Mn-doped Samples Research Articles

Effect of Mn doping on structural and optical properties of sol gel derived ZnO nanoparticles

We have synthesized the Zn1−x Mnx O (x=0.01, 0.02, 0.03 and 0.05) nanoparticles by the sol–gel method. These samples are characterized using x-ray diffraction (XRD), Scanning Electron Microscope (SEM), Ultraviolet/Visible (UV/Vis) spectroscopy, Fluorescence spectroscopy, Raman spectroscopy and Fourier transform infra red (FTIR) spectroscopy. The x-ray diffraction patterns show that all the samples are formed in single phase with a complete solubility of Mn ions in the ZnO matrix. SEM micrographs show that the Mn doped ZnO nanoparticles are hexagonal with wurtzite structure.The particle sizes range between 18 and 35nm. We have observed a decrease in fluorescence intensity on Mn doping and all the Mn doped samples show lower value of intensity as compared to pure ZnO in the visible range of spectrum. Raman spectroscopy reveals that the characteristic intense band of ZnO at 435cm−1 exhibits a decrease in intensity and slightly red shifts for 5% Mn doping. FTIR spectra exhibit additional bands on Mn doping as compared to pure ZnO.

Dielectric properties of Mg- and Mn-doped (Ba1−xSrx)(Ti1−yZry)O3

This study showed that the substitution of SrO and ZrO2 in BaTiO3 results in a change in the unit cell volume, Curie temperature shift and temperature dependence of dielectric constants. The unit cell volume decreased with an increasing SrO content (≤15 mol%), but increased with an increasing ZrO2 (≤10 mol%). Substitution of Zr4+ ions for Ti sites in Ba(Ti1−yZry)O3 shifted the Curie point (Tc) to lower temperatures by 4.1 °C per mol% of ZrO2 at y≤0.10. SrO substitution in the samples with 10 mol% ZrO2 (Ba1−xSrx)(Ti0.9Zr0.1)O3 brought about relatively small shifts in Tc (2.2 °C/mol%), and their dielectric constants decreased with an increasing SrO content near Tc. Mg- and Mn-doped (Ba0.9Sr0.1)(Ti0.9Zr0.1)O3 broadened the dielectric constant peaks at Tc with uniform microstructures, which satisfies the temperature characteristics of Y5V specifications. The leakage currents of the Mg- and Mn-doped samples were significantly suppressed.

Effect of PEG on Structural and Magnetic Properties of Mn Doped ZnO Nanocrystals

Nanosized Mn doped ZnO samples were synthesized by co-precipitation method using Polyethylene glycol (PEG) as a capping agent. X- ray diffraction patterns confirm that the pure and Mn doped ZnO nanocrystals have wurtzite structure without any seconadary phases. Lattice parameters of pure and Mn doped ZnO nanocrystals increase slightly with increasing Mn concentration. The average crystalline size of pure and Mn doped ZnO nanocrystals are in the range of 14-18 nm. The X-ray density for pure and Mn doped ZnO sample is calculated using lattice parameters. It is found that almost static for Mn doped ZnO samples. In the Zn1-xMnx samples, room temperature magnetic hysteresis is observed and the saturation magnetization increases with increasing Mn content. However, these samples show room temperature ferromagnetic in nature. Result of the present investigation compared without PEG.

Photoluminescence and radioluminescence study of Eu and Mn doped RbMgF3 nanoparticles

Photoluminescence (PL) and radioluminescence (RL) measurements were made on RbMgF3 nanoparticles doped with Mn or Eu. We find that the Mn doped samples contain only Mn2+ and the Eu doped samples contained Eu3+ and Eu2+. The Mn2+ PL lifetimes are nearly independent of Mn2+ concentration but the RL spectra increases at high doses for 1% Mn2+ and decreases slightly at high doses for 5% Mn2+. The 5% Mn2+ is more radiation hard and the integrated RL intensity only starts to significantly decrease above 1 kGy. The Eu doped sample displays a PL lifetime that is lower for high Eu concentrations and this can be accounted for by a model where there is energy transfer between Eu3+ and more nonradiative decay sites at the surface. The RL is independent of dose between 10 mGy and ∼200 Gy, where the 1% Eu sample is more radiation hard and the Eu3+ RL intensity has decreased by only 3.4% at 6.7 kGy.

Structural, optical and magnetic properties of Mn-doped ZnO thin films prepared by sol–gel method

Undoped and Mn-doped ZnO thin films were prepared on quartz glass and Si(100) substrates by the sol–gel method at room temperature, and the effects of Mn content on the structural, optical, and magnetic properties of these films were investigated. X-ray diffraction patterns reveal that all the films are single phase and have wurtzite structure with (002) preferential orientation along c-axis, indicating there are not any secondary phases. X-ray photoelectron spectroscopy patterns suggest that Mn2+ ions were successfully incorporated into the lattice position of Zn2+ ions in ZnO host. Optical transmittances of the films were recorded in the wavelength range of 300–800nm, and the band gaps of the films were determined. As the content of Mn increases, the crystallite size and the optical band gap of the films decrease while the crystalline quality deteriorates gradually. The intensity of photoluminescence spectra is suppressed with Mn doping. Magnetic measurements indicated that undoped ZnO was diamagnetic in nature whereas Mn-doped ZnO samples exhibited ferromagnetic behavior at room temperature, which is possibly related to the substitution of Mn2+ ions for Zn2+ ions in the ZnO lattice. It is also found that the Mn doping content can affect the ferromagnetic behavior of the films effectively.

Synthesis of Mn-Doped AlN Nanostructures via Chemical Vapor Deposition

Hexagonal Mn-doped AlN nanostructures were successfully synthesized through a catalyst-free chemical vapor deposition at higher temperature using Mn powder, Al powder and NH3 as the starting materials. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) were employed to characterize the structure and morphology of the products. It was found that the as-prepared AlN was wurtzite structure and flower-shape with uniform geometry. The intensity of PL emission band from the Mn-doped AlN sample is located at 398 nm, corresponding to the deep level O defect caused by the introduced Mn into AlN matrix.

Dopant induced diameter tuning of Mn-doped CdTe nanorods in aqueous solution

High quality Mn-doped CdTe nanorods with uniform diameter were synthesized in aqueous phase by spontaneous self-organization of Mn-doped CdTe nanoparticles into nanorods. The diameter of the CdTe nanorods increased gradually from 4.1 to 10.2 nm for 0–4.2% Mn incorporations. The intermediate step in the nanorod growth was found to be double or triple chain aggregation. The X-ray diffraction (XRD) patterns of the Mn doped samples retained the same crystal structure as the CdTe nanocrystals, indicating no second phase formation for Mn ion. XPS, ICP-AES and ESR data demonstrate successful incorporation of Mn ions in CdTe nanorods. Superconducting quantum interference device (SQUID) measurements reveal that all of these nanocrystals exhibited ferromagnetic behavior, with a coercive field (Hc) of 2.6 kOe.

CO2 splitting via two step thermochemical reactions over doped ceria/zirconia solid solutions

Thermochemical CO2 splitting was carried out over Ni-, Fe-, Mg- and Mn-doped ceria/zirconia solid solutions, where the sample was thermally reduced at 1400 °C under inert atmosphere followed by the re-oxidization of CO2 to generate CO at 1100 °C in the subsequent step. Compared with the undoped sample, all the doped ceria/zirconia had a high reduction yield in the first thermal reduction step. Due to the low thermal stability, Ni-, Fe- and Mn-doped samples showed lower CO production in the CO2 splitting step than the stoichiometric amounts. In contrast, the Mg-doped sample produced more CO with the volumes of 5.64 and 5.17 mL g−1 during the two thermochemical cycles. Moreover, a 10% Mg-doped sample prepared via hydrothermal treatment with P123 showed a more stable reactivity during cycling due to the relatively stable microstructure under the successive high temperature thermal treatment.

Optical and magnetic properties of Mn doped ZnO thin films grown by SILAR method

Polycrystalline Mn doped ZnO (MZO) semiconductor thin films were deposited onto glass substrates employing different number of dipping at room temperature using Successive Ionic Layers by Adsorption Reaction (SILAR) technique. The thin film deposition conditions were optimized by altering the various deposition parameters based on their structure. The structural study was carried out using X-ray diffractometer (XRD). The XRD analysis indicated that there is no change in the structure of ZnO thin films due to Mn doping. The films exhibited hexagonal wurtzite structure. The structural studies on Mn doped samples revealed that the predominant orientation is (002) lattice plane and the position of this orientation shifted toward lower angle during doping. The intensity of photoluminescence (PL) emission of ZnO is found to be augmented for Mn doped samples. The room temperature Raman spectra measurements revealed the presence of additional modes. The Vibrating Sample Magnetometer (VSM) studies show that MZO thin film has ferromagnetic properties.

Electrical and reliability characteristics of Mn-doped nano BaTiO3-based ceramics for ultrathin multilayer ceramic capacitor application

Nano BaTiO3-based dielectric ceramics were prepared by chemical coating approach, which are promising for ultrathin multilayer ceramic capacitor (MLCC) applications. The doping effects of Mn element on the microstructures and dielectric properties of the ceramics were investigated. The degradation test and impedance spectroscopy were employed to study the resistance degradation and the conduction mechanism of Mn-doped nano-BaTiO3 ceramic samples. It has been found that the reliability characteristics greatly depended on the Mn-doped content. Moreover, the BaTiO3 ceramic with grain size in nanoscale is more sensitive to the Mn-doped content than that in sub-micron scale. The addition of 0.3 mol. % Mn is beneficial for improving the reliability of the nano BaTiO3-based ceramics, which is an important parameter for MLCC applications. However, further increasing the addition amount will deteriorate the performance of the ceramic samples.

Electric field gradient in nanostructured SnO2 studied by means of PAC spectroscopy using 111Cd or 181Ta as probe nuclei

Electric quadrupole interactions were studied in pure and Mn-doped powder samples and thin films of SnO2 using perturbed γγ angular correlation spectroscopy (PAC). The powder samples were prepared by Sol gel method and the thin film were prepared on the Si (100) substrate by sputtering technique using Sn in the oxygen atmosphere. The samples were characterized by x-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The thickness of the film was 100 nm. The average particle size of the SnO2 powder samples was determined to be smaller than 60 nm. The radioactive 111In and 181Hf tracers were introduced in the powder samples during the sol gel chemical process. Radioactive 111In was implanted on the SnO2 thin films using the University of Bonn ion implanter (BONIS). PAC measurements were carried out in a four BaF2 detector spectrometer in the temperature range of 77–973 K for samples annealed at different temperatures. The PAC results for both nuclear probes show the presence of two electric quadrupole interactions. The major fractions in both cases correspond to the substitutional sites in the rutile phase of SnO2. The results are compared with previous PAC measurements.

Influence of Mn doping on structural and optical properties of ZnO nano thin films synthesized by sol–gel technique

Undoped and Mn-doped ZnO samples with different percentages of Mn content (1, 5 and 10 at%) were synthesized by a dip-coating sol–gel method. We have studied the structural, chemical and optical properties of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. We note that doping favors c-axis orientation along (002) planes. Up to 5 at% of Mn doping level, the c-axis lattice parameter shifts towards higher values with the increase of manganese content in the films. The expansion of the lattice constant of ZnO–Mn indicates that Mn is really doped into the ZnO. The SEM investigations of all samples revealed that the crystallites are of nanometer size. The surface quality of the ZnO–Mn film increases with Mn doping but no significant change of the grain size is observed from SEM images. The transmittance spectra show that the transparency of all the samples is greater than 85 %. We note, also, that a small doping (1 %) lowered the refractive index while the thickness of the layers and the gap increase. However, on raising the proportion of Mn beyond 5 %, practically the same values of index and gap as pure ZnO are found.

Preparation and Photoluminescence of (3C-ZnS)/(2H-ZnS) Superlattice in Mn-doped ZnS Nanoribbons

In this paper, we report the first successful growth of (3C-ZnS)n/(2H-ZnS)m superlattice structures in Mn-doped ZnS nanoribbons prepared on Au-coated Si substrates by a chemical vapor transport method. The lattice-resolved HRTEM image presents the self-assembled (3C-ZnS)(111)/(2H-ZnS)(100) superlattices, where both the (3C-ZnS) ZnS atom layer and the (2H-ZnS) atom layer are alternately arrayed in the plane of nanoribbons along the axis growth direction. The individual Mn-doped ZnS nanoribbons, with uniform widths ranging from 100 to 800 nm and lengths ranging from tens to one hundred micrometers, are composed of the hexagonal wurtzite atom layers growing along the [100] axis direction and [001] vertical direction and the zinc-blende atom layers growing along the ⟨111⟩ direction. An identical strong photoluminescence transition peak at 580 nm was observed for all ZnS:Mn samples, and the peak intensity reaches a maximum with a Mn content of 0.68 atom % from the EDX analysis in 2 atom % Mn-doped ZnS samples.

Effect of paramagnetic Mn ion on the superconductivity of Cu0.5Tl0.5Ba2Ca2−xMnxCu3O10−y

The Mn-doped Cu0.5Tl0.5Ba2(Ca2−xMnx)Cu3O10−y(x = 0, 0.15, 0.25, 0.35, 0.5, 0.75 1.0, and 1.25) superconductor samples were prepared at atmospheric pressure using solid state reaction method. The objectives of Mn doping at the Ca site were to improve the inter plane coupling and to see the effect of paramagnetic Mn atom on copper spins in the CuO2 planes and in turn on superconductivity in the light of charge stripe theory. The Mn doped samples have orthorhombic structure and the cell parameters were decreased after the increase of Mn concentration. The onset critical temperature and zero resistance critical temperature have been decreased, which were further decreased after oxygen annealing.

Abnormal dielectric behaviors in Mn-doped CaCu3Ti4O12 ceramics and their response mechanism

► Mn-doping affects the electric behaviors remarkably in CCTO ceramics. ► The activation energy of grain and grain boundary disappears with increasing the Mn doping concentration. ► The XANES spectra reveal that valence states of Ti, Mn and Cu in the grain and grain boundary changes greatly. Mn-doped CaCu 3 Ti 4 O 12 (CCTO) polycrystalline ceramics have been prepared by the conventional solid state sintering. Our results indicate that 10% Mn doping can decrease the dielectric permittivity in CaCu 3 Ti 4 O 12 by about 2 orders of magnitude (from 10 4 to 10 2 ). The grain and grain boundary activation energies show an obvious increase from 0.054 eV to 0.256 eV, and decrease from 0.724 eV to 0.258 eV with increasing the Mn doping concentration, respectively, which may be caused by the variation of Cu and Ti valence states in the CCTO samples evidenced by the X-ray absorption spectra. The similar grain and grain boundary activation energies result in invalidation of the internal boundary layer capacitance effect for the 10% Mn-doped CCTO sample, and thus result in the dramatic decrease of dielectric permittivity.

PH- and Dopant-Dependent CdMoO4:Mn Nanocrystals: Luminescence and Magnetic Properties

CdMoO(4):Mn nanocrystals with a tetragonal crystal structure were prepared by aqueous coprecipitation method at a low temperature of 2 °C under different pH values. The size of the CdMoO(4):Mn nanocrystals of spherical morphology increases with the Mn dopant concentration from 35 to 55 nm for pH = 4. The morphology could be tuned from nanocrystals to microstructures consisting of smaller nanoparticles by the Mn concentration when the pH value of the precursor was increased to 8. The thermal stability of the luminescence and magnetic properties of the Mn-doped samples also depend on the pH and the doping level. The effects of the pH and dopant on the luminescence and magnetic properties, including magnetic susceptibility and electron paramagnetic resonance, were investigated. This approach contributes to better understanding of aqueous chemistry methods to control the growth of nanocrystals.

Role of donor defects in stabilizing room temperature ferromagnetism in (Mn, Co) co-doped ZnO nanoparticles

We report the effects of co-doping ZnO with Co and Mn in an n-type environment on ferromagnetism (FM). Two sets of samples, Zn0.95−xCo0.04MnxO (0.000 ≤ x ≤ 0.02) and Zn0.95−yCoyMn0.04O (0.000 ≤ y ≤ 0.02), were synthesized by the chemical route with oxygen vacancies introduced via annealing in a forming gas (reducing the atmosphere). In addition to the magnetization, the particles were characterized by x-ray diffraction, diffuse reflectance spectroscopy and x-ray absorption near-edge emission spectroscopy. The Co and Mn ions were determined to be in the + 2 state in a tetrahedral symmetry, with no evidence of metallic Co or Mn. We find that while a purely Mn-doped sample exhibits weak FM at room temperature, the general effect of Mn as a co-dopant with Co, in an n-type environment, is to decrease the moment strongly. All of our results can be systematically explained within the context of defect mediated FM in these wide bandgap semiconductors, where the coincidence of the spin-split-impurity (defect) band states and the 3d states leads to the development of a net moment alongside the formation of spin polarons.

Thermoluminescence, photoluminescence and EPR studies on Mn2+ activated yttrium aluminate (YAlO3) perovskite

Thermoluminescence (TL) measurements were carried out on undoped and Mn2+ doped (0.1mol%) yttrium aluminate (YAlO3) nanopowders using gamma irradiation in the dose range 1–5kGy. These phosphors have been prepared at furnace temperatures as low as 400°C by using the combustion route. Powder X-ray diffraction confirms the orthorhombic phase. SEM micrographs show that the powders are spherical in shape, porous with fused state and the size of the particles appeared to be in the range 50–150nm. Electron Paramagnetic Resonance (EPR) studies reveal that Mn ions occupy the yttrium site and the valency of manganese remains as Mn2+. The photoluminescence spectrum shows a typical orange-to-red emission at 595nm and suggests that Mn2+ ions are in strong crystalline environment. It is observed that TL intensity increases with gamma dose in both undoped and Mn doped samples. Four shouldered TL peaks at 126, 240, 288 and 350°C along with relatively resolved glow peak at 180°C were observed in undoped sample. However, the Mn doped samples show a shouldered peak at 115°C along with two well defined peaks at ∼215 and 275°C. It is observed that TL glow peaks were shifted in Mn doped samples. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped, and Mn doped samples were determined at different gamma doses using the Chens glow peak shape method and the results are discussed in detail.

Structural, optical and magnetic properties of Zn1 − xMnxO micro-rod arrays synthesized by spray pyrolysis method

Undoped and Mn-doped ZnO micro-rod arrays were fabricated by the spray pyrolysis method on glass substrates. X-ray diffraction and scanning electron microscopy showed that these micro-rod arrays had a polycrystalline wurtzite structure and high c-axis preferred orientation. Photoluminescence studies at 10K show that the increase of manganese content leads to a relative decrease in deep level band intensity with respect to undoped ZnO. Magnetic measurements indicated that undoped ZnO was diamagnetic in nature whereas Mn-doped ZnO samples exhibited ferromagnetic behavior at room temperature, which is possibly related to the substitution of Mn ions (Mn2+) for Zn ions in the ZnO lattice.

Contrasting effects of magnetic ions on the superconductivity in Tl0.4K0.4Fe2−y−xMxSe2 (M = Mn and Ni)

The transport and magnetic properties together with the superconductivity of Tl0.4K0.4Fe2−y−xMxSe2 (M = Mn and Ni) single crystals are studied. On the transport side, both Mn doping and Ni doping lead to a decrease of charge carrier density. However, contrasting effects on superconductivity are found, i.e. substitution of Fe by Ni results in a drastic depression of the onset superconducting transition temperature (Tonsetc), while the Tonsetc value remains nearly unchanged in Mn-doped samples. A remarkable ferromagnetic interaction is found in Ni-doped samples but is absent in Mn-doped samples. The present results suggest that the magnetic pair-breaking effect alone cannot explain the different behavior of depression of superconductivity in Mn-doped and Ni-doped samples. The occurrence of ferromagnetic interaction is responsible for the rapid decrease of Tonsetc in Ni-doped samples.