Static bismuth disorder in Bi2−x(CrTa)O7−y

The crystal structure of the pyrochlore Bi_2−x(CrTa)O_7−y has been refined by the Rietveld method from powder neutron and synchrotron X-ray diffraction data. Using the ideal pyrochlore structural model, anomalously high atomic displacement parameters (APD), which could not be satisfactorily explained with anisotropic ADP, of both Bi and O′ sites were observed. The structure was successfully refined with a model that incorporated static displacive disorder of both the Bi and O′ atoms. Using this model physically reasonable ADP parameters for both the Bi and O′ atoms, and improvement in the various measure of fit were obtained. The underbonding of the Bi atoms, observed in ideal pyrochlore model, but removed in the disordered structure, is believed to be the main driving force for this disorder.     

N2O decomposition over (Mg6−xAx) MnO8 (A = Li, Al)

Two different murdochite-type mixed oxides, (Mg_6–x Li _x )MnO₈ (x = 0, 0.1, 0.2 and 0.3) and (Mg_6–x Al _x )MnO₈ (x = 0, 0.2, 0.4, 0.6) were examined for the catalytic decomposition of N₂O in order to make clear the effects of mixed valencies of pairing manganese ions and oxygen vacancies. The valence of manganese ions and the amount of surface oxygen vacancies have been examined with X-ray photoelectron spectroscopy (XPS). (Mg_6–x Li _x )MnO₈ had mixed valence manganese ions and oxygen vacancies on the surface after the substitution. The substituted (Mg_6–x Al _x )MnO₈ had a mixed valence state but oxygen vacancies decresed with x and excess oxygen over stoichiometry was observed at x = 0.4 and 0.6. The reaction rate of N₂O decomposition increased after substitution with lithium but hardly increased after the substitution with aluminum in (Mg_6–x A _x )MnO₈. We assumed that the presence of oxygen vacancies on the surface along with pairing altervalent manganese ions affected strongly to enhance the reactivity of N₂O decomposition.     

Rietveld analysis, magnetic, vibrational and impedance properties of (Bi1−xPrx)(Fe1−xZrx)O3 ceramics

(Bi_1?xPr_x)(Fe_1?xZr_x)O₃ ceramics with x = 0.03, 0.06 and 0.10 were prepared via solid state reaction route. X-ray diffraction and Raman spectra of the ceramics were recorded for calculating its lattice parameters and structural analysis. Magnetic studies indicated a significant enhancement in magnetization of (Bi_1?xPr_x)(Fe_1?xZr_x)O₃ ceramics with maximum remnant magnetization of 0.12 emu g^?1 for x = 0.06 sample. Fourier transform infrared spectra and Rietveld analysis confirmed the change in bond length arising due to Pr and Zr codoping. Dielectric measurements showed dielectric anomaly around Neel temperature, indicating magnetoelectric coupling in the samples as well as the dielectric relaxation for higher doping. The effect of Pr and Zr codoping on the impedance and modulus behavior of BiFeO₃ lattice is discussed. The frequency dependence of electric modulus and impedance of the material show the presence of non-Debye relaxation in the samples. All samples showed energy band gap in the range 2.16–2.0 eV, indicating possibility of optical activity in visible range and making it suitable for photocatalytic applications.     

The orthorhombic-to-tetragonal phase transition in YBa2(Cu1−xFex)3O7−y

The phase transition YBa₂(Cu_1–x Fe _x )₃O_7–y (0x0.05) prepared through solid-state reaction was studied with X-ray diffraction analysis and optical microscope. It was found that the orthorhombic-to-tetragonal phase change was induced between x=0.02 and x=0.03 by X-ray diffraction. The phase transition was also identified by the disappearance of striations in plate-like grains under polarized light. The microstructures of the specimens with compositions of x=0.01 and x=0.02 showed faint striation images. It is considered that a mixture of the orthorhombic and tetragonal phase exists in these compositions.     

Superstructures exhibited by oxides of the aurivillius family, (Bi2O2)2+ (An−1BnO3n+1)2−

Bi₅Ti₃FeO₁₅ and Bi₇Ti₃Fe₃O₂₁ which are n=4 and n=6 members of the family of oxides of the general formula (Bi₂O₂)²⁺(A_n−1B_nO_3n+1)²⁻ show unusual superstructures, possibly due to cation ordering.     

New Pb-Based 1222 Cuprates, (Pb0.5B0.5)Sr2(RE2−x−y Ce x Sr y )Cu2O z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y)

New Pb-based layered cuprates with the 1222 structure have been synthesized in the (Pb_0.5B_0.5)Sr₂ (RE_2−x−y Ce _x Sr _y )Cu₂O _z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single-phase samples in the systems can be obtained for a nominal composition of x=0.7 and y=0.1. The crystal structure of the samples has a tetragonal symmetry, the lattice parameters of a and c are increasing with increasing the ionic radius of RE element. Despite treatment under high O₂ pressure of 100 atm, the samples are semiconductors with the transport process characteristic of three-dimensional variable range hopping conduction.     

High dielectric tunability of ferroelectric (Ba1−x,Srx)(Zr0.1,Ti0.9)O3 ceramics

(Ba_1?x,Sr_x)(Zr_0.1,Ti_0.9)O₃ (BSZT) ceramics with x = 0, 0.05, 0.15, 0.25, 0.35 and 0.45 were prepared by conventional solid state reaction method. The structural characterization with X-ray diffraction and scanning electron microscopy indicate a monotonical drop in lattice constants and grain size with the increase of Sr concentration. Consequently, the Curie temperature and remnant polarization of the ceramics exhibit a strong compositional dependence. A linear relationship between the Curie temperature and Sr concentration is revealed. At x = 0.45, the BSZT ceramics show substantially high tunability of over 55 % under 20 kV/cm dc electric field with very low dielectric loss value of 0.0025 at room temperature, suggesting the BSZT ceramics could be a promising alternative to traditional (Ba,Sr) TiO₃ ferroelectrics for developing high frequency tunable dielectric devices.     

Fluctuation Conductivity of La0.5RE0.5BaCaCu3O7−d (RE=Y, Sm, Dy) Superconductor

We report production, conductivity fluctuation and magnetoconductivity fluctuation measurements of the system La_0.5RE_0.5BaCaCu₃O_7?δ RE=(Y,Sm,Dy) high-temperature superconductors. Samples were synthesized by the standard solid state reaction recipe. By Rietveld-like refinement of X-ray diffraction patterns we determined that the material crystallizes in a tetragonal structure. DC resistivity measurements show a bulk critical temperature T _c (71, 72 and 72 K for RE=Y, Sm, Dy, respectively) for the analyzed samples. In order to examine the effect of substitution of rare earth into the lanthanum structural sites on the pairing mechanism close to T _c , we performed conductivity fluctuation analysis by using the method of logarithmic temperature derivative of the conductivity excess. We found the occurrence of Gaussian and genuinely critical fluctuations. Our results are in agreement with reports on non-doped systems, but we observe minor values of the coherence length of the fluctuation regimes for the doped case. Correlations of critical exponents with the dimensionality of the fluctuation system for Gaussian regimes were made by using the Aslamazov–Larkin theory. The genuinely critical exponent was interpreted by the 3D-XY.     

Decomposition of (Sn2xFe1−xSb1−x)O4 solid solutions with x≤0.50

Thermal stabilities of the rutile-type (Sn_2xFe_1−xSb_1−x)O₄ solid solutions with x≤0.5 were investigated by TG–DTA in flowing O₂ up to 1673 K. After thermal analysis the samples were characterised by means of powder X-ray diffraction analysis (XRD), optical and scanning electron microscopy (SEM) observation and electron dispersive spectrometry (EDS) analysis. The decomposition of the solid solution involves the formation of hematite and a volatile Sb oxide, probably Sb₄O₆. The decomposition temperature increases with the Sn content of the solid solution.     

Ionic conductivity in the ternary system (ZrO2)1−0.08x−0.12y–(Y2O3)0.08x–(CaO)0.12y

The total electrical conductivity of the samples in the ternarysystem (ZrO₂)_{1-0.08x-0.12y} –(Y₂O₃)_0.08x –(CaO)_0.12y was measured by adirect current four-probe method in the temperature range 773 to1673 K. It was found that partial replacement of Y₂O₃ by CaO in thesystem ZrO₂–Y₂O₃ may enhance the electrical conductivity at highertemperatures. At lower temperatures, however, doping CaO as the thirdcomponent into the system ZrO₂–Y₂O₃ depresses the conductivity. Theobserved mixed dopant effect was then analyzed by considering thecombined effect of both parameters appeared in the traditionalArrhenius equation, the activation energy, E, and the preexponentialfactor, ₀, on the temperature-dependence of the measured conductivity.     

Fabrication and characterization of high permittivity ceramics in the Ba(Ti1−x−ySnxZry)O3 system

Ceramics of solid solution compositions in the system BaTi_1–x–ySn_xZr_yO₃ have been fabricated using conventional mixed oxide processing routes. Samples with y = 0 or 0.01 exhibited maximum relative permittivities, _r ^max of ~ 65000 and ~ 62000 respectively. The Curie peaks became broader and _r ^max decreased with increasing zirconium substitutions. The Curie temperature decreased linearly from 35°C for y = 0 to –40°C for y = 0.11: for the latter, _r ^max was equal to ~ 20000. The results are interpreted on the basis of microstructural features and on the degree of compositional inhomogeneity in the system.     

Composite dielectrics (1−x)(Mg0.97Zn0.03)2(Ti0.95Sn0.05)O4−xCaTiO3 suitable for microwave applications

(Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄ ceramics by adding CaTiO₃ have been prepared via the solid-state reaction method. The microstructures of samples are systematically studied in order to establish the effects of sintering temperature and additives on microwave dielectric properties of (Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄ ceramics by X-ray diffraction and scanning electron microscopy. A fine combination of microwave dielectric properties (ε_r = 14.57, Q × f = 183,468 GHz, τ_f = ?43.7 ppm/°C) was achieved for (Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄ ceramics sintered at 1,390 °C for 4 h. CaTiO₃, as a τ_f compensator, was added to form a temperature-stable ceramic system. For (1?x) (Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄?xCaTiO₃ system, 0.93(Mg_0.97Zn_0.03)₂(Ti_0.95Sn_0.05)O₄?0.07CaTiO₃ ceramic sintered at 1,390 °C had optimal dielectric properties (ε_r = 18.32, Q × f = 94,715 GHz, τ_f = ?4.1 ppm/°C) which satisfied microwave applications in resonators, filters and antenna substrates.     

Synthesis,phase confirmation and electrical properties of (1 − x)KNNS−xBNZSH lead-free ceramics

Journal of Materials Science: Materials in Electronics - In the present work, lead-free piezoelectric ceramics (Rx)(K0.5Na0.5)(Nb0.96Sb0.04O3)?x(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 [abb. as...     

Oxygen vacancy induced dielectric relaxation studies in Bi4−xLaxTi3O12 (x = 0.0, 0.3, 0.7, 1.0) ceramics

In the present work, oxygen vacancy induced dielectric relaxations were studied for Lanthanum substituted Bi_4?xLa_xTi₃O₁₂ (x = 0.0, 0.3, 0.7, 1.0) ceramics. X-ray diffraction patterns reveal the formation of single phase orthorhombic structure in all the samples. The partial substitutions of lanthanum ions were found to significantly influence the grain morphology of the sintered ceramics. Temperature dependent dielectric measurements indicate a well-defined dielectric constant peak around 150 °C, with strong frequency dispersion. This dielectric anomaly was attributed to the Maxwell–Wagner space charge relaxation phenomenon related to oxygen vacancies. The space charges related to oxygen vacancies were confirmed by annealing the samples in oxidative atmosphere. The electrical modulus analysis shows that the samples exhibit non-Debye type relaxation behavior. Doubly ionized oxygen vacancies were found to influence the relaxation behaviour at higher temperature. The observed dielectric relaxation as a function of temperature and frequency were explained on the basis of oxygen vacancies.     

Microwave dielectric properties of Ba(Sn x Zn(1−x)/3Nb(1−x)2/3)O3 (0 ⩽ x ⩽ 0.32) ceramics

The dielectric properties of the (1–x)Ba(Zn_1/3Nb_2/3)O₃–xBaSnO₃ (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO₃, the dielectric Q(Q _d) value of Ba(Zn_1/3Nb_2/3)O₃ (BZN) can be improved and a small temperature coefficient of resonant frequency (_f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn_0.226Zn_0.258Nb_0.516)O₃ ceramics sintered at 1500°C are as follows: dielectric constant _r = 32, _f = + 12 p.p.m.°C¹ and high Q _d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO₃ on the microwave dielectric properties of Ba(Zn_1/3Nb_2/3)O₃ can be mostly explained.     

Low temperature synthesis of Co3O4 and (Co1−xMnx)3O4 spinels nanoparticles

The (Co_1?xMn_x)₃O₄ solid solution have been synthesized in water at 60 °C by soda addition to a cationic solution. XRD patterns show that spinel oxide has been obtained except for pure cobalt composition which exhibits also the presence of hydroxide and oxy-hydroxide. Therefore, to reach this composition, a different synthesis route has been developed: the cationic solution is added to the soda and for the first time Co₃O₄ nanoparticles have been synthesized by a direct precipitation in aqueous solution at low temperature. For each composition, the particles are well crystallized and exhibit a size close to 50 nm. Each particle is composed by several crystallographic domains of about 10 nm. The cubic to tetragonal transition reported in the literature for x = 0.46 is observed in between x = 0.33 and x = 0.50. Raman spectra show that substitution of Co by Mn, in the cubic phase, introduces a random high disorder. In the tetragonal phase, occupation of the octahedral site remains a random occupation, while the tetrahedral site seems to be preferentially occupied by Co ions. All these results show that the precipitation is a simple, fast and safe process to synthesize pure phase of (Co_1?xMn_x)₃O₄ spinel solid solution in aqueous media at low temperature.     

Mixtures of (N2)1−x : (O2) x at High Pressures and Low Temperatures

We performed Raman measurements at 18 K and pressures up to 25 GPa in order to construct a tentative phase diagram of the (N ₂)_1–x :(O ₂)_x –system at low temperatures. We varied the composition of the mixed system over the whole concentration range. Here we focused on the systems with high nitrogen concentration and pressures above 2 GPa. It is known that at room temperature oxygen is highly solvable in the –phase of N ₂. The experimental results show that oxygen suppresses the disorder–order transition –N ₂.     

Structure,nonstoichiometry, sintering and oxygen permeability of perovskite SrCo1−2x(Fe,Nb)xO3−δ (x = 0.05, 0.10) oxides

The novel Fe/Nb co-substituted SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides have been synthesized and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG), and scanning electron microscopy (SEM). The XRD and DSC results demonstrate that the structural stability of the Fe/Nb co-substituted samples x = 0.05, 0.10 is improved greatly compared to the sample x = 0.00. The Fe/Nb co-doping in the SrCoO_3?δ oxide results in the improved structural stability of the SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides. The nonstoichiometric and sintering properties were investigated by TG and SEM, and the oxygen permeation fluxes were measured at 800–950 °C for the sample x = 0.10. The improved oxygen permeability of the ceramic SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.10) membrane compared to the (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3?δ and SrCo_0.8Fe_0.2O_3–δ membranes, was observed under an air/He oxygen partial pressure gradient at 800–950 °C.     

Fabrication, growth mechanism, and characterization of α-Fe(2)O(3) nanorods

This work reports the facile synthesis of α-Fe(2)O(3) nanorods and nano-hexagons and its application as sunlight-driven photocatalysis. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), diffused reflectance spectroscopy (DRUV-vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The phase and crystallinity were confirmed from the XRD study. Electron microscopy study clearly indicates the formation of different morphologies of nanocrystals. These hematite nanostructures were used as a model system for studying the shape-dependent photocatalytic degradation of phenol, methylene blue, and congo red. Amongst all the nanostructured semiconductors, Pt-doped hematite nanorod showed 55% efficiency towards the decolonization of methylene blue and 63% toward congo red under sun light illumination. The difference in photocatalytic activity is discussed in terms of their crystallize size and morphological ordering.