Valence States Of Mn Ions Research Articles

EXAFS study on local structure of GaMnAs thin film made by Mn ion implantation following with ion beam induced epitaxial crystallization

In this study, we used Mn ion implantation following with helium ion irradiation to prepare GaMnAs thin film. Extended X-ray absorption fine structure, and X- ray absorption spectrum were applied to analyze the crystalline of Mn implanted GaAs layer. And the results showed implanted Mn ions stand on the substitutional site of Ga ions of GaAs lattice. Also from X-ray absorption spectrum, we confirmed the electronic valence state of Mn ions in the implanted layer were 2+.

Tailoring the visible emissions in ZnS:Mn films for white light generation

Abstract This paper reports the effect of manganese incorporation on the structural, optical and luminescence properties of the as-deposited ZnS films prepared by RF magnetron sputtering process. Mn act as a nucleation centre for the growth of highly crystalline defect free ZnS films with mixed cubic and hexagonal phases. The +2 valence state of Mn ions in ZnS lattice is confirmed by the XPS analysis. An absorption band due to d-d transition of Mn2+ ions is visible in the absorption spectra of ZnS film with highest Mn doping concentration. ZnS:Mn films present an intense orange emission along with the host emissions of ZnS. Optimum Mn content for superior orange emission from ZnS:Mn films is found to be 3 wt %. Origin of orange photoluminescence emission due to the incorporation of Mn2+ in Zn2+ host lattice and its quenching due to cross-relaxation mechanism in the films with higher Mn doping concentration is discussed in detail. We report the possibility of one-step generation of white light emission from the as-synthesized ZnS:Mn films by the adequate tailoring of ZnS host emissions in the blue and green regions (445 nm and 530 nm respectively) and Mn related emission in the orange region (585 nm) employing only one excitation wavelength by suitably tuning the Mn doping concentrations. PL decay of the orange emission is monitored to explore the luminescence mechanism and lifetime of the emission.

Structural evolution and dielectric properties of Nd and Mn co-doped BaTiO3 ceramics

(Ba1−xNdx) (Ti0.97Mn0.03)O3 (BNTM) (x = 0.01, 0.02, 0.04, 0.06) ceramics were prepared using a conventional cold-pressing ceramic technique. The structure, valence state and dielectric properties were investigated using XRD, RS, SEM, TEM, EPR, and dielectric temperature and frequency measurements. XRD, RS analysis coupled with SEM and TEM observations indicate that the samples have a coexistence of tetragonal and hexagonal phase at room temperature as x ≤ 0.02 and become a single phase in the tetragonal as x = 0.04 and in the cubic as x = 0.06 (air-sintered, 1400 °C/12 h). It reveals that Nd3+ ions can suppress hexagonal phase effectively and benefit the formation of single-phase ceramics. Improvement of dielectric properties is accompanied by the structural evolution. Particularly a cubic ceramic with x = 0.06, the dielectric-peak temperature is found to shift to room temperature, meeting the EIA Y5V specification with tan δ < 0.04. Up to x = 0.04, the phase transition remains first order. The valence state of Mn ions was analyzed by EPR. It is found that Mn ions transform from high valence (+3 and + 4) to low valence (+2) with the increase of Nd concentration, and all of the Mn ions exist as Mn2+ when x = 0.06. The unit cell volume and dielectric-peak temperature of BNTM decrease nonlinearly with increasing x, which can be ascribed to the incorporation of Nd ions and the formation of 2NdBa·−MnTi″ donor-acceptor defect complexes.

The evolution of magnetization switching of LuCrO3 by the effect of Mn doping

The crystal structure, magnetic properties and electronic structures of LuCr1-xMnxO3 (x = 0, 0.1, 0.2, and 0.3) series samples were systematically investigated. The crystal structure of the Mn-doped LuCrO3 samples is orthorhombic structure with Pbnm, consistent with the pristine LuCrO3. Synchrotron radiation x-ray absorption spectroscopy of Mn 2p, Cr 2p and O 1s core levels show that Cr ion is trivalent and its valence state does not change with doping. However, the valence state of Mn ions for samples with x = 0.1 and 0.3 is mainly in Mn2+ while it is dominated by Mn3+ for the sample x = 0.2. This leads to the diversely unoccupied 3d states of transitional metal ions, which hybridized with O 2p levels. The energy diagram of each transitional metal ions in our samples were provided. More interesting, magnetic data shows the negative magnetization in zero-field-cooling MZFC(T) curve below TN. And the evolution of MFC(T) and MZFC(T) curves coming to converge and intersect with each other are caused by Mn doping. Also, multiple magnetic phases with a new magnetic phase transition at 30 K were induced by the effect of Mn doping. Our results demonstrate that the antiferromagnetic coupling of Mn2+ being antiparallel with spin moment of Cr3+ is favor of the magnetization switching while the ferromagnetic coupling of Mn3+ overcomes the Cr3+ ions ordering and destroys the magnetization switching.

Synthesis and characterization of CuFeMnO4 prepared by co-precipitation method

CuFeMnO4 spinel oxide was synthesized by co-precipitation method through calcination of the precipitate precursor at 500–900 °C. The reaction process was investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The structure, valence state and magnetic properties of the powders obtained were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) further. The results revealed that the precipitate is composed of amorphous metal hydroxides and oxides, after which the spinel structure and several phases, such as CuO, Fe3O4 and Mn3O4, turned up in the calcined powders. As the calcining temperature raising, these phases began to transform into a single phase of CuFeMnO4. However, CuO phase segregated from the spinel structure with further calcining. The valence state of Mn ions in octahedral sites and Cu ions in tetrahedral sites were ascertained by XPS, which showed the reduction of Mn4+ and Cu+ during the calcining procedure. Besides, the magnetization of the samples increased obviously with the calcining temperature.

Defect induced room temperature ferromagnetism in lead-free ferroelectric Bi0.5K0.5TiO3 materials

Development the multiferroic materials based on the lead-free ferroelectric materials is the new possible channel to create the next generation devices. The pure Bi0.5K0.5TiO3 and Mn-doped Bi0.5K0.5TiO3 materials were synthesized using sol-gel method. While the substitution of Mn for Ti site reduces the optical band gap in Bi0.5K0.5TiO3, the room temperature ferromagnetism is obtained in both un-doped and Mn-doped Bi0.5K0.5TiO3 materials. By means of the first-principles calculations, the ferromagnetism in Mn-doped Bi0.5K0.5TiO3 materials can be explained by the mixed valence states of Mn ions through the crystal field mechanism and that in un-doped Bi0.5K0.5TiO3 materials is ascribed to the formation of O or Ti vacancies during the sample growth.

Local Structure of Core–Shell MnFe2O4+δ-Based Nanocrystals: Cation Distribution and Valence States of Manganese Ions

We investigate the local structure of nanoparticles based on a manganese ferrite core surrounded or not by a maghemite layer obtained after hydrothermal surface treatment. Results of X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) measurements are crossed with those of in-field Mossbauer spectroscopy and X-ray absorption spectroscopy (XANES/EXAFS) to study the valence state of Mn ions and the cation distribution at interstitial sites of the core–shell nanoparticle structure. Linear combination fitting of XANES data clearly indicates the existence of mixed valence states of Mn cations in the Mn ferrite phase. As a direct consequence, it induces nonequilibrium cation distributions in the nanoparticle core with the presence of a large amount of Mn cations at octahedral sites. The quantitative results of the inversion degree given by NPD, Mossbauer spectroscopy measurements, and EXAFS are in good accordance. It is also shown that both the proportions of each oxidation degree of Mn ions and...

Nonthermal effects in photostimulated solid state reaction of Mn doped SrTiO3

The effect of a photostimulated solid state reaction was investigated in Mn doped SrTiO3 samples. Light irradiation was performed by either halogen or UV lamps in order to study the effect of the spectral composition, and the results were compared with samples prepared at the same temperatures in a conventional furnace. The obtained samples were studied by X-ray diffraction for structural characterization and by Electron Paramagnetic Resonance, which provides microscopic information about the local environment as well as the valence state of Mn ions. It was found that light irradiation significantly enhances the solid state reaction rate compared to synthesis in the conventional furnace. Moreover, it was observed that UV lamp irradiation is much more effective compared to halogen lamps. This indicates that the absorption of light with energy larger than the materials band gap plays an important role and points towards the nonthermal mechanism of the photostimulated solid state reaction.

Three Oxidation States of Manganese in the Barium Hexaferrite BaFe12-xMnxO19.

The coexistence of three valence states of Mn ions, namely, +2, +3, and +4, in substituted magnetoplumbite-type BaFe12-xMnxO19 was observed by soft X-ray absorption spectroscopy at the Mn-L2,3 edge. We infer that the occurrence of multiple valence states of Mn situated in the pristine purely iron(III) compound BaFe12O19 is made possible by the fact that the charge disproportionation of Mn3+ into Mn2+ and Mn4+ requires less energy than that of Fe3+ into Fe2+ and Fe4+, related to the smaller effective Coulomb interaction of Mn3+ (d4) compared to Fe3+ (d5). The different chemical environments determine the location of the differently charged ions: with Mn3+ occupying positions with (distorted) octahedral local symmetry, Mn4+ ions prefer octahedrally coordinated sites in order to optimize their covalent bonding. Larger and more ionic bonded Mn2+ ions with a spherical charge distribution accumulate at tetrahedrally coordinated sites. Simulations of the experimental Mn-L2,3 XAS spectra of two different samples with x = 1.5 and x = 1.7 led to Mn2+:Mn3+:Mn4+ atomic ratios of 0.16:0.51:0.33 and 0.19:0.57:0.24.

Synthesis and optical properties of turquoise- and green-colored brownmillerite-type Ba2In2−x−y Mn x Al y O5+x codoped with manganese and aluminum

Brownmillerite-type oxides Ba2In2−x−yMnxAlyO5+x (0 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.5) were prepared at 1300°C through solid-state reaction. X-ray diffraction (XRD) analysis showed that the structure symmetry evolved from orthorhombic to cubic with increasing Mn and Al contents. When y was greater than 0.3, peaks associated with small amounts of BaAl2O4 and Ba2InAlO5 impurities were observed in the XRD patterns. When substituted with a small amount of Mn (x ≤ 0.3), the Ba2In2−x−yMnxAlyO5+x samples exhibited an intense turquoise color. The color changed to green and dark-green with increasing Mn concentration. UV–vis absorbance spectra revealed that the color changed only slightly upon Al doping. The valence state of Mn ions in Ba2In2−x−yMnxAlyO5+x was confirmed to be +5 on the basis of X-ray photoelectron spectroscopic analysis. According to this analysis, the intense turquoise color of the Ba2In2−x−yMnxAlyO5+x samples is rooted in the existence of Mn5+; thus, the introduction of Al does not affect the optical properties of the compounds.

Understand the Voltage Fade Mechanism of Li-Rich Layered Oxide Cathodes during Extended Cycling

Recently, Li-rich layered oxides have attracted much attention for Lithium-ion Batteries (LIBs) because of their high theoretical capacities, low cost, and friendliness. Like other cathodes for a widespread use, Li-rich layered oxides also suffer from natural obstacles, such as low coulombic efficiency at initial charge/discharge process, insufficient rate performance and inferior ability to remain output voltage during the cycles. In this work, Li1.2Mn0.6Ni0.2O2 cathode material was synthesized via a co-precipitation method. Both ex - situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) measurements are used to reveal its fundamental voltage fade mechanism. The collected results confirm that the change in valence state of Mn ions and structural evolution lead to its voltage fade. Along with increasing the cycles, a shift of the Mn K-edge gradually shifts to a lower energy region, suggesting that an increasing amount of trivalent manganese ions. In contrast, no change is observed on Ni2+ ions. Ligand oxygen ions are directly involved in the charge compensation mechanism. Figure 1

Cationic Distribution and Electrical Properties of Ni0.6Mn2Si0.4-xAlxO4 (0≤x≤0.04) NTC Thermistor

Negative temperature coefficient (NTC) ceramics with general composition Ni0.6Mn2Si0.4-xAlxO4 (0≤x≤0.04) were prepared by conventional solid-state reaction method and were investigated for cationic distribution and electrical properties. X-ray diffraction (XRD) confirmed that the Si cations occupied the tetrahedral site. The valence states of Mn ions were characterized by X-ray photoelectron spectral (XPS). The results showed that Mn4+ content decreased from 0.19 mol to 0.185 mol when the Si molar content declined from 0.4 to 0.1, i.e. the content of Mn4+ was 0.197mol when x was equal to 0.4. Besides, the resistivity (ρ25) reached the minimum value when the Si molar content was 0 (ρ25=4.07×104Ω·cm).

Improved ferromagnetic behavior and novel near-infrared photoluminescence in Mg/Mn-codoped CuCrO2 ceramics

Cu(Cr0.96−xMg0.04Mnx)O2−δ ceramics (0 ≤ x ≤ 15 at.%) were prepared by solid-state reaction. The influence of Mg acceptor codoping on microstructure, magnetic, and optical properties was studied. The codoping with Mg acceptors and the resulting lattice expansion are both favorable for the enhancement of hole density. Furthermore, the lower valence of Mg2+ compared with Cr3+ enables the mixed valence state of Mn ions: Mn3+ and Mn4+, and hence induces the hole-mediated double-exchange mechanism not only between Mn3+ and Cr3+ but also between Mn3+ and Mn4+. The coexistence of two ferromagnetic interactions and the high hole density are responsible for the improved saturation magnetization and Curie temperature. For photoluminescence, an unusual near-infrared emission at 1.5 eV is observed in the Mn-contained samples and can be attributed to the internal transition between the e and t2 states of the Mn3+ impurity band. The emission intensity is primarily affected by two factors: the Mn3+ concentration and the position of the Fermi level. The results show that codoping with Mg acceptors is an effective way to strengthen the hole-mediated ferromagnetic interactions in CuCrO2 delafossite.

Microstructure and Magnetic Properties of Sr, Fe Ions Co-substituted YMnO3 Multiferroic Ceramics

The crystal structure, valence state of magnetic ions and magnetic properties of Y0.98Sr0.02Mn0.8Fe0.2O3 ceramics were investigated. The results showed that the same ferroelectric hexagonal structure as YMnO3 was maintained in the present Y0.98Sr0.02Mn0.8Fe0.2O3 ceramics. Compared with YMnO3, the magnetic transition temperature of Y0.98Sr0.02Mn0.8Fe0.2O3 was enhanced and the valence state of Mn ions was increased. In Y0.98Sr0.02Mn0.8Fe0.2O3 ceramics, Fe ions presented the valence state of +2 and +3. The enhanced magnetic properties should be related to the ferromagnetic double-exchanges between Mn4+ and Mn3+ ions.

Negative magnetism in perovskite manganites Gd1-x Sr x MnO3(0.1≤x≤0.3)

A series of Sr-substituted Gd1-x Sr x MnO3(0.1≤x≤0.3) materials was prepared via a standard method involving solid-state reaction. Their crystal structure within the entire doping region was determined to be orthorhombic perovskite type. The magnetic properties of the perovskite Gd1-x Sr x MnO3(0.1≤x≤0.3) were thoroughly investigated. It appears that Mn ions with high valence state can induce stronger magnetization, and negative magnetization is evident in the manganites with x=0.1 and x=0.2, suggesting that valence fluctuation plays an important role in such systems. The result of XPS analysis indicates that the valence state of Mn ions is 3.25 and there seems to be excess amounts of oxygen in the structure of Gd0.8Sr0.2MnO3+δ. In addition, the results of magnetization measurements demonstrate that spin reversal occurs only when the applied field is less than 1.99×105 A/m, which presumably could be due to the negative exchange interaction between Mn sub-lattice and Gd sites.

Preparation and electrochemical properties of Li3V1.8Mn0.2(PO4)3 doped via different Mn sources

This work attempts to substitute V of Li3V2(PO4)3 (LVP) by the doped ion of manganese with the valence of +2, +3 and +4 and various ionic radiuses. A series of Mn-doped LVP composites (LVMP) by different manganese sources are synthesized by sol–gel and heat-treatment. Manganese ion with the valences of +3 and +4 have been successfully inserted into the lattice of Li3V2(PO4)3 to form a stable solid-solution even the substitution mole ratio reaches to 0.2, except the impurity phase of LiMnPO4 in LVMP when manganese ions with the valence of +2 involve in the substitution. Mn2+ exists in all three samples as expected, but the main valence state of Mn ions in LVMP-A, LVMP-B and LVMP-C are Mn4+, Mn3+ and Mn2+, respectively. LVMP-B (MnOOH as dopant) delivers the highest capacity of 137 mAh g−1, than LVMP-A (MnO2 as dopant) 125 mAh g−1 and LVMP-C (Mn3O4 as dopant) 123 mAh g−1. LVMP-B shows the best cycle performance, remaining 98% of the initial capacity after 50 cycles in range 3.0–4.3 V. Mn source of MnOOH properly substituted the structure of LVP enhances the lithium diffusion ability and stability of LVP during charge/discharge.

Enhanced oxide ion conductivity in stabilized cubic BaInO2.5 by Mn5+ doping

Abstract The preparation of room-temperature stabilized cubic BaInO 2.5 was successfully achieved by adjusting Mn 5 + doping (0.13 ≤ x ≤ 0.33) using high-temperature solid state reactions. XPS and magnetic investigations revealed that the valence state of Mn ions in stabilized cubic BaInO 2.5 was + 5. The stabilized cubic BaInO 2.5 showed enhanced oxide ion conductivity, and the best low-temperature conductivity at 400 °C was 3.0 × 10 − 3 S cm − 1 , which was larger than previously reported highest conductivity for stabilized cubic BaInO 2.5 .

The structural and electrical properties of Mn-doped Ba0.6Sr0.4TiO3 films prepared by metal organic deposition method

Abstract Both undoped and Mn-doped BST films are fabricated on (1 1 1) Pt/Ti/SiO 2 /Si by metal organic deposition. X-ray diffraction and atomic force microscopy reveal the microstructure of the samples. The effect of Mn dopant on structural and electrical properties is studied. It is found that the dc leakage behavior and dielectric loss of the BST films are greatly improved due to the change of the valence state of Mn ions. Meanwhile, the tunability of Mn-doped BST films is suppressed, and the possible causes of tunability dependence are discussed.

Thermoluminescence study of MnO doped borophosphate glass samples for radiation dosimetry

MnO doped calcium fluoroborophosphate glasses of the composition 20 CaF2–50 P2O5–(30−x)B2O3:x MnO in mol% with x ranging from 0.2 to 1.0 (in steps of 0.2) were synthesized. The samples were exposed to different γ-ray doses in the range 250–1000Gy and their thermoluminescence (TL) was recorded in the temperature range ambient to 300°C. The glow curves of all these samples exhibited an intense principal peak at about 200°C followed by a feeble high temperature peak at about 300°C. The TL response of integral TL output as well as TL of the principal peak exhibited perfectly linear increase with the dose within the range of 250–1000Gy. However, the gradual increase of MnO content in the glass matrix caused a decrement in the TL output. Such mechanism is explained based on different valence states of Mn ions in the glass matrix and the quenching effect is assumed to be well exploited to measure the high radiation doses required in radiation processing facilities without saturating the PMT of the reader. The comparison of TL response of the studied glasses with that of CaSO4:Dy phosphor indicated an improvement in the dose response in terms of linearity and adequate sensitivity for the measurement of high doses.

Local Atomic and Electronic Structure with Magnetism of La0.7Ca0.3Mn1−x Cu x O3 (x=0, 0.03, 0.06, 0.1)

Local atomic and electronic structure with magnetic properties, especially Griffiths phase, of polycrystalline samples La0.7Ca0.3Mn1−x Cu x O3 (x=0, 0.03, 0.06, 0.1) have been studied. The X-ray absorption spectra (XAS) of Cu 2p core level prove that the valence state of Cu ions exhibits trivalent state when doping content x≤0.06 and divalent Cu2+ ions begin to show for x=0.1. For the valence states of Mn ions, the X-ray photoelectron spectroscopy data show that they are in mixed states of Mn3+ and Mn4+, and a shift to lower binding energy is observed, which is not attributed to the variation of valence states of Mn ions but the change of crystallographic surroundings, because there is no obvious change detected by X-ray absorption fine structure spectroscopy (XAFS). The Debye-Waller factor (σ 2) of x=0.1 sample is only slightly larger compared to x=0, which may be the origin of enhancement of Griffiths phase observed in the inverse-susceptibility as a function of temperature (H/M∼T). The H/M∼T curves of Cu doped samples indicate coexistence of FM, AFM and PM phase above Curie temperature T C , which may be related to the strong hybridization of O 2p and Mn 3d reflected by O 1s XAS spectra.