Surface of Zn-Mn-O and its role in room temperature ferromagnetism: An XPS analysis

The existence of ferromagnetism in Zn-Mn-O semiconductor samples and dependence on the preparation condition were investigated. We systematically examined the samples with manganese concentration ranging from 0 to 10 at.%, prepared by a solid state reaction route using (ZnC₂O₄·2H₂O)_1−x and (MnC₂O₄·2H₂O)_x as precursors. Thermal treatment was carried out in air at temperatures ranging from 400 to 900 °C. The samples were investigated by X-ray diffraction, transmission electron microscopy, magnetization measurements and XPS spectroscopy. XPS surface composition, chemical analysis and depth profiling were successfully employed on powder revealing the chemical composition at the surface of the grains and underneath. The present investigation suggests that physical properties and observed room temperature ferromagnetism might be due to grain surface effects. It seems that the ferromagnetic phase is correlated with oxygen build up at the surface.     

Phase- and shape-controlled synthesis of cadmium hydroxyl chloride microstructures via an ammonia-assisted conversion of 1D CdQCl (Q=quinoline) complex microwires

In this paper we reported a NH₃·H₂O-assisted solvothermal route for successful synthesis of cadmium hydroxyl chlorides (Cd_x(OH)_yCl_z) microstructures with different phases and shapes, employing 1D CdQCl (Q=quinoline) complex microwires as the precursor. Experiments contained two processes: firstly, CdQCl complex microwires with 500–600 nm in diameter and several hundreds of micrometers in length were prepared by the complexation between CdCl₂·2.5H₂O and quinoline at room temperature; then, CdQCl microwires were solvothermally treated at 150 °C for 10 h in the presences of different amounts of NH₃·H₂O to produce Cd_x(OH)_yCl_z microstructures with various phases and shapes. The as-obtained precursor and Cd_x(OH)_yCl_z microstructures were characterized by scanning electron microscopy, transmission electron microscopy, Infrared spectrometry and X-ray powder diffraction. Experiments showed that hexagonal Cd(OH)Cl was obtained from water–methanol system, while rhombohedral Cd₄(OH)₅Cl₃ from methanol system. Also, it was found that the shapes of Cd_x(OH)_yCl_z could be tuned by the amounts of NH₃·H₂O. Furthermore, the UV diffuse reflection and photoluminescence spectra of the precursor and Cd_x(OH)_yCl_z were also investigated.     

Electrical transport and optical properties of vanadyl phosphate—polyaniline nanocomposites

The nanocomposites of conducting polyaniline and layered vanadyl phosphate, VOPO₄·2H₂O are synthesized by redox intercalation method. Water content decreases with insertion of polyaniline molecules. In scanning electron micrographs plate like structures are observed for both VOPO₄·2H₂O and intercalated nanocomposites. Protonation of polyaniline and interaction with vanadyl phosphate are observed in infrared and UV absorption spectroscopy. Intercalation improves conductivity of pristine vanadyl phosphate. Thermally activated electrical dc conductivity at low temperature shows two distinct slopes around 210 K for both the nanocomposites. The optical band gap of vanadyl phosphate decreases from 4.0 to 3.7 eV due to insertion of polyaniline.     

Intercalative route to heterostructured nanohybrids

We have successfully synthesized inorganic–inorganic, organic–inorganic and bio-inorganic nanohybrids by applying an intercalation technique systematically to layered titanate, molybdenum disulfide (MoS₂), Bi-based cuprate superconductors (Bi₂Sr₂Ca_m−1Cu_mO_y (m=1, 2, and 3; BSCCO)), and to layered double hydroxides (LDHs), those which are of high importance in terms of basic understanding of intercalation reactions and of their practical applications. The inorganic–inorganic systems such as TiO₂-pillared titanate, TiO₂-pillared MoS₂, and CdS–MoS₂ hybrids were synthesized by exfoliation–restacking method. A novel pillaring process using an osmotic swelling was developed to prepare TiO₂-pillared layered titanate with a large surface area, high thermal stability, and enhanced photocatalytic activity. And the intercalation of TiO₂ and/or CdS nanocluster into the two dimensional MoS₂ lattice could be also realized by exfoliating and reassembling the lithiated molybdenum disulfide (LiMoS₂) in the presence of cationic TiO₂ and/or CdS nanocluster in an aqueous solution, respectively, to obtain the semiconductor–semiconductor hybrids. On the other hands, the organic–inorganic hybrids were achieved via intercalative complexation of iodine intercalated BSCOO with organic salt of Py–C_nH_2n+1I (Py=pyridine). The high-T_c superconducting intercalate with its remarkable lattice expansion can be applied as a precursor for superconducting colloids when dispersed in an appropriate solvent. This superconducting hybrid material had an unique structural feature of a superconducting-insulating-superconducting multilayer with atomically clean interfaces. Especially, this organic–inorganic nanohybrid is expected to be a promising precursor for preparing the superconducting colloidal suspension, which could be applied to the fabrication of superconducting films or wires. Recently, we were very successful in demonstrating in which the formation of bio-inorganic hybrids stabilized in the interlayer space of LDH retain their chemical and biological integrity. If necessary, LDH, as a reservoir, can be intentionally removed by dissolving it in an acidic media in such a way the interlayer biomolecules can be recovered or the intercalated biomolecules can be released from the LDH via ion-exchange reaction in electrolyte. It is, therefore, concluded that the inorganic LDH can play a role as a gene reservoir or carrier for various unstable organic or bio-molecules such as drugs and genes.     

Static susceptibility and heat capacity studies on V3O7·H2O7 nanobelts

V₃O₇·H₂O nanobelts were prepared by a hydrothermal method at 190 °C using V₂O₅·nH₂O gel and H₂C₂O₄·2H₂O as starting agents. The obtained nanobelts have diameters ranging from 40 to 70 nm with lengths up to several micrometers. Measurements of the static magnetic susceptibility and the specific heat show a discontinuous phase transition at around T=145 K, which separates two regions of paramagnetic behavior.     

Effect of anions on the phase stability of γ-FeOOH nanoparticles and the magnetic properties of gamma-ferric oxide derived from lepidocrocite

The effect of anions such as Cl⁻, SO₄²⁻, and HPO₄²⁻ on the phase stability of FeOOH (α or γ) during precipitation is investigated. Oxidation of Fe(OH)₂·xH₂O from FeCl₂ solution with high Cl⁻ concentration ([Cl⁻]/[Fe]=R_Cl≥8) or (NH₄)₂Fe(SO₄)₂ (FAS) with [HPO₄²⁻]/[Fe]=R_P≥0.02 yields phase-pure γ-FeOOH. In the medium ranges of R_Cl and R_P, mixed phases of α-FeOOH and γ-FeOOH are obtained. Replacement of OH⁻ by Cl⁻ with the bridging cations or strongly bonded HPO₄²⁻ ions in the matrix of the intermediate phase (Fe_x²⁺Fe_y³⁺(OH)_2x+2y−nz·xH₂O(A)_zⁿ⁻, where A is anions such as Cl⁻, SO₄²⁻, HPO₄²⁻, etc.), promoted the lower density γ-FeOOH. However, the particles are less developed and have poor crystallinity as evidenced from transmission electron microscope and thermogravimetry-differential thermal analysis of the precipitates. Whereas, monophasic, uniformly sized, nano-lath shaped particles with high aspect ratio >10 are obtained when morphology-controlling cation additives such as Pt⁴⁺, Pd²⁺ or Rh³⁺ are present in FeCl₂ (R_Cl≥8) solution. Preferential adsorption of additives on (0k0) and (h00) planes limits the growth in the perpendicular directions leading to high aspect ratios. The effect of these additives are suppressed by the phosphate ion, a strong complexing ligand, giving rise to fibrous aggregate with the length of individual particles as small as 10-30 nm. While most of the Cl⁻ ion is removed from the final precipitates on washing, phosphate remained as HPO₄²⁻ as evidenced from IR absorption spectra. Maghemite obtained by dehydroxylating γ-FeOOH contains randomly distributed micropores bringing in the relaxation effects of spins on the surface atoms as deciphered from Mössbauer spectroscopy. This leads to the low σ_s (44-48 emu/g) and H_c (120-130 Oe) for γ-Fe₂O_3−δ particles. Whereas nearly pore-free single crystalline particles obtained by reduction followed by reoxidation has high value of σ_s (73 emu/g) and H_c (320 Oe), which decreases to 30 emu/g and 75 Oe, respectively, for nanoparticles obtained from phosphate stabilized lepidocrocite. The mobility of iron ions and counter mobility of vacancies during the topotactic transformation of γ-FeOOH to magnetite to γ-Fe₂O_3−δ renders the particles pore-free.     

Characteristics of mixed crystals Co(1−x)Fe x SO4· 7H2O

The characteristics of the mixed crystal (Fe,Co)SO₄·7H₂O (x=Fe/(Fe+Co)) are studied from the Mössbauer spectroscopy. They are quite similar atx>0.3 to those of FeSO₄·7H₂O. Whenx decreases from 0.2, the characteristics deviate from those of FeSO₄·7H₂O and approach gradually to those of CoSO₄·7H₂O.     

Synthesis of basic magnesium carbonate microrods with a “house of cards” surface structure using rod-like particle template

Basic magnesium carbonate (Mg₅(CO₃)₄(OH)₂·4H₂O) microrods with a surface structure of “house of cards” have been synthesized without any alkaline reagent, using rod-like particles, magnesium carbonate trihydrate, as templates. The product was characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The transformation process from rod-like MgCO₃·3H₂O particles to Mg₅(CO₃)₄(OH)₂·4H₂O microrods with a surface structure of “house of cards” was recorded. Preliminary discussions on possible growth mechanisms of Mg₅(CO₃)₄(OH)₂·4H₂O microrods are also proposed in this paper.     

Magnetic properties of CoFeP films prepared by electroless deposition

Structure and magnetization of CoFeP films prepared by the electroless deposition were systematically investigated by varying the bath composition and deposition parameters to optimize soft magnetic properties. The cobalt content in the CoFeP films varies from 40.4 to 94.9 wt% by controlling the bath composition. Increase of the metallic ratio FeSO₄·7H₂O/(CoSO₄·7H₂O+FeSO₄·7H₂O) affects the films’ microstructure, which switches from amorphous to crystalline structure. The magnetic properties of CoFeP films reveal that the coercivity (H_c) values range from 80 up to 185 A/m and the saturation magnetization (M_s) from 82 to 580 eum/g depending on the bath composition, deposition parameters and heat-treatment conditions. Increase of M_s and remanent magnetization (M_r) as well as decrease of H_c are observed for the CoFeP films with bath pH, temperature and the metallic molar ratio increasing. It is also found that the H_c is enhanced with the increase of NaH₂PO₂·H₂O concentration. CoFeP films showing good soft magnetic properties with coercivities less than 140 A/m and M_s close to 600 emu/g can be obtained in high pH bath and thereafter heat treatment. The deposit is found to be suitable as soft magnetic materials for core materials.     

α-Fe2O3-In2O3 mixed oxide nanoparticles synthesized under hydrothermal supercritical conditions

α-Fe₂O₃-In₂O₃ mixed oxide nanoparticles system has been synthesized by hydrothermal supercritical and postannealing route, starting with (1−x)Fe(NO₃)₃·9H₂O·xIn(NO₃)₃·5H₂O aqueous solution (x=0-1). X-ray diffraction and Mössbauer spectroscopy have been used to study the phase structure and substitutions in the nanosized samples. The concentration regions for the existence of the solid solutions in the α-Fe₂O₃-In₂O₃ nanoparticle system together with the solubility limits of In³⁺ ions in the hematite lattice and of Fe³⁺ ions in the cubic In₂O₃ structure have been evidenced. In general, the substitution level is considerably lower than the nominal concentration x. A justification of the processes leading to the formation of iron and indium phases in the investigated supercritical hydrothermal system has been given.     

Study on the transformation from NaCl-type Na2TiO3 to layered titanate

NaCl-type crystal structure sodium titanate (Na₂TiO₃), which exhibits a unit cell parameter of a=4.49 Å, was obtained by high temperature molten salt reaction. An intermediate phase product with layered structure was prepared by leaching the obtained Na₂TiO₃. We propose that the layered titanate structure is composed of Na₂TiO₃ and H₂O, corresponding to the host-layer and guest-substance, respectively. Furthermore, the crystal structures of layered titanate were optimized by the density functional theory (DFT). This indicates that water molecules are distributed in an orderly manner in the interlayer through the formation of hydrogen-bonded chain. Moreover, the position of the adjacent lamella translates to c/2 along the c-axis after the intercalation of water.     

Reactivity and XAFS study on (1−x)CeO2-xNiO (x=0.025-0.3) system in the two-step water-splitting reaction for solar H2 production

The redox reaction of Ce⁴⁺-Ce³⁺ promoted by the catalytic function of nickel ions in a (1−x)CeO₂-xNiO solid solution was investigated for solar H₂ production by the two-step water-splitting reaction. By irradiation using an infrared imaging lamp as a solar simulator, the O₂-releasing reaction with (1−x)CeO₂-xNiO solid solution proceeded at 1673-1873 K, and its reduced form was produced. The amounts of H₂ gas evolved by the reduced form were 1.2-2.5 cm³/g and the evolved gases amounts ratio of H₂/O₂ was nearly 2, which is equal to the stoichiometric value of the water-splitting reaction (H₂O=H₂+1/2O₂). The maximum amounts of evolved H₂ and O₂ gases were obtained at the Ce:Ni mole ratio of 0.95:0.05 (x=0.05) in the (1−x)CeO₂-xNiO system. The X-ray absorption fine structure (XAFS) measurement showed that the O₂-releasing and H₂-generation reactions with (1−x)CeO₂-xNiO solid solution were repeatable with the redox system of Ce⁴⁺-Ce³⁺, which was enhanced by the catalytic function of Ni²⁺-Ni⁰.     

Preparation and characterization of polymer coated superparamagnetic magnetite nanoparticle agglomerates

In order to produce magnetic microparticles (agglomerates), magnetite (Fe₃O₄) particles were synthesized using coprecipitation of FeSO₄·7H₂O and FeCl₃·6H₂O with the presence of poly(methacrylic acid) (PMAA) in aqueous solution.. Transmission electron microscopy (TEM), X-ray diffraction, and vibrating sample magnetometry (VSM) methods were used to characterize the PMAA coated superparamagnetic agglomerates. The influences of various processing parameters such as the process temperature, PMAA content, and the addition of surfactant on the agglomerate size and size distribution of produced magnetic microparticles were investigated. The particle size and size distribution characteristics, (the volume weighted mean size (D[4,3], surface weighted mean size D[3,2], the geometric standard deviation, and span value) of the magnetic agglomerates were determined using the laser diffraction technique. The PMAA coated magnetic agglomerates with surface weighted mean sizes ranging from 1.5 to 3 μm were produced successfully.     

Intercalative route to heterostructured nanohybrid☆

We have successfully synthesized inorganic–inorganic, organic–inorganic and bio-inorganic nanohybrids by applying a chimie douce intercalation technique systematically to layered titanate, to Bi-based cuprate superconductors, Bi₂Sr₂Ca_m−1Cu_mO_y (m=1, 2, and 3; BSCCO), and to layered double hydroxides (LDHs), those which are of high importance in terms of basic understanding of intercalation reactions and also having practical application. The inorganic/inorganic hybrids were synthesized by exfoliation-restacking methods to obtain TiO₂-pillared titanate. A novel pillaring procedure using an osmotic swelling had been developed to prepare TiO₂-pillared layered titanate with a large surface area, high thermal stability, and enhanced photocatalytic activity. On the other hands, the organic/inorganic hybrids were achieved via intercalative complexation of iodine intercalated BSCOO with an organic salt of Py–C_nH_2n+1I (Py=pyridine). The high-T_c superconducting intercalate with its remarkable lattice expansion can be applied as a precursor for superconducting colloids when dispersed in an appropriate solvent. We were also able to demonstrate that the biomolecules stabilized in the interlayer space of layered double hydroxides (LDH), bio-inorganic hybrids, retain their chemical and biological integrity. If necessary, LDH, as a reservoir, can be intentionally removed by dissolving it in an acidic medium or interlayer biomolecules in LDH can be released via ion-exchange reaction in electrolyte. It can, therefore, be concluded that the inorganic LDH can play a role as a good host lattice for gene reservoir or carrier. These intercalative methods will provide remarkable synthetic routes to design new heterogeneous hybrid materials, which have the intrinsic properties starting materials and create synergetic effects by hybridization.     

The first synthesis of a graphite bis(oxalato)borate intercalation compound

A new graphite intercalation compound containing the bis(oxalato)borate anion, B[OC(O)C(O)O]₂⁻, is prepared for the first time by chemical oxidation of graphite with fluorine gas in the presence of a solution containing the intercalate anion in anhydrous hydrofluoric acid. The products of stage 1-3 compounds are characterized by powder X-ray diffraction, thermogravimetric analysis, and elemental analyses. X-ray diffraction data indicate a standing-up orientation for the borate anion, with long axis perpendicular to the graphene sheets. Elemental analyses provide x and δ for the nominal composition of C_xB[OC(O)C(O)O]₂·δF, where the chelate borate and fluoride are co-intercalates, and indicate a low borate, and high fluoride, intercalate content as compared to anion packing in other graphite intercalation compounds.     

Compositional dependence of in-vitro bioactivity in sodium calcium borate glasses

Borate glasses with composition xCaO (100−x) B₂O₃ (20≤x≤50), where x is in mole percent) and 50CaO·45B₂O₃·5Na₂O have been prepared using conventional melt quench technique. Samples were submerged in simulating body fluid solution (SBF) at 37 °C for various periods of time. After storage the samples were analyzed in order to investigate if a surface layer of hydroxyl carbonate apatite layer (HCA layer/Ca-P layer) had formed. The analysis technique used included Fourier-Transform Infrared Spectroscopy (FTIR). The rate of HCA layer formation on the surface of exposed glass samples is determined by FTIR, percentage weight loss measurements of glass samples in SBF and variation of pH of SBF as a function of time. Increase in calcium content in the glass matrix has shown to decrease the rate of HCA formation on glass surfaces. The borate glass with x=20 has shown HCA layer formation on glass surface within two days of dipping. The bone like apatite formation of glass surface demonstrates the potential of glass for integration with bone.     

Photocatalytic O2 evolution performances of Cd1+xIn2−2xSnxO4 (x=0.1, 0.3, 0.5, 0.7, 1.0) conducting oxides

The conducting oxides solid solutions of Cd_1+xIn_2−2xSn_xO₄ (x=0.1, 0.3, 0.5, 0.7, 1.0) were prepared via a solid state reaction method. The band gaps were estimated to be 2.4 eV for x=1.0, 2.5 eV for x=0.7, 2.6 eV for x=0.5, 2.7 eV for x=0.3 and 2.8 eV for x=0.1. Oxygen could be evolved over Cd₂SnO₄ under the irradiation of Xe-lamp or even visible light (λ>420 nm), while the others could only work in the UV-light range. Raman showed the cation distribution in Cd₂SnO₄ is ordered, while that in the others is disordered. The cations distribution was proposed to be the cause of the difference in photocatalytic O₂-evolution activities.     

Single-calcination synthesis of pyrochlore-free Pb(Ni1/3Nb2/3)O3-PbTiO3 using a coating method

Pyrochlore-free 0.64Pb(Ni_1/3Nb_2/3)O₃-0.36PbTiO₃ (0.64PNN-0.36PT) powder has been successfully synthesized by only one calcination step using a coating method. The formation of pyrochlore phase is prevented by coating NiCO₃·2Ni(OH)₂·2H₂O on Nb₂O₅ particles. NiCO₃·2Ni(OH)₂·2H₂O-coated Nb₂O₅ powder is prepared by heterogeneous precipitation method. The coating structure is confirmed by transmission electron microscope (TEM) with energy dispersive spectroscope (EDS). Single calcination treatment of the coating powder mixed with appropriate amounts of Pb₃O₄ and TiO₂ powders at 900 °C for 2 h produces the pure-perovskite 0.64PNN-0.36PT powder. The elimination of the pyrochlore phase can be explained in terms of the separating of Pb₃O₄ and Nb₂O₅ by the NiCO₃·2Ni(OH)₂·2H₂O coating layer.     

Luminescence of Ce in hydrated rare earth bromides

Intense photoluminescence is reported for hydrated bromides of Gd, La and Y (LaBr₃·7H₂O, CeBr₃·7H₂O, YBr₃·8H₂O and GdBr₃·n H₂O) prepared by the wet chemical method and activated with Ce³⁺. Intensities are comparable to that for a commercial phosphor (SrB₄O₇:Eu²⁺—Sylvania 2052). Luminescence in hydrated salt is usually quenched. The observation of intense luminescence in hydrated bromides is remarkable.     

A new isomorph of ferrous chloride tetrahydrate: A Fe Mössbauer and X-ray crystallography study

This paper outlines the discovery of a newly characterised isomorph of ferrous chloride tetrahydrate, Fe(H₂O)₆·FeCl₄(H₂O)₂, which was initially identified by X-ray crystallography and confirmed by Mössbauer spectroscopy. The X-ray analysis identified the space group as P2₁/c with essentially the same unit cell dimensions as the well-known isomorph, FeCl₂·4H₂O, except that one edge is doubled due to two discrete [Fe(H₂O)₆]²⁺ and [FeCl₄(H₂O)₂]²⁻ species per unit cell. Time-series Mössbauer studies revealed this new isomorph to be unstable upon atmospheric exposure, decaying to the well-known structure over a period of days. Density functional theory calculations support an energetically favourable catalytic interconversion involving adsorbed water. A high-precision redetermination on the FeCl₂·4H₂O crystal structure, which is also in space group P2₁/c, is also reported, providing the unit cell parameters: a=5.8765(3) Å, b=7.1100(3) Å, c=8.4892(5) Å and β=111.096(1)°.