Mn Doping Concentration Research Articles

Prediction of the electronic structures, thermodynamic and mechanical properties in manganese doped magnesium-based alloys and their saturated hydrides based on density functional theory

The crystal structures, electronic structures, thermodynamic and mechanical properties of Mg2Ni alloy and its saturated hydride with different Mn-doping contents are investigated using first-principles density functional theory. The lattice parameters for the Mn-doped Mg2Ni alloys and their saturated hydrides decreased with an increasing Mn-doping content because of the smaller atomic size of Mn compared with that of Mg. Analysis of the formation enthalpies and electronic structures reveal that the partial substitution of Mg with Mn reduces the stability of Mg2Ni alloy and its saturated hydride. The calculated elastic constants indicate that, although the partial substitution of Mg with Mn lowers the toughness of the hexagonal Mg2Ni alloy, the charge/discharge cycles are elevated when the Mn-doping content is high enough to form the predicted intermetallic compound Mg3MnNi2.

Investigation on Structural and Optical Properties of Willemite Doped Mn2+Based Glass-Ceramics Prepared by Conventional Solid-State Method

Mn-doped willemite (Zn2SiO4:Mn2+) glass-ceramics derived from ZnO-SLS glass system were prepared by a conventional melt-quenching technique followed by a controlled crystallization step employing the heat treatment process. Soda lime silica (SLS) glass waste, ZnO, and MnO were used as sources of silicon, zinc, and manganese, respectively. The obtained glass-ceramic samples were characterized using the X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared (FTIR), UV-Visible (UV-Vis), and photoluminescence (PL) spectroscopy. The results of XRD revealed that ZnO crystal and willemite (β-Zn2SiO4) were presented as major embedded crystalline phases. This observation was consistent with the result of FESEM which showed the presence of irregularity in shape and size of willemite crystallites. FTIR spectroscopy exhibits the structural evolution of willemite based glass-ceramics. The optical band gap shows a decreasing trend as the Mn-doping content increased. Photoluminescent technique was applied to characterize the role of Mn2+ions when entering the willemite glass-ceramic structure. By measuring the excitation and emission spectra, the main emission peak of the glass-ceramic samples located at a wavelength of 585 nm after subjecting to 260 nm excitations. The following results indicate that the obtained glass-ceramics can be applied as phosphor materials.

Electron Spin Resonance Study of BaFe2−x Mn x As2 Single Crystals

The transport and magnetic properties of BaFe2−xMnxAs2 single crystal samples are investigated by means of resistivity, magnetic susceptibility, thermopower, and electron spin resonance studies. No superconductivity is observed in these compounds. Our electron spin resonance study reveals that the intensity of a paramagnetic signal monotonously increases with increasing Mn doping content, indicating that the introduction of Mn leads to the localization of the Mn/Fe 3d electrons. It is suggested that the Mn ions act as the local scatterers, which hardly interact with neighboring Fe ions. The present results partially explain why the BaFe2−xMnxAs2 samples are not superconducting.

Increased Eu²⁺ content and codoping Mn²⁺ induced tunable full-color emitting phosphor Ba(1.55)Ca(0.45)SiO₄:Eu²⁺,Mn²⁺.

We demonstrated that a new intermediate composition of Ba(1.55)Ca(0.45)SiO4 between the orthosilicates Ca2SiO4 and Ba2SiO4 yields the best phosphor hosts, and interesting luminescence properties can be found from the Eu(2+) singly doped and/or Eu(2+)/Mn(2+) codoped Ba(1.55)Ca(0.45)SiO4 phosphors. The phosphors can be excited by near-ultraviolet (nUV) light at wavelengths ranging from 200 to 450 nm matching well with the nUV light-emitting diode (LED) chips. As a result of fine-tuning the activators of different Eu(2+) content and Eu(2+)/Mn(2+) couples with different ratios, tunable full-color emission under UV light excitation can be realized by combining the blue emission (460 nm) and green emission (520 nm) originating from Eu(2+) with the red emission (595 nm) from Mn(2+) in the Ba(1.55)Ca(0.45)SiO4 host lattice. Energy-transfer efficiency between Eu(2+) and Mn(2+) increases and tunable emission can be obtained with increasing Mn(2+) doping content. These results indicate that the Ba(1.55)Ca(0.45)SiO4:Eu(2+),Mn(2+) phosphor will have potential use in nUV chip pumped white LED devices.

Evidence for the Ligand-Assisted Energy Transfer from Trapped Exciton to Dopant in Mn-Doped CdS/ZnS Semiconductor Nanocrystals

Trapping of charge carriers is the major process competing with radiative recombination or transfer of charge carriers important in the application of semiconductor nanocrystals in photonics and photocatalysis. In typical semiconductor quantum dots, trapping of charge carriers usually leads to quenching of exciton luminescence. In this study, we present evidence indicating that thiol ligands on the surface that quench exciton luminescence can have an opposite effect on sensitized dopant luminescence in doped semiconductor nanocrystals by facilitating the recovery of the trapped exciton for sensitization. Despite the increase in hole trapping by the added octanethiol to the surface of Mn-doped CdS/ZnS nanocrystals, the sensitized Mn luminescence increased by the added octanethiol and the enhancement became stronger with increasing Mn doping concentration. While the role of octanethiol as the hole trap and the enhancement of Mn luminescence may seem contradictory, the thiol-induced enhancement of Mn lumines...

Enhanced thermoelectric performance of Cu2CdSnSe4 by Mn doping: experimental and first principles studies.

Serials of Mn doping by substituting Cd sites on Cu2CdSnSe4 are prepared by the melting method and the spark plasma sintering (SPS) technique to form Cu2Cd1−xMnxSnSe4. Our experimental and theoretical studies show that the moderate Mn doping by substituting Cd sites is an effective method to improve the thermoelectric performance of Cu2CdSnSe4. The electrical resistivity is decreased by about a factor of 4 at 723 K after replacing Cd with Mn, but the seebeck coefficient decreases only slightly from 356 to 289 μV/K, resulting in the significant increase of the power factor. Although the thermal conductivity increases with the doping content of Mn, the figure of merit (ZT) is still increased from 0.06 (x = 0) to 0.16 (x = 0.10) at 723 K, by a factor of 2.6. To explore the mechanisms behind the experimental results, we have performed an ab initio study on the Mn doping effect and find that the Fermi level of Cu2CdSnSe4 is shifted downward to the valence band, thus improving the hole concentration and enhancing the electrical conductivity at the low level doping content. Optimizing the synthesis process and scaling Cu2Cd1−xMnxSnSe4 to nanoparticles may further improve the ZT value significantly by improving the electrical conductivity and enhancing the phonon scattering to decrease the thermal conductivity.

Preparation of Visible-Light Active Mn-Doped TiO<sub>2</sub> Photocatalyst and its Photodegradation of Methylene Blue from Solution

Mn-doped TiO2nanocrystal photocatalysts were prepared by the sol-gel method using MnSO4·H2O as manganese source. The catalysts were characterized by XRD, SEM, EPR, UV-Vis, their photocatalytic activity for methylene blue (MB) degradation was investigated. The results showed that Mn was doped into the crystal lattice of TiO2, and had no influence on TiO2crystal structure; the size of TiO2nanoparticle gradually decreased with Mn doping concentration increasing. The Mn-doped TiO2catalysts have enhanced absorption in the visible light region, and its visible light absorptivity increased with Mn doping concentration increasing. The UV-Vis showed the Mn-doped TiO2showed higher photocatalytic activity than the undoped TiO2for methylene blue degradation under visible light irradiation. It is also found that the MB photodegradation rate of Mn-doped TiO2improved by 46% than that of the undoped TiO2.

Magnetic exciton relaxation and spin-spin interaction by the time-delayed photoluminescence spectra of ZnO:Mn nanowires.

ZnO:Mn nanostructures are important diluted magnetic materials, but their electronic structure and magnetic origin are still not well understood. Here we studied the time-delayed and power-dependent photoluminescence spectra of Mn(II) doped ZnO nanowires with very low Mn concentration. From the time-delayed emission spectra, we obtained their electronic levels of single Mn ion replacement of Zn ions in ZnO nanowire. The high d-level emissions show up unusually because of the stronger p-d hybridization than that in ZnS, as well as the spin-spin coupling. After increasing Mn doping concentration, the ferromagentic cluster of the Mn-O-Mn with varied configurations can form and give individual emission peaks, which are in good agreement with the ab initio calculations. The presence of clustered Mn ions originates from their ferromagnetic coupling. The lifetimes of these d levels show strong excitation power-dependent behavior, indication of strong spin-dependent coherent emission. One-dimensional structure is critical for this coherent emission behavior. These results indicate that the d state is not within Mn ion only, but a localized exciton magnetic polaron, Mn-O-Mn coupling should be one source of ferromagnetism in ZnO:Mn lattice, the latter also can combine with free exciton for EMP and produce coherent EMP condensation and emission from a nanowire. This kind of nanowires can be expected to work for both spintronic and spin-photonic devices if we tune the transition metal ion doping concentration in it.

Influence of Mn doping content on magnetic properties of a (Mn, N) co-doped ZnO system

In this paper, by investigating the magnetic properties of (Mn, N) co-doped ZnO films with various Mn doping contents, we found that the total magnetic moments of the samples would reach a limit under a certain N doping condition even if more Mn ions were incorporated into the ZnO lattice. Based on first-principles calculations, we propose that the unique magnetic interactions between Mn2+ dopants in the presence of nitrogen and the very low solubility of substitutional N relative to Mn in ZnO are responsible for the experimental observation.

Comparative Study of Room-Temperature Ferromagnetism in Undoped and Mn-Doped CdSe Quantum Dots

We report a comparative study of room-temperature ferromagnetism (RTFM) in undoped and Mn-doped CdSe quantum dots (QDs) synthesized by a pyrolysis method. Both undoped and Mn-doped CdSe QDs exhibited the RTFM with a coercive field of ${\sim}{\rm 160}~{\rm Oe}$ . The magnetic moment of the QDs showed a strong dependence on the QD size, indicating that the RTFM of the QDs was due to an intrinsic effect. The saturation magnetization value of QDs increased with a decreasing of the QD size. Compared with the undoped QDs, the Mn-doped CdSe QDs exhibited the enhancement of saturation magnetization value with a slight doping concentration. By further increasing the Mn doping concentration to 4 at.%, the increase of the saturation magnetization value of the doped-QDs was not observed, which could be attributed to the enhancement of antiferromagnetic coupling between ${\rm Mn}^{2+}$ ions.

Study on Mn-induced Jahn–Teller distortion in BiFeO3 thin films

Present work reports Raman spectroscopy study of single-phase Mn-doped BiFeO3 [BiFe1−x Mn x O3 (0 ≤ x ≤ 0.20)] polycrystalline thin films carried out in backscattering geometry. De-convolution of Raman spectra showed a gradual transition in the crystal symmetry from rhombohedral (−R) to multiphase [rhombohedral (−R) + tetragonal (−T)] structure with increasing Mn doping concentration in BiFe1−x Mn x O3 (BFMO) thin films. X-ray diffraction (XRD) along with Le-Bail extraction refinement confirms that the structural symmetry lowering in BFMO thin films occurs at about 10 % Mn doping concentration. A blue shift is observed in the direct energy band gap of BFMO thin films from 2.53 to 2.87 eV (at T = 295 K) and is attributed to the local symmetry lowering and local induced strain in Fe3+ environment resulted from Jahn–Teller distortion in (MnFe)3+O6 octahedral unit. Second-derivative analysis of FTIR spectra in the spectral regions (420–470) cm−1 and (480–680) cm−1 further indicates the favourable structure distortion leading to the simultaneous exhibition of enhanced ferromagnetic and ferroelectric properties owing to Mn substitution in host BiFeO3 lattice.

Influence of Mn doping on structural, optical and electrical properties of CdO thin films prepared by cost effective spray pyrolysis method

Transparent and conducting cadmium oxide (CdO) and manganese doped CdO (Mn: CdO) thin films were deposited using a low cost spray pyrolysis method on the glass substrate at 300°C. For Mn doping, various concentrations of manganese acetate (1–3wt%) was used in the spraying precursor solution. The structural, electrical and optical properties of CdO and Mn: CdO films were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), UV–vis and Hall measurement. X-ray diffraction study reveals that the CdO and Mn: CdO films are possessing cubic crystal structures. SEM and AFM studies reveal that the grain size and roughness of the films are increased with increasing Mn doping concentration. Optical transmittance spectra of the CdO film decreases with increasing doping concentration of manganese. The optical band gap of the films decreases from 2.42eV to 2.08eV with increasing concentration of manganese. A minimum resistivity of 1.11×10−3Ωcm and maximum mobility of 20.77cm2V−1s−1 is achieved for 1wt% of manganese doping.

X-Ray Absorption Spectroscopy Analysis of the Effect of MnO2 Doping on Local Structure of ((K0.5Na0.5)0.935Li0.065)NbO3 Ceramics

In this work, the extend x-ray absorption fine structure (EXAFS) analysis was performed in combination with the density functional theory (DFT) calculation to investigate local structure of Mn-doped ((K0.5Na0.5)0.935Li0.065)NbO3. From the structural relaxation, Mn3+ is substituted on Nb5+ to produce oxygen vacancy in the longest bond length in c-axis. Further, from the EXAFS Fourier transform comparison in R-space, the bond lengths between Mn3+ and O2− are almost equal in both ab- and c-axis with increasing Mn-doping contents. This is strong evidence that Mn-doping played an important role in producing the polarization domains in opposite direction, which diminish remnant polarization, pinning the domains wall movement and increase coercive field.

Effect of manganese concentration on photoluminescence properties of Zn2SiO4:Mn nanophosphor material

Nanophosphor β-Zn2SiO4:Mn with bright yellow light emission were synthesized by a sol–gel process. These samples were prepared by a simple solid-phase reaction under natural atmosphere at 1500°C after the incorporation of ZnO:Mn nanoparticles, in silica monolith. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the phase purity, particle size and morphology. In addition photoluminescence (PL) was used for optical study. The PL spectrum for the β-Zn2SiO4:Mn nanophosphors showed a dominant peak at 574nm, which originated from the 4T1→6A1 transitions of Mn2+ ions. The level of manganese doping did not greatly affect the crystallinity, but did affect the luminescence of nanophosphors. Upon 255nm excitation, the luminescence decay time of the yellow emission of β-Zn2SiO4 with a Mn doping concentration of 2at.% around 574nm is 13ms. The characteristics of crystallinity, morphology and luminescence property of the obtained nanophosphors were investigated.

Influence of manganese concentration and annealing temperatures on the physical properties of CdO films grown by the SILAR method

Undoped and doped Cadmium oxide (CdO) films with different Mn concentrations were prepared on glass substrates by the successive ionic layer adsorption and reaction method and annealed at two different temperatures. Structural, morphological and optical conditions were performed by XRD, scanning electron microscope (SEM) and UV–vis spectrum measurements. The deposited films were dense and they adhere well to the glass substrates. From the SEM photographs, it was seen that Mn doping concentration and annealing process affect the morphologies of the nanostructures. It was found that the growth process modifies the microstructures of the CdO films. XRD results and UV–vis analysis reveal that the crystal structure and optical band gap of the films could be adjusted by varying the Mn concentration and annealing temperature. The results also indicate that there is a direct dependence of the physical and optical properties of the metal oxide films on doping concentration and annealing process.

Magnetic and optical properties of Mn-doped SnO2 films

ABSTRACTMagnetic nanoparticles have drawn much attention due to their potential in magnetic recording as well as many biological and medical applications such as magnetic separation, hyperthermia treatment, magnetic resonance contrast enhancement and drug delivery. The magnetic fields generated by these nanoparticles can be used for diagnostics in Magnetic Resonance Imaging (MRI) etc. Manganese doped tin dioxide (SnO2:Mn) possess interesting physical and chemical properties. The physical and chemical properties of the particles themselves like the size, shape, crystallinity and composition, will control the magnetic properties and response of the particles to magnetic fields. Our work is rooted to control the properties of the particles as well as tailor their magnetic properties for specific applications. In this study, SnO2: Mn films with different Mn doping concentrations (0-3 mol%) were deposited on the glass substrates by sol-gel dip coating technique. XRD patterns shows tetragonal structure for all the SnO2:Mn films and crystallite size decreased as Mn doping concentration increased from 0 - 3 mol%. The magnetic property shows that pure SnO2 film is diamagnetic and 1- 3 mol% SnO2:Mn films posses room temperature ferromagnetism. The optical properties of the films revealed that transmittance of the films decreased with increase in Mn doping concentration. The optical energy band gap values (3.55 eV-3.71 eV) increased with the increase in Mn doping concentrations. Such SnO2:Mn films with structural, optical and magnetic properties can be used as dilute magnetic semiconductors.

Phase Separations in LiFe1–xMnxPO4: A Random Stack Model for Efficient Cathode Materials

Olivine-type LiFe1-xMnxPO4 compounds were systematically synthesized by a solvothermal method. Synchrotron radiation X-ray absorption spectroscopy combined with first-principles calculations and energy-dispersive Xray spectroscopy measurements show that the as-prepared LiFe1-xMnxPO4 samples contain two different phases: LiFePO4 and LiMnPO4. Actually, due to the crystal field effect, these two structures are randomly stacked and characterized by a pronounced structural distortion of the MO6 (M: Fe or Mn) octahedra. Moreover, increasing the Mn doping concentration, the distortion of the MO6 octahedra increases. Considering the size of LiMnPO4 stacks and the distortion of MO6 octahedra, the best performance occurs at the optimal Mn doping concentration. Among, the different Fe/Mn ratios, the electrochemical tests show that the as-prepared LiFe0.75Mn0.25PO4 sample exhibits the best electrochemical performance. Moreover, in order to optimize electrochemical performances, data point out that the doping procedure may control the size of the LiMnPO4 stacks, but it is also necessary to control the interplay between the increase of the working voltage and the electrical conductivity of LiMnPO4 stacks.

SPECTROSCOPIC STUDY OF DEEP LEVEL EMISSIONS FROM ACCEPTOR DEFECTS IN ZnO THIN FILMS WITH OXYGEN RICH STOICHIOMETRY

This paper reports the tailoring of acceptor defects in oxygen rich ZnO thin films at different post-deposition annealing temperatures (500–800°C) and Mn doping concentrations. The XRD spectra exhibited the nanocrystalline nature of ZnO thin films along with inconsistent variation in lattice parameters suggesting the temperature-dependent activation of structural defects. Photoluminescence emission spectra revealed the temperature dependent variation in deep level emissions (DLE) with the presence of acceptors as dominating defects. The concentration of native defects was estimated to be increased with temperature while a reverse trend was observed for those with increasing doping concentration. A consistent decrease in DLE spectra, with increasing Mn content, revealed the quenching of structural defects in the optical band gap of ZnO favorable for good quality thin films with enhanced optical transparency.

Yellow emission of SiO2/Zn2SiO4:Mn nanocomposite synthesized by sol–gel method

A two-step sol–gel process was used for the preparation of Mn doped β-Zn2SiO4 nanoparticles embedded in silica host matrix after the incorporation of ZnO:Mn nanoparticles in silica monolith. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the phase purity, particle size and morphology. XRD results indicate that pure phase of β-Zn2SiO4 with triclinic structure was obtained after thermal treatment at 1500°C. However, photoluminescence (PL) technique was investigated for optical study. It was illustrated that the Mn doping content influenced the degree of aggregation and luminescence of the nanocomposite. This manganese doped zinc silica phase in silica host matrix, exhibit yellow emission centred at about 575nm driven by 4T1 to 6A1 relaxation in Mn2+. The crystallinity and luminescent property of nanocomposite were investigated.

Effect of Mn doping on the structural and optical properties of ZrO2 thin films prepared by sol–gel method

Homogeneous and transparent Mn doped ZrO2 thin films were prepared by sol–gel dip coating method. The films were annealed in air atmosphere at 500°C. The X-ray diffraction pattern of the undoped ZrO2 thin film revealed a mixed phase of tetragonal and monoclinic ZrO2 with preferred orientations along T(111) and M(−111). Grazing Incidence X-ray Diffraction of Mn doped ZrO2 thin films reveals the introduction of Mn interstitial in ZrO2 which stabilize the mixed phase of ZrO2 into tetragonal phase. Atomic force microscope image shows the addition of catalyst (Mn) which stops isotropic agglomeration of particles, instead of anisotropic agglomeration that occurred resulting in growth of particles in certain direction. Average transmittances of >70% (in UV–vis region) were observed for all samples. The optical band gap decreased from 5.72 to 4.52eV with increase in Mn doping concentration. The reduced band gap is due to the introduction of impurity levels in the band gap, by incorporation of the metal ions into the ZrO2 lattice. The d-electron of Mn (t2g level) can easily overlap with the ZrO2's valence band (VB) because t2g of Mn is very close to VB of ZrO2. This overlap caused a wide VB and consequently decreases the band gap of ZrO2. The photoluminescence (PL) spectrum of undoped zirconia thin film exhibits an intense near band edge emission peak at 392.5nm (3.15eV) and weak emission peaks at 304 (4.07eV), 604nm (2.05eV) and 766nm (1.61eV). Additional PL peaks were observed for Mn doped ZrO2 located at around 420, 447 (blue), 483 (blue) and 529 (green)nm respectively. These peaks were due to the redox properties of various valence state of Mn in ZrO2. The prepared Mn doped ZrO2 thin films can be applied in optical devices.