Obtain Single-phase Samples Research Articles

Synthesis and physical properties of multiferroic BaDyFeO4

Materials exhibiting magnetoelectric effects have drawn great interest because of their intriguing physical phenomena and potential applications in electronic devices. The magnetoelectric (ME) coupling makes the materials promising for use in multifunctional devices with electric-field-tunable magnetism and magnetic-field-controlled ferroelectricity. Very recently, a strong ME effect has been found in the BaRFeO4 system (R is a rare-earth element), in which the ferroelectricity is driven by the onset of a long-range cycloidal antiferromagnetic order of Fe spins. However, previous studies have shown how complicated the synthesis procedure is to obtain single-phase samples of the materials. In this work, we present a simple and easy fabrication process to synthesise high-quality BaDyFeO4 using the conventional solid-state reaction method. The structural, morphological, and optical properties of the synthesised sample were investigated by means of X-ray diffraction, scanning electron microscopy, and UV-Vis spectroscopy, respectively. The sample was formed from high-quality microparticles. The X-ray diffraction study reveals the single-phase nature of the sample adopting the Pnma orthorhombic structure without any impurity phases. The detailed structural parameters were refined with Rietveld refinement. The sample demonstrates a direct gap semiconducting behaviour. The experimental results of the structural and electronic properties of BaDyFeO4 are complemented by density functional theory (DFT) calculations.

Tremendous oxygen capacity, defect equilibration and thermodynamic stability of PrBaMn2-xCoxO6–δ solid solutions

Solid solutions with the overall composition PrBaMn2–xCoxO6–δ were extensively studied with respect to their crystal structure, oxygen non-stoichiometry and thermodynamic properties. A multistep synthetic route was successfully applied to obtain single-phase samples, with cobalt solubility limit found to lie within the range 0.33 ≤ x ≤ 0.67. Small amounts of Co3O4 impurity were clearly observed as the leading admixture. The use of high temperature coulometric titration technique revealed tremendous oxygen non-stoichiometry in the oxides studied. Accordingly, possible δ values in PrBaMn2–xCoxO6–δ, under certain external conditions, were found to range from 0.0 to 1.35 and 0.0 to 1.25, for x = 0.11 and x = 0.33, respectively. The observed phenomenon was shown to result in the highest heat values for the reduction of PrBaMn1.89Co0.11O6–δ. A theoretical model of defect equilibration under the varying ambient conditions was developed. Cobalt incorporation was found to be a key factor for the facilitation of oxygen exsolution from the lattice at reduction, and for subsequent intensification of charge disproportionation within a manganese sublattice.

Influence of synthesis conditions on phase formation and functional properties of prospective anode material Sr2Ni0.75Mg0.25MoO6-δ

Double perovskite Sr2Ni0.75Mg0.25MoO6-δ powders were synthesized by the combustion method using systems containing nitrates and varying amounts of the following organic components: glycine, glycerol, and polyvinyl alcohol. The characteristics (temperature, gas composition, etc.) of the synthesis process were studied and the optimal conditions for obtaining single-phase samples were determined. It was established that the usage of one-and-a-half excess of glycerol as organic component provides the formation single-phase complex oxide. The crystal structure of the obtained complex oxide, which is of interest as an anode material for solid oxide fuel cells, was refined and its physico-chemical properties (specific surface area, particle size, electrical conductivity, and catalytic activity in the reaction of methane oxidation) were investigated.

Novel rare-earth-containing manganites Ba 4REMn 3O 12 ( RE=Ce, Pr) with 12 R structure

Novel rare-earth-containing manganites, Ba 4 REMn 3O 12 ( RE=Ce, Pr), with 12 R structure, have been prepared by solid-state reaction. Although the phases are formed at 950°C, to obtain single-phase samples high temperatures (up to 1300°C) and long synthesis periods are needed. Their structure is built up from chains of BO 6 face-sharing and corner-sharing octahedra running along the c-axis giving a quasi-one-dimensional oxide. Every polyhedral column consists of (Mn 3O 12) units of three face-sharing octahedra, both ends connected by the three terminal oxygen atoms to three different ( REO 6) octahedra. Mixed occupation of the three octahedral positions in the structure, (Mn(1), Mn(2) and Re), was not found. Vacancies are not observed, neither in the cationic sublattice nor in the oxygen one. Thus, as in all the other 1-D manganites, the oxidation state of manganese ions seems to be four, as the rare-earth valence is. High-resolution electron microscopy suggests the eventual existence of ordered polytypes for different compositions, which could be stabilized by adjusting the thermodynamic conditions.

LiF addition to (Cu,C) Ba2Ca3Cu4Oy superconductor

Samples of (Cu0.6C0.4)Ba2Ca3Cu4Oy ((Cu,C)-1234) with addition of 0.1 mol LiF have been synthesized by high pressure technique. It was found that LiF promotes the formation of superconducting phases with n higher than 4 of the (Cu,C)Ba2Can−1CunOy series. In order to obtain single-phase samples, for the same synthesis conditions, the oxygen content in the starting mixture (supplied by AgO) should be increased from 0.45 to 0.73 mol AgO, when using LiF. Samples with LiF have shown a certain morphology suggesting an enhanced 2D and suppressed 3D type of growth assisted by a liquid phase. Tc decreased from 116.5 to 113 K for the sample with LiF, but at the same time the transition width also decreased and Jc has shown a fish-tail effect.

Effect of the Processing Parameters on the Crystalline Features of the Solid Solution Y(CoxMn1−x)O3, x= 0.6, 0.7

The preparation and crystalline features of perovskite solid solution Y(CoxMn1−x)O3, x= 0.6 and 0.7, belonging to the Co‐rich region of the pseudobinary system YMnO3‐YCoO3 have been studied. Dilatometric experiments performed under different atmospheres have been carried out for determining the best conditions to obtain single‐phase samples. The influence of the thermal cycle and of the sintering density on the appearance of secondary phases has also been established. Firing in O2 atmosphere favors the formation of the pure perovskite. The cooling rate plays an important role for inhibiting the formation of secondary phases. All of the parameters depend ultimately on the final density of the polycrystalline bodies.

Ferromagnetic and superconducting properties of pure RuCe 0.5Eu 1.5Sr 2Cu 2O 10 samples prepared by polymerizable complex method

The polymerizable complex method was successfully applied for synthesis of RuCe 0.5Eu 1.5Sr 2Cu 2O 10 compound. To obtain single-phase samples one should control oxygen partial pressure and prevent Ru loss by conducting synthesis in the sealed volume. Prepared single-phase samples became ferromagnetic below 120 K and did not show bulk superconductivity down to 7 K. The additional annealing in oxygen at 500 °C, P O 2 =10 atm resulted in the R( T) dependence of more metallic character, however it did not increase superconducting phase fraction to a significant extent. On the other hand, preparation of Ru x Ce 0.5Eu 1.5Sr 2Cu 2O 10 samples and studies of their superconducting properties revealed that appearance of superconductivity in the case of Ru-1222 phases might be related to the Ru loss during high temperature synthesis.

Effect of Mg and C contents in MgCNi3, and structure and superconductivity of MgCNi3-x -Co x

The effect of Mg and C contents on TC in MgCNi3, and structure and superconductivity of MgCNi3-xCox were studied. It is found that the excess of Mg and C in initial material mixture is favorable to improve TC and obtain single-phase samples. For preparing MgCNi3 superconductor, the optimum composition of starting materials is MgC1.45Ni3 with 20wt.% excess of Mg of the stoichiometric composition. In MgCNi3-xCox system, a continuous solid solution is formed, lattice parameter decreases slightly and TC decreases obviously with increasing x. A suppression of superconductivity is observed due to the substitution of Co (Mn) for Ni. The suppression effect is smaller for the substitution of Co than that of Mn.

Phase-relations study of Sr-Mo-O system for new superconductors search

In order to obtain single-phase samples of perovskite-related strontium molybdates, especially of Sr 2MoO 4, we started to explore the ternary phase diagram of Sr-Mo-O. When we heated in an evacuated quartz tube the starting material whose composition was Sr : Mo : O = 2 : 1 : 4, we obtained no Sr 2MoO 4 phase. By using the compositions away from 2 : 1 : 4, we found multi-phase samples containing Sr 2MoO 4, Sr 3Mo 2O 7, and Mo metal. However, we were able to obtain single-phase samples of Sr 2MoO 4 from the stoichiometrically-prescribed starting materials by proper control of atmosphere in the quartz tube. We emphasize that for new superconductors search in metal oxides we should avoid the use of SrO as a starting material in order to suppress the formation of metal carbides.

酸化物超伝導体の合成と評価 Ｃｕ３Ｏ４面を有する銅酸化物（Ｓｒ，Ｂａ）２Ｃｕ３Ｏ４（Ｃｌ，Ｂｒ）２へのキャリアドーピング

A trial of the carrier doping into (Sr, Ba)2Cu3O4(Cl, Br)2 with the Cu3O4 plane, which is composed of Cu(1)O2 and extra Cu(2) sublattices, has been carried out through the partial substitution. We have succeeded in obtaining single-phase samples of Ba2Cu3-xLixO4Cl2(0≤x≤1.0). With increasing x, the α-axis tends to decrease and the c-axis is almost constant. All samples exhibit semiconductive behavior. The electrical resistivity decreases with increasing x up to 0.5 and tends to increase slightly for x>0.5 due to disorder in the Cu3O4 plane through the substitution of Li+ for Cu2+. Both of the antiferromagnetic transition temperatures with respect to Cu (1) and Cu (2) decrease with increasing x. However, the antiferromagnetic ordering in the Cu(1)O2 sublattice still remains even for x=0.5. Considering that the formal valence of Cu is + 2.2 for x=0.5, holes doped through the Li-substitution maybe localized in the Cu(2) site. We will also discuss the possibility of the appearance of the superconductivity in the present system with the Cu3O4 plane.

Synthesis of Materials Using a Domestic Microwave Oven.

Recently, much attention has been paid to the microwave processing in the preparation of inorganic materials. The advantages of microwave processing are uniformity of heat treatment and saving of energy and time, which are similar to those of microwave cooking. In this report, our recent research of the synthesis of High-Tc superconductors using a domestic microwave oven is described. We have succeeded in obtaining single-phase samples of the Y-123, Bi-2201 and Bi-2212 phases for several ten min without any post-heat-treatment using an electric furnace. In addition, several reports on the synthesis of other inorganic materials using a domestic microwave oven are introduced.

Synthesis of the Pb-based superconductor of the Pb3201 phase (Pb 2Cu)Sr 0.9La 1.1CuO 6+δ by the modified polymerized complex method

We have succeeded in obtaining single-phase samples of the Pb3201 phase (Pb 2Cu)Sr 0.9La 1.1CuO 6+δ by the modified polymerized complex method. At the first step of the synthesis, a transparent gel is found to be obtained by increasing the molar ratio of citric acid to total metal ions up to 5 without controlling the pH of the solution and without ethylene glycol. Secondly, the precursor is prepared by calcining the transparent gel. Finally, highly homogeneous samples with the onset temperature of the superconducting transition, ∼ 37 K, are obtained by sintering the precursor and subsequently annealing it. Moreover, the Pb3201 phase is found to be stable only for x = 1.1 in (Pb 2Cu)Sr 2− x La xCuO 6+δ.

Effect of hydrolysis catalyst on the Ti deficiency and crystallite size of sol-gel-TiO2 crystalline phases

We prepared sol-gel titania by using different hydrolysis catalysts, and characterized it by x-ray powder diffraction. The structure of the crystalline phases—brookite, anatase, and rutile—in the samples annealed between 70 and 900 °C was refined by using the Rietveld technique. From the refinement we obtained the structure parameters, the concentration of each phase, and their average crystallite size. These quantities and their evolution with temperature depended on the hydrolysis catalyst. Anatase and rutile were deficient in Ti, suggesting that their crystalline structure contained hydrogen atoms, forming OH− ions inside. In anatase this deficiency depended on its crystallite size, but it was constant in rutile. When anatase was annealed, it dehydroxylized, producing either crystallitc growing up or its conversion into rutile. From the analysis we also found the conditions for obtaining single-phase samples that could be used as precursors for making up titania single-phase thin films.

Raman scattering from high-Tc superconductors.

Raman scattering experiments from high-1; superconductors of the RBa2Cu307-~ type, with R Y, Pr, Nd, Eu, Gd, Dy, and Yb, are reported. Because of the great difBculty in obtaining single-phase samples, spectra from all starting compounds and other known phases of Y-Ba-Cu are presented. This systematic approach has allowed the identi6cation of the lines observed in Raman spectra of the superconducting compounds as well as those of impurity phases. The lines originating from the superconducting yttrium compound were investigated as a function of quench temperature, and oxygen de5ciency. Polarization studies on single crystals are also presented. L IM acODUi-nON An important experiment to test the conventional electron-phonon-mediated Bardeen-Cooper-Schrieffer (BCS) mechanism for superconductivity in the recently discovered metallic copper oxides'2 is the isotope effect, s s in which ' 0 is replaced by ' O. On substitution no changes were observed in the superconducting properties in Refs. 3 and 4; while in Ref. 5 a small isotope effect is claimed. Nevertheless, a study of the phonon properties is crucial for an understanding of these intriguing materials even if the superconducting mechanism is proven not to be phonon mediated. During the short time since the discovery of these materials, there have already been numerous reports dealin~ with phonon properties, including infrared studies, 7 ' Raman studies, ' 's and inelastic neutron scattering studies. 's Even among the eleven Raman-scattering references substantial discrepancies are present. In agreement with Ref. 15, we find that many of these discrepancies are due to impurity phases, which, because of the usual preparation techniques, are almost always present in these compounds. Many of these phases are not metallic and consequently have much larger cross sections for Raman scattering so, that even though the impurities may be a small volume fraction, they can dominate the Raman spectra. Here we report the results of a systematic study of the YBa2Cus07 s system. We present spectra obtained from the usual starting compounds as well as from the known impurities which are likely to be present in typical samples. A comparison of these spectra with the ones obtained from nominally pure YBa2Cu307 — s has allowed the identification of many impurity lines, and more importantly, those hnes belonging to the superconducting compound. In addition to the identification of the lines originating from the superconducting compound, the behavior of a number of them as a function of quench temperature, oxygen stoichiometry, substitution of Y by a number of rareearth metals, and polarization studies on single crystals, are presented. Section II is a detailed factual report of our results. In Sec. III these are discussed and compared with other reports in the literature and our conclusions are given in Sec. IV.