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A new and "flexible" microwave-assisted hydrothermal (MWH) synthesis of crednerite CuMnO 2 materials is proposed. Single-phase compounds are synthesized by means of the MWH method in a significantly shorter time than by conventional hydrothermal heating. CuMnO 2 single-phase compounds are obtained in the 80–180 °C temperature range, with times ranging from 5 min to 1 h, starting from nitrate reactants. The structure and the phase composition were studied by X-Ray diffraction and FT-IR spectroscopy, and reveal that all samples crystallize within the crednerite structure with the C2/m space group and without other impurities. The surface area is 59.5 m 2 /g for the sample obtained at 120 °C, 5 min, and 76.8 m 2 /g for the sample obtained at 80 °C, 5 min, respectively. The morphological analysis by transmission electron microscopy revealed plate-like nanoparticles, 20–50 nm in diameter. As application, in the case of the as-obtained products the catalytic activity was tested for hydrogen evolution in aqueous sulphide solution. [ABSTRACT FROM AUTHOR]

The physico-chemical properties of substituted perovskites materials have been analyzed with the aim of studying the relationships between structure and properties in this class of materials. Investigations were carried out into the effect of substitution in lanthanum manganites La 1– x Ca x MnO 3 ( x = 0; 0.05; 0.1; 0.15) materials obtained through sol-gel method followed by heat treatment at low temperatures and X-ray diffraction, into the surface area thereof, as well as into transmission electron microscopy for purposes of morpho-structural characterization. The results indicated a well-crystallized P m-3m perovskite-type structure, and 20 nm average crystallite sizes for all samples. By means of complex impedance measurements in the 20 Hz–2 MHz frequency range, the electrical conductivity was determined at temperatures between 30 °C and 120 °C; the results showed that the conductivity obeys a Jonscher's universal law. It was found that below 10 kHz, the dc component of the conductivity increases with temperature for all samples, indicating that electrical conduction processes are activated thermally, in agreement with Mott's variable-range hopping (VRH) model; the model parameters (hopping distance and hopping energy) were also determined. In the high frequency range (f > 200 kHz) the ac conductivity is attributed to charge carriers hopping between the nearest neighboring states, in agreement with the correlated barrier hopping (CBH) model. Using this model, the energy band gap values: 0.364 eV , 0.372 eV and 0.424 eV of the substituted samples were found. [ABSTRACT FROM AUTHOR]

A series of CuMnMO (M = Mg, Al; x = 0-0.08) samples was prepared using the low-temperature hydrothermal method. Crednerite-type materials are obtained for a low level of substitution, i.e. up to x = 0.08, and transmission electron microscopy observations indicate that the average crystallite size decreases with an increase in x. The evolution of unit cell parameters in function of x, from Rietveld refinements using X-ray powder diffraction data, presents a distinct behaviour for both series, but corresponds in both cases to a regularisation of the triangular network in the ( a, b) plane. The investigation of the structural, thermal and magnetic properties reveals that the substitution has a significant role on the magnetism in CuMnMO (M = Mg, Al). It was found that the Mg and Al substitution on the Mn site leads to a small increase in the magnetisation values at low temperature, although the particle size decreases, which can be related to a release of magnetic frustration. [ABSTRACT FROM AUTHOR]

A fast and effective method for the preparation of NaTaO nanomaterials reported here is ultrasonic method with immersed sonotrode in the reaction medium followed by annealing at 600 °C. In order to remove the organic material and increase phase crystallinity, the materials were annealed at different temperatures (400, 600, 800 °C), for 6 h. The as-prepared samples were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTG/HF), IR spectroscopy, surface area analysis (BET), and scanning electron microscopy (SEM/EDX). The structural characterization by X-ray powder diffraction revealed that heat-treated materials at 600 °C are well crystallized and the average size of the crystallites being approximately 60 nm, confirmed also by scanning electron microscopy. Thermal analysis has revealed five transformations process of NaTaO, the highest mass loss (10.67 %) taking place in the range 23-323.5 °C. It was found that the BET surface area decreases with temperature increasing which indicates a change in pores due to the removal of organics. From morphological analysis, it can be seen that particles have spherical shape and EDX revealed the purity of obtained materials. [ABSTRACT FROM AUTHOR]

Branded for its potential electronic ferroelectricity, charge-ordered LuFe2O4 has a layered Fe triangular framework, whose topology is a source of degeneracy, both at the charge and spin levels. Here we present an in-depth characterization of LuFe2O4-hp, the high-pressure (hp) polymorph of LuFe2O4, using electron, x-ray, and neutron diffraction, combined with transport and magnetization measurements. We show that LuFe2O4-hp is characterized by a misfit-related monoclinic structure, accommodating a buckled triangular [Lu]∞ layer and two shifted adjacent rectangular [Fe]∞ planes belonging to a distorted rock salt-type layer. The release of the geometric frustration of the Fe magnetic lattice in the hp form leads to collinear antiferromagnetic ordering at TN=380K. Possible coexistence of charge and magnetic orders in this material opens research pathways for the design of tunable multifunctional devices using high-pressure techniques. [ABSTRACT FROM AUTHOR]

The Ni 11 □(HPO 3 ) 8 (OH) 6 phosphite was prepared using a hydrothermal method. Depending on the pressure used during the synthesis, different hierarchical superstructures were encountered, including a new original cross-shaped star. The as-obtained products were characterized by X-ray diffraction, scanning and transmission electron microscopy and magnetization. In agreement with the presence of transition metal dimers in the structure, a complex magnetic behavior is observed at low temperature. This magnetic ground-state, combined with the non-centrosymmetry of the space group, creates new opportunities for applications in this class of open framework inorganic materials. [ABSTRACT FROM AUTHOR]

Single crystals and polycrystalline samples of barbosalite Fe 3 (PO 4) 2 (OH) 2 iron phosphate were successfully synthesized by hydrothermal method at low pressure and temperature. Careful investigations of the crystal structure by high resolution X-ray diffraction and transmission electron microscopy evidence a complex barbosalite framework where trimers of face sharing FeO 6 octahedra along the <110> direction are connected by an additional Fe site, partly occupied. Despite this structural disorder, the spins order in a rather simple magnetic structure below 160 ​K. The corresponding magnetic point group of P 2 1 makes the barbosalite a promising candidate for the design of new multiferroics. Double barbosalite structure in the P 2 1 space group: PO 4 tetrahedrons (yellow), FeO 6 octahedrons (red and orange) and where the blue octahedrons correspond to the additional Fe7 site. Image 1 [ABSTRACT FROM AUTHOR]

The pure water scarcity is a serious, emerging issue and this affects roughly the 40% of the world's population thus new efficient wastewater treatment techniques are required. Lanthanum manganite (LaMnO 3), is one of the most promising and efficient photocatalysts for the degradation of organic pollutants. In this work, undoped and Eu, Ho, Tb doped LaMnO 3 materials were successfully synthesized via sol–gel process using citric acid as chelating agent. The as-obtained samples are well crystallized within the perovskite structure and from the optical properties measurements it is determined that the value for the band gap energy is not influenced by the doping, i.e.Eg ~ 3.4 eV for all samples. In the photocatalytic studies,the potential water purification possibility is proved for the newly synthesized perovskite nanomaterials, and the best removal efficiency was reached in the presence of LMO:Ho, when 77% of endocrine disruptors EE2 (e.g. 17α-ethynilestradiol) was degraded after 30 min of UV irradiation. In addition, there usability of the LMO:Ho nanomaterials was also investigated. Based on the reutilization findings, it can be concluded that the mentioned photocatalyst has not lost its efficiency after three successive runs for photodegradation. Furthermore, the possible mechanism of the photocatalytic degradation of EE2, using different scavengers was also determined, and among the applied scavengers, the most important role had EDTA × 2Na, NaF and p-benzoquinone. According to our findings, the EE2 degradation mechanism mostly took place via positively charged holes, ● OH ads radicals, as well as through O 2 • − radicals, however they had a weaker effect on the degradation efficiency. [Display omitted] • The photocatalytic activity of undoped and doped LaMnO 3 perovskite is revelead. • The possible mechanism of the photocatalytic degradation of EE2 was determined. • For these perovskite the important scavangers are EDTA × 2Na, NaF and p-benzoquinone. • The best removal efficiency was reached in the presence of LMO:Ho and UV light. [ABSTRACT FROM AUTHOR]

The title compound is hydrothermally synthesized from aqueous mixtures of FePO4, Fe(NO3)3, and 2M aq. [ABSTRACT FROM AUTHOR]

Abstracts We report herein the synthesis and morpho-structural properties of potassium niobate (KNbO 3 ) nanopowders obtained by sol-gel starting from C 4 H 4 NNbO 9 ·H 2 O (ammonium niobate (V) oxalate hydrate), KOH (potassium hydroxide) solution, citric acid (used as a chelating agent) and ethylic alcohol (used as a gelling agent). The thermal behaviour of the KNbO 3 compound was studied by thermo-gravimetric analysis (TG/DTG) at different temperatures and atmospheres. Moreover, different thermal treatments at 300, 450, 600 and 800 °C were performed in order to study the thermal stability of the powders obtained, whose morphology, particle size, structure and degree of crystallization were comparatively characterized by X-Ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

Abstract: A LuFe2O4+δ sample, previously characterized by X-ray synchrotron and neutron diffraction, has been studied by electron microscopy techniques, in order to get a precise description of its micro- and nanostructures at room temperature. The X-ray synchrotron data vs. temperature show that the monoclinic distortion is associated with the charge ordering; this distortion results in elongated twinning domains, which enhance the complexity of the microstructural state at room temperature. The structural modulation associated with oxygen excess is observed in large domains inside a non modulated matrix, in contrast with the modulations associated with the charge ordering of the Fe2+ and Fe3+ species, which are mostly short-range. The investigation of the nature and density of defects in the sample shows that they are nano-scaled, preserving the regularity of the layer stacking mode, and limited to the formation of one- or two-units large stacking faults, associated with gliding mechanisms. Based on these observations, an original description of the LuFe2O4 ferrite structure, through puckered [LuO4]∞ sandwiching [Fe2]∞ layers, is proposed. [Copyright &y& Elsevier]

The effects of applied external pressure on the low temperature crystal and magnetic structures of LuFe2O4 have been investigated by means of synchrotron X-ray and neutron diffraction experiments in the range 0-3 GPa. Although the crystal structure is nearly rhombohedral at RT and ambient pressure, a marked monoclinic distortion is seen at low temperature, which increases with increasing pressure. In the magnetically ordered regime, the ordered magnetic moment value at 50 K decreases by up to 30% at 3 GPa, although no evidence for magnetic diffuse scattering can be inferred from the data. A tentative explanation is proposed, based on the delocalization of the magnetic moment, and possibly related with a melting of the charge ordered state in this pressure range. [ABSTRACT FROM AUTHOR]

Apolycrystalline sample of LuFe204 has been investigated by means of powder synchrotron x-ray and neutron diffraction and transmission electron microscopy (TEM), along with Mössbauer spectroscopy and transport and magnetic properties. A monoelinic distortion is unambiguously evidenced, and the crystal structure is refined in the monoelinic C2/m space group [aM = 5.9563(1 )&ARING;, bU = 3.4372(1)&ARING;, cU = 8.6431(1)&ARING;, &BGR; = 103.24(1)°]. Along with the previously reported modulations distinctive of the charge-ordering (CO) of the iron species, a new type of incommensurate order is observed, characterized by a vector q1&RARR; = &AGR;1a&RARR;*M + &GGR;1c&RARR; (with &AGR;1 = 0.55, &GGR;1 = 0.13). In situ heating TEM observations from 300 to 773 K confirm that the satellites associated with q{ vanish completely, only at a temperature significantly higher than the CO temperature. This incommensurate modulation has a displacive character and corresponds primarily to a transverse displacive modulation wave of the Lu cations position, as revealed by the high resolution, high angle annular dark tield scanning THM images and in agreement with synchrotron data refinements. Analyses of vacuum-annealed samples converge toward the hypothesis of a new ordering mechanism, associated with a tiny oxygen deviation from the 04 stoichiometry [ABSTRACT FROM AUTHOR]

The interest of SiGeO single crystals with alpha-quartz structure is connected to improvement of electromechanical coefficients and rise of α - β phase transition of quartz one. Growth of an α-SiGeO crystal was realized by a hydrothermal method of temperature gradient in autoclaves, made from Cr-Ni alloys. Nutrient material was prepared from synthetic quartz as crashed rods and placed in the bottom of autoclaves. There was loaded GeO powder additive in proportions to quartz nutrient. Single crystals were investigated by electron microprobe analysis, X-ray diffraction and atomic force microscopy. The most important result, which was obtained during the investigations, is an experimental proof of growth of α-SiGeO single crystals under the hydrothermal conditions. The present results thus open the possibility to tune the piezoelectric properties of these materials by varying the chemical composition. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Marine shells are a natural, cheap, abundant and renewable resource, which can be used to produce useful materials, such as for the construction industry. The present study focuses on the transformation of Mya arenaria exoskeletons from the Black Sea into calcium hydroxide by using low-temperature hydrothermal synthesis. In contrast with other methods, this energy-saving process does not involve calcination of shells prior to the hydrothermal treatment. XRD results show the formation of calcium hydroxide with preferential orientation and interesting atypical morphology, which is strongly influenced by the composition of the reaction medium. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of Cu 1+x Mn 1-x O 2 (x = 0 and 0.06) have been obtained by solid state reaction in silica tubes. Measurements of complex impedance (Z = Z′ +  i Z′′) at various temperatures T , between 30 °C and 120 °C and over the frequency range 100 Hz–2 MHz were performed. The frequency dependence of Z′′(f) exhibits a maximum which moves towards higher frequencies by increasing the temperature, proving thus the hopping of the charge carriers between the localized states is the dominant mechanism for the electrical conduction in the investigated samples. The barrier energy values were: 0.287 eV for CuMnO 2 and 0.208 eV for Cu 1.06 Mn 0.94 O 2 . The conductivity spectrum, σ(f) follows the Jonscher universal law at each constant temperature. Based on the temperature and frequency dependencies of the electrical conductivity and using the variable-range-hopping (VRH) model, the frequency and temperature dependencies of the density of localized states near the Fermi level, N(E F ) , the hopping distance, R and the hopping energy, W were computed. The results show that at constant frequency, N(E F ) does not depend on temperature for both samples. At constant temperature and frequencies up to 30 kHz, increasing the concentration of Cu ions leads to the decrease of R and W , whilst at high frequencies (over 100 kHz), R and W increase with the increase in the concentration of Cu ions. [ABSTRACT FROM AUTHOR]

The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF 2 and BaF 2 fluoride crystals doped with 0.1 mol% ErF 3 were investigated. The crystals structure has been studied using a synchrotron and laboratory X-ray diffraction. The C 3v and C 4v sites symmetry were determined using erbium probed high resolution emission spectroscopy (HRPL) at low temperature (LT) of 10 K. The considerable difference in room temperature (RT) optical properties for CaF 2 compared to BaF 2 crystals was observed. Such difference in absorption intensity of 4.7 times of erbium 4G 11/2 manifold in UV, and 7.5 times in green emission from 4S 3/2 manifold, could be due to the distinction in the host crystals cationic radius (Δr Ca,Ba) and the dopant-host ionic radius (Δr Ca-Er , Δr Ba-Er). Those Δr differences influence the structure and lead to the following symmetry formation: In CaF 2 , the C 4v and C 3v isolated centers were identified, with the determined Er3+- F− i bond lengths of 2.734 Å and 4.735 Å respectively; In BaF 2 , only C 3v isolated centers were identified with the determined Er3+- F− i bond lengths of 5.380 Å. The present work is the first study that takes into account correlations of optical properties, the local symmetry and the structure in mentioned fluorides crystals, and it could be a step forward in the lanthanide doped optical materials systematics. [Display omitted] • Detailed analysis of the Er3+ spectra in CaF 2 and BaF 2 crystals based on site symmetry. • Relations between Er3+ states splittings and structural properties are highlighted. • Proposed method can be readily applied to other activators and hosts. [ABSTRACT FROM AUTHOR]

Combining functionalities in devices with high performances is a great challenge that rests on the discovery and optimization of materials. In this framework, layered oxides are attractive for numerous purposes, from energy conversion and storage to magnetic and electric properties. We demonstrate here the oxygen storage ability of ferroelectric LuFe2O4+x within a large x range (from 0 to 0.5) and its cycling possibility. The combination of thermogravimetric analyses, X-ray diffraction and transmission electron microscopy evidences a complex oxygen intercalation/de-intercalation process with several intermediate metastable states. This topotactic mechanism is mainly governed by nanoscale structures involving a shift of the cationic layers. The ferrite is highly promising because absorption begins at a low temperature (), occurs in a low oxygen pressure and the uptake of oxygen is reversible without altering the quality of the crystals. The storage/release of oxygen coupled to the transport and magnetic properties of LnFe2O4 opens the door to new tunable multifunctional applications. [ABSTRACT FROM AUTHOR]

The magnetic properties of a polycrystalline sample of LuFe204 have been investigated by means of magnetization measurements combined with neutron scattering, between 1.5 and 300 K. Magnetic Bragg peaks appear below TN = 240 K and can be indexed in a monoclinic cell, using two propagation vectors, k1 = (0 2/3 0)m and k2 = (0 2/3 l/2)m [or k2 = (0 2/3 1/6)m], which correspond to either a ferromagnetic or an antiferromagnetic stacking of the [Fe204]oo bilayers. A modeling of possible magnetic structures evidences in addition that the coupling within a bilayer can be either ferromagnetic or antiferromagnetic. Results point out a complex magnetic ground state, which can be understood as coexisting antiferromagnetic and ferrimagnetic phases with a large axial magnetic anisotropy of about 8 meV. [ABSTRACT FROM AUTHOR]

Abstract: Electronic band structure calculations using the augmented spherical wave method have been performed for CuCrO2. For this antiferromagnetic () semiconductor crystallizing in the delafossite structure, it is found that the valence band maximum is mainly due to the t2g orbitals of Cr3+ and that spin polarization is predicted with per Cr3+. The structural characterizations of CuCr1−x Mg x O2 reveal a very limited range of Mg2+ substitution for Cr3+ in this series. As soon as , a maximum of 1% Cr ions are substituted by Mg site is measured in the sample. This result is also consistent with the detection of Mg spinel impurities from X-ray diffraction for . This explains the saturation of the Mg2+ effect upon the electrical resistivity and thermoelectric power observed for . Such a very weak solubility limit could also be responsible for the discrepancies found in the literature. Furthermore, the measurements made under magnetic field (magnetic susceptibility, electrical resistivity and Seebeck coefficient) support that the Cr4+ “holes”, created by the Mg2+substitution, in the matrix of high spin Cr3+ () are responsible for the transport properties of these compounds. [Copyright &y& Elsevier]