Growth and structure of Mg(Fe<Subscript>0.8</Subscript>Ga<Subscript>0.2</Subscript>)<Subscript>2</Subscript>O<Subscript>4 − δ</Subscript> films

Films 150–200 nm in thickness, with the nominal composition Mg(Fe_0.8Ga_0.2)₂O_{4 − δ} have been grown on (100) single-crystal silicon substrates by ion-beam sputtering in vacuum. The effect of growth and annealing conditions on the crystal structure and morphology of the films has been studied, and the thermal conditions for the growth of spinel-structure films have been optimized.     

Crystal structure of a Np(V) sesquioxalate,Na<Subscript>4</Subscript>(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

The crystal structure of a previously unknown Np(V) sesquioxalate, Na₄(NpO₂)₂(C₂O₄)₃·2H₂O was studied. The crystal structure consists of neptunyl(V) cations, sodium cations, oxalate anions, and water molecules of crystallization. Neptunyl(V) cations and oxalate ions form anionic chains [(NpO₂)₂(C₂O₄)₃] _n ^4n? . The coordination polyhedron (CP) of Np (pentagonal bipyramid) contains two apical “yl” oxygen atoms and five equatorial O atoms of three oxalate ions. The CP of Na(1) and Na(2) cations are combined through the common edges into zigzag chains in the [010] direction. Two independent oxalate ions are tridentate and tetradentate ligands.     

Crystal structure and properties of BaTiO<Subscript>3</Subscript>–(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> ceramic system

(1 − x)BaTiO₃–x(Bi_0.5Na_0.5)TiO₃ (x ranged from 0.01 to 0.96) ceramics were fabricated by the conventional ceramic technique. The crystal structure, as well as dielectric and piezoelectric properties of the ceramics were studied. All the ceramics formed single-phase solid solutions with perovskite structure after sintering in air at 1150–1250 °C for 2–4 h. The crystal structure and microstructure varied gradually with the increase of (Bi_0.5Na_0.5)TiO₃ (BNT) content. The Curie temperature, T _c, shifted monotonously to high temperature as BNT increased. The ceramics with 20–90 mol% BNT had relatively low and stable dielectric loss characteristics. The piezoelectric constant, d ₃₃, enhanced with the increase of BNT content through a maximum value in a composition of 93 mol% BNT and then tended to decrease. The maximum value, 148 pC/N, of piezoelectric constant d ₃₃ together with the electromechanical coupling factors, k _t, 19.8% and k _p, 15.8%, were obtained when BNT was 93 mol%.     

Spectroscopic characterisation of local structure in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses doped with gadolinium

Gadolinium doped bismuth borate glasses containing up to 30 mol% Y₂O₃ were prepared by fast melt quenching method. The effect of yttrium on the local order in 3B₂O₃ · Bi₂O₃ and B₂O₃ · Bi₂O₃ glass matrices, particularly on the bismuth sites, was investigated by infrared (IR) spectroscopy and electron paramagnetic resonance (EPR) of Gd³⁺ ions. The IR results show that the local structure is more ordered in the glass system with higher bismuth content and the progressive addition of yttrium increases the local disorder in both bismuth–borate glass matrices. The EPR results indicate that Gd³⁺ ions occupy both bismuth and yttrium sites and reflect the same structural disorder like that suggested by IR results.     

Atomistic structure and energetics of interface between Mn-doped γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>

The interface between an Mn-doped γ-gallium oxide (Ga₂O₃) thin film and an MgAl₂O₄ (001) substrate has been investigated using high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and first-principles calculations. A high-quality Mn-doped γ-Ga₂O₃ film with a defective spinel structure has been epitaxially grown by pulsed laser deposition. The γ-Ga₂O₃ crystal shows an uniform tetragonal distortion with a tetragonality of 1.05 throughout the film thickness of 75 nm. HRTEM and HAADF-STEM observations reveal that the γ-Ga₂O₃ and MgAl₂O₄ crystals form a coherent interface without any interfacial layers or precipitates. The atomistic structure and energies are theoretically evaluated for the interfaces with two types of termination plane, i.e., Mg- and Al₂O₄-termination of MgAl₂O₄. The cation sublattice is found to be continuous for both interfaces despite the defective spinel structure of Mn-doped γ-Ga₂O₃ with some vacant cation sites. The Al₂O₄-termination shows a lower interfacial energy than the Mg-termination under most conditions of the chemical potentials. This behavior is attributed to the energetic preference of the Mn–Al₂O₄ local configuration at the interface.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Crystal structure of a Pu(VII) potassium salt,K<Subscript>3</Subscript>PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O

A new Pu(VII) compound, K₃PuO₄(OH)₂·2H₂O, was synthesized, and its structure was studied by single crystal X-ray diffraction. This compound is isostructural to the previously described K₃NpO₄(OH)₂·2H₂O. The structure of the latter compound was redetermined to obtain more precise interatomic distances in the NpO₂(OH) ₂ ^3? anion. Changes in An-O bond lengths in the tetragon-bipyramidal coordination polyhedron of the compounds K₃AnO₄(OH)₂·2H₂O in going from Np(VII) to Pu(VII) were considered.     

Kinetics of Thermal Transformation of Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 8H<Subscript>2</Subscript>O to Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The kinetics of thermal dehydration of Mg₃(PO₄)₂ · 8H₂O was investigated using thermogravimetry at four different heating rates. The activation energies of the dehydration step of Mg₃(PO₄)₂ · 8H₂O were calculated through the isoconversional Ozawa and Kissinger-Akahira-Sunose (KAS) methods and iterative methods, which were found to be consistent and indicate a single mechanism. The possible conversion function of the dehydration reaction for Mg₃(PO₄)₂ · 8H₂O has been estimated through the Coats and Redfern integral equation, and a better kinetic model such as random nucleation of the “Avrami–Erofeev equation (A _3/2 model)” was found. The thermodynamic functions (ΔH*, ΔG*, and ΔS*) of the dehydration reaction are calculated by the activated complex theory and indicate that it is a non-spontaneous process when the introduction of heat is not connected.     

Synthesis and study of structural,dielectric, magnetic and magnetoelectric properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–CoMn<Subscript>0.2</Subscript>Fe<Subscript>1.8</Subscript>O<Subscript>4</Subscript> composites

Magnetoelectric (ME) composites consisting of K_0.5Na_0.5NbO₃ (KNN) as ferroelectric phase and CoMn_0.2Fe_1.8O₄ (CMFO) as ferrite phase with general formula (x) CoMn_0.2Fe_1.8O₄–(1???x) K_0.5Na_0.5NbO₃ (x?=?10, 20, 30, 40 and 50 wt%) were synthesized using solid state reaction method. X-ray diffraction analysis asserts the existence of component phases including spinel phase of CMFO and orthorhombic phase of KNN. Field emission scanning electron microscopy has been used for studying the morphology and calculation of average grain size. The temperature dependent dielectric properties including dielectric constant (\(\varepsilon ^{\prime}\)) and dielectric loss (tan δ) at different frequencies has been studied and both are found to increase with incorporation of CMFO. Magnetic hysteresis loops have been measured at temperatures of 300 and 5 K. Variation of magnetization versus temperature has been studied in field cooled and zero field cooled modes. Polarization versus electric field (P–E) hysteresis loops are obtained at room temperature indicating presence of ferroelectric ordering in the composites at room temperature. The remnant polarization (2P_r) and coercive field (2E_c) are found to decrease linearly with incorporation of CMFO. ME voltage coefficient (α_ME) has been measured. The maximum value of α_ME is found to be 5.941 mV/cm-Oe for 10% CMFO–90% KNN bulk composite.     

Preparation,structure and microwave dielectric properties of 3MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–3TiO<Subscript>2</Subscript> ceramics

3MgO–Al₂O₃–3TiO₂ (MAT) ceramics were prepared by a conventional solid-state reaction method. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and network analyzer. MAT ceramics contained the coexistence of three phases, including MgAl₂O₄, MgTiO₃ and MgTi₂O₅. The ceramics sintered at 1350 °C for 4 h presented excellent comprehensive performances with relative permittivity (ε _r ) of 15.4, quality factor (Q × f) of 91,000 GHz and temperature coefficient of resonant frequency (τ _f ) about ?55.1 ppm/°C.     

The effect of Fe contents on the local structure and crystallization behavior of SiO<Subscript>2</Subscript>–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The glass and glass ceramics containing SiO₂–CaO–Fe₂O₃–P₂O₅ were prepared by sol–gel method. The influence of the Fe contents on the crystallization and local structure of the glass and glass ceramics was systematically investigated. The crystal structure of the glass ceramics was identified by XRD characterization. Hematite phase can be precipitated from the glass matrix in all glass ceramics with various Fe contents, and the crystallographic parameters of hematite were determined by XRD Rietveld refinement. The crystallization kinetics of the glasses was investigated in detail. Relative low activation energies were obtained at low Fe contents. The local structure evolution of the glass and glass ceramics has been studied in-depth by means of FTIR and Mössbauer spectroscopy. Fe element is present both as network former and network modifier which significantly influenced the crystallization activation energies of the glasses. The results of this work may be of great significance for the material design and practical applications of bioactive magnetic glass ceramics for hyperthermia.     

Crystal structure of U(VI) phthalate dihydrate [UO<Subscript>2</Subscript>(OOC)<Subscript>2</Subscript>C<Subscript>6</Subscript>H<Subscript>4</Subscript>•H<Subscript>2</Subscript>O]•H<Subscript>2</Subscript>O

Crystalline uranyl phthalate dihydrate was prepared by hydrothermal method, and its crystal structure was determined. The crystal structure consists of infinite chains [UO₂LH₂O]_n coupled in bands [(UO₂)₂L₂(H₂O)₂]_n [L = C₆H₄(COO)₂], between which water molecules of crystallization are located. The coordination polyhedron of uranium atoms is a pentagonal bipyramid with the equatorial plane formed by oxygen atoms of three phthalate ions and coordinated water molecule. The U-O bond length in the UO ₂ ²⁺ cations is 1.766 . The coordination capacity of the ligands is 4. Anions are bidentately coordinated to uranium atoms to form seven-membered rings. Being bridging ligands, phthalate ions combine the neighboring uranium atoms into chains through one carboxy group, and the chains into bands, through the other carboxy group.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 513–515.Original Russian Text Copyright © 2004 by Charushnikova, Krot, Starikova.     

Chemical interaction of InAs,InSb, GaAs,and GaSb with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–C<Subscript>4</Subscript>H<Subscript>6</Subscript>O<Subscript>6</Subscript> etching solutions

This paper presents results on the kinetics and mechanism of the physicochemical interaction of InAs, InSb, GaAs, and GaSb semiconductor surfaces with (NH₄)₂Cr₂O₇–HBr–C₄H₆O₆ etching solutions under reproducible hydrodynamic conditions in the case of laminar etchant flow over a substrate. We have identified regions of polishing and nonpolishing solutions and evaluated the apparent activation energy of the process. The surface morphology of the crystals has been examined by microstructural analysis after chemical etching. The results demonstrate that the presence of C₄H₆O₆ in etchants helps to reduce the overall reaction rate and extend the region of polishing solutions.     

Synthesis,structure and photocatalytic properties of <Emphasis Type="Italic">β</Emphasis>-ZrMo<Subscript>2</Subscript>O<Subscript>8</Subscript>

Monoclinic ZrMo₂O₈ was synthesized via solid state method and single crystals of the title compound have been grown by the hydrothermal method. The crystals belong to monoclinic crystal system with space group C2/c (No. 15) with a = 11·4243(19) Å, b = 7·9297(6) Å, c = 7·4610(14) Å and β = 122·15(2)°, Z = 4. The bandgap of the compound was 2·57 eV. Unlike the other polymorphs of ZrMo₂O₈, the monoclinic form has unique crystallographic features with ZrO₈ and Mo₂O₈ polyhedra. The photocatalytic activity of this compound has been investigated for the first time for the degradation of various dyes under UV irradiation and has been compared with the photoactivity of the trigonal form of ZrMo₂O₈. It has been observed that this compound exhibits specificity towards the degradation of cationic dyes.     

Crystal structure,optical behavior and electrical conduction of the new organic–inorganic compound CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>CdI<Subscript>3</Subscript>

A new organic–inorganic compound CH₃NH₃CdI₃ (MACdI₃) was prepared by solvent diffusion method. Single crystal diffraction results showed that MACdI₃ had a monoclinic system with P2₁/c space group at room temperature. UV–Visible absorption spectra revealed that the optical band gap (\({E_g}\)) of 3.45 eV is in agreement with the theoretical value. Band structure and density of states calculations indicated that the valence band is mainly iodine 5p in character and the conduction band is the interaction between Cd 4d in character and iodine 5p states. The temperature dependent dielectric constant and alternating current (AC) conduction analysis displayed a phase transition at about 348 K, which could be confirmed by temperature dependent Raman spectra. AC conduction results demonstrated that the conduction in MACdI₃ was attributed to correlated barrier hopping at 308–348 K and non-overlapping small polaron tunneling at 348–398 K.     

BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> films produced from BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> heterostructures

BaFe₁₂O₁₉ hexaferrite films have been produced on thermally oxidized single-crystal silicon (SiO₂/Si) substrates by sequential ion-beam sputtering of BaFe₂O₄ and α-Fe₂O₃ targets in an argon-oxygen atmosphere. Their crystal structure has been studied, and the origin of the impurity phases forming during heat treatment has been identified. The results show that heat treatment may lead to the formation of eutectic melts. As a result, the hexaferrite films may contain spherulites.     

Effect of refractory nitride nanoadditives on the properties of (Bi,Pb)<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10+δ</Subscript>

We have investigated the interaction between (Bi,Pb)₂Sr₂Ca₂Cu₃O_10+δ (Bi-2223) and small additions (0.05–0.3 wt %) of nitride powders (TaN, AlN, HfN, NbN, Si₃N₄, TiN, and ZrN) with a particle size from 0.02 to above 0.5 μm and the effect of these nitrides on the microstructure, phase composition, distribution, and morphology of the resulting second-phase inclusions. The concentration and particle size of the nitrides and sintering conditions are shown to influence the superconducting transition temperature T _c, critical current density j _c, irreversible remanent magnetization, bulk density, and mechanical properties of the Bi-2223/nitride composites.     

Evolution of magnetic structure of Dy(Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>B<Subscript>2</Subscript>C

DyNi\(_{2}\)B\(_{2}\)C superconducts at \(T_{c} \approx 6\,{\text{K}}\) and orders antiferromagnetically at \(T_{N}\approx 10\,{\text{K}}.\) Its non-superconducting isomorph DyCo\(_{2}\)B\(_{2}\)C is a ferromagnet with \(T_{C}\approx 6\,{\text{K}}.\) With the aim of mapping out the magnetic properties, in particular magnetic structures, of their solid solutions, we synthesized \(^{11}\)B-enriched Dy(Co\(_{x}\)Ni\(_{1-x}\))\(_{2}\)B\(_{2}\)C (\(x=0.2,0.4,0.6,0.8\)). We investigated the evolution of their magnetic, thermal and transport properties by means of the magnetization, resistivity, specific heat and neutron diffraction techniques. Their crystal structures were confirmed to be ThCr\(_{2}\)-Si\(_{2}\)-type tetragonal (I4/mmm) phase. The magnetic structure was found to be antiferromagnetic with k_0.2 = (0, 0, 1) for x = 0.2; helicoidal with k\(_{0.4}\) = (0, 0, 0.49) and k\(_{0.6}\) = (0, 0, 0.46) for, respectively, x = 0.4 and 0.6 and ferromagnetic with k\(_{0.8}\) = (0, 0, 0) for x = 0.8. We discuss the evolution of such magnetic modes assuming a scenario of an idealized one-dimensional chain of transverse magnetic moments.     

Enhanced microwave dielectric properties of Ba<Subscript>0.40</Subscript>Sr<Subscript>0.60</Subscript>TiO<Subscript>3</Subscript>–Zr<Subscript>0.80</Subscript>Sn<Subscript>0.20</Subscript>TiO<Subscript>4</Subscript> composite ceramics

The (1−x) Ba_0.40Sr_0.60TiO₃ (BST)−xZr_0.80Sn_0.20TiO₄ (ZST) composite ceramics with x = 10, 20, 30, and 40 wt% were fabricated by conventional solid-state reaction method. With increasing of ZST content, the dielectric constant of composite ceramics was decreased and dielectric loss increases. The effect of ZnO addition to 70 wt% BST–30 wt% ZST composition on the microstructure and dielectric properties was investigated. The improvements in dielectric constant, dielectric loss, and microwave dielectric properties of composite ceramics can be achieved by ZnO addition. The sample with 98 wt% (70 wt% BST–30 wt% ZST)–2 wt%ZnO composition exhibits promising dielectric properties, with dielectric constant, loss tangent and tunability at 4 kV/mm, of 125, 0.0016 and 12%, at 10 kHz and room temperature. At ~2 GHz, it possesses a dielectric constant of 101 and a Q factor of 187, which makes it a good candidate for tunable microwave device applications.