomaterials obtained with the combustion synthesis yield the most intense luminescence though showing significant afterglow, as well. The thermoluminescence measurements revealed the existence of traps with depths between 0.68 and 1.03 eV well matching to room temperature persistent emission. Finally, the mechanism for the persistent up-conversion luminescence was introduced based on the experimental results and discussed. (C) 2014 Elsevier B.V. All rights reserved. (Less)

High-pressure Raman and mid-infrared spectroscopic studies were carried out on ZrP2O7 to 23.2 and 13 GPa respectively. In the pressure range 0.7-4.3 GPa the lattice mode at 248 cm(-1) disappears, new modes appear around 380 and 1111 cm(-1) and the strong symmetric stretching mode at 476 cm(-1) softens, possibly indicating a subtle phase transition. Above 8 GPa all the modes broaden, and all of the Raman modes disappear beyond 18 GPa. On decompression from the highest pressure, 23.2, to 0 GPa all of the modes reappear but with larger full width at half maximum. Lattice dynamics of the high temperature phase of ZrP2O7 were studied using first principles method and compared with experimental values. (C) 2009 Elsevier Ltd. All rights reserved.

Experimental study of the phase transition in the lithium-excess lithium-manganese spinel over the pressure range 0-13 GPa has shown its suppression. This observation implies that the Li/Mn ratio, associated with the manganese oxidation state, plays an important role in the high-pressure phase transformation of the lithium-manganese spinels. As indicated by the results, the occupation of the octahedral sites with Li+ and Mn4+ ions stabilizes the crystallographic structure of this cubic spinel even at a high pressure. (C) 2009 Elsevier Ltd. All rights reserved.

Silver behenate, a salt of the behenic acid, known mostly for its applications in photothermographic imaging and use as a diffraction reference material, was studied by X-ray diffraction under pressures up to 11.4 GPa. Diffraction patterns were collected using a diamond anvil cell and synchrotron radiation at the 1711 beamline (MAXlab, Lund). The variation of the d spacing with pressure is determined and the potential usefulness of this dependence for pressure calibration is discussed. (C) 2009 Elsevier Ltd. All rights reserved.

The high-pressure Raman and infrared spectra of hafnium tungstate (HfW2O8) are measured up to 24 GPa at room temperature. The changes under pressure of the stretching and bending modes of the WO4 tetrahedra. as well as lattice modes have been studied. An estimate of the thermal-expansion coefficient has been made based upon the mode Gruneisen parameters and found to be in reasonable agreement with the measured value. The high-pressure spectra indicate that the alpha-gamma phase transition occurs at 0.6-0.9 GPa. in agreement with previous work. Around 2 GPa. HfW2O8 undergoes an irreversible transition from the gamma phase to an amorphous structure.

Colossal magnetoresistance (CMR) - the dramatic reduction of electrical resistivity in a magnetic field and charge ordering (CO) in rare earth manganites of the type Ln(1-x)A(x)MnO(3) [Ln: rare earth, A: divalent cation] are manifestations of the intricate relation between orbital, spin, charge and lattice degrees of freedom. Recent studies indicate that the inhomogeneous state of mixed-valence manganites - evidenced by the presence of texture and multiple phase coexistence - is important for the CMR property of manganites. Theoretical models that explain the multiphase coexistence are based on quenched disorder or strain. Here we show that lattice strain due to the Jahn-Teller (IT) distortions of MnO6 octahedra and their tilt rotations are not sufficient to provide a unique structure-property relation. We present evidence that the science of manganites should take into account shear distortions of the MnO6 octahedra as well. Pressure evolution of the lattice strain of Nd0.5Ca0.5MnO3 shows a minimum around 7 GPa, with the same lattice strain above and below this pressure achieved by shear- and JT-type distortions, respectively. In general, a particular lattice strain of manganites can be achieved by different combinations of JT-type and shear-type distortions of the MnO6 octahedra, together with their tilts, which suggest a plausible description of the inhomogeneous state in manganites as one where phases with differently distorted states having the same lattice strain are preserved. (C) 2007 Published by Elsevier Ltd.

High-pressure investigations of titanium pyrophosphate, TiP2O7, in diamond anvil cell have been performed at room temperature using in situ Raman scattering and Fourier transform infrared spectroscopy (FTIR). The endeavor was to acquire information on pressure-induced structural transformations such as phase transitions and amorphization occurring in the crystal lattice. The pressure-stimulated alterations in the spectral profile, the position, and the intensity of the stretching and bending modes Of PO4 tetrahedral structural units have been investigated up to 42.8 and 49.4 GPa for Raman and infrared-active modes, respectively. The spectral changes pointed mostly to the densification and partial amorphization of the crystal lattice. FTIR spectra confirmed that the investigated compound, TiP2O7, compressed smoothly up to the highest investigated pressures. The spectroscopic studies did not indicate an unambiguous structural transformation matching to a pressure-driven phase transition. The reversibility to ambient pressure structure upon decompression was implied by FTIR but was not confirmed by Raman spectroscopy. The mode Gruneisen parameters were calculated for the various Raman and infrared-active vibrational modes. The results obtained are consistent with our previous high-pressure synchrotron radiation-based X-ray diffraction investigations. (C) 2003 Elsevier B.V. All rights reserved. (Less)

Single crystals of Cs2CuCl4 and Cs2CoCl4 have been investigated at high pressures by X-ray diffraction techniques, using a diamond anvil cell. Increasing the pressure to just below 40 kbar caused the crystallinity of Cs2CuCl4 to deteriorate rapidly. This was accompanied by a color change from yellow/orange at lower pressures to deep red, suggesting, e.g., a major change of the coordination geometry around the Cu2+ ions. Decreasing the pressure to a few kilobars below the transition showed that the observed color change is reversible. No similar color change was observed for a Cs2CoCl4 specimen. Diffraction patterns collected at pressures further above the transition pressure do not indicate the formation of more crystalline new high-pressure phases. Single-crystal structure determinations of orthorhombic Cs2CuCl4, space group symmetry Puma, were performed just below the transition at 27, 33, and 36 kbar. Refinements, based on about 400 unique diffraction intensities to determine 41 structural parameters, converged to R values well below 0.10. The results show that the main features of the structure are rather unaffected at pressures close to the phase collapse. The main effect in the structure is a shortening of the Cs-Cl distances by 0.2 A. The flattening of the coordination tetrahedra around Cu2+ decreases slightly with pressure as reflected by a decrease of 4°for one of the Cl-Cu-Cl angles. The Cu-Cl distance decreases only by about 0.02 A from ambient to 36 kbar. Despite tire detailed structural information obtained the origin of the observed color change at the phase transition is still unresolved. However, the lack of any phase transition of Cs2CoCl4 in the investigated pressure range suggests that the transition depends on the presence of the highly distorted coordination tetrahedra in Cs2CuCl4. The structures of Cs2CuCl4 and CsCoCl4 both have very high compressibilites, with bulk moduli of 15.0(2) and 17(1) GPa, respectively. (C) 2000 Academic Press. (Less)

Crystalline Cs2KMnF6, when prepared below 500°C, adopts a tetragonal elpasolite structure type. Differential scanning calorimetric investigations indicated that Cs2KMnF6 undergoes a phase transition from the low-temperature tetragonal phase (LT) to a high-temperature phase (HT) at about 530°C. Single crystals of the new HT phase could be obtained by annealing a crystalline LT specimen at 600°C followed by rapid quenching to room temperature. In the present study the structures of both phases have been studied by single-crystal X-ray diffraction techniques. The LT phase has the tetragonal space group symmetry I4/mmm, with unit-cell parameters a = 6.319(1) (a· √2 = 8.936) and c = 9.257(2) A, and Z= 2. The HT phase has the cubic symmetry Fm3m, with the cell parameter a = 9.067 A and Z = 4. Structural models of the LT and HT phases have been refined vs collected single-crystal X-ray reflection data to R values of 0.034 and 0.022, respectively. The uneven Mn-F bond distance distribution in the LT form, four bonds of 1.860(6) two of 2.034(9) A, are typical for an octahedrally coordinated high-spin Mn3+ ion affected by Jahn-Teller effects. Due to symmetry constraints, all six octahedral Mn-F bonds in the HT form are equal to 1.931(5) A. However, the mean square atomic displacement parameters of the fluorine atoms increases significantly from about 0.022 A2 for the LT phase to 0.042 A2 for the HT phase. The increased displacement parameters indicate that the phase transition from the LT to the HT form is associated with a directional disorder of the Jahn-Teller distortions around the Mn3+ ions. (C) 2000 Academic Press. (Less)

The valence of the europium dopant and selected rare earth co-dopants (Ce3+, Dy3+, and Yb3+) in the Sr2MgSi2O7:Eu2+,R3+ persistent luminescence materials were studied by room temperature XANES measurements. The results indicated the co-existence of both divalent and trivalent europium in all the studied materials. The relative amount of Eu3+ was observed to increase upon increasing exposure to X-rays, as expected by the persistent luminescence mechanism. This suggests a simultaneous filling of oxygen vacancies initially created by the reducing preparation conditions. For the Dy and Yb co-dopants, only trivalent species were observed. On the other hand, traces of tetravalent cerium were present in the Eu,Ce co-doped materials. (c) 2009 Elsevier B.V. All rights reserved. (Less)

The crystal structure of Na 3 ScF 6 was investigated by high-pressure single-crystal X-ray diffraction techniques in the range from ambient conditions to 68.2 kbar. Pressure was measured by the ruby fluorescence method. The single-crystal structure determination at 27.9 kbar resulted in the cell parameters a =5.484(1) A, b =5.732(1) A, c =7.948(2) A, and β =90.96(3)° and the same space group symmetry, P 2 1 / n (Z=2), as at ambient conditions. The 19 structural parameters needed to describe a model with isotropic displacement parameters were refined by least-squares techniques. For the 143 most significant observed unique reflection amplitudes, the R value became 0.047. When the pressure was increased from ambient to 27.9 kbar, the change in the geometry and the relative change in the volume of the coordination polyhedron around the six-coordinated Sc 3+ ion were negligible. Significant changes of the coordination volumes around the Na + ions were observed. The volume decreases for the six-coordinated and the eight-coordinated Na + ions were similar, viz., 7 and 8%. The layered stacking of the larger, low-charged F − and Na + ions along [103] offers an explanation for the pattern which determines the changes of the unit cell parameters with pressure. The relative change in unit cell volume versus pressure in the range from ambient to 68.2 kbar was fit to the Birch type equation of state. The isothermal bulk modulus at ambient pressure and its pressure derivative were determined to be B 0 =46.0(7) GPa and B ′ 0 =3.3(2), respectively.

The structural changes of crystalline WO3induced by the changes in pressure from ambient pressure up to 47 kbar have been studied with a diamond anvil cell. The investigations have been performed by single crystal X-ray diffraction techniques using MoKαradiation. The results obtained show that triclinic WO3, considered to be the thermodynamically stable form at ambient pressure, undergoes a reversible phase transition already in the range 0.3–1.2 kbar to give a monoclinic high-pressure (HP) form with a halved unit cell volume. The pressure transition, is expected as a consequence of the fact that the pseudo-C-centered lattice of the triclinic phase becomes a true lattice symmetry when the pressure is increased. Atomic displacements of only a few tenths of an A are involved in the transition. These observations agree in general with the results previously obtained by E. Salje and G. Hoppmann from their studies of the Raman spectra of WO3at high pressure. (1980High Temp. High Pressure12, 213–216. The HP phase has the space group symmetryP21/c, witha=5.261(1),b=5.128(1),c=7.650(4) A, andβ=92.05(3)° at 5.7 kbar. The compressibility of the HP phase is largest along the [010] direction. The isothermal bulk modulus,B0=44.5(9) GPa, at ambient pressure and its derivative,B′0=2.5(4), were determined by least squares techniques using the Birch equation of state. Apart from the general decrease in the cell parameters when the pressure was increased to 47 kbar, no apparent symmetry changes were detected. Thus, the monoclinic HP form appears to be the stable form in the investigated pressure range. Single crystal diffraction data of the HP form at 5.7 kbar were collected and a derived structure model was refinedversus227 reflection amplitudes to anRvalue of 0.040. The 3+3 coordination around W is more pronounced in the HP structure (three shorter bonds of 1.78 to 1.84 A and three longer bonds of 2.02 to 2.14 A) than in that at ambient pressure. The phase transition involves a significant change of the W positions relative to the centroids of the coordination octahedra.

Studies of the new type of alkaline earth copper(II) borates, represented by SrCu2(BO3)2, have been performed by high temperature techniques. In the parent structure of SrCu2(BO3)2, the strontium content can be partially substituted by calcium or barium. A series of such phases with the composition Sr1-xMxCu2(BO3)2 where M = Ca or Ba and 0 ≤ x