Rare Earth Substitution Research Articles

Microstructure and Texture Evolution of the Magnesium Alloy ZMX210 during Rolling and Annealing.

The processability during massive deformation of magnesium-wrought products is hampered by the low formability of magnesium alloys. The research results of recent years demonstrate that rare earth elements as alloying elements improve the properties of magnesium sheets, such as formability, strength and corrosion resistance. The substitution of rare earth elements by Ca in Mg-Zn-based alloys results in a similar texture evolution and mechanical behaviour as RE-containing alloys. This work is an approach to understanding the influence of Mn as an alloying element to increase the strength of a Mg-Zn-Ca alloy. For this aim, a Mg-Zn-Mn-Ca alloy is used to investigate how Mn affects the process parameters during rolling and the subsequent heat treatment. The microstructure, texture and mechanical properties of rolled sheets and heat treatment at different temperatures are compared. The outcome of casting and the thermo-mechanical treatment are used to discuss how to adapt the mechanical properties of magnesium alloy ZMX210. The alloy ZMX210 behaves very similarly to the ternary Mg-Zn-Ca alloys. The influence of the process parameter rolling temperature on the properties of the ZMX210 sheets was investigated. The rolling experiments show that the ZMX210 alloy has a relatively narrow process window.

Doping effects of alkaline earth element on oxygen reduction property of high-entropy perovskite cathode for solid oxide fuel cells

The nearly infinite arrangement and combination of multiple components in high entropy materials provide a huge platform for the modification and performance regulation of new materials. It is an attractive idea to introduce the concept of high entropy into material design and improve its electrochemical performance through component regulation. In this paper, cobalt-based high-entropy perovskite oxides with different alkaline earth metal contents were successfully synthesized. The phase structure, direct current conductivity, oxygen mobility characters and electrochemical properties of these materials are studied. It is found that with the continuous substitution of rare earth elements by alkaline earth elements in high-entropy materials, the content of oxygen vacancies increases and the electrochemical performance is enhanced. The chemical oxygen diffusion coefficient (Dchem) and surface exchange coefficient (Kchem) of the high-entropy oxide La0.2Pr0.2Ba0.2Sr0.2Ca0.2CoO3 are 2.8 × 10−6 cm2 s−1 and 9.1 × 10−3 cm s−1 at 700 °C, respectively. The electrochemical impedance spectroscopy measurement results show that La0.2Pr0.2Ba0.2Sr0.2Ca0.2CoO3 has the minimum polarization resistance, which is 0.03 Ω cm2 at 700 °C in air. The anode-supported fuel cell with the high entropy oxide reaches a peak power density of 792 mW cm−2 at 700 °C and exhibits attractive long-term stability and excellent CO2 resistant properties.

Evidence of a moderate refrigerant capacity in cation disordered Ruddlesden-Popper compounds A1.4Sr1.6Mn2O7 (A = La, Pr, Nd) probed with various figures of merit

We investigated the influence of structural disorders on the magnetic and magnetocaloric (MC) properties upon A-site rare-earth substitution in A1.4Sr1.6Mn2O7 (A = La, Pr, Nd) Ruddlesden-Popper (R–P) compounds. The samples were produced through the solid-state method, and the structural analysis indicated formation of R–P phase with the Jahn-Teller distortion parameter varying from highest in La1.4Sr1.6Mn2O7 (LSMO) to Nd1.4Sr1.6Mn2O7 (NSMO) and followed by Pr1.4Sr1.6Mn2O7 (PSMO). Hence, the magnetization value was increased in LSMO sample implying an enhanced interbilayer and interlayer spin correlations. It resulted in a high value of MC parameters like temperature average entropy change (TEC) and relative cooling power (RCP) of 4.21 J/kgK and 87 J/kg for LSMO, while lowest value of 0.53 J/kgK and 27 J/kg for PSMO respectively, at 2.5 T field. The room temperature MC response in PSMO, whereas a large TEC in LSMO and NSMO compounds advocate their candidacy in broad range of refrigeration applications.

Effect of grain boundary reconstruction and regenerated main phase shell on magnetic properties in high-abundance (NdLaCeY)-Fe-B magnets

The (NdLaCeY)-Fe-B magnets with 45–50 wt% high-abundance rare earth substitution were systematically investigated by co-mixing high boron content matrix phase and Pr–Fe alloy powders (0, 1, 3, 5, 7, and 9 wt%) during the preparation process. The coercivity of magnets increased successively with the addition of Pr70Fe30 (wt.%) and reached 9.32 kOe at the addition amount of 9 wt% from the initial 7.33 kOe without addition, while the remanence had a very small decrease of only 0.13 kGs. The analyses showed that the B-rich phase in the high-boron powders reacted with Pr70Fe30 to form the main phase shell, forming a core-shell structure with a Pr-rich shell and a Y-rich core. Meanwhile, the grain boundary was significantly widened with the introduction of Pr70Fe30. Then, just the improved anisotropy of the main phase grain surface, accompanied with the enhanced magnetic de-coupling effect between the main phase grains, resulted in a great coercivity increment. Notably, on the remanence, the beneficial effect of increased main-phase proportion by regenerated grain shell had a competitive relationship with the deteriorating effect of the magnetic dilution by the non-magnetic material introduction, thus under the combined effects, the remanence firstly increased and then decreased with the addition of Pr–Fe.

Minimizing rare earth content of FCC catalysts: Understanding the fundamentals on combined P-La stabilization

Fluidized Catalytic cracking (FCC) is one of the main conversion processes in conventional refineries and employs a multicomponent catalyst with Y zeolite as the main source of activity and selectivity towards value added products. In order to meet the severe requirements of the FCC unit, the hydrothermal stability of this large pore zeolite is traditionally improved by means of controlled hydrothermal treatments that can be combined with acid washing cycles, with rare earth (RE) ion exchange or with a combination of both. Phosphorus has also been described as a hydrothermal stabilization element. Although most of the studies are based on ZSM-5 zeolites, a new Y zeolite containing FCC catalyst, PhinesseTM, was developed recently. This catalyst, based on the partial substitution of RE by P allowed obtaining the same activity and the same yields to the main products as its conventional RE stabilized counterpart in the catalytic cracking of a vacuum gas oil (VGO). In this work, we present a systematic study where the hydrothermal stability of P- and La-free USYs with different dealumination degrees is compared with that of the corresponding USYs containing P or La alone or a combination of both stabilizing elements. The samples have been thoroughly characterized and their catalytic performance has been tested in a MAT unit. According to the results obtained, when using RE alone, only high contents (> 3.5 wt% RE) are able to stabilize the catalysts towards steaming under severe conditions (100% steam, 750 ºC). However, lower RE ( wt%) can lead to similar hydrothermal stabilization when combined with intermediate phosphorus contents (∼1.0 wt%). The results obtained provide the bases for understanding the reasons behind the benefits of this combined P-La stabilization observed for the commercial Phinesse™ catalyst as compared to a high REO catalyst.

Investigation on the Formation of Rare-Earth Metal Phenoxides via Metathesis

A number of alkali organometallic complexes with suitable thermodynamic properties and high capacity for hydrogen storage have been synthesized; however, few transition metal–organic complexes have been reported for hydrogen storage. Moreover, the synthetic processes of these transition metal–organic complexes via metathesis were not well characterized previously, leading to a lack of understanding of the metathesis reaction. In the present study, yttrium phenoxide and lanthanum phenoxide were synthesized via metathesis of sodium phenoxide with YCl3 and LaCl3, respectively. Quasi in situ NMR, UV-vis, and theoretical calculations were employed to characterize the synthetic processes and the final products. It is revealed that the electron densities of phenoxides in rare-earth phenoxides are lower than in sodium phenoxide due to the stronger Lewis acidity of Y3+ and La3+. The synthetic process may follow a pathway of stepwise formation of dichloride, monochloride, and chloride-free species. Significant decreases in K-band and R-band absorption were observed in UV-vis, which may be due to the weakened conjugation effect between O and the aromatic ring after rare-earth metal substitution. Two molecular structures, i.e., planar and nonplanar, are identified by theoretical calculations for each rare-earth phenoxide. Since these two structures have very close single-point energies, they may coexist in the materials.

Trivalent rare earth elements substitution in 58S bioactive glass matrix for bone repair applications - An in vitro and in vivo study

The development of bone grafts and prosthetic implants for clinical need is still difficult due to the complexity of integrated physiological processes. The 58S glass ceramic is one of the most widely accepted biomaterial for preparing hard tissue damages due to its capability to react at molecular level. On the other hand, 58S glass ceramic are suffers some extent to expedite the new bone formation. The incorporation of rare earth elements into the bioactive glass ceramic matrix significantly improved the new bone formation. In addition, the cytotoxicity and biocompatibility properties of the obtained ceramic powder were investigated in vitro and in vivo for bone graft efficiency. The results showed that the rare earth elements in bioactive glass ceramic have the potential to repair damaged hard tissues.

Accurate Determination of the Bandgap Energy of the Rare-Earth Niobate Series.

We report diffuse reflectivity measurements in InNbO4, ScNbO4, YNbO4, and eight rare-earth niobates. A comparison with established values of the bandgap of InNbO4 and ScNbO4 shows that Tauc plot analysis gives erroneous estimates of the bandgap energy. Conversely, accurate results are obtained considering excitonic contributions using the Elliot-Toyozawa model. The bandgaps are 3.25 eV for CeNbO4, 4.35 eV for LaNbO4, 4.5 eV for YNbO4, and 4.73-4.93 eV for SmNbO4, EuNbO4, GdNbO4, DyNbO4, HoNbO4, and YbNbO4. The fact that the bandgap energy is affected little by the rare-earth substitution from SmNbO4 to YbNbO4 and the fact that they have the largest bandgap are a consequence of the fact that the band structure near the Fermi level originates mainly from Nb 4d and O 2p orbitals. YNbO4, CeVO4, and LaNbO4 have smaller bandgaps because of the contribution from rare-earth atom 4d, 5d, or 4f orbitals to the states near the Fermi level.

Possible structural quantum criticality tuned by rare-earth ion substitution in infinite-layer nickelates

Materials with competing phases that have similar ground state energies often exhibit a complex phase diagram. Cuprates are a paradigmatic example of such a system that show competition between charge, magnetic, and superconducting orders. The infinite-layer nickelates have recently been revealed to feature similar characteristics. In this paper, I show that these nickelates are additionally near a structural quantum critical point by mapping the energetics of their structural instabilities using first-principles calculations. I first confirm previous results that show a phonon instability in the $P4/mmm$ phase leading to the $I4/mcm$ structure for $R\mathrm{Ni}{\mathrm{O}}_{2}$ with $R$ = Sm--Lu. I then study the non-spin-polarized phonon dispersions of the $I4/mcm$ phase and find that they exhibit rare-earth size-dependent instabilities at the $X$ and $M$ points for materials with $R$ = Eu--Lu. Group-theoretical analysis was used to enumerate all the isotropy subgroups due to these instabilities, and the distorted structures corresponding to their order parameters were generated using the eigenvectors of the unstable phonons. These structures were then fully relaxed by minimizing both the atomic forces and lattice stresses. I was able to stabilize only five out of the twelve possible distortions. The $Pbcn$ isotropy subgroup with the ${M}_{5}^{+}(a,a)$ order parameter shows noticeable energy gain relative to other distortions for the compounds with late rare-earth ions. However, the order parameter of the lowest-energy phase switches first to ${X}_{2}^{\ensuremath{-}}(0,a)+{M}_{5}^{+}(b,0)$ and then to ${X}_{2}^{\ensuremath{-}}(0,a)$ as the size of the rare-earth ion is progressively increased. Additionally, several distorted structures lie close in energy for the early members of this series. These features of the structural energetics persist even when antiferromagnetism is allowed. Such a competition between different order parameters that can be tuned by rare-earth ion substitution suggests that any structural transition that could arise from the phonon instabilities present in these materials can be suppressed to 0 K.

Tuning the Intermediate Valence Behavior in the Zintl Compound Yb14ZnSb11 by Incorporation of RE3+ [Yb14-xRExZnSb11 (0.2 ≤ x ≤ 0.7), RE = Sc, Y, La, Lu and Gd

The solid solutions of Yb14-xRExZnSb11 (RE = Sc, Y, La, Lu, and Gd; 0.2 ≤ x ≤ 0.7) were prepared to probe the intermediate valency of Yb in Yb14ZnSb11. The substitution of Yb with RE3+ elements should reduce or remove the intermediate valency of the remaining Yb ions. Large crystals are grown from Sn-flux, and the structure and magnetic susceptibility are presented. All compounds crystallize in the Ca14AlSb11 structure type and the RE3+ ions show Yb site substitution preferences that correlate with size. Two compositions of Yb14-xYxZnSb11 were investigated [x = 0.38(3), 0.45(3)] by temperature-dependent magnetic susceptibility and the broad feature in magnetic susceptibility measurements at 85 K in pristine Yb14ZnSb11 attributed to valence fluctuation decreases and is absent for x = 0.45(3). In compounds with nonmagnetic RE3+ substitutions (Sc, Y, La, and Lu), temperature-dependent magnetic susceptibility shows a transition from intermediate valency fluctuation toward temperature-independent (Y, La, and Lu) or Curie-Weiss behavior and possibly low temperature heavy Fermion behavior (Sc). In the example of the magnetic rare earth substitution, RE = Gd, the Curie-Weiss-dependent magnetic moment of Gd3+ is consistent with x. Hall resistivity of Yb14-xYxZnSb11 showed that the carrier concentration decreases with x and the signature of the low-T intermediate valence state seen for x = 0 is suppressed for x = 0.38 and gone for x = 0.45.

Bioinorganic Preparation of Hydroxyapatite and Rare Earth Substituted Hydroxyapatite for Biomaterials Applications.

Rare Earth elements in the lanthanide series are regarded as one of the finest options for the cationic substitution of calcium ions in hydroxyapatite (HA) because of their favorable impact on the biological characteristics of substituted HA. Neodymium and cerium were used to substitute 5% of calcium ions in HA, prepared via the wet precipitation method. Characterization tests for pure and substituted HA were conducted using XRD, FTIR, EDS, and FESEM. The results showed that changing part from calcium ions in hydroxyapatite to Nd and Ce ions altered its structure, composition, and morphology. Regarding the biological tests, the cytotoxicity test revealed a change in IC50 for both normal and cancer cell lines, where substitution part of the Ca ions with rare Earth elements led to increasing antitumor activity in comparison with HA without substitution; in addition, antibacterial and fungicide activity was evident for both HA and Nd-Ce/HA, with a modest increase in antibacterial activity of Nd-Ce/HA against S. epidermidis and E. coli in comparison with HA. These findings may shed light on the process by which Nd and Ce ions improve the biological characteristics of pure HA and the increased potential of these bioceramics.

Enhancement in the electrical transport properties of CaMnO3via La/Dy co-doping for improved thermoelectric performance.

The untiring endeavour towards green energy is a trending research among the research community. Thermoelectric materials are of vital importance here owing to their emission-free operation. As a righteous candidate, calcium manganate materials are being explored to increase its figure of merit. In this study, the structural, microstructural, electrical transport, and high-temperature thermoelectric measurements of LaxDyxCa1-2xMnO3 {x = 0.025 (L25D25), 0.05 (L50D50), 0.075 (L75D75), and 0.1 (L100D100)} were systematically performed. The structural confirmation of the synthesised sample was validated using X-ray diffraction, which also revealed the orthorhombic (space group: Pnma) crystallisation of co-doped samples with no traces of secondary peaks. A significant increase in the unit cell volume was observed with rare earth substitutions. The morphological studies revealed that the prepared samples were highly dense and the grain size was reduced with rare earth concentration. The substitution of La and Dy enhanced the conductivity values of pristine CMO by two orders of magnitude due to the high concentration of charge carriers and the presence of Mn3+ ions due to rare earth doping. The conductivity increased with rare earth concentrations but diminished for x = 0.1 due to the localization of charges. The Seebeck coefficient values were negative for all the prepared samples, indicating electrons as the predominant carriers over the entire operating range. A minimum κ of 1.8 W m-1 K-1 was achieved for La0.1Dy0.1Ca0.8MnO3 and the maximum value zT obtained was 0.122 at 1070 K for La0.075Dy0.075Ca0.85MnO3.

Magnetic characteristics adjustment through rare-earth lanthanum substitution in mechanically alloyed yttrium iron garnet nanoparticles

Magnetic characteristics adjustment through rare-earth lanthanum substitution in mechanically alloyed yttrium iron garnet nanoparticles

Investigation of Dielectric, Magnetic and Electrical Behavior of BFO/GNPs Nano-Composites Synthesized via Sol-Gel Method

Nano composites of Ba0.5Bi0.5Nd0.05Fe0.95O3 multiferroic with graphene nano platelets (GNPs)x (x = 0, 0.125 %, 0.375 %, and 0.5 %) were synthesized using sol-gel auto ignition process. XRD analysis revealed a single rhombohedrally distorted phase of Ba0.5Bi0.5Nd0.05Fe0.95O3. The present study unfold the impact of GNPs on the structural, electrical, dielectric, and magnetic properties of Ba0.5Bi0.5Nd0.05Fe0.95O3 multiferroics. The substitution of Rare earth elements in pure BFO reduced the value of leakage current which is the basic drawback related with pure BFO. The prepared nanocomposites are then sintered at 800 °C for 7 hrs. The X-ray diffraction patterns showed the rhombohedral distorted perovskite crystal structure of the prepared samples including lattice constant, crystallite size, and X-ray density. The average crystallite sizes of the prepared nanocomposites are noticed in the range 28.14 -to 29.74 nm with increasing the GNPs concentration and lattice constant is found in the range 11.59 -to 11.61 Å. Temperature-dependent resistivity is first observed to increase with an increase in temperature then resistivity decreased with increasing the temperature which indicates a semi-conductor-like behavior as measured by two probe I-V characteristics. LCR technique showed that both the dielectric constant and the dissipation factor are decreased with an increase in frequency. VSM results indicated that saturation magnetization is noted to increase while remanent magnetization decreases with increasing concentration of GNPs.

Magnetic interactions of 4f electrons in the topological insulator chalcogenide Bi2Se3

The gap-opening mechanism of a topological insulator, the quantum anomalous Hall effect, and the axion physics are still pressing open questions, and a microscopic viewpoint to further understand the role of magnetism in topology is highly desirable. In this work we have performed a microscopic investigation, by means of electron spin resonance (ESR) along with complementary bulk measurements, on the chalcogenide ${({\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x})}_{2}{\mathrm{Se}}_{3}$ ($x=0$, 0.001, 0.002 and 0.006). Our analysis of the ${\mathrm{Gd}}^{3+}$ spin dynamics reveals no significant change of the Fermi surface as a function of ${\mathrm{Gd}}^{3+}$ concentration, which indicates that the $4f$ magnetism is different from the nonlocal effects induced by transition metal ($d$ electrons) substitutions. Additionally, we observe an unusual evolution of the ${\mathrm{Gd}}^{3+}$ ESR spectra as a function of the applied magnetic field, which we discuss considering the magnetic interaction between ${\mathrm{Gd}}^{3+}\phantom{\rule{4pt}{0ex}}4f$ electrons and impurity centers such as Se vacancies. This interaction would give rise to a local weak antilocalization effect surrounding the ${\mathrm{Gd}}^{3+}$ ions. Such a mechanism is observable due to particular details of the ${\mathrm{Gd}}^{3+}\phantom{\rule{4pt}{0ex}}4f$ electrons' magnetism in this system compared to that of $d$ electrons. Our work points out that rare-earth substitutions in this model topological insulator are a promising path to explore the axion insulating systems.

RCoO3 {R=Pr, Nd and Sm} electrode-based for efficient solid-state symmetric supercapacitor

Tunable electrical conductivity and energy storage ability have been achieved by controllable rare earth substitution at the A-site in hydrothermally synthesized single perovskite oxides. Controlling the electrochemical performance of these electro-active materials has been attractive for futuristic energy storage devices. Crystallographic analysis confirmed a distorted orthorhombic Pnma structure for PrCoO3 (PCO), NdCoO3 (NCO) and SmCoO3 (SCO). The morphology of the materials showed significant changes in size, texture and porosity; with shape morphology varied from rectangular shaped crystallites in SCO and NCO to spherical shaped crystallites in PCO. The comparison of room temperature electrical conductivity shows good correlation with the structural features. A gradual decrease in the activation energies, obtained from the small polaron hopping (SPH) model, was observed as a function of the increasing ionic radii (Pr3+>Nd3+>Sm3+). The electrochemical properties are systematically investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectra (EIS) analysis. The charge storage mechanism in PCO, NCO and SCO is clearly demonstrated to be a diffusion controlled process. An effective correlation is drawn between the electrical and electrochemical parameters and their inherent structural disorder. PCO based materials show superior electrochemistry with a specific capacitance of ∼557 F/g at 1 A/g and ∼88% capacity retention even after 10,000 charging and discharging cycles. Based on its superior 3-electrode performance, a solid-state symmetric supercapacitor (SSC–P) was fabricated using PCO-based electrodes. It shows an energy and power densities of ∼40 W-h/Kg and ∼5574 W/kg respectively retaining 81% stability even after 5000 operational cycles. Finally, our fabricated solid-state symmetric supercapacitor (SSC–P) illuminated a LED for 3 min after 1 min charging, which shows its applicative potential for optimal smart energy storage device applications.

Deleterious effect of rare earth elements substitution on the auxetic behavior of CoFe2O4 thin films

CoFe2−xGdxO4 (x = 0, 0.2) thin films of about 70 nm thickness were epitaxially grown on (001) MgO substrates using pulsed laser deposition and a controlled O2/N2 deposition pressure within the 0.01–1 mbar range. Using Resonant elastic X-Ray scattering (REXS) experiments, we bring the proof that the Gd cations are inserted in the spinel cell. As expected, they mostly occupy the octahedral sites and drive the Co cations towards the tetrahedral ones. However, they also surprisingly partly occupy the tetrahedral sites. Despite the increase of the amount of Co in the tetrahedral sites, the insertion of the rare earth element, globally inflating the volume of the cell, precludes the occurrence of the auxetic behavior observed in the undoped samples. The out-of-plane cell parameters indeed never reach values lower than those of the in-plane parameters, fully strained by the MgO substrate. This study brings a new light on the parameters controlling the auxetic behavior in CFO thin films and demonstrates that the location of the Co cations in the tetrahedral sites is not a sufficient condition.

Energy storage, electrocaloric and optical property studies in Ho-modified NBT – BT lead-free ferroelectric ceramics

A comprehensive investigation of structural, microstructural, optical, electrocaloric, and energy storage properties of Ho-modified NBT-BT lead-free ceramics was conducted from room temperature to a high-temperature region. Rietveld refinement confirms the coexistence of dual-phase monoclinic (Cc) and tetragonal (P4mm) phases in Ho-modified NBT-BT ceramics. A prominent monoclinic distortion was found with increasing Ho composition up to x=0.02, and then an abrupt decrease for x=0.03 ceramic was noticed. Of particular importance is the composition of x = 0.02, which exhibits a high electrocaloric temperature change (ΔT) of 0.73 K @ E = 20 kV/cm at a temperature of 373 K, and an optimal high recoverable energy storage density (Wrec) of 1.8846 J/cm3 along with an efficiency 83% was achieved. The frequency dependence ac-conductivity study promotes the reduction of oxygen vacancies at room temperature and the dominance of single ionized oxygen vacancies at very high temperatures well above 300 °C. A small considerable increase in the energy bandgap values with the Ho3+ ion substitution in NBT-BT was observed. Under the excitation of 532 nm light, the two most prominent red fluorescence emission peaks were emitted, where the first emission band with weak intensity was observed at 657 nm which corresponds to the 5F5→5I8 transition, and a strong 2nd peak at 756 nm corresponds to the 5F4/5S2→5I7 level transition of the Ho3+ ion. These findings provide a feasible multifunctional property in the applications of power electronic devices with lead-free NBT-BT ceramics via rare-earth substitution.

Fortified relaxor ferroelectricity of rare earth substituted 4-layered BaBi3.9RE0.1Ti4O15 (RE = La, Pr, Nd, and Sm) Aurivillius compounds

In this report, the effect of rare-earth (RE3+) ion substitution on structural, microstructural, and electrical properties in barium bismuth titanate (BaBi4Ti4O15) (BBTO) Aurivillius ceramics has been investigated. The Rietveld refinements on X-ray diffraction (XRD) patterns confirm that all the samples have an orthorhombic crystal system with A21am space group. Meanwhile, temperature dependent synchrotron XRD patterns reveal that the existence of dual phase in higher temperature region. The randomly oriented plate-like grains are experimentally strived to confirm the distinctive feature of bismuth layered Aurivillius ceramics. The broad band dielectric spectroscopic investigation signifies a shifting of ferroelectric phase transition (Tm) towards low temperature region with a decrease of the RE3+-ionic radii in BBTO ceramics. The origin of diffuse ferroelectric phase transitions followed by stabilization of the relaxor ferroelectric nature at high frequency region is explained using suitable standard models. The temperature dependent ac and dc conductivity results indicate the presence of double ionized oxygen vacancies in BBTO ceramics, whereas the dominance of single ionized oxygen vacancies is observed in RE-substituted BBTO ceramics. The room temperature polarization vs. electric field (P–E) hysteresis loops are shown to be well-shaped symmetric for BBTO ceramics, whereas slim asymmetric ferroelectric characteristics developed at RE-substituted BBTO ceramics.

Density functional theory study of rare earth Y, Ce and La-catalyzed oxidation mechanism of Ta(1 0 0) and Ta(1 1 0) surfaces

The density functional theory (DFT) calculations were conducted to study the adsorption and diffusion of oxygen on Ta(100) and Ta(110) with and without the substitution of rare earth (RE, RE = Y, Ce and La) in the surface layer, which aims to reveal the possible RE-catalyzed oxidation mechanism of those two surfaces. The calculated results show that the oxygen atoms are preferentially adsorbed on the hollow site of clean Ta(100) and Ta(110). The RE doping in the subsurface layer weakens the adsorption strength of oxygen on Ta(110), while it has a negligible influence on that on Ta(100). In contrast, the substitution of RE in the surface layer can enhance the adsorption ability of oxygen atom on the two surfaces, which is also proved by the analysis of Bader charge and electron localization function. Additionally, the oxygen atoms are predicted to preferentially occupy the octahedral site in the subsurface of Ta slabs with and without RE doping. The investigations of oxygen diffusion behaviors indicate that the RE, especially for La, doping in the surface layer decrease the energy barrier of oxygen penetration into Ta surface, and thus catalyze the oxidation process of Ta slabs. Those results could help to provide a fundamental basis for comprehending the oxidation mechanism of Ta surface with RE doping.