Increase Of Gd3 Research Articles

Effect of lattice strain on structure, morphology and magneto-dielectric properties of spinel NiGdxFe2−xO4 ferrite nano-crystallites synthesized by sol-gel route

Nanocrystalline powders of Gadolinium (Gd3+) substituted nickel ferrite spinel (NiGdxFe2−xO4: x = 0.00, 0.025, 0.050, 0.075 and 0.1) samples were synthesized via sol-gel method. Nickel nitrate hexahydrate and Ferric nitrate hexahydrate were used as the precursors and rare earth Gadolinium nitrate hexahydrate [Gd(NO3)3·6H2O] was used as the dopant. The structural, morphological, magnetic and dielectric properties of the synthesized nanoparticles were examined by XRD, FTIR, HRSEM, EDX, TEM, VSM and dielectric studies. The Scherrer method and Williamson-Hall (W-H) method were used to evaluate the crystallite sizes and lattice strain. The crystallite size of NiGdxFe2−xO4 samples were found to decrease from 25 nm to 11 nm with increase in Gd3+ content. Lattice parameters decrease and lattice strain increases with the increase in Gd3+ content in the sample. HRSEM images showed the spherical morphology and uniform size distribution. The elemental composition analysis confirms the stoichiometric presence of expected elements in the samples. The crystallite size and the particle size calculated from the XRD analysis and HRTEM monographs indicate the correlation of the data obtained from both the measurements. Magnetic studies of the samples were performed using vibrating Sample Magnetometer, in which magnetizations (Ms) decrease with increase in Gd3+ concentration from 36.51 emu/gm to 19.69 emu/gm. As the gadolinium content was gradually increased, coercivity and remnant magnetization were also decreased. Magnetic anisotropy of nickel ferrite was also found to decrease with increasing gadolinium content. The saturation magnetization values were achieved by using the “Law of Approach (LA) to Saturation magnetization” technique. Specific correlation between magnetic interaction and lattice strain was observed in Gd3+ substituted nickel ferrite. Dielectric parameters such as dielectric constant and dielectric loss of the prepared samples decrease with increase of applied frequency and increasing of Gd3+ doping concentration.

Phase evolution, microstructure and chemical stability of Ca1-xZr1-xGd2xTi2O7 (0.0 ≤ x ≤ 1.0) system for immobilizing nuclear waste

In order to ascertain the structural relationship of zirconolite and pyrochlore for their potential application in HLW immobilization, the Gd-doped zirconolite-pyrochlore composite ceramics (Ca1-xZr1-xGd2xTi2O7) were systematically synthesized with x = 0.0–1.0 by traditional solid-phase reaction method. The phase evolution and microstructure of the as-prepared samples have been elucidated by XRD and Rietveld refinement, Raman spectroscopy, BSE-EDS and HRTEM analysis. The results showed that zirconolite-2M, zirconolite-4M, perovskite and pyrochlore, four phases were identified in Ca1-xZr1-xGd2xTi2O7 system and could be coexisted at x = 0.4 composition. With the increase of Gd3+ substitution, the phase evolution was followed by zirconolite-2M→zirconolite-4M→pyrochlore. It is illustrated that the phase transformation from zirconolite-2M to zirconolite-4M was promoted by the preferential substitution of Gd3+ for Ca2+. And the solubility of Gd3+ in zirconolite-2M, zirconolite-4M and pyrochlore increased in sequence. The chemical stability test was also measured by the PCT leaching method. The normalized elemental release rates of Ca, Zr, Ti and Gd in Ca1-xZr1-xGd2xTi2O7 system were fairly low and in the range of 10−6−10−8 g m−2 d−1, which indicated a potential ceramics composite ensemble of CaZrTi2O7-Gd2Ti2O7 system for nuclear HLW immobilization.

Effects of isovalent substitution on structural and magnetic properties of nanocrystalline Y3−xGdxFe5O12 (0 ≤ x ≤ 3) garnets

We fabricated Gd-doped Y3Fe5O12 (YIG) nanoparticles by a modified sol–gel method. We investigated the effects of isovalent Gd3+-ion substitution on the structural and magnetic properties of Y3−xGdxFe5O12 (0 ≤ x ≤ 3) nanoparticles. Isovalent Gd3+-ion substitution for Y3+ leads to lattice expansion and change in the Fe(a)–O–Fe(d) bond angle. The X-ray photoemission spectroscopy and Mössbauer measurements revealed a high-spin state of Fe3+. The Mössbauer analysis showed an increase in the Fe(d)3+/Fe(a)3+ ratio, indicating a relocation of Y3+ ions at the dodecahedral sites and Fe3+ ions at the octahedral sites. The magnetic properties could be explained in terms of magnetic-structural evolution with increasing Gd3+ content. The field dependence of magnetization indicated a clear decrease of the magnetization while the magnetic anisotropy first decreases and then increases with the increase of Gd3+ content. These Gd3+-ion-substituted nanocrystalline garnet ferrites are suitable for use in a variety of magneto-optical applications.

Study on the sensitization of Gd3 + on Ce3 +/Tb3 + co-doped GBS scintillating glass

The composition of the matrix glass has a significant effect on the luminescent property and density of the scintillating glass. In this paper, the Ce3+/Tb3+ co-doped Gd2O3-B2O3-SiO2 (GBS) scintillating glasses were melted in reducing atmosphere. The effects of Gd3+ on the luminescent property and density of scintillating glass were studied. The results show that increasing Gd3+ ions concentration can increase the density of the scintillating glass. The energy transfer from Gd3+ to Tb3+ in the glass can sensitizes the luminescence of Tb3+ ions. Meanwhile, the increase of Gd3+ ions concentration increases the optical basicity of the glass and the electrons on the Ce3+ ion 4f orbit are more likely to migrate to 5d orbit, which promotes the energy transfer from Ce3+ to Tb3+. However, the concentration of Gd3+ ions is too high to cause concentration quenching and Ce3+ ion charge transfer quenching, which are not conducive to the light of the glass.

Sol-Gel Synthesis and Characterization of Ba1-xGdxTiO3+δ Thin Films on SiO2/Si Substrates Using Spin-Coating Technique

Ba1-xGdxTiO3+δ, at x = 0, 0.05, 0.1, 0.15, 0.2, (BGT) thin films have been fabricated on SiO2/Si substrate using Sol-Gel method. The microstructure and surface morphology of the fabricated films have been investigated using X-ray diffraction (XRD) and atomic force microscopy (AFM). The XRD results show that the fabricated films are crystalline with perovskite structure. There is a shifting of the preferred peak at 31.5o to a higher angle as the doping ratio increases suggesting a distortion lattice exists in the films, which could be due to the substitution of Gd3+ ions into Ba-site. The decreasing of lattice constants confirms the substitution of Gd3+ in BaTiO3 lattice structure. The microstrain and dislocation density are found to be increased with the increase of Gd3+ doping, which attributed to the reduction of lattice volume that due to the ionic size mismatch effect. The AFM results show decreasing trend in both average grain size and roughness parameters. Therefore, the microstructure and surface morphology of BGT samples is strongly dependent on the Gd3+ doping concentration that mainly due to the difference ionic radius substitution.DOI: http://dx.doi.org/10.5755/j01.ms.23.1.13954

Inter-atomic bonding and dielectric polarization in Gd3+ incorporated Co-Zn ferrite nanoparticles

A series of ferrite with a chemical composition Co0.7Zn0.3GdxFe2−xO4 (where x=0.0 to x=0.1) were prepared by sol-gel auto-combustion method. X-ray diffraction pattern were used to determine the crystal structure and phase formation of the prepared samples. Scanning electron microscopy is used to study the surface morphology of the prepared samples. Elastic properties were determined from the infrared spectroscopy. Debye temperature, wave velocities, elastic constants found to increase with the increase in Gd3+ substitution. Dielectric properties such as dielectric constant and dielectric loss were studied as a function of Gd3+ substitution and frequency. Dielectric constant decreased with the increase in frequency and Gd3+ substitution. Behavior of dielectric properties was explained on the basis of Maxwell-Wagner interfacial polarization which in accordance with Koops phenomenological theory. Real and imaginary part of impedance was studied as a function of resistance and Gd3+ substitution. The behavior of impedance is systematically discussed on the basis of resistance-capacitance circuit.

Quenching cooperative transitions by destroying Yb3+-clusters.

In our previous study, we have reported the cooperative luminescence of Yb3+-trimers and cooperatively sensitized Gd3+ luminescence by Yb3+-tetramers in a doped CaF2 host. In this study, we experimentally observed an unusual luminescent phenomenon of Gd3+ in CaF2:Yb3+/Gd3+. Upon excitation with a 980 nm laser, the upconversion luminescence of Gd3+ first increases and then decreases in the Gd3+ concentration range of 0-0.9 mol%; this is different from the monotonic increase of Gd3+ luminescence observed in the downconversion spectra via the direct excitation of Gd3+. This special luminescent behavior was indicated to be related to the energy transfer from the Yb3+-tetramers to Gd3+ and the destruction of Yb3+-clusters. Herein, we proposed a new luminescence quenching mechanism, Yb3+-cluster destructive quenching, which was verified by fluorescence dynamic analysis and an optically inactive rare-earth ion-doping experiment.

Structural and electrical studies of Gd3+ substituted zinc ferrite nano particles

ABSTRACTZinc ferrite nanoparticles with Gadolinium (Gd) ions substituted for iron in ZnGdxFe2-xO4 (x = 0.00, 0.05, 0.10, 0.15) were prepared by sol – gel method. The X ray diffraction measurement confirmed the formation of single crystalline spinel structure in all the samples. The lattice constant increases with increase in Gd3+ ion concentration. The crystallite size calculated by Scherrer formula from the (311) peak varies from 19 nm to 8 nm. The particle morphology was studied by Transmission Electron Microscope (TEM). The XRF analysis confirmed the purity of the prepared samples. The variation of dielectric constant and loss factor with frequency showed normal behavior. The values of dielectric constant, dielectric loss factor and AC conductivity were found to increase with increase in Gd3+ ion concentration in zinc ferrite. AC conductivity measurements suggested conduction due to small polaron hopping. The composition and frequency dependence of dielectric parameter and AC conductivity is qualitatively explained.

Upconversion Luminescence Properties of Er3+ Doped Yb2Ti20 Nanophosphor by Gd3+ Codoping.

Er3+ doped Yb2Ti207 nanophosphors by Gd3+ codoping with nominal composition of (Er0.05Yb0.95-xGd3+)2Ti2O7 (x = 0, 0.2, 0.4, 0.6, 0.8, and 0.95) have been prepared by sol-gel method. Er3+-Gd3+ codoped Yb2Ti2O7 was characteristic of a typical face-centered cubic crystal phase, and the unit cell parameter increased linearly with the increase of Gd3+ concentration. Under a 976 nm laser diode excitation, both green and red upconversion emissions were observed and the upconversion emissions were enhanced significantly by Gd3+ codoping, showing the strongest green and red emissions at 80 mol% Gd3+ codoping. The intensity ratio of green to red emissions (Igreen/Ired) increased monotonously with the increase of Gd3+ concentration. The energy transfer between Yb3+ and Er3+ and the variation of local crystal field symmetry of Er3+ by the substitution of Yb3+ by Gd3+ ions led to the improvement of upconversion properties of Er3+-Gd3+ codoped Yb2TiO7 nanophosphors.

Structural, dielectric and magnetic properties of Gd substituted manganese ferrite nanoparticles

Gd3+ ion-substituted manganese ferrite nanoparticles with the chemical formula MnGdxFe2-xO4 (x = 0.0, 0.05, and 0.1) were synthesized by sol–gel auto combustion method. Thermal stability of the as-prepared sample was analyzed using thermo gravimetric and differential thermal analysis (TG–DTA) and the result reveals that the prepared sample is thermally stable above 300 °C. Structural and morphology studies were performed using powder x-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Indexed PXRD patterns confirm the formation of pure cubic spinel structure. The average crystallite sizes calculated using Sherrer’s formula decreased from 47 nm to 32 nm and lattice constant was enhanced from 8.407 Å to 8.432 Å. The FTIR spectrum of manganese ferrite shows a high frequency vibrational band at 564 cm−1 assigned to tetrahedral site and a low frequency vibrational band at 450 cm−1 assigned to octahedral site which are shifted to 556 cm−1 and 439 cm−1 for Gd3+ substitution and confirm the incorporation of Gd3+ into manganese ferrite. SEM analysis shows the presence of agglomerated spherical shaped particles at the surface. Room temperature dielectric and magnetic properties were studied using broadband dielectric spectroscopy (BDS) and vibrating sample magnetometry (VSM). Frequency dependent dielectric constant, ac conductivity and tan delta were found to increase with Gd3+ ion substitution. The measured values of saturation magnetization decrease from 46.6 emu g−1 to 41 emu g−1 with increase in Gd3+ concentration and coercivity decreases from 179.5 Oe to 143 Oe.

Chemical bonding and magnetic properties of gadolinium (Gd) substituted cobalt ferrite

Polycrystalline gadolinium (Gd) substituted cobalt ferrites (CoFe2−xGdxO4; x=0–0.3, referred to CFGO) ceramics have been synthesized by solid state reaction method. Chemical bonding, crystal structure and magnetic properties of CFGO compounds have been evaluated as a function of Gd-content. X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure. However, a secondary ortho-ferrite phase (GdFeO3) nucleates for higher values of Gd-content. A considerable increase in the saturation magnetization has been observed upon the initial substitution of Gd (x=0.1). The saturation magnetization drastically decreases at higher Gd content (x⩾0.3). No contribution from ortho-ferrite GdFeO3 phase is noted to the magnetic properties. The increase in the magnetic saturation magnetization is attributed to the higher magnetic moment of Gd3+ (4f7) residing in octahedral sites is higher when compared to that of Fe3+ (3d5) and as well due to the migration of Co2+ (3d7) ions from the octahedral to the tetrahedral sites with a magnetic moment aligned anti-parallel to those of rare earth (RE3+) ions in the spinel lattice. Increase in coercivity with increase in Gd3+ is content is attributed to magnetic anisotropy in the ceramics.

Enhanced near-infrared emission in phase and size controlled NaLnF4: Pr3+-Yb3+ (Ln = Gd3+ and Y3+) nanocrystals

NaLnF4 (Ln = Y, Gd): Pr3+, Yb3+ nanocrystals were prepared through a facile modified solvothermal method, in which the cubic to hexagonal phase transformation and size evaluation of NaLnF4 nanocrystals could be well controlled by carefully adjusting Gd3+ content. In this system, the infrared emission associated with Yb3+: 2F5/2 → 2F7/2 transition could be obtained under the excitation of Pr3+: 3P0 energy level as a result of efficient energy transfer from Pr3+ to Yb3+. The structural and spectral measurement indicated that the energy transfer efficiency from Pr3+ to Yb3+ firstly increased with the increase of Gd3+ content due to the formation of a higher percentage of hexagonal phase NaLnF4 in the final production, and then decreased with further increase in Gd3+ content due to the expansion of NaLnF4 unit-cell volume. However, a monotonous increase in Yb3+ infrared emission intensity could be observed with the increasing of Gd3+ content until the radiative emission was suppressed by the nonradiative transition originating from the surface defects in smaller NaLnF4 nanocrystals.

Remarkable magnetization with ultra-low loss BaGd x Fe 12−x O 19 nanohexaferrites for applications up to C-band

Abstract Sol–gel synthesized BaGdxFe12−xO19, (x=0.0, 0.1, 0.2, 0.3) nanohexaferrites, have been explored for magnetic and microwave properties. X-ray diffraction studies revealed the hexagonal structure of the synthesized ferrites. The particle size was observed to be in the range 90–84 nm. The dc resistivity was found to be increasing with an increase in Gd3+ content and the variation of dc resistivity with temperature confirmed the semiconducting behavior of all nanohexaferrites. The observed values of saturation magnetization and coercivity, at room temperature, are 81.34 emu/g and 6020 Oe respectively which are very high as compared to the values ever reported till date. Additionally, we observed ultra-low magnetic loss (0.004–0.01) and dielectric loss (0.004–0.06) over the GHz frequency region. The obtained results make these nanohexaferrites a competent material for antenna applications up to C-band.

Effect of Gd3+ ion distribution on structural and magnetic properties in nano-sized Mn–Zn ferrite particles

Nanoparticles of Gd3+ ions doped Mn0.5Zn0.5GdxFe2−xO4 (x=0.1, 0.2, 0.3, 0.4) mixed ferrite were prepared using chemical co-precipitation method. The X-ray diffraction measurements confirmed the formation of a cubic spinel structure. The structural parameters like crystallite size, lattice parameter and strain induced have been calculated. The lattice parameter increases with the increase in Gd3+ ion concentration and shows non linear behaviour. HRTEM investigation confirms the nano size formation of the Gd doped Mn–Zn ferrite nanoparticles. EPR was used to evaluate resonance peak intensity, Lande’s splitting factor (g value), peak to peak line width (ΔHp–p), spin concentration (Ns) and relaxation time (τs). Line width, line intensity, relaxation time and spin concentration increase with Gd3+ ions doping (for x=0.1 to x=0.3) and then decrease for x=0.4, whereas the g value shows the reverse trend for the same composition. IR spectra shows two strong absorption bands at 570cm−1 and 416cm−1 of tetrahedral and octahedral bond stretching respectively in all the samples. IR spectrum also shows that Gd3+ occupies the octahedral B-sites. Magnetic parameters such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) were measured by search coil method. The value of saturation magnetization increases from 29.94emu/gm for x=0.1 to 46.01emu/gm for x=0.4.

Self-ignited synthesis of Mg–Gd–Mn nanoferrites and impact of cation distribution on the dielectric properties

Mg0.9Mn0.1GdxFe2−xO4 nanoferrites were processed for the first time by a solution combustion technique. X-ray diffraction studies revealed the spinel cubic structure of the synthesized ferrites. The particle size was observed to increase (13–16nm) with an increase in Gd3+ ion content. The cation distribution is inferred from the X-ray diffraction. It is observed from cation distribution that Gd3+ ions preferred octahedral (B) sites. The DC resistivity was found to be increasing with an increase in Gd3+ content. The dielectric constant ε′ and loss tangent (tan δ) was observed to decrease with the addition of Gd3+ content as well as with the increase in frequency. The variations in DC resistivity as well as dielectric constant with the increasing substitution of Gd3+ ions have been correlated to the cation distribution. The very high values of DC resistivity (~108Ωcm) and low values of loss tangent (0.9–0.008) are the prime achievements of this work.

Sensitization of Gd3+ ions by Tb3+ ions in Tb3+ doped (La, Gd)PO4

The role of Tb3+ ions, with respect to efficient energy transfer, on sensitization of Gd3+ ions in (La,Gd)PO4 has been investigated. A series of Tb3+ doped (La, Gd)PO4 were characterized by steady state spectroscopy and efficient energy transfer from Tb3+ 4f75d to Gd3+ 4f7 states was observed. The decay curves of Gd3+6P7/2 and Tb3+5D3, 5D4 states upon Tb3+ 4f75d and Gd3+6IJ states excitation were also performed to reveal the energy transfer processes. With the increase of Gd3+ concentration, the energy transfer efficiency increase accordingly. Based on steady state spectra, around 73% energy transfer efficiency in Gd0.99Tb0.01PO4 was determined.

Luminescence properties of YAG:Ce, Gd phosphors synthesized under vacuum condition and their white LED performances

Modified YAG:Ce, Gd phosphors were synthesized by vacuum solid-state reaction. With the increase of Gd3+ concentration, the emission spectra of YAG:Ce, Gd phosphors shifted greatly to longer wavelength. At 400 K, YAG:Ce, Gd phosphors with 20 at.% Gd3+ could maintain 78% of room temperature intensity. Within the maximum junction temperature of a high brightness LED (around 400 K), the color coordinates of phosphors changed very little. In addition, white LEDs with a color rendering index of 82, luminous efficiency of 109 lm/W and color temperature of 5656 K were achieved by using optimized YAG:Ce, Gd phosphors.

Excited state dynamics of Gd3+ and energy transfer efficiency from Gd3+ to Tb3+ in (La, Gd)PO4:Tb3+

Energy transfer processes from Tb3+ 4f75d state to Gd3+ 4f7 state and from Gd3+6P7/2 state to Tb3+ 4f8 state occur in La0.99−xGdxTb0.01PO4 under Tb3+ 4f75d state excitation. The decay of Gd3+6P7/2 state upon Tb3+ 4f75d state excitation is faster than that upon Gd3+6IJ state excitation when Gd3+ concentration is lower than 30mol%. A model describing different decay properties of Gd3+6P7/2 state was established and corresponding semiquantitative analysis was given. It was observed that the energy transfer efficiency from Gd3+ to Tb3+ was increasing with increase of Gd3+ concentration and an efficiency of close to 100% in Gd0.99Tb0.01PO4 was determined.

Effect of Gd3+ on dielectric and magnetic properties of Y3Fe5O12

The Gd3+ doped Y3−xGdxFe5O12 (x=0.0, 0.05, 0.15, and 0.25) nanopowders were prepared using modified sol–gel route. The structural characterizations such as X-ray diffraction, transmission electron microscopy has been carried out. The nanopowders were sintered at 700°C/3h. The lattice parameters and density of the samples were increased with an increase of Gd3+ concentration. The microstructure was analyzed using atomic force microscopy. The room temperature dielectric (ε′ and ε″) and magnetic (μ′ and μ″) properties were measured in the frequency range 5–50GHz. with Gd3+ the dielectric properties were enhanced, but there is a decrease in the magnetic properties. The room temperature magnetization studies were carried out up to 1.5T. the saturation and remnant magnetization were decreased with an increase of gadolinium concentration. These garnets have low permeability, low losses and a broad distribution of FMR line width which makes them a promising material for microwave devices can be used in the high frequency range i.e. up to 50GHz.

Luminescence properties and energy transfer of Gd3+, Mn2+ co-doped cubic NaYF4 nanocrystals

NaYF4 co-doped with Gd3+ and Mn2+ nanocrystals were synthesized by a solvothermal route with PEI as the surfactant. X-ray diffraction analyses evidenced that the phases of synthesized NaYF4: Gd3+, Mn2+ nanocrystals were all pure cubic structure. The luminescence intensity of 20mol% Gd3+ doped NaYF4 was stronger than that of any other concentration under the 272nm excitation. The photoluminescence emission intensity of NaYF4: Gd3+, Mn2+ at 561nm was increased with the increase of Gd3+ doping concentration. The energy transfer mechanisms between Gd3+ and Mn2+ were discussed. The results showed that the energy level of 6PJ of Gd3+ ions played a key role in the energy transfer process. Furthermore, the Mn2+ ions doped NaYF4: Gd3+ nanocrystals with a strong green emission and proper paramagnetism originated from Gd3+ and Mn2+ may find potential applications in bio-probes and magnetic resonance imaging.