Octahedron Sites Research Articles

Increase the inversion degree in Er-doped MgGa2O4 spinel nanofilms to obtain strong electroluminescence

The Ga2O3/MgO/Er2O3 nanolaminates are fabricated by atomic layer deposition and crystallized into Er-doped MgGa2O4 spinel (MGS:Er) nanofilms after annealing, with their electroluminescence (EL) performance characterized. The annealing above 600 °C achieves the polycrystalline spinel nanofilm, and the crystallization is promoted by the higher annealing temperature and Ga2O3/MgO ratio. The dopant Er3+ ions preferably substitute into the octahedron sites occupied by Ga3+ ions in ordinary spinel and Mg2+ in anti-spinel lattice, while the inversion degree is confirmed to increase with the reduction of Ga2O3/MgO ratio and annealing temperature, resulting the relatively enhanced secondary EL at 1542 nm. This perturbation by Er3+-substitution into anti-spinel sites improves the emission intensity and excitation efficiencies, the main EL emission peaking at 1531 nm from the optimal MGS:Er device exhibits the excitation efficiency reaching 5.8 %, with the enhanced electrical injection realizing the maximum EL intensity above 17.3 mW/cm2. The fluorescence lifetime of these MGS:Er devices is established in the range of 371–760 μs, which decreases mainly with the Er concentrations. The prototype device using the near-stoichiometric Ga2O3/MgO ratio shows the operation time of 1.12 × 105 s. This work explores the fabrication of Si-based spinel nanofilms with designed composition and special microstructure, and their practical application in optoelectronics.

Tuning Octahedron Sites of CoV2O4 via Cationic Competition for Efficient Oxygen Evolution Reaction.

Doping transition metal oxide spinels with metal ions represents a significant strategy for optimizing the electronic structure of electrocatalysts. Herein, a bimetallic Fe and Ru doping strategy to fine-tune the crystal structure of CoV2O4 spinel for highly enhanced oxygen evolution reaction (OER) is presented performance. The incorporation of Fe and Ru is observed at octahedral sites within the CoV2O4 structure, effectively modulating the electronic configuration of Co. Density functional theory calculations have confirmed that Fe acts as a novel reactive site, replacing V. Additionally, the synergistic effect of Fe, Co, and Ru effectively optimizes the Gibbs free energy of the intermediate species, reduces the reaction energy barrier, and accelerates the kinetics toward OER. As expected, the best-performing CoVFe0.5Ru0.5O4 displays a low overpotential of 240mV (@10mAcm-2) and a remarkably low Tafel slope of 38.9mVdec-1, surpassing that of commercial RuO2. Moreover, it demonstrates outstanding long-term durability lasting for 72h. This study provides valuable insights for the design of highly active polymetallic spinel electrocatalysts for energy conversion applications.

Probing Bond Length and Compositional Disorder in β‐(AlxGa1−x)2O3 Alloys Using Extended X‐Ray Absorption Fine Structure Spectroscopy

Local structure of β‐(AlxGa1−x)2O3 alloys with Al contents is determined from extended X‐ray absorption fine structure spectroscopy (EXAFS). A model to fit the EXAFS data for monoclinic β‐(AlxGa1−x)2O3 is suggested to independently determine local structure parameters. An increase in compositional disorder corresponding to the near neighbors (NNs) for lower Al contents establishes that the Al atom does occupy tetrahedron sites in addition octahedron sites even for smaller Al contents. NNs and next‐nearest neighbor (NNN) bond lengths corresponding to tetrahedron and octahedron coordinated gallium (Ga) atoms with surrounding oxygen (O) atoms as well as tetrahedron–tetrahedron/octahedron–octahedron coordinated GaGa atoms on average decrease with Al content up to x = 33.3% and then they saturates with further increase in Al content. However, tetrahedron–octahedron coordinated GaGa atoms move far apart with Al content up to x = 33.3% and then it saturates. The physical picture indicates the creation of tetrahedra and octahedra sublattices locally for β‐(AlxGa1−x)2O3, and their sizes decrease, but they move far apart up to a certain Al content. Thereafter, both saturate. Thus, EXAFS provide a clear insight into the evolution of local structure of β‐(AlxGa1−x)2O3 with Al content, which is useful for better understanding of their physical properties.

Amorphous Vanadium Oxide Nanosheets with Alterable Polyhedron Configuration for Fast-Charging Lithium-Ion Batteries.

Transition metal oxides with high theoretical capacities are promising anode materials for lithium-ion batteries (LIBs). However, the sluggish reaction kinetics remain a bottleneck for fast-charging applications due to its slow Li+ migration rate. Herein, a strategy is reported of significantly reducing the Li+ diffusion barrier of amorphous vanadium oxide by constructing a specific ratio of the VO local polyhedron configuration in amorphous nanosheets. The optimized amorphous vanadium oxide nanosheets with a ratio ≈1:4 for octahedron sites (Oh ) to pyramidal sites (C4v ) revealed by Raman spectroscopy and X-ray absorption spectroscopy (XAS) demonstrate the highest rate capability (356.7mAhg-1 at 10.0Ag-1 ) and long-term cycling life (455.6mAhg-1 at 2.0Ag-1 over 1200 cycles). Density functional theory (DFT)calculations further verify that the local structure (Oh :C4v = 1:4) intrinsically changes the degree of orbital hybridization between V and O atoms and contributes to a higher intensity of electron occupied states near the Fermi level, thus resulting in a low Li+ diffusion barrier for favorable Li+ transport kinetics. Moreover, the amorphous vanadium oxide nanosheets possess a reversible VO vibration mode and volume expansion rate close to 0.3%, as determined through in situ Raman and in situ transmission electron microscopy.

Structural and theoretical investigations on the “coloring” scheme of γ-brass type phase Ag5Cd8

The γ-brass type phase in the binary Ag–Cd system has been synthesized by high-temperature method, and its composition and crystal structure were analyzed by energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The compound Ag5Cd8 crystallizes in the I4¯3m (cI52) space group, having cell parameter of ∼9.9 ​Å, and the unit cell contains 52 atoms distributed over 4 crystallographically independent positions. Due to the weak X-ray scattering contrast between Ag and Cd, the first principle DFT calculations using the Vienna Ab Initio Simulation Package (VASP) code have been employed to address the “coloring problem” in the structure of Ag5Cd8. Like the ideal cubic γ-brass type phases, the structure can be conveniently described by 26-atom γ-cluster made of four concentric shells: inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), and cuboctahedron (CO). Theoretical calculations guide that in Ag5Cd8, Cd prefers IT and CO sites and Ag in OT and OH sites of the γ-cluster. The electronic structure calculation for the model Ag5Cd8 shows the appearance of a pseudogap near the Fermi level, which validates the phase stability by the Hume-Rothery mechanism as a result of the Fermi surface-Brillouin zone (FS-BZ) interaction. Bonding analysis (COHP) using the LOBSTER package shows the Ag–Cd heteroatomic interaction being the highest contributor towards the overall stability of the γ-brass type Ag5Cd8.

Tuning octahedron sites in MnFe2O4 spinel by boron doping for highly efficient seawater splitting

Seawater splitting requires highly active and stable electrocatalysts to sustain electrolysis without chloride corrosion, especially for the anode. Herein, a boron (B) doped MnFe2O4 spinel-type electrocatalyst with a heterostructure was derived from MnFe-MOF-74 precursor and applied for seawater electrolysis. It is found that the introduction of B species can effectively optimize the electronic configuration of MnFe2O4 with the promoted electron transfer ability between neighboring O to FeOh, thereby significantly reducing the energy barrier of the electron transfer and boosting the reaction process. As expected, in the real seawater environment, it required a low overpotential of 330 mV for oxygen evolution reaction (OER) to drive a current density of 100 mA cm−2 at 60 ℃, and exhibited high stability for over 200-h continuing test without producing hypochlorite and corrosion. This work provides a new strategy for enhancing the intrinsic activity of spinel-type oxides in seawater splitting.

Oxidation state, local structure distortion, and defect structure analysis of Cu doped α-MnO2 correlated to conductivity and dielectric properties

Cu-doped MnO2 with the composition of Mn1-xCuxO2 (x = 0–0.15) was synthesized and characterized. The synthesis was carried out by hydrothermal method at 140 °C for 5 h of reaction dwell time. The characterizations include X-Ray Diffraction (XRD), Microscopy, X-ray Absorption Spectroscopy (XAS), and Impedance complex analysis. It was revealed that all samples have nanorod morphology. Their size increases with the increasing dopant. Additionally, K ions are detected by EDX. All samples pose α-MnO2 type structures performing (2 × 2) and (1 × 1) tunnels permitting large ions incorporated and oxygen deficiency. The octahedron was distorted to elongate up to x = 0.10, then compressed for x = 0.15, inducing the Jan Teller effect. Oxidation state analysis revealed that the manganese has Mn3+ and Mn4+, while the copper is mainly attributed to Cu2+ and Cu3+ respectively. The small ionic size and highly oxidized Cu3+ substitute Mn4+, while Cu2+ substitutes Mn3+ or simultaneously with the larger K+ incorporated in the tunnel. Accordingly, the defects to exist in the sample, namely CuMn′, MnMn′, VO••, and e′. Electrical characterization at room temperature revealed that the conductivity of Cu-doped MnO2 is dominated by electrons influenced by the various oxidation state of the cations in the octahedron sites, while space charges dominate the dielectric response.

Cr2S3 a bipolar semiconducting fully compensated ferrimagnet

The promises of spintronics have longed for the realization of fully compensated states and full spin polarization. Half-metallic/half-semiconducting (HM/HS) and fully compensated materials are suggested as candidates. We use density functional theory to report that the experimentally realized rhombohedral ${\mathrm{Cr}}_{2}{\mathrm{S}}_{3}$ is a promising candidate as a bipolar magnetic semiconducting (BMS)/HS fully compensated ferrimagnetic (FCFiM) material. Our calculations demonstrate that the uniquely layered structure of ${\mathrm{Cr}}_{2}{\mathrm{S}}_{3}$ produces different interlayer and intralayer $d\text{\ensuremath{-}}p\text{\ensuremath{-}}d$ hybridization schemes between Cr atoms. Strong interlayer and weak intralayer antiferromagnetic coupling between different Cr sites make the overall magnetic state a fully compensated structure. The origin of BMS/HS and fully compensated state has been explained by a structural analysis, where magnetic exchange interaction between Cr sites is dependent on bond distance and bond angle of each Cr-centered octahedron. Furthermore, by applying strains perpendicular to the basal plane, distortion of Cr octahedron sites and Cr--Cr distance is altered, resulting in the phase transition of the material both electronically and magnetically from BMS-FCFiM to HS-FCFiM to ferrimagnetic (FiM). These studies enable us to rediscover ${\mathrm{Cr}}_{2}{\mathrm{S}}_{3}$ as a novel class of BMS materials.

Luminescence Spectroscopy of 3d3 (Mn4+, Cr3+) Ions in Multiple Octahedral-Site Phosphors

Investigating spectroscopic properties of luminescent ions in multiple sites of host materials is not only of scientific interest, but also technological importance. The present investigation focuses on this problem and reports the analysis results of the optical properties of 3d 3 ions in the multiple octahedron sites. The phosphor materials considered are double-perovskite La4Ti3O12:Mn4+ and Ca3−x Lu x Hf2Al2+x Si1−x O12:Cr3+ (x = 0−1.0) phosphors. An analysis method is demonstrated for obtaining reliable and site-dependent crystal-field (Dq) and Racah parameters (B and C) based on a ligand field theory with paying an attention to difficulty in the exact estimation of such important crystal-field-related parameters. For example, the difference in the crystal-field splitting energies between the slightly and highly-distorted octahedron sites determined are ΔDq ∼ 1615 and 405 cm−1 (x = 0) for the [MnO6]8− and [CrO6]9− octahedrons, respectively. All results are in satisfactory agreement with the Tanabe−Sugano energy-level diagram plots, promising good understanding of such 3d 3-ion-activated phosphors with multiple octahedron sites.

Synthesis, microstructure and magnetic properties of Co2+ and Al3+ substituted La-Zn nano ferrites

Co2+ and Al3+ substituted La-Zn ferrites synthesized by sol-gel auto-combustion method with glycine as a fuel, calcination temperature of samples confirmed from TGA analysis. The observed elemental analysis (EDAX) is in good agreement with the theoretical composition. The lattice constant decreases while the crystalline size increases with the increase in concentrations of dopant. Zn2+ ions prefer to occupy the tetrahedron site and other ions mainly enter octahedron site. The I.R. spectra have shown two principle absorption bands near 600 and 400 cm−1. SEM and TEM images reveal well defined nanoparticles with slight agglomeration. Magneton number decreased with dopant substitution.

Structure and Spin-Glass Magnetism of the MnxNi2Zn11–x Pseudobinary γ-Brasses at Low Mn Contents

The pseudobinary MnxNi2Zn11–x γ-brass-type phases at low Mn dopant levels (x = 0.1–0.5) were investigated. Crystal structures were determined for the two loading compositions of x = 0.3 and 0.5. The structures were solved in the cubic space group of I43m and are described in close analogy to the Ni2Zn11 parent γ-brass that is based on the 26-atom cluster, consisting of inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), and cuboctahedron (CO). The refined site occupancies of the MnxNi2Zn11–x (x = 0.3, 0.5) reveal that the cluster center, which is empty in the Ni2Zn11, shows a partial occupation by Zn, with a partial depletion of Zn at the IT sites. The OH sites show a mixed Zn/Mn occupation. The OT and CO sites remain intact with respect to Ni2Zn11. Magnetic properties were studied for the Mn0.3Ni2Zn10.7 composition. The temperature-dependent zero-field-cooled and field-cooled magnetization, the ac susceptibility, the M(H) hysteresis curves, the thermoremanent magnetization, and the memory effect demonstrate typical broken-ergodicity phenomena of a magnetically frustrated spin system below the spin freezing temperature Tf ≈ 16 K. The Mn0.3Ni2Zn10.7 γ-brass phase classifies as a spin glass, originating predominantly from the random distribution of diluted Mn moments on the octahedral partial structure.

Crystal structure and Cu/Fe K-edge analysis of Ba0.5Sr0.5Fe1-xCuxO3-δ (x = 0–0.2) and the influence on conductivity

Ba0.5Sr0.5Fe(1-x) CuxO3-δ (BSFC-x; x = 0–0.2) was synthesized and characterized. A sol-gel self-combustion method with mixed cation nitrate solutions and citric acid was used to synthesize BSFC-x precursors. Calcination was conducted in air at 850 °C for 6 h, followed by sintering in air at 1100 °C for 6 h. The phase, structure, and lattice parameters of the sintered BSFC-x were determined by X-ray diffraction (XRD). X-ray absorption near-edge spectroscopy (XANES) was used to analyze the oxidation state of the cation in the octahedron site (Cu/Fe). It showed that copper's oxidation state was predominantly 3+ due to oxygen octahedron neighbors in the crystalline symmetry and shifted to a lower oxidation state at 800 °C. The oxidation state was thought to be the predominant factor contributing to the overall conductivity through hole creation. The electrical analysis demonstrated semiconductor behavior at up to 500 °C that was influenced by the hole concentration, oxygen vacancies, and hopping distance. Above the maximum conductivity values, oxygen losses dominated the electrical response and disrupted the conductivity. Considering the doping quantity, the optimum doping was x = 0.1 with an electrical conductivity of ≈60 S/cm.

Effect of Mn3+ doping on crystal structure, point defects, and optical properties in green Ca3(VO4)2 single crystals

Calcium orthovanadate Ca3(VO4)2 (CVO) is an efficient media for laser applications. Czochralski-grown green CVO single crystals doped with over-stoichiometric 0.1 (CVO:0.1Mn) and 1.0 wt.%Mn (CVO:1.0Mn) were studied by X-ray diffraction and X-ray absorption spectroscopy for the first time. In the CVO:1.0Mn, an occurrence of Mn3+ in Ca3 (two-capped trigonal prism), Ca4 (distorted octahedron), and defective Ca5 and Ca5A (highly-distorted octahedron) sites and vacancies in V2 and V3 sites (distorted tetrahedra) were revealed. In the CVO:0.1Mn, a presence of Mn3+ in Ca3 and Ca5A sites and vacancies in V2 site were found. In the CVO, the Mn3+ form elongated octahedra (tetragonal bipyramid; coordination number, 4 + 2) typical for the Jahn-Teller ions. Models for the rearrangement of Ca3 and Ca4 polyhedra into a tetragonal bipyramid are proposed. Along with the Mn3+, the Mn2+ and Mn5+ ions were observed by optical spectroscopy in CVO:0.1Mn (predominantly Mn2+ ions) and CVO:1.0Mn (only Mn5+ ions).

Oxygen vacancy induced site-selective Mott transition in LaNiO3

While defects such as oxygen vacancies in correlated materials can modify their electronic properties dramatically, understanding the microscopic origin of electronic correlations in materials with defects has been elusive. Lanthanum nickelate with oxygen vacancies, LaNiO$_{3-x}$, exhibits the metal-to-insulator transition as the oxygen vacancy level $x$ increases from the stoichiometric LaNiO$_3$. In particular, LaNiO$_{2.5}$ exhibits a paramagnetic insulating phase, also stabilizing an antiferromagnetic state below $T_N\simeq152$K. Here, we study the electronic structure and energetics of LaNiO$_{3-x}$ using first-principles. We find that LaNiO$_{2.5}$ stabilizes a vacancy-ordered structure with an insulating ground state and the nature of the insulating phase is a "site-selective" paramagnetic Mott state as obtained using density functional theory plus dynamical mean field theory (DFT+DMFT). The Ni octahedron site develops a Mott insulating state with strong correlations as the Ni $e_g$ orbital is half-filled while the Ni square-planar site with apical oxygen vacancies becomes a band insulator. Our oxygen vacancy results can not be explained by the pure change of the Ni oxidation state alone within the rigid band shift approximation. Our DFT+DMFT density of states explains that the peak splitting of unoccupied states in LaNiO$_{3-x}$ measured by the experimental X-ray absorption spectra originates from two nonequivalent Ni ions in the vacancy-ordered structure.

γ-Brass type structures with I- and P-cell in the ternary Cu–Zn–In system

Abstract γ-Brass type phases in Cu–Zn–In ternary system were synthesized from the highly pure elements by conventional solid-state synthesis and characterized by X-ray diffraction and EDX analysis. Diffraction analysis confirmed the existence of cubic γ-brass type phases with I- and P-cell having a significant homogeneity range in the ternary Cu–Zn–In system. The phase homogeneity is connected with structural disorder based on mixed site occupancies. Site specific In substitution was observed during single-crystal structure analysis. The γ-brass structures with body-centered cubic lattice (I 4 ‾ $‾{4}$ 3m) are viewed as 26-atom γ-clusters. Like Cu5Zn8, the inner tetrahedron (IT), outer tetrahedron (OT) and octahedron (OH) sites in the 26-atom clusters of γ-brass structures with I-cell are occupied by Zn, Cu, Cu, respectively. Indium substitution is restricted to the cuboctahedral (CO) site and the CO site is assumed to be mixed with In, Cu and Zn throughout the homogeneity range. The structures of cubic γ-brass type (P 4 ‾ $‾{4}$ 3m) phases with P-cell are built up with two independent 26‐atom γ‐clusters and centered at the special positions A (0, 0, 0) and B (½, ½, ½) of the unit cell. According to the single‐crystal X‐ray analyses, In substitutions are largely restricted to the cuboctahedral sited B clusters. In the cubic γ-phases with P-cell, site occupancy pattern of cluster positioned at A is similar to the γ-cluster in Cu5Zn8, whereas cluster B bears a close resemblance to Cu-poor γ-cluster (Cu14In12) of Cu9In4 (P 4 ‾ $‾{4}$ 3m). The vec values for cubic γ-brass type phases in the Cu–Zn–In ternary system ranges between 1.57 and 1.64.

Synthesis, crystal structures, phase width and electrochemical performances of γ-brass type phases in Cu–Zn–Sn system

Cu–Zn–Sn ternary phases were synthesized by high-temperature solid-state synthesis. Structural characterization was performed by means of X-ray diffraction and energy dispersive X-ray analysis. The ternary compounds were found to adopt γ-brass (Cu5Zn8) structure type. X-ray diffraction analyses show that γ-brass type phases in Cu–Zn–Sn system crystallize in P4¯3m space group (cP52, 215). Ternary Cu–Zn–Sn γ-brass type phases exist in an extended homogeneity range. The phase-pure ternary compounds are found to exist for compositions ranging between 48 and 70 atomic % Cu, between 15 and 46 atomic % Zn, and between 5 and 15 atomic % Sn. The phase width arises due to the statistical distribution of constituent elements, which is typical for intermetallic compounds. The Cu–Zn–Sn γ-brass structures consist of two compositionally different γ-clusters (consists of the four polyhedral shells: inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), cuboctahedron (CO)) centered at high symmetric sites in a primitive cubic unit cell. The γ-brass cluster (A) at (0,0,0) site is Cu-rich, chemically more ordered than the cluster (B) present at (½,½,½). For A cluster, only IT site is mixed (Zn/Sn) and OT, OH, CO sites are exclusively occupied by Cu, throughout the entire homogeneity range. The B cluster is heavily disordered; only the OT site is exclusively occupied by Cu all over the phase region. For Zn rich region IT site is fully occupied by Zn, then mixed occupied between Cu and Zn at intermediate Zn-concentration, and completely occupied by Cu at Cu-rich side of the Cu–Zn–Sn phases. OH site is fully occupied by Zn at Zn rich side. The same site is mixed occupied between Cu, Zn and Sn for the composition at intermediate Zn-concentration and Cu/Sn at Zn poor side. CO site of B cluster is occupied by Zn and Sn. The electrochemical properties of four Cu–Zn–Sn based samples with different compositions were studied as an anode material for lithium and sodium-ion storage using galvanostatic charge-discharge cycles. Li-ion half-cells transpired excellent retention of charge capacity (>80%) with more than 99% Coulombic efficiency. The results further encourage the prospects of ternary Cu–Zn–Sn alloy anodes to utilize in real energy storage applications.

Local structure analysis of BO6 (B = Fe, Cu) octahedron correlated with the magnetic properties of Cu-doped Ba0.5Sr0.5FeO3–δ

Perovskite-based Ba0.5Sr0.5Fe1–xCuxO3–δ (BSFCO-x, x = 0–0.2) was synthesized by sol–gel self-combustion method. The crystallinity was evaluated through X-ray diffraction, besides further local structure analysis, using X-ray absorption spectroscopy (XAS) showed a cubic symmetry for x = 0.05; 0.10, which was tetragonal at higher values, x = 0.15; 0.20. XAS analysis predicted the oxidation state (OS) of Cu to be a mixture of 3+ and 2+, while Fe includes 3+ and 4+. Conversely, the OS of Fe and Cu in the octahedron site influence the number of an unpair electron that determine the magnetic properties of perovskite. In addition, the magnetization for Ba0.5Sr0.5FeO3–δ is 0.172 emu g−1, originating from the ferromagnetic ordering Fe3+(t 2g 3 e g 2 )–O (2p)–Fe4+(t 2g 3 e g 1 ) interaction. This effect increase, due to the presence of oxygen vacancy in BSFCO-0.05, which weakens the d–p interaction of Fe-O, while the generation of higher Cu doping to increase the amount of Fe4+ leads to a decline in Cu3+. Therefore, Cu doping is confirmed to play a role in the paramagnetic–ferromagnetic transition.

Synthesis and luminescence properties of a novel deep red phosphor Li2ZnTi3O8:Mn4+ for plant-cultivation.

In this thesis, a novel ultraviolet-activated Li2ZnTi3O8:Mn4+ red emitting phosphor is prepared by the traditional high-temperature solid-state reaction method in air. The crystal structure, luminescence properties and decay curves of the phosphor are studied in detail. The sample belongs to spinel cubic crystal structure and there are abundant [TiO6]8- octahedron sites can be occupied by Mn4+. The Li2ZnTi3O8:Mn4+ phosphor shows the red emission in region of 600-800nm with a maximum at ~681nm under 330nm excitation, which can promote the plant growth. The optimal Mn4+ doping concentration is ~0.3mol%, which is higher than that of other hosts. By calculating the crystal field strength (Dq) and Racah parameter B, we can evaluate that there is a strong crystal environment of Mn4+ in the Li2ZnTi3O8 host lattice, which major comes from the 2Eg→4A2g transition of Mn4+ ion. Furthermore, the characteristics of thermal quenching are also studied, poor thermal quenching performance may be due to high doping concentration of Mn4+. All data suggest that Li2ZnTi3O8:Mn4+ phosphor can be a potential application in plant-cultivation.

Electron paramagnetic resonance and optical properties of Cu+2 in PbO-Li2O-As2O3-B2O3 glasses

The room temperature electron paramagnetic resonance (EPR) and optical absorption studies of PbO-Li2O-As2O3-B2O3 glasses have been done by introducing a transition metal ion Cu+2 ion as a spin probe with fixed mole% in the given glass composition. Glasses containing transition metal (TM) ion give the information of site symmetry around the Cu+2 ion of the host glass. The EPR spectra of Cu+2 in all glass samples recorded in the X-band frequency (9.1–9.7 GHz) have similar features. The spin-Hamiltonian parameters have been calculated; the observed values are g|| > g⊥ > ge and A|| > A⊥. It suggests that the site symmetry around Cu+2 ion is tetragonal distorted octahedral and the ground state of Cu+2 is dx2-y2 (2B1g) orbital. The Cu+2 ion is coordinated with six ligand atoms in a distorted octahedron site symmetry. The optical absorption spectra exhibit a broadband corresponding to d-d transition bonds of Cu+2 ion. Calculated bonding parameters suggest the covalent nature of in-plane σ-bonding (α2) and pure ionic nature for out-of-plane (β2) and in-plane π-bonding (β12). This data is correlated with the theoretical optical basicity (Λth) values, and it is observed that the Γσ value increases whereas Γπ values decrease with increasing Λth.

Investigation of the structural, magnetic, impedance properties in samarium-doped yttrium iron garnet

Y3-xSmxFe5O12 (x = 0, 1, 2, 3) ferrites with pure single phase were prepared by sol-gel method. The effects of Sm3+-substitution on crystal structure and magnetic properties were systematically investigated. The Sm3+ ions substitution in Y3+ sites resulted in lattice expansion and structural distortion by changing Fe[a]-O-Fe(d) bond length and bond angle, which further modified the magnetization properties and led to the decrease of saturation magnetization by regulating super-exchange interaction between tetrahedron and octahedron sites. The relationships between complex impedance with frequency and temperature were studied, suggesting that asymmetric and depressed semicircle spectrum is owing to a non-Debye like relaxation process controlled by thermal vibration charge carriers, and the electrical conduction within grains is dominated by the charge carrier transition between Fe3+ and Fe2+ sites due to the ionization effect of oxygen vacancies. By fitting the equivalent circuits, it was found that grain boundary and grain have different contributions to complex impedance spectrum while grain boundary relaxation play the dominant role at higher temperature. The slope anomalies of relaxation frequency and conductivity were observed near the ferromagnetic transition temperature (TC) owing to the magneto-electric coupling effect, revealing that magnetic ordering has a great influence on electrical conduction. Ac conductivity analysis reveal that the main conduction mode experiences a gradual transition from a small polaron hopping model (T < 550K) to an overlapping large polaron tunneling model (T > 550K). Moreover, the increase in conductivity is ascribed to two factors: the thermally assisted charge carrier hopping and the ionization effect of oxygen vacancy due to the incorporation of Sm ions.