Gd Doping Concentration Research Articles

Fe3O4-TiO2: Gd nanoparticles with enhanced photocatalytic activity and magnetic recyclability

In this study, photocatalytic Fe3O4-TiO2: Gd berry-like pseudo-core-shell (BL-PCS) nanoparticles with various Gd doping content for wastewater treatment were prepared. Their characteristics were evaluated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS). The results show that Gd3+ ions are incorporated in the TiO2 lattice. A secondary phase of FeTiO3 was observed for undoped and low Gd doping level, phase which is no longer present for high doping content. By TEM and XPS depth profile analysis it was showed that a BL-PCS structure is formed. All the samples have superparamagnetic behavior. The optimum concentration of Gd dopant which assures the best photocatalytic performance on the RhB degradation under visible light irradiation was obtained. The photocatalytic degradation was examined by varying the operational parameters such as: catalyst amount and irradiation time. The photocatalyst can be easily separated from solution due to its magnetic component and presents a good stability with a minor loss of efficiency after 4 repeated cycles. According to the analysis of the reaction intermediates and final products, a mechanism of photodegradation was proposed. Additionally, electron paramagnetic resonance (EPR) study on the ability of Fe3O4-TiO2: Gd to generate reactive oxygen species was conducted and shows that hydroxyl radical and superoxide anion radical are generated under light irradiation, radicals which are involved in the photocatalytic process.

Effect of Gd3+ Ions on the Thermal Behavior, Optical, Electrical and Magnetic Properties of PbS Thin Films

This paper reports the effect of Gd doping concentration on the thermal behavior, structural, morphological, optical, electrical and magnetic properties of PbS thin films. Gd doping concentration in PbS was varied as 0 wt.%, 1 wt.%, 2 wt.%, 3 wt.% and 4 wt.%, respectively. Thermogravimetric–Differential Thermal Analysis curves confirm that both the undoped and doped films become well crystallized above 354°C and 342°C, respectively. X-ray diffraction studies confirm that all the films exhibit face-centered cubic crystal structure with a strong (2 0 0) preferential growth. Undoped films exhibit triangular-shaped grains which modify to small cuboids with Gd doping. Energy dispersive x-ray spectra confirm the presence of Gd in the doped films. Transmission electron microscopy images confirm the presence of nanosized grains for both the undoped and doped films. The doped films showed increased transparency and improved magnetic behaviour. The results obtained confirm that Gd3+, a rare earth ion, strongly influences the physical properties of PbS thin films to a large extent.

Gadolinium-doped strontium titanate for high-efficiency electromagnetic interference shielding

Sr1-xGdxTiO3-δ(x = 0, 0.05, 0.1, 0.15, 0.2) ceramics were prepared by hot-pressing process in vacuum successfully for electromagnetic interference (EMI) shielding applications. The microstructure, phase composition, compensation mechanism, electrical conductivity and EMI properties were analyzed respectively. The result shows that there are oxygen vacancies in Sr1-xGdxTiO3-δ ceramics. What's more, with the Gd doping content increased the concentration of oxygen vacancy decreases. EMI result shows total EMI shielding effectiveness (SE) SEtotal of all the Sr1-xGdxTiO3-δ ceramics is greater than 21 dB in the whole frequency range of 8.2–12.4 GHz with a 1.5 mm thickness, which suggests that the Sr1-xGdxTiO3-δ ceramics could be good candidates for EMI shielding materials in the measured frequency region.

Effect of Gd3+ doping on key structural, morphological, optical, and electrical properties of CdO thin films fabricated by spray pyrolysis using perfume atomizer

Gadolinium-doped cadmium oxide (CdO) thin films were fabricated by spray pyrolysis technique using a perfume atomizer on the glass and silicon substrates at 350 °C. The effect of increasing Gd concentration on the electrical, morphological, optical, and structural properties of deposited films was analyzed. Structural analysis of the pristine and doped CdO thin films showed cubic structures with preferred orientation of (200) direction. The estimated crystallite values ranged from 15 to 21 nm. The structural parameters like dislocation density, microstrain, a number of crystallites per unit area, and texture coefficient were also studied. Scanning electron microscope (SEM) images showed uniformly oriented and cauliflower-like nanostructures grown on the glass substrate for 3at.%-doped CdO films. The doped films' optical transmittance is found to be initially increased and systematically decreased with respect to doping concentrations. The band gap value is in the range of 2.42–2.30 eV for various Gd-doping concentrations (0, 1, 3, and 5%), respectively. The photoluminescence spectra (PL) of films were studied at room temperature and confirms the visible and green emission’ peaks are at wavelength 463 and 528 nm, respectively. From the Hall Effect studies, it proved that all the CdO films belong to an n-type degenerate semiconductor, and the low electrical resistivity value was around 3.64 × 10−4 Ω cm. The n-CdO/p-Si structure with different doping concentrations was subjected to photoconductivity studies and found that it is the maximum of 3% Gd concentration. Higher values of photo responsivity and quantum efficiency was found ~365 mA/W and ~76.64%, respectively, for 3at.% Gd-doped CdO films.

Modulation of the Dielectric Properties of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> System with Gd-Substitution

To specify the effects of modulating mechanism of Gd substitution on the dielectric properties for Ca1-xGdxCu3Ti4O12 system, the XRD, SEM and positron positron annihilation technique have been implemented. The results display that both grain size and vacancy-type defect concentration play important roles in controlling the dielectric properties of CaCu3Ti4O12. The dielectric properties are improved by adding an appropriate amount of Gd additives (x=0.01) but weakened by higher Gd doping content since this is closely related to the grain size and concentration of vacancy-type defect in the samples.

Effect of Gd doping concentration and sintering temperature on structural, optical, dielectric and magnetic properties of hydrothermally synthesized ZnO nanostructure

Abstract Nanoparticles of Gd 3+ ions doped ZnO were prepared by hydrothermal method. To obtain the desired nanocrystalline phase and also, to enhance the oxygen vacancy inside the host ZnO nanoparticles, the as prepared sample is sintered at 400 and 600 °C for 2 h in vacuum atmosphere. X-ray diffractograms (XRD) analysis reveals the absence of any impure phases in the Gd 3+ ions doped ZnO nanostructure. The presence of intrinsic defects/oxygen vacancies were confirmed by the analysis of UV–Visible, PL and Raman spectra of the doped sample. The qualitative and quantitative analysis of intrinsic defects was successfully explained by three-state trapping model using positron annihilation study. Room temperature ferromagnetism was found in the sample of 5% Gd 3+ ions doped ZnO, which has been successfully explained by the vacancy assisted bound magnetic polaron model. Frequencies as well as temperature dependent dielectric constant of the samples were investigated. The dielectric constants were recorded at 40 Hz and 100 kHz frequencies and the values are nearly ∼2.76 х 10 6 and 12782 respectively, in the 5% Gd 3+ ions doped ZnO sample.

Effect of Gd doping on the structural, optical band-gap, dielectric and magnetic properties of ZnO nanoparticles

Nanostructured Zn1−xGdxOδ (0≤x⩽0.02) powders were synthesized by the combustion reaction method (CR) with the purpose to investigate the effect of Gd doping on the structural, optical band-gap, dielectric and magnetic properties at room temperature. The structure and morphology of all samples were characterized by X-ray diffraction (XRD), and transmission electron microscope (TEM). The XRD patterns of all samples exhibited sharp and intensive peaks of hexagonal wurtzite structure of ZnO without any evidence of spurious crystalline phases. The nanoparticles crystalized in roughly spherical morphology with bimodal particle size distribution centered at ∼30, ∼100 and ∼70, ∼160nm for undoped and Gd – doped ZnO (x=0.02), respectively. Diffuse reflectance spectrum of each sample was obtained by using a UV/VIS/Near spectrometer and the optical band-gap, Eg, values decreased with increasing Gd doping concentration; being ∼3.23, and ∼3.17eV for x=0 and 0.02, respectively at room temperature. This red shift on the band-gap was discussed in terms of new band levels below the conducting band. Also, the dielectric permittivity data of all samples could be evaluated by the Cole– Cole model. Seems that both oxygen vacancies (VO) or/and interstitial oxygen (O″ı¨) defects present in the Gd – doped ZnO samples play an important rule in the dielectric permittivity at room temperature. Furthermore, all Gd – doped ZnO samples exhibited typical paramagnetic behavior at rom temperature.

EXAFS studies on Gd-doped ZrO2 thin films deposited by RF magnetron sputtering.

ZrO2 thin films with 0%, 7%, 9%, 11%, and 13% Gd doping have been prepared by RF magnetron sputtering and have been characterized by grazing incidence x-ray diffraction, spectroscopic ellipsometry, and optical transmission measurements to probe their structural and optical properties. Extended x-ray absorption fine structure (EXAFS) measurements have also been carried out on the samples at the Zr K- and Gd L3-edges. It has been observed that Gd goes to Zr sites up to 9%-11% doping concentration, and for Gd doping concentrations beyond 11%, Gd precipitates out as a separate Gd2O3 phase. The local structure information surrounding the Zr and Gd sites obtained from the analysis of the EXAFS studies have also been used to explain the macroscopic optical properties of the samples.

Enhanced visible light photocatalytic activity of Gd-doped BiFeO3 nanoparticles and mechanism insight.

To investigate the effect of Gd doping on photocatalytic activity of BiFeO3 (BFO), Gd-doped BFO nanoparticles containing different Gd doping contents (Bi(1−x)GdxFeO3, x = 0.00, 0.01, 0.03, 0.05) were synthesized using a facile sol-gel route. The obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, and ultraviolet-visible diffuse reflectance spectroscopy, and their photocatalytic activities were evaluated by photocatalytic decomposition of Rhodamine B in aqueous solution under visible light irradiation. It was found that the Gd doping content could significantly affect the photocatalytic activity of as-prepared Gd-doped BFO, and the photocatalytic activity increased with increasing the Gd doping content up to the optimal value and then decreased with further enhancing Gd doping content. To elucidate the enhanced photocatalytic mechanism of Gd-doped BFO, the trapping experiments, photoluminescence, photocurrent and electrochemical impedance measurements were performed. On the basis of these experimental results, the enhanced photocatalytic activities of Gd-doped BFO could be ascribed to the increased optical absorption, the efficient separation and migration of photogenerated charge carriers as well as the decreased recombination probability of electron-hole pairs derived from the Gd doping effect. Meanwhile, the possible photocatalytic mechanism of Gd-doped BFO was critically discussed.

Luminescence Enhanced Eu(3+)/Gd(3+) Co-Doped Hydroxyapatite Nanocrystals as Imaging Agents In Vitro and In Vivo.

Biocompatible, biodegradable, and luminescent nano material can be used as an alternative bioimaging agent for early cancer diagnosis, which is crucial to achieve successful treatment. Hydroxyapatite (HAP) nanocyrstals have good biocompatibility and biodegradability, and can be used as an excellent host for luminescent rare earth elements. In this study, based on the energy transfer from Gd(3+) to Eu(3+), the luminescence enhanced imaging agent of Eu/Gd codoping HAP (HAP:Eu/Gd) nanocrystals are obtained via coprecipitation with plate-like shape and no change in crystal phase composition. The luminescence can be much elevated (up to about 120%) with a nonlinear increase versus Gd doping content, which is due to the energy transfer ((6)PJ of Gd(3+) → (5)HJ of Eu(3+)) under 273 nm and the possible combination effect of the cooperative upconversion and the successive energy transfer under 394 nm, respectively. Results demonstrate that the biocompatible HAP:Eu/Gd nanocrystals can successfully perform cell labeling and in vivo imaging. The intracellular HAP:Eu/Gd nanocrystals display good biodegradability with a cumulative degradation of about 65% after 72 h. This biocompatible, biodegradable, and luminescence enhanced HAP:Eu/Gd nanocrystal has the potential to act as a fluorescent imaging agent in vitro and in vivo.

Optical and transport properties of Gd doped BaSnO3 epitaxial films

(Ba1-xGdx)SnO3 (BGSO) (x = 0–0.15) films were epitaxially grown on MgO substrates by pulsed laser deposition. Structure analysis was performed using X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. Transport properties were investigated by Hall effect and temperature dependent resistivity measurement. Results show that the film resistivity decreases systematically with increasing Gd doping concentration. The lowest room-temperature resistivity of 6.18 mΩcm was observed in film at x = 0.07, with the metal-insulator transition at 30 K, which was attributed to the formation of a degenerate band in films. Optical transmission spectra measurement shows that all the BGSO films have high transmittance of more than 80% in the visible range. The band gap variation with the Gd doping concentration was interpreted by the Burstein-Moss effect. Excellent optical and electrical properties suggest that BGSO films have potential applications in the optoelectronic devices as transparent and conducting oxide material.

Cation distribution correlated with magnetic properties of nanocrystalline gadolinium substituted nickel ferrite

Nano crystalline NiFe2−xGdxO4 (0.0≤x≤0.4) ferrite was prepared by citrate method. The samples were characterized with X-ray diffraction, FT-IR spectroscopy, TEM and magnetic measurements. The effect of Gd3+ cations substitution on structural, microstructural and magnetic properties of prepared nanoparticles was investigated. From Rietveld analysis, the system was found to be inverse spinel structure with Gd3+ residing on octahedral B-site 16c and the grain boundary, while Ni2+ occupying the B-site at both 16c and 16d. The lattice parameter (a) changes nonmonotonically, first increases then decreases with Gd doping content. The M–H and M–T relations had demonstrated a change in the magnetic moment and a ferrimagnetic–superparamagnetic transition in the ferrite system. For low temperature measurements, an increase in gadolinium content resulted in increasing the coercive field while the saturation of magnetization (Ms), first deceases then increases with Gd doping content. At room temperature Ms decreases with increasing Gd substitution.

Computational investigation of the phase stability and the electronic properties for Gd-doped HfO2

Rare earth doping is an important approach to improve the desired properties of high-k gate dielectric oxides. We have carried out a comprehensive theoretical investigation on the phase stability, band gap, formation of oxygen vacancies, and dielectric properties for the Gd-doped HfO2. Our calculated results indicate that the tetragonal phase is more stable than the monoclinic phase when the Gd doping concentration is greater than 15.5%, which is in a good agreement with the experimental observations. The dopant's geometric effect is mainly responsible for the phase stability. The Gd doping enlarges the band gap of the material. The dielectric constant for the Gd-doped HfO2 is in the range of 20–30 that is suitable for high-k dielectric applications. The neutral oxygen vacancy formation energy is 3.2 eV lower in the doped material than in pure HfO2. We explain the experimental observation on the decrease of photoluminescence intensities in the Gd-doped HfO2 according to forming the dopant-oxygen vacancy complexes.

Nanostructured GdxZn1−xO thin films by nebulizer spray pyrolysis technique: Role of doping concentration on the structural and optical properties

Nanostructured GdxZn1−xO thin films with different Gd concentration from 0% to 10% deposited at 400°C using the NSP technique. The films were characterized by structural, surface and optical properties, respectively. X-ray diffraction analysis shows that the Gd doped ZnO films have lattice parameters a=3.2497Å and c=5.2018Å with hexagonal structure and preferential orientation along (002) plane. The estimated values compare well with the standard values. When film thickness increases from 222 to 240nm a high visible region transmittance (>70%) is observed. The optical band gap energy, optical constants (n and k), complex dielectric constants (εr and εi) and optical conductivities (σr and σi) were calculated from optical transmittance data. The optical band gap energy is 3.2eV for pure ZnO film and 3.6eV for Gd0.1Zn0.9O film. The PL studies confirm the presence of a strong UV emission peak at 399nm. Besides, the UV emission of ZnO films decreases with the increase of Gd doping concentration correspondingly the ultra-violet emission is replaced by blue and green emissions.

Structural, optical and electrical properties of cerium and gadolinium doped CdO thin films

Cadmium oxide thin films doped with different concentration of cerium (Ce) and gadolinium (Gd) have been prepared by radio frequency magnetron (RF) sputtering. Thin films are deposited on glass substrates at a substrate temperature of 400°C and pressure of 0.1mbar in Ar:O2=4:1 atmosphere. The structural, optical and electrical properties of deposited film are studied. X-ray diffraction reveals that Ce and Gd doped CdO films have good crystallinity and are apt to grow on (200) orientation with increasing Ce and Gd doping concentrations. These films are highly transparent with an average transmittance over 80%. With a moderate doping (0.4at.% Ce and 0.8at.% Gd), the optical band gap (Eg) blue-shift from 2.59eV to 2.99eV. The electrical conductivity increases with increasing Ce and Gd doping concentrations, but for higher doping concentration (0.5at.% Ce and 1.0at.% Gd), the conductivity decreases. The increase in carrier concentration due to Ce and Gd doping is the main reason responsible for the increase of and conductivity and the blue shift of band gap.

Optical and electrical characterization of transparent conductive Gd‐doped AZO thin films

AbstractThe Gd‐doped Al‐doped Zn oxide (AZO) thin films are prepared and characterized in this study. The findings show that when the Gd doping concentration exceeded a threshold of approximately 3–5 wt%, the resistivity of the Gd:AZO thin film was reduced to a point that was lower than the resistivity of the pure AZO thin film. The reduction in resistivity was caused by the increase of the carrier concentration. This study proposes that the increase in carrier concentration was caused by the additional Gd3+Zn2+ substitution reaction. After performing 10 wt% Gd doping, the transmittance of the Gd:AZO thin film in the near UV region was increased. Following an annealing process at 200 °C, the transmittance of the annealed 100‐nm Gd:AZO (10 wt%) thin films was over 80% at the 375 nm wavelength, which was approximately 40% higher than that of the annealed pure AZO thin film. The 600‐nm Gd:AZO (10 wt%) annealed at 200 °C is found to have the best figure of merit value (0.24 ohm−1) at 375 nm (near UV regime) among all studied Gd:AZO (10 wt%) thin films in this study.

Effects of Gd substitution on microstructures and low temperature dielectric relaxation behaviors of SrTiO3 ceramics

In this paper, Sr1 − 3x/2GdxTiO3 ceramics (0.00 ≤ x ≤ 0.05) were prepared from powders obtained by a sol–gel method. X-ray diffraction results showed that the Gd ion substituted Sr site, and the unit cell volume of doped samples decreased with increasing Gd doping concentrations, which was due to the difference between Sr/Gd ionic radii. Moreover, the structural change also led to an increase in the antiferrodistortive transition temperature. Dielectric properties of all samples were investigated over broad temperature and frequency ranges, and four dielectric relaxation behaviors were identified in different samples. It was found that two intrinsic dielectric relaxation behaviors for the pure SrTiO3 ceramics could be gradually disappeared with increasing Gd doping concentrations, which was ascribed to the change of domain state induced by Sr vacancies. On the other hand, the other two dielectric relaxation behaviors were induced by Gd doping. The relaxation behavior with activation energy in the range of 100–130 meV was originated from oxygen vacancies, while another relaxation behavior with activation energy in the range of 200–230 meV corresponded to the thermal motions of Ti4+ ions.

Preparation of gadolinia doped ceria via metal complex decomposition method: Its application as catalyst for the steam reforming of ethane

The ceria (CeO2) and gadolinia doped ceria (GDC; Ce1−xGdxO2−δ with x=0.10, 0.15, and 0.20) catalysts were successfully prepared via metal complex decomposition method at 900°C for 2h. The synthesized CeO2 and GDC were found to have useful activity to convert ethane to syngas via the steam reforming reaction at the temperature range of 800–900°C. The catalytic activity was improved with increasing Gd doping amount from 0 to 0.1 and 0.15; nevertheless, at higher Gd doping content (0.2), the improvement becomes less pronounced. Among all catalysts, Ce0.85Gd0.15O2−δ showed the best steam reforming activity; furthermore, the amount of carbon formation over this catalyst was relatively low. These enhancements are mainly due to the high specific surface area and the good oxygen storage capacity (OSC) of the material. During the steam reforming process, the gas–solid reactions between the gaseous components presented in the system (C2H6, C2H4, and CH4) and the lattice oxygen (Ox) on the surface CeO2 or GDC occurs. The reactions of hydrocarbons adsorbed on the surface with Ox (CnHm+Ox→nCO+m/2(H2)+Ox−n) can prevent the formation of carbon species from hydrocarbons decomposition reaction (CnHm⇔nC+m/2H2). Moreover, the formation of carbon via Boudouard reaction (2CO⇔CO2+C) is also reduced by the gas–solid reaction of CO with the lattice oxygen (CO+Ox⇔CO2+Ox−1).

The increase of the spin-transfer torque threshold current density in coupled vortex domain walls

We have studied the dependence on the domain wall structure of the spin-transfer torque current density threshold for the onset of wall motion in curved, Gd-doped Ni80Fe20 nanowires with no artificial pinning potentials. For single vortex domain walls, for both 10% and 1% Gd-doping concentrations, the threshold current density is inversely proportional to the wire width and significantly lower compared to the threshold current density measured for transverse domain walls. On the other hand for high Gd concentrations and large wire widths, double vortex domain walls are formed which require an increase in the threshold current density compared to single vortex domain walls at the same wire width. We suggest that this is due to the coupling of the vortex cores, which are of opposite chirality, and hence will be acted on by opposing forces arising through the spin-transfer torque effect.

The optical properties of rare earth Gd doped ZnO nanocrystals

We present a study of the light emission properties, from UV to blue spectral region, of Gd doped ZnO nanocrystals fabricated by means of a thermal evaporation vapor phase deposition process. The samples were grown from a mixed Zn/Gd source, with a molar percentage of Gd ranging from 0% (pure ZnO) to 5%, 10%, or 15%, in a constant O2/Ar gas mixture flowing at 500°C. The pure ZnO nanocrystals exhibited a strong and predominant UV emission peaking at 375nm. Besides the UV emission of ZnO nanocrystals, two strong blue emissions, located at 432 and 397nm, are observed for the sample doped with 5% Gd. The strong blue emissions are mainly induced by the impurity levels of Gd introduced into the band gap of the ZnO nanocrystals. The UV emission of ZnO decreases as the doping concentration of Gd increases, and the blue emission is replaced by a broad defect emission due to the greater number of defects and impurities, as well as Gd2O3 on the surface. The results show that the optical properties of ZnO can be tuned by the doping concentration of Gd.