Effect Of Rare Earth Substitution Research Articles

Effect of rare earth substitution on electromagnetic and microwave absorption properties of nickel-cobalt nano ferrite

Oxygen vacancy engineering is one of the most effective strategies for tuning the microstructural properties of oxide nanomaterials. However, the connection between oxygen vacancies and electromagnetic (EM) wave absorption capacities is unclear. Herein, oxygen vacancy-boosted microwave absorption is realized over Gd-doped Ni0.5Co0.5Fe2O4 (NCFO) nanoceramics. All magnetic properties are studied with the influence of induced lattice strain. Except for Ni0.5Co0.5 Gd0.075Fe1.925O4 (NCFOG3), which has an elevated saturation magnetization (Ms) of 63 emu/g, the Ms decreases with increasing Gd content. In addition, remnant magnetization (Mr), coercivity (Hc), and anisotropic constant (K) increased until Ni0.5Co0.5 Gd0.050Fe1.95O4 (NCFOG2) and then declined. The EM wave parameters: dielectric permittivity (ϵ'), magnetic permeability (μ'), dielectric loss (ϵ''), and magnetic loss (μ'') are systematically examined and found in the ranges of 2.07–3.5, 1.73–4.7, (4 × 10-2) – (2.2 × 10-1) and 0.18–0.35 respectively. Our finding shows that a small amount of Gd favors the high oxygen vacancy concentration, an appropriate lattice defect, and high magnetic and dielectric losses. The possible mechanism for EM wave absorption revealed the largely localized electrons and dipole centers created by the numerous oxygen vacancies causing the multiple reflection and scattering, which enhanced conductive loss, defect, and dipole polarizations. The maximum reflection loss (RL) -28.37 dB is observed at 17.80 GHz of a 2 mm thick sample for NCFOG3. This research reveals a distinct link between oxygen vacancy defects and EM wave dissipation capability, providing important information for developing better EM wave absorbents.

Effect of rare earth substitution on pyroelectric, ferroelectric, and piezoelectric properties lead-free Ba0.85Ca0.12RE0.03Ti0.90Zr0.04Nb0.042O3 (RE = Ce or Pr) ceramics

Effect of rare earth substitution on pyroelectric, ferroelectric, and piezoelectric properties lead-free Ba0.85Ca0.12RE0.03Ti0.90Zr0.04Nb0.042O3 (RE = Ce or Pr) ceramics

NADİR TOPRAK KATKISININ SPİNEL FERRİTLERİN MANYETİK ÖZELLİKLERİNE ETKİSİ

Nano-size ferrites (NSF) are magnetic nanoparticles (MNPs) which have attracted great interest in the last decades owing to their high surface area-to-volume ratio, high saturation magnetization, initial permeability, etc. Nickel-copper-zinc ferrites are especially used in multi-layer chip inductors (MLCIs) which are found in mobile phones, camcorders, notebook computers, etc. MLCIs are composed of alternating layers of silver electrodes and soft ferrites. Thus, it is important to develop magnetic characteristics in ferrites for requiring less ferrite layers and hence to obtain further miniaturized devices. The goal of our study is to investigate the effect of rare earth substitution of Ni-Cu-Zn ferrite nanoparticles. Ni-Cu-Zn NSFs substituted with rare earth metal (RE) ions Eu3+, Tb3+, and Dy3+ in varying concentrations were obtained by a sonochemical method. We investigated the crystal structure, chemical bonding, morphology and magnetic characteristics of the Ni-Cu-Zn NSFs by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM), respectively. The phase purity of the samples was confirmed by the XRD analysis. Stretching vibrations of spinel ferrites were verified by the FT-IR analysis. VSM results reveal that the rare earth substitution has a significant effect on the magnetic properties of the Ni-Cu-Zn NSFs.

The effect of rare-earth substitution on the Debye temperature of inorganic phosphors

In the quest to predict photoluminescent efficiency in rare-earth substituted inorganic phosphors, research has shown that materials consisting of ordered, rigid crystal structures tend to possess the highest photoluminescent quantum yields. A compound's Debye temperature (ΘD), which can be calculated using ab initio calculations, is an ideal proxy for quantitatively comparing structural rigidity among different inorganic compounds, allowing potentially efficient phosphors to be selected from large crystal structure databases. However, the high computational cost of these calculations limits estimating ΘD for unsubstituted host crystal structures only. It is assumed that the low substitution concentration of the rare-earth luminescent center does not significantly influence a material's Debye temperature. This work evaluates the validity of this approximation by examining the effect of luminescent center substitution on a host structure's ΘD. Two well-known phosphors, (Y1–xCex)3Al5O12 (x = 0 − 0.05) and Ba1-δEuδMgAl10O17 (δ = 0 − 0.15), were synthesized with varying rare-earth concentrations, while ΘD was computationally estimated and then determined by ultrasonic pulse-echo speed-of-sound and low-temperature heat capacity measurements. The ensuing results provide key implications for using ΘD as a proxy for structural rigidity in substituted inorganic compounds.

Scratch hardness of rare-earth substituted calcium aluminosilicate glasses

Abstract We report lateral deformation experiments on rare earth substituted glasses from percalcic CaO-Al2O3-SiO2-Tm2O3. Using instrumented Berkovich indentation with normal loads below 100 mN, the scratch hardness was obtained from the work of lateral deformation per deformed volume in the elastic-plastic regime. The positive effect of rare-earth substitution on normal hardness, Poisson's ratio and Young's modulus was found to extent also to scratch hardness: in 25CaO-15Al2O3-60SiO2, partial replacement of alumina by Tm2O3 leads to an enhancement of the scratch hardness by about 1 GPa per 2 mol% of substitution, reaching the highest values of scratch hardness which have been reported for oxide glasses thus far. The enhancement of scratch hardness is attributed to enhanced cation packing fraction and super-structural cohesion as a result of rare earth substitution. The previously reported linear correlation between scratch hardness and bulk modulus is confirmed.

Rare earth effect on the critical behavior of La0.75Ln0.05Sr0.2MnO3 manganites

In this work, we have investigated the effect of rare earth substitution in La0.75Ln0.05Sr0.2MnO3 (Ln˭La, Sm, Eu, Gd, Dy and Ho) manganites on the critical behavior near the magnetic phase transition temperature. Different techniques were used to determine the values of the critical exponents β, γ and δ as well as transition temperature TC. The reliability of the critical exponents values was confirmed by both Widom relation and scaling hypothesis. In the case of Ln˭La, Sm, Eu, Gd and Ho, the magnetic interactions were described by 3D-Ising model. However, the substitution by Dy ions changes the universality class from 3D-Ising to tricritical mean field, which can be ascribed to the intrinsic contribution of Dy3+ ions.

Effect of rare-earth substitution on the electrical properties and Raman spectroscopy of BCTZ ceramics

A-site deficient rare-earth (Nd, Gd, and Y) doped (Ba0.99Ca0.01)(Zr0.2Ti0.8)O3 ceramics (noted BCTZ) were obtained by the conventional solid-state reaction method. X-ray powder diffraction experiments combined with first-order Raman scattering analysis were performed to provide detailed description of the structures with different ferroelectric/non-ferroelectric phases. Raman spectra investigations give evidence of compositional disorder as well as a significant change of polar order with the incorporation of rare-earth ions on the A-site of BCTZ lattice. The dielectric and ferroelectric properties of the (Ba1-xLn2x/3)0.99Ca0.01)(Zr0.2Ti0.8)O3 ceramics (x = 0 and x = 0.015, Ln = Nd, Gd and Y) were thoroughly investigated as a function of frequency and temperature.This work highlights and demonstrates that the diffuseness of the phase transition increases and that the relaxor behavior is intensifies with rare-earth substitution. Moreover, the transition temperature is remarkably shifted to lower temperature for doped BCTZ ceramics. In the low temperature region, slim ferroelectric hysteresis loops with a low coercive field were observed for all compositions emphasizing their soft character.

Modification of Co/Cu nanoferrites properties via Gd3+/Er3+doping

Pure nanoparticles of the rare earth-substituted cobalt and copper ferrites with general formula Me Gd0.025 Er0.05 Fe1.925 O4 (Me = Co, Cu) were prepared by the chemical citrate method. X-ray diffraction, field emission scanning electron microscopy, BET analysis are utilized to study the effect of rare earth substitution and its impact on the physical properties of the investigated samples. Rare earth-doped cobalt shows type IV isotherm suggesting mesopore structure with its hysteresis loop. The estimated crystallite sizes are found in the range of 21.49 and 36.11 nm for the doped Co and Cu samples, respectively. The magnetic properties of rare earth-substituted cobalt and copper ferrites showed a definite hysteresis loop at room temperature. An increase in coercivity and a decrease in saturation magnetization were detected. This can be explained in view of weaker nature of the Re3+–Fe3+ interaction compared to Fe3+–Fe3+ interaction. Greater than 1.13-fold increase in coercivity (Hc = 2184 Oe) was observed in doped cobalt nanoferrite samples compared to copper (Hc = 1936 Oe). It was found that the decreasing in temperature leads to great improvement in the magnetic properties of the investigated samples. As the magnetic recording performance of the magnetic samples is improved for well-crystallized samples with nano-structural, the effect of rare earth substitution seems to be particularly valuable in this regard.

Mössbauer study of the effect of rare earth substitution into montmorillonite

Novel montmorillonites were prepared by the exchange of the interlayer cations with a series of rare earth cations (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, and Er) and characterized by XRD, XRF, SEM, chemical analysis and 57Fe Mossbauer spectroscopy. An unexpected magnetically split component, assigned to iron being in the interlayer space, was observed in the Mossbauer spectra at 78K in some rare earth cation exchanged montmorillonite. This paper is the initial report about this observation. The transition of iron from the octahedral site to the interlayer and possible incorporation of rare earths in sites different from those which are in the interlayer space was concluded.

Effect of rare earth substitution on magnetic and structural properties of Co1−xREx Fe2O4 (RE: Nd, Eu) nanoparticles prepared via EDTA/EG assisted sol–gel synthesis

Four groups of the series of rare earth (RE) substituted cobalt ferrite Co1−x REx Fe2 O4; x = 0–0.2 in steps of 0.05 and RE is Nd and Eu were prepared using the sol–gel method at annealing temperatures 550° C. The materials were characterized by powder X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopes (FESEM) and Fourier Transform Infrared spectroscopy (FTIR). The phase identification of the materials by XRD reveals the single-phase nature of the materials. The crystallite sizes of the materials were varied by altering the substitution content within the range of a minimum of 11 nm–31 nm. The magnetic parameters have been studied by using vibrating sample magnetometer (VSM). The saturation magnetization of the ferrite materials at room temperature decreases with the reduction of size. This has been attributed to increased surface to volume ratio and spin canting phenomena. The substituted rare-earth ions inhibit the grain growth of the materials in a systematic manner compared with that of the pure cobalt ferrite materials. There is an improvement in coercivities of the rare earth substituted cobalt ferrite especially for 5% Neodymium substituted cobalt ferrite with approximately 2 kOe coercive field. This is attributed to the contribution from the single ion anisotropy of the rare-earth ions present in the crystal lattice and the effects of a change in magnetic structures on the surface of the nanoparticles.

Effect of rare earth substitution on the structural and electrical properties of Cu–Mg ferrite

The samples of Cu 0.9 Mg 0.1 R y Fe 2-y O 4, where y = 0.01 and R = Sm , Dy , Ho and Hf , were prepared by standard ceramic method. All investigated samples were sintered at 1150°C with a heating rate of 4°C/min and sintering time of 8 h. X-ray diffraction study of the compositions revealed the formation of cubic spinel structure with the appearance of small peaks indicating the presence of secondary phases. Seebeck coefficient was obtained from thermo-electromotive force (emf) measurements. The alternation of the Seebeck coefficient sign between (+)ve and (-)ve means that the two conduction mechanisms take place simultaneously. The dielectric parameters such as dielectric constant, quality factor were determined as a function of temperature and at different frequencies. The decrease in Fe 3+ ions on the octahedral site decreased the polarization of the system, through the dielectric transition point.

Effect of rare earth substitution in cobalt ferrite bulk materials

The study was focused on the influence of small amounts of rare earth (RE=La, Ce, Sm, Gd, Dy, Ho, Er, Yb) addition on the microstructure, phase content and magnetic properties of cobalt ferrite bulk materials. The X-Ray diffraction measurements confirmed the formation of the spinel structure but also the presence of secondary phases of RE oxides or orthoferrite in small percentages (up to 3%). Density measurements obtained by Archimedes method revealed a ~1gcm−3 decrease for the RE doped cobalt ferrite samples compared with stoichiometric one. Both the Mössbauer and Fourier Transform Infrared Spectrocopy analysis results confirmed the formation of the spinel phase. The saturation magnetization and coercive field values of the doped samples obtained by Vibrating Sample Magnetometry were close to those of the pure cobalt ferrite. For magnetostrictive property studies the samples were analyzed using the strain gauge method. Higher maximum magnetostriction coefficients were found for the Ho, Ce, Sm and Yb doped cobalt ferrite bulk materials as related to the stoichiometric CoFe2O4 sample. Moreover, improved strain derivative was observed for these samples but at higher magnetic fields due to the low increase of the coercive field values for doped samples.

Effects of rare earth substitution on the optical properties of Bi2MoO6 for coloring applications

A new class of colored inorganic compounds, BiREMoO6 (RE=Pr, Nd, Sm, Tb and Yb) has been synthesized by a solid state route. The substitution of different rare earths for Bi3+ in Bi2MoO6 produces visible light responsive compounds by gently red shifting the absorption edge to low energy side. The visible light absorption is based on the charge transfer transitions from O2p valence band to conduction band made of primary Mo4d and secondary Bi6p. The substitution of RE3+ introduces partially occupied 4f electronic levels in between the band gap and the position of 4f level depend on the number of f electrons which allows tuning the band gap. Thus the rare earth substitution provides an opportunity to tailor the band gap of Bi2MoO6 from 2.99eV to 2.19eV. The developed compounds exhibited different shades of yellow hue and demonstrated good coloration to plastics.

Effect of rare earth substitution on properties of barium strontium titanate ceramic and its multiferroic composite with nickel cobalt ferrite

Effect of substitution of rare earth ions (Dy3+, Gd3+ and Sm3+) on various properties of Ba0.95Sr0.05TiO3 (BST) i.e. the composition Ba0.95−1.5xSr0.05RxTiO3 (where x=0.00, 0.01, 0.02, 0.03 and R are rare earths Dy, Gd, Sm) and that of their multiferroic composite with Ni0.8Co0.2Fe2O4 (NCF) has been studied. Shifting of peaks corresponding to different compositions in the X-ray diffraction pattern confirmed the substitution of rare earth ions at both Ba2+ and Ti4+ sites in BST. It is clear from scanning electron microscopy (SEM) images that rare earth substitution in BST increases its grain size in both pure and composite samples. Substitution of rare earth ions results in increase in value of dielectric constant of pure and composite samples. Sm substitution in BST significantly decreases its Curie temperature. Dy substituted pure and composite samples possess superior ferroelectric properties as confirmed by polarization vs electric field (P–E) loops. Composite samples containing Dy, Gd and Sm substituted BST as ferroelectric phase possess lower values of remanent and saturation magnetizations in comparison to composite sample containing pure BST as ferroelectric phase (BSTC). Rare earth substituted composite samples possess higher value of magnetoelectric coefficient as compared to that for BSTC.

Effect of rare earth substitution on the composite prepared by nickel ferrite with graphite nanosheet

In this work, the composite NiNdxFe2−xO4/NanoG was prepared by coprecipitation reaction of Nd3+ substituted nickel ferrite with graphite nanosheet (NanoG). The structures of NiNdxFe2−xO4 (x=0.03, 0.06, 0.09) and NiNdxFe2−xO4/NanoG were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and laser particle size appliance. Results show that when x=0.06, the particle size of NiNd0.06Fe1.94O4 is in the range of 60–70nm and can be chemically precipitated on the surface of NanoG. The saturation magnetization of NiNd0.06Fe1.94O4 is 41.79emu/g while it is 26.24emu/g for NiNd0.06Fe1.94O4/NanoG. The conductivity of NiNd0.06Fe1.94O4/NanoG is in the semiconductor sphere. Measurement of electromagnetic parameters shows that the minimum reflection loss of NiNd0.06Fe1.94O4 is −13.15dB at 11.88GHz. When the mass ratio of NiNd0.06Fe1.94O4 to NanoG reaches 4:1, the minimum reflection loss of NiNd0.06Fe1.94O4/NanoG is −17.03dB at 9.29GHz.

Effect of rare earth substitution in the density of electronic states of LnOFeAs

Measurements of the Fe K-edge x-ray absorption near edge (XANES) spectra of LnOFeAs (Ln being a lanthanide) high Tc superconductors exhibit significant changes in the pre-edge peak region upon rare earth substitution. Ab initio XANES calculations, based on the local structure centered at the Fe site obtained by crystallographic investigations, reproduce the observed changes in the spectra, indicating variations of the Fe d-local unoccupied electronic states. The calculated Fe density of states (DOS) at the Fermi energy shows an increase of the Fe d-density of states with increasing height of the arsenic atomic position with respect to the iron plane, similar to that observed for the superconducting transition temperature, Tc. These calculations show that not only the atomic position variation of the Fe-As layers induced by the rare earth substitution is relevant in the increase of the DOS at the Fermi-level, but the actual change in electronic configuration of the rare earth also plays a role in the increase of Fe d-density of states at the Fermi energy.

Synthesis, structure, and magnetic characterization of La2−xRxRuO5(R=Pr, Nd, Sm, Gd, Dy)

Polycrystalline samples of La${}_{2\ensuremath{-}x}{R}_{x}$RuO${}_{5}$ ($R$ $=$ Pr, Nd, Sm, Gd, Dy) have been prepared, applying a soft-chemistry route based on the thermal decomposition of citric acid precursors. By powder x-ray and neutron diffraction the crystal structures have been investigated in detail. For the unsubstituted parent compound La${}_{2}$RuO${}_{5}$, synchrotron x-ray diffraction patterns reveal a broad structural phase transition regime around 170 K without any significant hysteresis. This structural transition is linked with a drastic reduction of the magnetic susceptibility. A similar behavior was also observed for the lanthanide-substituted compounds La${}_{2\ensuremath{-}x}{R}_{x}$RuO${}_{5}$. Magnetic measurements reveal the coexistence of two weakly interacting magnetic sublattices. The effect of rare-earth substitution on the magnetic phase transition is resulting from structural modifications caused by the smaller radius of the ${R}^{3+}$ ions. These ions are predominantly located within the LaO-layers, which are alternating with LaRuO${}_{4}$ layers. The transition temperatures determined by differential scanning calorimetry (DSC) are compared to data derived from the susceptibility measurements.

Effects of rare-earth substitution on the stability and electronic structure of REZnOSb ( RE = La–Nd, Sm–Gd) investigated via first-principles calculations

The structural stability, chemical bonding, Mulliken populations, and charge-density distribution of REZnOSb ( RE = La–Nd, Sm–Gd) were investigated by first-principles calculations. Unit cell parameters calculated by the generalized gradient approximation (GGA) are in better agreement with experimental results than those derived from the local density approximation (LDA). Binding energy comparisons indicate that the structural stability of REZnOSb decreases with the increment of the atomic number of the RE, as confirmed by X-ray diffraction (XRD) results. Semimetal or narrow band-gap semiconductor behaviors are found for selected REZnOSb. Moreover, chemical bonding analysis shows that there exist considerable polar covalent interactions between the participating atoms. It also reveals that the [ZnSb] layers receive some electrons from the [LaO] layers (donor) as an electrons acceptor and holes transport tunnel. The covalent interactions between the [ZnSb] and [LaO] layers, which are enhanced by 4 f-electrons of the RE, are supposed to improve the electrical transport properties.

Effects of rare-earth substitution in the oxyarsenides REFeAsO ( RE=Ce, Pr, Nd, Sm, Gd) and CeNiAsO by X-ray photoelectron and absorption spectroscopy

X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) have been applied to examine the electronic structure of the rare-earth transition-metal oxyarsenides REFeAsO ( RE=Ce, Pr, Nd, Sm, Gd) and CeNiAsO. Within the metal–arsenic layer [ MAs], the bonding character is predominantly covalent and the As atoms are anionic, as implied by the small energy shifts in the M 2 p and As 3 d XPS spectra. Within the rare-earth–oxygen layer [ REO], the bonding character is predominantly ionic, as implied by the similarity of the O 1 s binding energies to those in highly ionic oxides. Substitution with a smaller RE element increases the O 1 s binding energy, a result of an enhanced Madelung potential. The Ce 3 d XPS and Ce L 3-edge XANES spectra have lineshapes and energies that confirm the presence of trivalent cerium in CeFeAsO and CeNiAsO. A population analysis of the valence band spectrum of CeNiAsO supports the formal charge assignment [Ce 3+O 2−][Ni 2+As 3−].

Magnetic properties of Fe‐(Nd, Sm)‐B amorphous alloys

AbstractThe magnetization behaviour of amorphous alloys Fe80–xRExB20 (RE = Nd, Sm) with 0 ≤ x ≤ 16, prepared by melt‐spinning technique. The effect of rare earth substitution on the magnetic properties (Tc, M 0, Hc …) of amorphous alloy has been investigated. Using Random Magnetic Anisotropy Model (RMA), we have analysed our results and obtained some fundamental parameters. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)