Increasing Gd Content Research Articles

Influence of Gd+3 incorporation on ethanol sensing properties of Barium Stannate microrod films prepared by coprecipitation method

Ethanol sensing is an important area of research given its relevance to human health, traffic control and various industries. Metal oxide semiconductor nanostructures are most commonly used as gas sensors. In this study, enhanced ethanol sensing properties were obtained by incorporation of Gd3+ ions into Barium Stannate (GBSO), a bimetallic oxide microrods prepared through a simple co-precipitation method. The GBSO films, when exposed to ethanol, showed that incorporation of Gd improved the sensing response till 3 wt% of Gd (3GBSO) loading while further increase in Gd content resulted in reduced response. 3GBSO sample showed response as high as 76 to 500 ppm of ethanol vapor at an operating temperature of 220 °C along with a very low detection limit of 0.1 ppm (response of 1.5). Good repeatability and moderate stability were also observed suggesting its potential as low-cost ethanol sensor. Significant increase in both specific surface area as well as oxygen content (as measured by x-ray photoelectron spectroscopy) was observed in 3GBSO sample compared to that of BSO. Thus, we showed that incorporation of Gd improved the surface area of BSO microrods and in turn the surface adsorption of oxygen which led to their enhanced response to ethanol.

Simultaneously improving strength and ductility of AZ91-type alloys with minor Gd addition

The microstructure and mechanical properties of as-cast AZ91 + xGd (x = 0, 0.1, 0.3 and 0.5 wt%) alloys were investigated in this work. The results showed that the α-Mg grains and Mg17Al12 particles were significantly refined with minor Gd addition. This was because that the addition of Gd resulted the formation of Al8Mn4Gd phase, which can act as the heterogeneous nucleation site for the α-Mg grains and Mg17Al12 particles. Besides, the Al8Mn4Gd phase were spherical and dispersed in the matrix. With the increase of Gd content, the tensile strength and ductility were improved simultaneously, which was attributed to the grain refinement strengthening and second-phase strengthening. During tensile test, the cracks initiated from the Mg17Al12 and Al8Mn5/Al8Mn4Gd particles, from which the cracks propagated into the Mg matrix. The fracture mode changed from the cleavage fracture in as-cast AZ91 alloy to the ductile fracture in Gd-containing AZ91 alloys.

Change in structural, ferroelectric, and magnetic properties of bismuth ferrite induced by doping with gadolinium

Abstract Bismuth ferrite, BiFeO3, was doped with a wide range of concentrations (0–30%) of Gd in order to investigate structural, ferroelectric, and magnetic properties and their correlation. Powder samples of Bi1-xGdxFeO3 (x = 0.00–0.30) were prepared using the hydro-evaporation synthesis method. Sintering process at 870 °C for 6 h of as-prepared, Gd doped BiFeO3 powders resulted in ceramic samples with relative densities in the range of (74–86) %. XRD analysis revealed that Bi1-xGdxFeO3 samples (x = 0.00–0.09) crystallized in rhombohedral phase; Bi1-xGdxFeO3 samples (x = 0.10–0.20) contained both rhombohedral and orthorhombic phases, while Bi1-xGdxFeO3 (x = 0.30) sample contained only the orthorhombic phase. The structural parameters obtained after Rietveld refinement for single-phase Bi1-xGdxFeO3 ceramic samples and microstructure image analysis were correlated with the results of ferroelectric and magnetic measurements. Bi1-xGdxFeO3 (x = 0.0625, 0.075, 0.09) samples showed improved ferroelectric properties and reduced leakage current density in comparison with undoped BiFeO3. Gradual increase in Gd content in BiFeO3 led to enhanced magnetic responses and weak ferromagnetic behavior.

Mechanical and Corrosion Properties of Mg-Based Alloys with Gd Addition.

Magnesium alloys with rare earth metals are very attractive materials for medical application because of satisfactory mechanical properties. Nevertheless, low corrosion resistance is an obstacle in the use of Mg alloys as resorbable orthopedic implants. The paper presents results of mechanical and corrosion properties of MgCa5-xZn1Gdx (x = 1, 2, and 3 wt. %) alloys. Based on the microscopic observations it was stated that the studied alloys show a dendritic microstructure with interdendritic solute rich regions. The phase analysis reveals an occurrence of α-Mg and Mg2Ca, Ca2Mg6Zn3 phases that are thermodynamic predictions, and stated Mg26Zn59Gd7 phases in MgCa5-xZn1Gdx (x = 1, 2, and 3 wt. %) alloys. The Mg26Zn59Gd7 phases are visible as lamellar precipitations along interdendritic regions. It was confirmed that an increase of Gd content from 1 to 3 wt. % improves ultimate tensile (Rm; from 74 to 89 MPa) and compressive strength (Rc; from 184 to 221 MPa). Moreover, the studied alloys are active in Ringer’s solution. They are characterized by an increase of corrosion potential (Ecorr) of about 150 mV in comparison with values of open circuit potential (EOCP). The best electrochemical parameters (e.g., corrosion current density, icorr, polarization resistance, Rp, and Ecorr) were obtained for the MgCa3Zn1Gd2 alloy.

Effects of Thermal Exposure on the Microstructure and Mechanical Properties of Al-Si-Cu-Ni-Mg-Gd Alloy

The present study focused on the effect of thermal exposure on the phase evolution and properties of the cast-T6 Al-12Si-4Cu-2Ni-0.8Mg-xGd (x = 0, 0.1, and 0.2) alloy used for cast piston.The thermal stability of the alloys was studied in the temperature range of 200-300 °C for exposure duration up to 500 h, thus obtaining the relationship between the microstructural evolution and its impact on the mechanical properties. The fine Al2Cu phase grew into the coarse θ-Al2Cu phases during the thermal exposure, resulting in a decrease in the mechanical strength of the alloy. The thermal stability and stiffness of the Al-Si-Cu-Ni-Mg alloys were improved with the increase in Gd content from 0 to 0.2%.

Effect of minor content of Gd on the mechanical and degradable properties of as-cast Mg-2Zn-xGd-0.5Zr alloys

RE-containing Mg alloys used as biodegradable medical implants exhibit good promising application due to their good mechanical properties and degradation resistance. In this work, effect of Gd on the microstructure, mechanical properties and biodegradation of as-cast Mg-2Zn-xGd-0.5Zr alloys was investigated. The results showed that there were mainly α-Mg, I-phase, W-phase and MgZn2 phase in Mg-Zn-Gd-Zr alloys. With increase of the Gd content, the strength of the alloys was enhanced due to the second phase strengthening and grain refinement. The degradation resistance of Mg-2Zn-0.5Zr alloy was increased by adding 0.5%–1% Gd due to the uniformly distributed second phases which acted as a barrier to prevent the pitting corrosion. However, increasing Gd content to 2% reduced the degradation resistance of the alloy due to the galvanic corrosion between the matrix and the second phases. The good degradation resistance and mechanical properties of as-cast Mg-2Zn-1Gd-0.5Zr alloy makes it outstanding for biomaterial application.

Effects of Gd solutes on hardness and yield strength of Mg alloys

Relative contribution of individual strengthening mechanisms to the yield strength of Mg–0–15 wt% Gd alloys were investigated. Alloys with different grain size were prepared by adding Zr and hot extrusion. Hardness and tensile/compression yield strength were tested on the alloys after solid solution treatment and extrusion. Hall-Petch constants were calculated with hardness and tensile/compressive data. The results showed that the hardness of Mg–Gd alloys with similar Gd content and different grain size were almost the same, which indicates that grain size had little effect on hardness. The hardness linearly increased with rising Gd content (dHv/dc ≈ 25 kg mm−2/at%Gd). The tensile and compressive yield strengths enhanced with the increase of Gd content for all alloys in different conditions. In addition, the tensile/compressive (t/c) yield asymmetry of extruded alloys decreased with increasing Gd content. Large t/c yield asymmetry ratio (1.77) was observed for pure Mg, and with increasing Gd content this value decreased to 1. With the increasing of tensile strength, the stress intensity factor, ky, decreased from 0.27 MPa m1/2 for Mg–2 wt% Gd alloy to 0.19 MPa m1/2 for Mg–5 wt% Gd alloy, then increased to 0.29 MPa m1/2 for Mg–15 wt% Gd alloy. However, ky increased linearly form 0.16–0.31 MPa for compression test. The influence of grain size strengthening was eliminated, and the yield strength of tension and compression both linearly increased with cn, where c is the atom concentration of Gd, and n = 1/2 or 2/3.

Martensite Transformation and Mechanical Properties of Polycrystalline Co-Ni-Al Alloys with Gd Doping

In order to improve the mechanical properties and phase transition temperature, the influence of Gd doping on the microstructure, phase transition temperature and mechanical properties of Co35Ni32Al33 alloy was investigated. The results show that the γ+β phase was observed in the microstructure of the sample with less Gd doping and the γ phase+martensite was found with more Gd content. The phase transition temperature apparently increases with Gd doping and the phase transition temperature goes over room temperature when the Gd is 3 at.% or more. With increasing Gd doping, more γ phase appears in the sample which results in decrease in hardness. The compressive strength decreases from 2274 to 1630 MPa and the ductility increase from 4.2 to 12.9% with increasing Gd content.

Enhancement of Néel temperature and electrical resistivity of Mn–Ni–Zn ferrites by Gd3+ substitution

Structural, magnetic, and dielectric properties of various Mn0.5Ni0.1Zn0.4Fe2−xGdxO4 sintered at 1200°C were investigated thoroughly. The samples were synthesized by standard solid state reaction technique. The crystal structure was characterized by X-ray diffraction (XRD), which has confirmed the formation of single phase spinel structure. Bulk density, average grain size and initial permeability are found to decrease with increasing Gd content. For Gd substituted compositions, the value of Néel temperature is found to increase considerably, about 200°C higher than that of the parent composition. The value of magnetic loss and dielectric loss are observed to decrease with the substitution of Gd3+ for the frequencies greater than 0.54MHz and 10kHz respectively. It is found that the AC resistivity (ρac) increases with the substitution of Gd3+ and the highest value of ρac is observed for the composition with x=0.03, about 600 times greater than that of parent composition.

Effect of the Size of the Dopants on the Dielectric and Magnetic Properties of Bi(La,Gd)FeO<sub>3</sub> Multiferroic Materials

Gd and La codoped multiferroics with the formula Bi(La,Gd)FeO3(0%≤La≤10%; 0%≤y≤10%) have been synthesised by low temperature sol gel method. XRD analyses confirm the phase formation of all the samples. The decrease in the intensity and shifting of (104) and (110) diffraction peaks of the doped samples towards the higher 2θ region confirms the lattice shifting with the addition of La and Gd but still exhibits perovskite structure. FTIR studies show the presence of the necessary bonds in the samples. Dielectric properties such as dielectric constant, ε' and dielectric loss, tanδ were studied as a function of frequency and compositions of La and Gd. The dispersive behaviour of both ε' and tanδ are explained in accordance to the double mechanism of grain and grain boundaries. However, the actual amount of contributions made by the grains and grain boundaries to the dielectric response and total resistance are not yet discussed. Enhanced dielectric constant and reduced loss factor has been observed with increasing Gd content (decreasing La content). Magnetic measurements of all the samples show an increment in the values of both coercivity (HC) and saturation magnetisation (MS) with the increase in Gd dopant (decrease in La dopant). The modification of the structural, dielectric and magnetic properties of the doped samples was explained on the basis of the size effect of the dopants.

Luminescence and scintillation characteristics of (GdxY3-x)Al2Ga3O12:Ce (x = 1,2,3) single crystals

The luminescence and scintillation characteristics of Czochralski-grown (GdxY3-x)Al2Ga3O12:Ce (x = 1,2,3) single crystals are presented. With increasing Gd content in this garnet host, the 5d2 absorption band was blue-shifted while the 5d1 absorption and 5d1 → 4f emission bands were red-shifted due to an increase in the crystal field splitting of the 5d levels. In addition, the luminescence quenching temperature of the Ce3+emission and activation energy for thermal quenching decreased with increasing Gd content. The Gd3+ → Ce3+ energy transfer was evidenced by photoluminescence excitation spectra of Ce3+ emission. At 662 keV γ - rays, the light yield (LY) of 48,600 ph/MeV and energy resolution of 6.5% was measured for a Gd3Al2Ga3O12:Ce crystal. Scintillation decay measurements were performed using the time-correlated single photon counting technique. Superior time resolution of Gd3Al2Ga3O12:Ce is due to its high LY and fast scintillation response. The total mass attenuation coefficients at 60 and 662 keV γ - rays were also determined.

Low temperature synthesis and manifestation of the structural, dielectric, magnetic and optical properties of Bi(Gd)FeO[formula omitted] nanoparticles

Gd doped multiferroics with the compositional formula Bi1−xGdxFeO3 (x=0.0, 0.05, 0.075, 0.10, 0.15, 0.20) (BGFO) have been prepared by low temperature sol gel method. Characterisations were carried out by using XRD, FESEM, EDAX and FTIR studies. Rietveld analysis of the XRD data reveals the structural transformation from rhombohedral to orthorhombic phase beyond x=0.10 Gd concentration. Dielectric properties such as dielectric constant (ε′) and loss factor (tanδ) of the samples were studied as a function of frequency and Gd concentration. Enhanced dielectric constant and reduced loss factor have been observed in the Gd doped samples as compared to the undoped sample. Room temperature M–H loop of all the samples show enhanced magnetisation with the increase in Gd content upto x=0.10 and then decreases. The decrease in the values of energy band gap with the increase in Gd content enhances the optical absorption capability in the range of visible spectrum. Explanation of the above results and the various possible applications were highlighted.

Effect of Gd on physics properties of the dual-phase Ni–Mn–Ga-based alloys

ABSTRACTThe microstructure, martensitic transformation (MT) and shape memory effect (SME) of the dual-phase Ni58Mn25Ga17−xGdx (x = 0, 0.1, 0.2, 0.5, 1) alloys have been investigated. The results show that the refined the grain size and adjust the distribution of γ phase by added rare earth Gd in the Ni58Mn25Ga17−xGdx alloys. With increasing Gd content, the MT temperatures of Ni58Mn25Ga17−xGdx alloys first gradually decrease and then increase with the increasing content of Gd, reaching their minimum values when the content of Gd is 0.5 at.-%. In addition, the Ni58Mn25Ga16.9Gd0.1 has a SME of 5.1% owing to the favourable γ phase distribution, which is mainly attributable to the γ phase grain refined and weaken resistance of reverse MT.

Dielectric, magnetic and optical properties of (Bi,Gd)FeO3- Ni0.8Zn0.2Fe2O4 nanocomposites

Bi1−xGdxFeO3 (x = 0.00, 0.05, 0.075, 0.10, 0.15, 0.20) (BGFO) and Ni0.8Zn0.2Fe2O4 (NZFO) exhibiting ferroelectric and ferromagnetic phases were synthesized independently by sol gel and auto combustion method respectively. Equal weight proportions were mixed to obtain the multiferroic nanocomposites having the compositional formula 0.5BGFO-0.5NZFO. Rietveld analysis shows the mixing of the constituent phases in the two-phase mixture and confirms the structural transformation of the ferroelectric component from perovskite to the orthorhombic phase when the concentration of Gd addition exceeds x = 0.10 concentration. SEM micrographs of the samples show uniform grain distribution with decreased grain size upto x = 0.10 Gd content and then increases. FTIR studies show the stretching and bending vibrations of the various bonds present in all the samples. Dielectric constant, ε′ and dielectric loss tangent, tanδ measurements shows the dispersion with enhanced behavior with the increase in Gd content. Room temperature M-H loop measurements of all the samples exhibit enhanced magnetization upto x = 0.10 concentration and follow a reducing trend thereafter. Optical absorbances of all the samples were measured and the energy band gaps were calculated from Tauc's plot. The reduction in the values of energy band gap with the increase in Gd addition enhances the optical absorption capability in the visible range. The enhancement in the dielectric, magnetic and optical properties of the nanocomposite samples simultaneously has proved its viability in various applications, making it a new technological ingredient for future smart materials.

Top-seeded infiltration growth of (Y, Gd)Ba2Cu3Oy bulk superconductors with high critical current densities

We employed the top-seeded infiltration-growth (IG) process for the fabrication of bulk (Y, Gd)Ba2Cu3Oy (YG-123) superconductors by varying the composition of (Y, Gd)2BaCuO5 (YG-211) and compared with bulk YBa2Cu3Oy (Y-123) superconductors grown under similar conditions. IG-processed YG-123 exhibited Jc (77 K) of 4.78 × 104 A cm−2 in zero field, which was higher than the value of 3.71 × 104 A cm−2 for Y-123. The superconducting transition temperature (Tc) of YG-123 increased with increasing Gd content. However, there was spatial variation in the superconducting properties of IG-processed YG-123 samples due to the inhomogeneous distribution of YG-211. Jc values of YG-123 decreased when increasing the distance from the seed both along the a and c-axis directions. The scaling studies of the pinning behavior for YG-123 showed that non-superconducting YG-211 particles act as effective pinning centers, supported by the fact that δTc type pinning is active in the system.

Investigations on the microstructure, mechanical, corrosion and wear properties of Mg–9Al–xGd (0, 0.5, 1, and 2 wt%) alloys

Abstract

Influence of Gd-content on the electrical transport properties of La0.67−x Gd x Sr0.33MnO3 polycrystalline ceramics by sol–gel method

Polycrystalline perovskite manganites La0.67−x Gd x Sr0.33MnO3 (x = 0.15, 0.20, 0.25, 0.30, 0.35, and 0.40) were prepared by sol–gel method. The crystal structure examined by X-ray powder diffraction indicates that the samples were single phase and crystallize in a rhombohedral structure with increasing Gd content. The grain size and surface morphology were investigated by scanning electron microscope, which reveals that that all the ceramic samples with better crystallization have high density. The relation between resistivity and temperature studied by the standard four-probe method shows that the metal–insulator transition temperature (T P) shifts to the lower temperature and temperature coefficient of resistivity decrease with increasing Gd doping. It is mainly due to Gd doping decreases the A-site average cationic radius 〈r A〉 and thus the Mn3+–O–Mn4+ angle decrease, which result in the reduction of double exchange between Mn3+ and Mn4+.

The Combined Influence of Gadolinium Doping and Non-stoichiometry on the Structural and Electrochemical Properties of Uranium Dioxide

The influence of Gd-doping level and oxygen stoichiometry on the structural properties and electrochemical reactivity of U1−yGdyO2±x have been investigated. The stoichiometry of UO2 matrices with different Gd contents was determined using the lattice parameter obtained by XRD. The extent of lattice contraction, defined by a contraction factor, was found to be dependent on the stoichiometry. The surface morphologies exhibited differences in grain size which varied with stoichiometry and its influence on the U atom diffusivity during fabrication. The differences in grain size and, hence, the density of grain boundaries was reflected in variations in electrical conductivity, with hyperstoichiometric specimens with a low number of boundaries, yielding an increase in conductivity with increasing Gd content. Cyclic voltammetry showed that a variation in Gd content had only a minor influence on the electrochemical reactivity of stoichiometric U1−yGdyO2. By contrast, the reactivity of hypostoichiometric U1−yGdyO2−x and hyperstoichiometric U1−yGdyO2+x increased and decreased, respectively, with increasing Gd content. The formation of Gd-Ov clusters in hyperstoichiometric U1−yGdyO2+x has a more marked influence on reactivity than the accompanying changes in grain size and electrical conductivity.

Reducing the Gadolinium Dopant Content by Partial Substitution with Yttrium in a Ce0.9Gd0.1O1.95-based Oxide-Ion Conductor

Because of its high oxide-ion conduction and the chemical inactivity, Ce1-xGdxO2-δ fluorites are used as a reaction protection layer between the electrode and the ZrO2 electrolyte and addition materials to electrode elements for intermediate-temperature SOFCs. The rare-earth ores have 17 kinds of rare-earth elements including Sc and Y. However, Gd exists a low mineral content in the ores. Gadolinium element is used as magnetic devices, magnetooptic disk device, and control rod of the nuclear reactor. Under the present conditions, demand for Gd increases. The conductivity and sintering characteristics are very important as SOFC components and it is well known that two typical compositions, Ce0.9Gd0.1O1.95 and Ce0.8Gd0.2O1.9, have be commercially available. Although many papers for the properties have been reported, the appropriate compositions of Gd are unclear. The reason for this is that the properties are strongly affected by synthesis methods and sintering conditions. In the present study, the appropriate compositions of Gd-doped cerias with a Gd content of 0 ≤ x ≤ 0.2, which were prepared using the conventional co-precipitation method, have been discussed from the viewpoint of sintering characteristics, electrical conductivity and its long term stability. Sintering characteristics of the doped ceria samples have a tendency to decrease with increasing Gd content. The maximum conductivity of 2.56×10-2 S/cm at 600ºC was observed for the sample with 10 mol% Gd dopant. During the annealing process at 600ºC, the conductivity decreased with annealing time due to the grain-boundary resistance. The synchrotron X-ray diffraction analysis showed to be Gd2O3 phase in the fluorite and the decrease of lattice parameter. These results suggest that the decrease of the conductivity should be related to the segregation of Gd element at the grain-boundary of the Ce0.9Gd0.1O1.95 fluorite.

Microstructural evolution, phase constitution and mechanical properties of directionally solidified Mg-5.5Zn-xGd (x = 0.8, 2.0, and 4.0) alloys

The microstructural evolution, phase constitution and mechanical properties of directionally solidified Mg-5.5Zn-xGd (x = 0.8, 2.0, and 4.0) alloys were firstly investigated under G = 30 K/mm at a wide range of V (10 μm/s - 100 μm/s). It was confirmed that there existed α(Mg) + I(Mg3Zn6Gd) in Mg-5.5Zn-0.8Gd alloy, and α(Mg) + I(Mg3Zn6Gd) + W(Mg3Zn3Gd2) in Mg-5.5Zn-(2.0, 4.0)Gd alloys, respectively. The criterion growth rate for cellular-columnar dendrite transition (CDT) for Mg-5.5Zn-xGd alloys decreased with the increase of Gd content. The relationships between the microstructural parameters (λ1, λ2) and V for Mg-5.5Zn-xGd alloys were established using a linear regression analysis. The values of λ1 and λ2 decreased exponentially with the increase of V and the exponent values were found to be close to the theory values of 1/4 and 1/3, respectively. The tensile test showed that the room temperature ultimate tensile strength (UTS) increased and the elongation decreased with the increase of the growth rate for a certain composition of Mg-5.5Zn-xGd alloy. For a certain growth rate, UTS first increased from 0 wt % to 2.0 wt % of Gd content, and then decreased with the further increase of Gd content. The directionally solidified Mg-5.5Zn-2.0Gd experimental alloy showed the maximum ultimate tensile strength.