scholarly journals Distribution of mixed-valence ions in Mn1+xFe2-xO4ferrites

2014 ◽  
Vol 70 (a1) ◽  
pp. C1354-C1354
Author(s):  
Yoshio Aoyagi ◽  
Maki Okube ◽  
Satoshi Sasaki
Keyword(s):  
Magnetic Moments ◽  
Mixed Valence ◽  
Site Occupancy ◽  
Resonant Scattering ◽  
Electronic Configuration ◽  
Site Preference ◽  
Careful Study ◽  
Intensity Measurements ◽  
Valence States ◽  
A Site

Mn ferrite has a spinel structure to show the ferrimagnetism, where the magnetic moments show a collinear ferrimagnetic ordering between tetrahedral A and octahedral B sites. Since Mn2+ and Fe3+ have the same electronic configuration, it is not easy to determine the cation distribution of Mn ferrite from usual magnetization measurements. Especially in Mn ferrite, both Mn2+ and Fe3+ have a large spin polarization to give strong magnetic moments through the super exchange interaction between the two sites. Replacing Fe3+ by Mn2+ and Mn4+, the ferrimagnetic property weakens through magnetic balance between the sites. Since Mn and Fe ions may have multiple valences in the oxide structure, the scheme of site preference, based on careful study of various valence states, has been investigated for Mn1+xFe2-xO4. Single crystals for Mn1+xFe2-xO4 (x = 0.05, 0.20, 1.36 and 1.50) were synthesized from stoichiometric proportions of Mn3O4 and Fe3O4 in an evacuated silica capsule at 1353 K for 96 h. Each of spherical or parallel-piped crystals, ranging 0.05 to 0.08 mm, was mounted on the glass fiber. Conventional intensity measurements were made using a Rigaku AFC-5S four-circle diffractometer with a graphite (002) monochromator for Mo Kα radiation. Least-squares refinements were made to obtain atomic parameters, converged with R factors ranging 0.023 to 0.029. The site occupancy of Mn and Fe atoms was then determined on the basis of the resonant scattering effect at the Fe K absorption edge (λ = 1.7535 Å), by using a vertical-type four-circle diffractometer at PF-BL-10A. The results show that 89, 82, 100 and 100 percent of Mn atoms occupy the A site for the four samples, respectively. In the third step of analyses, absorption experiments were performed at PF-BL-6C. XANES and XMCD spectra were used at Mn and Fe K edges for determining the valence states of Mn and Mn ions. Finally, the distribution of mixed-valence ions for Mn1.20Fe1.80O4 was determined by the valence-difference contrast method, where the intensity data were collected for a spherical single crystal of 0.08 mm in a diameter at both threshold and pre-edge regions of Mn K edge, by using an AFC-5u four-circle diffractometer installed in PF-BL-6C. The site occupancy with the valence state will be discussed in the presentation, compared with the other type of transition-metal ferrites.

scholarly journals Substitution effect in high-Tc mercury-based cuprate superconductor

2014 ◽  
Vol 70 (a1) ◽  
pp. C1364-C1364
Author(s):  
Ryutaro Matsumura ◽  
Maki Okube ◽  
Satoshi Sasaki
Keyword(s):  
Site Occupancy ◽  
Substitution Effect ◽  
Resonant Scattering ◽  
Steam Pressure ◽  
Hole Doping ◽  
Layered Perovskite ◽  
Site Preference ◽  
Interstitial Oxygen ◽  
Key Factor ◽  
The Stability

HgBa2Ca2Cu3O8+δ superconductor (Hg-1223) still has the highest critical temperature in various superconductors, which is a layered perovskite with the space group of P4/mmm. A structural unit of cation-layers is stacked in a sequence of -HgO-BaO-CuO-Ca- along the c-axis. The substitution of Hg by Pb enhances the stability of the Hg-1223 phase because the high steam pressure of Hg lowers the chemical stability in synthesis. However, the doping into Hg layers is related to an interstitial oxygen defect. On the other hand, the substitution of Ba by Sr improves the hole doping of CuO2 planes. Thus, the element substitution in Hg and Ba sites becomes a key factor in synthesizing high-quality superconductors. Therefore, the cation distribution in the two sites has been examined by the two-wavelengths anomalous dispersion (TWAD) method of synchrotron X-ray resonant scattering. Single crystals of Hg-1223 were grown at T = 1130 K by the liquid-assisted solid-state recrystallization method from the precursor powder prepared by spray drying or evaporation of the nitrate solutions. Oxygen contents in the precursors were determined by iodometric titrations. Four samples of Hg0.45Pb0.30Ba1.63Sr0.50Ca1.94Cu3O8 (Tc = 128 K), Hg0.42Pb0.41Ba1.19Sr1.06Ca1.97Cu3O8 (125 K), Hg0.50Pb0.50Ba0.59Sr1.24Ca1.83Cu3.34O8 (116 K) and Hg0.34Pb0.54Ba0.61Sr1.17Ca1.88Cu3O8 (115 K) were selected for single-crystal intensity measurements. A conventional measurement to determine the Ba-site occupancy was made to use a Rigaku AFC-5 four-circle diffractometer with Mo Kα radiation. After the absorption correction by the arbitrary-shape grid-integration method, crystal-structure refinements were successfully performed with R factors ranging 6.4 to 6.7 %. The site preference of Hg, Pb and Cu in the Hg site was determined with a vertical-type four-circle diffractometer in PF-BL-10A, where wavelengths of λ = 1.3906 and 1.0191 Å were used at Cu K and Hg LIII absorption edges, respectively. In the TWAD method with least-squares calculations, a variation of the residual factors gives a minimum against the contents of Hg or Cu, suggesting, for example, that Cu does not occupy the Hg site for all samples. In the presentation the site preference and structural change will be discussed in the aspects of superconductivity.

Neutron Diffraction Study on Ce-Doped Nickel Ferrite Nanoparticles

2020 ◽  
Vol 855 ◽  
pp. 22-27
Author(s):  
Engkir Sukirman ◽  
Yunasfi ◽  
Andon Insani ◽  
Wisnu Ari Adi
Keyword(s):  
Neutron Diffraction ◽  
Mole Fraction ◽  
Rietveld Method ◽  
Magnetic Moments ◽  
Site Occupancy ◽  
Neutron Diffraction Pattern ◽  
High Energy ◽  
Neutron Diffraction Study ◽  
Cubic Symmetry ◽  
A Site

The NiCexFe2-xO4 polycrystalline spinel compound with composition x = 0.005, 0.010, 0.015, and 0.02 was synthesized by the solid reaction method using the high energy milling (HEM) apparatus. Measurement of the neutron diffraction patterns is carried out at room temperature using a high resolution powder neutron diffractometer (HRPD), wavelength λ = 1.8213 Å. The measured neutron diffraction data were analyzed by the Rietveld method utilizing the FullProf analysis code. The results of the neutron diffraction pattern refinement revealed that the sample has a cubic symmetry, the Fd-3m space group, mixed inverse spinel structure, A-site occupied by cation Fe3+, Ni2+, dan Ce3+. Whereas the B-site is only occupied by Fe3+ and Ni2+. The mole fraction of Fe3+ at the B-site is greater than the Fe3+ mole fraction at the A-site, whereas the mole fraction of Ni2+ at the B-site is smaller than the mole fraction of Ni2+ at the B-site. As a result of Ce3+ doping, oxygen position parameters increase, magnetic moments on B-site, and the net magnetic moments decrease. Ni2+ concentrations at the A-site and the B-site were not affected by the amount of Ce3+ substitutions. Without substitution and after Ce3+ substitution, the O-site occupancy factor is still oxygen deficient.

scholarly journals Synthesis and electrical properties of BaBiO3 and high resistivity BaTiO3–BaBiO3 ceramics

2016 ◽  
Vol 06 (04) ◽  
pp. 1650032 ◽  
Author(s):  
Nitish Kumar ◽  
Stephen L. Golledge ◽  
David P. Cann
Keyword(s):  
Optical Spectroscopy ◽  
Photoelectron Spectroscopy ◽  
Site Occupancy ◽  
Ac Impedance ◽  
Tetragonal Symmetry ◽  
High Resistivity ◽  
X Ray Diffraction ◽  
X Ray ◽  
Valence States ◽  
A Site

Ceramics of the composition BaBiO3 (BB) were sintered in oxygen to obtain a single phase with monoclinic [Formula: see text]2/[Formula: see text] symmetry as suggested by high-resolution X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states — 3[Formula: see text] and 5[Formula: see text]. Optical spectroscopy showed presence of a direct bandgap at [Formula: see text] 2.2[Formula: see text]eV and a possible indirect bandgap at [Formula: see text] 0.9[Formula: see text]eV. This combined with determination of the activation energy for conduction of 0.25[Formula: see text]eV, as obtained from ac impedance spectroscopy, suggested that a polaron-mediated conduction mechanism was prevalent in BB. The BB ceramics were crushed, mixed with BaTiO3 (BT), and sintered to obtain BT–BB solid solutions. All the ceramics had tetragonal symmetry and exhibited a normal ferroelectric-like dielectric response. Using ac impedance and optical spectroscopy, it was shown that resistivity values of BT–BB were orders of magnitude higher than BT or BB alone, indicating a change in the fundamental defect equilibrium conditions. A shift in the site occupancy of Bi to the A-site is proposed to be the mechanism for the increased electrical resistivity.

Structure, Magnetic Properties and 151Eu, 119Sn Mössbauer Spectroscopy of Eu5Sn3S12 and Eu4LuSn3S12

2007 ◽  
Vol 62 (1) ◽  
pp. 5-14 ◽  
Author(s):  
Petra Jakubcová ◽  
Dirk Johrendt ◽  
Peter Sebastian ◽  
Sudhindra Rayaprol ◽  
Rainer Pöttgen
Keyword(s):  
Magnetic Moments ◽  
Mixed Valence ◽  
Magnetic Ordering ◽  
Structural Disorder ◽  
Site Preference ◽  
Hyperfine Fields ◽  
Temperature Dependent ◽  
One Dimensional ◽  
Divalent Europium ◽  
The Eu

Eu5Sn3S12 and Eu4LuSn3S12 were synthesized and their structures refined from single crystal data (Pmc21, Eu5Sn3S12: a = 3.908(1), b = 20.115(4), c = 11.451(2) Å ; wR2 = 0.0519 for 3048 F2 and 122 parameters; Eu4LuSn3S12: a = 3.920(1), b = 20.132(4), c = 11.459(2) Å ; wR2 = 0.0737 for 3298 F2 and 122 parameters). The structures contain one-dimensional chains of edge-sharing SnS2S4/2 octahedra and corner-sharing SnS3S2/2 trigonal bipyramids, running parallel to [100]. Five europium sites are seven- or eightfold coordinated by sulfur atoms. Lutetium atoms in Eu4LuSn3S12 show a strong site preference for one of the two Eu3+ positions of Eu5Sn3S12 and no structural disorder was observed. Both compounds show static mixed valence according to Eu2+3 Eu3+2 Sn4+3 S2−12 and Eu2+3 Eu3+Lu3+Sn4+3 S2−12 , which was confirmed by temperature dependent magnetic susceptibility measurements. The experimental magnetic moments of 14.6(1) (Eu5Sn3S12) and 14.1(1) (Eu4LuSn3S12) μB/f.u. indicate that each of the two sulfides contains three divalent europium atoms per formula unit. Magnetic ordering for Eu5Sn3S12 and Eu4LuSn3S12 sets in below 5 and 3 K, respectively. Both sulfides show metamagnetic or spin-flip transitions in the magnetization curves at 3 K (2 K) with full saturation of the europium magnetic moments at 3 K (2 K) and 80 kOe. 151Eu Mössbauer spectra fully confirm the Eu2+ and Eu3+ site occupancies. At 4.2 K an increase in line width indicates small hyperfine fields at the europium nuclei.

Cerium oxide nanomaterial with dual antioxidative scavenging potential: Synthesis and characterization

2021 ◽  
pp. 088532822110134
Author(s):  
Sushant Singh ◽  
Udit Kumar ◽  
David Gittess ◽  
Tamil S Sakthivel ◽  
Balaashwin Babu ◽  
...  
Keyword(s):  
Cerium Oxide ◽  
Biological Systems ◽  
Mixed Valence ◽  
Stable Solution ◽  
Ability To Act ◽  
Valence States ◽  
Transmission Electron ◽  
Efficient Reduction ◽  
Rich Media

Many studies have linked reactive oxygen species (ROS) to various diseases. Biomedical research has therefore sought a way to control and regulate ROS produced in biological systems. In recent years, cerium oxide nanoparticles (nanoceria, CNPs) have been pursued due to their ability to act as regenerative ROS scavengers. In particular, they are shown to have either superoxide dismutase (SOD) or catalase mimetic (CAT) potential depending on the ratio of Ce3+/Ce4+ valence states. Moreover, it has been demonstrated that SOD mimetic activity can be diminished by the presence of phosphate, which can be a problem given that many biological systems operate in a phosphate-rich environment. Herein, we report a CNP formulation with both SOD and catalase mimetic activity that is preserved in a phosphate-rich media. Characterization demonstrated a highly dispersed, stable solution of uniform-sized, spherical-elliptical shaped CNP of 12 ± 2 nm, as determined through dynamic light scattering, zeta potential, and transmission electron microscopy. Mixed valence states of Ce ions were observed via UV/Visible spectroscopy and XPS (Ce3+/Ce4+ > 1) (Ce3+∼ 62%). X-ray diffraction and XPS confirmed the presence of oxygen-deficient cerium oxide (CeO2-x) particles. Finally, the CNP demonstrated very good biocompatibility and efficient reduction of hydrogen peroxide under in-vitro conditions.

scholarly journals Rare-earth (RE) nanolaminates Mo4RE4Al7C3 featuring ferromagnetism and mixed-valence states

2018 ◽  
Vol 2 (11) ◽  
Author(s):  
Q. Tao ◽  
T. Ouisse ◽  
D. Pinek ◽  
O. Chaix-Pluchery ◽  
F. Wilhelm ◽  
...  
Keyword(s):  
Rare Earth ◽  
Mixed Valence ◽  
Valence States

scholarly journals A novel and potentially scalable CVD-based route towards SnO2:Mo thin films as transparent conducting oxides

2021 ◽  
Author(s):  
Tianlei Ma ◽  
Marek Nikiel ◽  
Andrew G. Thomas ◽  
Mohamed Missous ◽  
David J. Lewis
Keyword(s):  
Thin Films ◽  
Photoelectron Spectroscopy ◽  
Mixed Valence ◽  
Chemical Vapour ◽  
X Ray Diffraction ◽  
X Ray ◽  
Conducting Oxides ◽  
Valence States ◽  
3 Omega ◽  
First Time

AbstractIn this report, we prepared transparent and conducting undoped and molybdenum-doped tin oxide (Mo–SnO2) thin films by aerosol-assisted chemical vapour deposition (AACVD). The relationship between the precursor concentration in the feed and in the resulting films was studied by energy-dispersive X-ray spectroscopy, suggesting that the efficiency of doping is quantitative and that this method could potentially impart exquisite control over dopant levels. All SnO2 films were in tetragonal structure as confirmed by powder X-ray diffraction measurements. X-ray photoelectron spectroscopy characterisation indicated for the first time that Mo ions were in mixed valence states of Mo(VI) and Mo(V) on the surface. Incorporation of Mo6+ resulted in the lowest resistivity of $$7.3 \times 10^{{ - 3}} \Omega \,{\text{cm}}$$ 7.3 × 10 - 3 Ω cm , compared to pure SnO2 films with resistivities of $$4.3\left( 0 \right) \times 10^{{ - 2}} \Omega \,{\text{cm}}$$ 4.3 0 × 10 - 2 Ω cm . Meanwhile, a high transmittance of 83% in the visible light range was also acquired. This work presents a comprehensive investigation into impact of Mo doping on SnO2 films synthesised by AACVD for the first time and establishes the potential for scalable deposition of SnO2:Mo thin films in TCO manufacturing. Graphical abstract

scholarly journals Correction: Effects of mixed-valence states of Eu-doped FAPbI3 perovskite crystals studied by first-principles calculation

2021 ◽  
Vol 2 (8) ◽  
pp. 2759-2759
Author(s):  
Atsushi Suzuki ◽  
Takeo Oku
Keyword(s):  
First Principles ◽  
Mixed Valence ◽  
First Principles Calculation ◽  
Valence States

Correction for ‘Effects of mixed-valence states of Eu-doped FAPbI3 perovskite crystals studied by first-principles calculation’ by Atsushi Suzuki et al., Mater. Adv., 2021, DOI: 10.1039/D0MA00994F.

scholarly journals The thermochemistry of carbon: valence states, heats of sublimation and energies of linkage

1946 ◽  
Vol 187 (1010) ◽  
pp. 337-357 ◽  
Keyword(s):  
Ground State ◽  
Electronic Configuration ◽  
Dissociation Energies ◽  
True Value ◽  
Valence States ◽  
Chemical Combination ◽  
The Right ◽  
Right Order ◽  
Unambiguous Assignment ◽  
Apparent Conflict

The controversy which exists at the present time between the figures 125 and 170 kcal./g.- atom for the latent heat of sublimation of carbon into monatomic vapour in the ground state originates largely from the neglect to take into consideration the energy required to raise the carbon atoms from the ground ( 3 P ) state to the lowest tetravalent ( 5 S ) electronic configuration corresponding to that in which it is normally found in chemical combination. Consideration of the energies of removal of a hydrogen atom from the methane and ethane molecules and of the energies of reorganization of the resulting radicals leads to the figure 190 ± about 10 kcal. for L 2 , the heat of sublimation into free atoms in the 5 S state. This in turn leads to a satisfactory and unambiguous assignment of values to bond energies (as distinct from dissociation energies) which can now be expressed with an uncertainty of not more than a few kcal. In the light of the valency distinction there remains no sound evidence to maintain the higher value put forward for L 1 and 125 kcal. is unquestionably of the right order. There are strong indications that an earlier estimate of 100 kcal. for the energy level of the 5 S state above the 3 P (ground) state is about 50 % in excess of the true value. The necessity for establishing this branch of thermochemistry on a sound theoretical and experimental footing has long been a very obvious need. The scheme here suggested reconciles points hitherto in apparent conflict, and brings virtually all established experimental knowledge into alignment.

scholarly journals β-Li0.37Na0.63Fe(MoO4)2

2014 ◽  
Vol 70 (2) ◽  
pp. i9-i10 ◽  
Author(s):  
Amira Souilem ◽  
Mohamed Faouzi Zid ◽  
Ahmed Driss
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Solid State Reaction ◽  
Title Compound ◽  
General Position ◽  
Site Occupancy ◽  
The Other ◽  
Main Structure ◽  
Axis Direction ◽  
A Site

The title compound, lithium/sodium iron(III) bis[orthomolybdate(VI)], was obtained by a solid-state reaction. The main structure units are an FeO6octahedron, a distorted MoO6octahedron and an MoO4tetrahedron sharing corners. The crystal structure is composed of infinite double MoFeO11chains along theb-axis direction linked by corner-sharing to MoO4tetrahedra so as to form Fe2Mo3O19ribbons. The cohesion between ribbonsviamixed Mo—O—Fe bridges leads to layers arranged parallel to thebcplane. Adjacent layers are linked by corners shared between MoO4tetrahedra of one layer and FeO6octahedra of the other layer. The Na+and Li+ions partially occupy the same general position, with a site-occupancy ratio of 0.631 (9):0.369 (1). A comparison is made withAFe(MoO4)2(A= Li, Na, K and Cs) structures.

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