Rare-earth Radius Research Articles

Polar phonons features and intrinsic dielectric properties of RE2CoMnO6 (RE = Tb, Dy, Ho, Tm and Yb) double perovskites

RE-based double perovskite (DP) oxides of the RE₂TMTM'O₆ family exhibit intriguing magnetodielectric (MD) properties and magnetocaloric effects (MCEs), making them promising candidates for applications in high-performance supercapacitors, memories, spintronic devices, and cryogenic magnetic refrigeration. This paper addresses the vibrational properties of RE2CoMnO6 (RE = Tb, Dy, Ho, Tm, and Yb) ceramics for the first time using infrared reflectance spectroscopy. The dielectric merit factors in the microwave (MW) range, including the quality factor (Qu) and the static dielectric constant (ɛ0), were estimated. It was observed that the intrinsic dielectric constants decrease from approximately 26.2 to 14.4 as the rare earth ionic radius decreases. The mean values of these compounds suggest their suitability for applications in MW circuitry devices.

Effect of Rare Earth Ion Doping on the Performance of Lithium-Rich Cathode Materials for Lithium-Ion Batteries

Lithium-rich layered oxide cathode materials have the advantages of a high voltage and a high specific capacity. Their commercial applications have however been impeded by some disadvantages such as low initial coulombic efficiency and low cycle life. To overcome these issues, rare earth ion-doped lithium-rich layered oxide cathode materials are investigated in this work. The irreversible release of O2- in Li2MnO3 is suppressed by rare earth ions doping, which enhanced the initial coulombic efficiency of the materials. Meanwhile, the rare-earth ion radius used for doping is larger than the Mn4+ radius, which enlarges the (003)-crystalline plane spacing, resulting in a significant enhancement of the rate performance of the material.

Synthesis and physical properties of Sm2PdGe3 in a context of RE2PdGe3 family

In this study, we present the crystallographic and magnetic characterization of a new intermetallic compound Sm2PdGe3, which was synthetized by a two stage method employing an eutectic alloy. The investigations carried out exhibited, that Sm2PdGe3 crystallize in AlB2-type structure with lattice parameters a = 4.2189(1) Å and c = 4.1031(2) Å. This compound can be classified as a cluster-glass with a spin freezing temperature Tf = 10.5 K. Furthermore, there were carried out the analysis of the role of the rare earth (RE) elements on the structural parameters of RE2PdGe3 and draw a correlation between the RE radius and the unit cell parameters. We show that a deviation from the ideal 1:3 Pd:Ge ratio is necessary to synthesize RE2PdGe3 with smaller RE elements.

Thermal properties and anti-corrosion behavior of multicomponent (Dy1/5Er1/5Tm1/5Yb1/5Y1/5)2SiO5 monosilicate against water vapor attack at high temperature

Materials with a thermal expansion coefficient compatible with silicon carbide based ceramic matrix composites and low thermal conductivity at higher temperatures are crucial for developing environmental barrier coatings (EBCs) for aero-engines. Lately, high entropy silicate engineering has been a promising approach to develop optimized EBC materials. The solid solution reaction method was adopted for the fabrication of high entropy multicomponent (Dy1/5Er1/5Tm1/5Yb1/5Y1/5)2SiO5 or (5RE1/5)2SiO5 monosilicate. Scanning electron microscopy and X-ray diffraction show the homogenous distribution and a single-phase solution of (5RE1/5)2SiO5 monosilicate. Differential scanning calorimetry testing was done at 1450 °C which shows no exo/endothermic reaction has occurred. The value of the coefficient of thermal expansion (6 ppm/°C) up to temperature 1500 °C and low thermal conductivity values for (5RE1/5)2SiO5 monosilicate were observed (1.1–1.4 W/m°C) in the temperature range between 25 and 1500 °C. The water vapor corrosion resistance of (5RE1/5)2SiO5 monosilicate further confirms that the material is suitable for EBC applications due to the synergistic effect of different rare earth radii and stable crystal structure with a negligible weight loss value of 0.0005 mg/cm2 after 150 h corrosion time under 90 % H2O and 10 % O2 at 1300 °C. The results of this work suggest that (5RE1/5)2SiO5 monosilicate can be used as a promising candidate for environmental barrier coatings.

Evaluating the significance of rare earth and iron doping on structure-property of lead titanate

The samples (Pb0.8Ln0.2 Fe0.2 Ti0.8O3, (Ln= La, Nd, Sm, Gd)) were synthesized successfully by mixed oxide method. A significant reduction in tetragonality is observed with the modification of structure. The grain size from FESEM study was observed to be decreasing with increase in ionic radii of rare earth ions. Specifically, the dielectric constant is found to be maximum for the Sm-doped sample. Conductivity studies at varying temperature and frequencies reveal the NTCR behaviour of these samples. In Sm, Nd and Gd doped samples, tunnelling of small polarons is responsible for conduction process whereas for La doped sample, the conduction process is mediated through the combined effect of small polaron tunnelling and bipolaron hopping. The Sm-doped sample exhibits highest remanent polarization. All the results of this comprehensive study provide valuable insights into the effect of dopant ions on various properties of the studied materials, paving the way for device applications.

Mechanical and dielectric properties of RE2SiO5 (RE=Ho, Er, Tm, Yb, and Lu) as high-temperature wave-transparent materials

As the flight speed of aircraft continues to increase, high-temperature wave-transparent materials for radomes or antenna windows face great challenges. The shortage of new high-performance wave-transparent materials is limiting the improvement of aircraft performance. In this work, dielectric and mechanical properties of RE2SiO5 (RE = Ho, Er, Tm, Yb, and Lu) were investigated to explore their application as high-temperature wave-transparent materials. RE2SiO5 (RE = Ho, Er, Tm, Yb, and Lu) ceramics possess relatively low dielectric constant and it is insensitive to the RE species. For the dielectric loss, they gradually decrease as the radius of rare earth ions decreases. In addition, RE2SiO5 (RE = Ho, Er, Tm, Yb, and Lu) possesses good mechanical properties with high hardness and relatively low reduced modulus, and hardness is insensitive to the rare earth ion radii while the reduced modulus increases with the RE3+ ions radius decreases. They are larger than those of fused silica, the most used traditional high-temperature wave-transparent material. The results provide important material selection and optimization guidelines for RE2SiO5 as the candidate for next-generation high-temperature wave-transparent materials.

Phase transformation inhibition and improved thermo-mechanical properties of rare earth niobates for thermal barrier coatings

Rare earth niobate Re3NbO7 (Re=Rare earth element) possesses ultra-low thermal conductivity for application as thermal barrier coatings (TBCs). However, Re3NbO7 with large rare earth ion radius (ReLa, Nd, Sm) exhibits both low temperature phase transition and poor facture toughness which is detrimental to the durability of the coatings. In this work, an effective method was proposed to solve those problems by doping. Considering the low-temperature phase transition at about 340K, La3NbO7 is selected as representative material. In order to suppress phase transition, Y3+ with relatively smaller ionic radius is used as a doped ion, and (La1-xYx)3NbO7 (x = 0.0,0.1,0.3,0.5) were prepared and investigated. It is shown that, low temperature phase transition of La3NbO7 is effectively suppressed due to Y3+ doped. Facture toughness is increased significantly from 0.5 to 2.3 MPa m1/2 with the increase of doping concentration. Furthermore, the Vickers hardness is also improved by doping. Considering the phase stability and ultra-low thermal conductivity, (La1-xYx)3NbO7 solid solution (x = 0.5) maybe promising candidates for high temperature thermal insulation materials such as TBCs, thermoelectric materials, etc.

Uranium Oxide Hydrate Frameworks with Dy(III) or Lu(III) Ions: Insights Into the Framework Structures With Lanthanide Ions.

Two uranium oxide hydrate frameworks (UOHFs) with either Dy3+ or Lu3+ ions, Dy1.36(H2O)6[(UO2)10UO13(OH)4] (UOHF-Dy) or Lu2(H2O)8[(UO2)10UO14(OH)3] (UOHF-Lu), were synthesized hydrothermally and characterized with a range of structural and spectroscopic techniques. Although SEM-EDS analysis confirmed the same atomic ratio of ~5.5 for U : Dy and U : Lu, they displayed different crystal morphologies, needles for UOHF-Dy in the orthorhombic C2221 space group and plates for UOHF-Lu in the triclinic P-1 space group. Both frameworks are composed of β-U3O8 type layers linked by pentagonal bipyramidal uranium polyhedra, with the Dy3+/Lu3+ ions inside the channels. However, the arrangements of Dy3+/Lu3+ ions are different, with disordered Dy3+ ions well aligned at the centers of the channels and single Lu3+ ions well-separated in a zigzag pattern in the channels. While the characteristic vibrational modes were revealed by Raman spectroscopy, the presence of a pentavalent uranium center in UOHF-Lu was confirmed with diffuse reflectance spectroscopy. The formation of two types of UOHFs with lanthanide ions, high or low symmetry, and the structure trend were discussed regards to synthesis conditions and lanthanide ionic radius. This work highlights the complex chemistry driving the formation of UOHFs with lanthanide ions and has implications to the spent nuclear fuel under geological disposal.

Medium-Entropy Monosilicates Deliver High Corrosion Resistance to Calcium-Magnesium Aluminosilicate Molten Salt.

For decreasing the global cost of corrosion, it is essential to understand the intricate mechanisms of corrosion and enhance the corrosion resistance of materials. However, the ambiguity surrounding the dominant mechanism of calcium-magnesium aluminosilicate (CMAS) molten salt corrosion in extreme environments hinders the mix-and-matching of the key rare earth elements for increasing the resistance of monosilicates against corrosion of CMAS. Herein, an approach based on correlated electron microscopy techniques combined with density functional theory calculations is presented to elucidate the complex interplay of competing mechanisms that control the corrosion of CMAS of monosilicates. These findings reveal a competition between thermodynamics and kinetics that relies on the temperatures and corrosion processes. Innovative medium-entropy monosilicates with exceptional corrosion resistance even at 1500°C are developed. This is achieved by precisely modulating the radii of rare earth ions in monosilicates to strike a delicate balance between the competition in thermodynamics and kinetics. After 50 and 100h of corrosion, the thinnest reactive layers are measured to be only 28.8 and 35.4µm, respectively.

Exploration of structural, magnetic, and magnetocaloric characteristics of double perovskites HoRCoMnO6 (R=Ho, Gd, Eu or Nd)

A conventional solid-state process was used to synthesize the double perovskite materials HoRCoMnO6 (R=Ho, Gd, Eu, Nd). The structural properties of the compounds were investigated using X-ray powder diffraction (XRD). The results revealed that Ho₂CoMnO₆ crystallizes in a monoclinic structure with the P21/n space group. In contrast, the other compounds HoRCoMnO6 (R=Gd, Eu, or Nd) exhibit an orthorhombic structure with the Pnma space group. As a result, the average crystallite size also changes as a function of rare-earth element doping. This investigation reveals that the magnetic properties of the compounds studied are significantly dependent on the doping elements. The Curie temperature TC, for example, increases from 80 to 118 °C with the ionic radii of rare earths increasing. Furthermore, the study of the magnetocaloric effect (MCE) shows that the maximum of the entropy variation (−ΔSMmax) increases from 4.97 to 6.06 J/(kg∙K) under a magnetic field of 5 T with substitution by rare-earth ions. To examine the efficiency of MCE materials, the relative cooling power (RCP) was evaluated and is found to increase with increment of rare-earth radius till 406.69 J/kg for Nd. The mean entropy variation with temperature (TEC) was also studied. Due to their significant magnetocaloric performance, HoRCoMnO6 (noted as HRCMO) compounds (with R=Ho, Gd, Eu or Nd) could be good candidates for low-temperature magnetic cooling applications

Structural, optical and electrical studies of non-toxic oxide- RMnO3 [R=Y, Er, Yb] hexagonal manganite thin-films

Recently, ferroelectric-photovoltaics have come under the spotlight as a potential class of materials for application in photovoltaic devices. However, the broad bandgap of these ferroelectric-photovoltaic materials causes them to have modest photocurrents[1]. To overcome this challenge hexamanganites can be used to achieve high photovoltaic efficiency as it has a small band gap. Here we present a stable, non-toxic, and cost-efficient hexamanganite RMnO3 [R=Y, Er, Yb] thin films prepared by spray pyrolysis method. The formation of the single phase is confirmed by X-ray diffraction analysis. Morphological studies show grains are uniform and closely packed and the grain size increases with the decrease in ionic radii of rare earth ions. A narrow optical band gap of nearly 1.5 eV is observed for the films. The results of this investigation show that Ultraviolet ray irradiation can be used to tune the bandgap. With a carrier concentration of around 10+14 cm−3, Hall measurements proved that the films are p-type semiconductors. This research illuminates the exploration of stable oxide semiconductors with a small band gap for applications in futuristic solar cells.

Manifestation of chemical pressure: Magnetism and magnetostriction in nanoscale RFeO3 (R = Sm, Dy, Ho, and Lu)

AbstractThe effect of ionic radii sizes on magnetostriction is studied in relation to structural and magnetic properties. To explore the effect of the chemical pressure, nanoparticles of rare‐earth (RE) orthoferrites, SmFeO3, DyFeO3, HoFeO3, and LuFeO3 are studied using X‐ray diffraction, field emission scanning electron microscopy, and Raman spectroscopy. Magnetic and magnetostriction measurements are also performed. In these orthoferrites, the coordination of the RE ion is eightfold, whereas the RE ionic radii are significantly different, which directly influences the structural parameters. The distortion of FeO6 octahedra is observed as a result of changing chemical pressure within the lattice. The different magnitudes of magnetostriction in RE orthoferrites can be attributed to the different degrees of distortion of FeO6 octahedra, R–O dynamics, and spin–orbit interactions in the system. The maximum value of magnetostriction (∼ 19 ppm) and magnetization at 2 K (30.64 emu/g) is demonstrated by HoFeO3. Comparison of structural parameters of the samples to their respective bulk counterparts indicated relative structural distortion in nanoparticles.

Thermodynamic analysis of defect equilibration in highly nonstoichiometric perovskites LnBaMn2O6–δ (Ln=Nd, Sm)

Double-ordered manganites LnBaMn2O6–δ (Ln = Nd, Sm) were shown to possess a variable oxygen content from δ = 0 to 1 while maintaining a tetragonal structure within the temperature range of 973–1223 K and under partial oxygen pressure 10−22 – 1 atm. Coulometric titration technique was successfully utilized to reveal three separated phase in these materials depending on oxygen content. Thermodynamic analysis based on experimentally obtained isothermal functions δ=f(pO2) enabled one to develop a defect formation model suggesting a coexistence three main processes of defect formation in the studied oxides. Thus oxidation and partial disproportionation of manganese supplemented by intrinsic oxygen disordering were demonstrated to govern defect equilibrium. Different influence of activity coefficients involved in the thermodynamic model was considered. Moreover, a reduction in the radius of lanthanide was found to be favorable to expand oxygen homogeneity region and to decrease in the enthalpy of oxidation reaction.

Bipyridyldicarboxamides and f-metals: the influence of electron effects on the structure, stability, separation, and photophysical properties of their complexes.

In this work, three isomeric fluorinated bipyridyldicarboxamides were studied to evaluate the impact of the fluorine atom position on the structure, stability, Am(III)/Ln(III) separation, and photophysical properties of their complexes. The complexes of the fluorinated amides have a metal-to-ligand composition of 1 : 1, which is independent of the fluorine atom position or lanthanide metal. The bipyridyl fragments in the fluorinated complexes are flattened compared with those in unsubstituted ones. Ln-to-heteroatom distances are more affected by steric hindrance in the ligand and further by lanthanide ion radius contraction. This leads to significant effectivity of heavy lanthanide extraction compared with the light ones, particularly for 4F diamide. Fluorination leads to a slight variation in the excited triplet state of the complexes, and hence, the effectiveness of luminescence increases for Eu, Sm, and Tb complexes. Moreover, fluorination significantly affects the CIE chromaticity coordinates for the complexes.

Thermochemical Study of Bismuth Cobalt Dysprosium Oxide: The Enthalpy of Formation and Lattice Enthalpy

Bismuth cobalt dysprosium oxide of composition Bi12.5Dy1.5CoO22.325 has been prepared by solid-state reactions. The compound has a cubic structure (space group Fmm) with the unit cell parameter a = 0.55279(5) nm. The solution enthalpy and standard enthalpy of formation of Bi12.5Dy1.5CoO22.325 have been measured by solution calorimetry: ΔsolH0 = −1017.0 ± 7.5 kJ/mol, and ΔfH0 = −5338.8 ± 19.9 kJ/mol. The lattice enthalpy has been calculated using the Born–Haber cycle: ΔlatH0 = −99020 kJ/mol. The lattice enthalpy increases in magnitude as the lanthanide radius decreases in the neodymium–dysprosium–holmium series.

Synthesis, Thermodynamic Properties, and Ionic Conductivity of Compounds Based on Bismuth Niobates Doped by Rare-Earth Elements (A Review)

Synthesis methods, thermodynamic and functional properties of compounds based on bismuth niobates doped with rare-earth elements (REEs) are presented. These compounds are promising materials for fuel cells, ceramic oxygen generators, electrocatalysis, etc. As show the data generalized, most compounds have a cubic structure of the δ-form of bismuth oxide, which has the highest ionic conductivity among solid-state ionic conductors. The compounds have high lattice enthalpy and are therefore promising high-energy compounds. The review summarizes studies on the basic thermodynamic characteristics of bismuth niobates doped with rare earth elements. The change in standard enthalpies of formation, lattice enthalpies, and heat capacity when replacing one rare earth element with another is analyzed. It is shown that as the radius of rare earth elements decreases, the standard enthalpies of formation increases and lattice enthalpies increases. The change in ionic conductivity with changes in temperature and rare earth element content has been studied. It has been shown that with increasing temperature and REE content, conductivity increases.

Magnetic/optical assessments of RFeO3 (R=La, Pr, Nd, and Sm) ceramics: An experimental and theoretical discernment

Experimental and Density Functional Theory (DFT) studies on the structural, magnetic and optical properties of rare-earth orthoferrites RFeO3 (R = La, Pr, Nd, and Sm) were performed. The synthesis was carried out via the Ethylenediaminetetraacetic acid (EDTA)-citrate method. All these perovskites exhibited orthorhombic crystal structures with a space group Pbnm, and their lattice parameters and unit cell volumes decreased as a function of the rare earth ionic radius, as it was expected. The microstructural analysis indicates that all the perovskites share similar textural properties. The magnetic characterization revealed a weak ferromagnetic behavior attributed to the canted antiferromagnetic Fe3+ sublattices, with the dominant magnetic configuration identified as the G-type. Super-exchange interactions between Fe3+-O-Fe3+, R3+-O-Fe3+, and R3+-O-R3+ couplings facilitated a long-range magnetic ordering. The optical characterization indicated d-d electronic transitions, and the perovskites were confirmed as semiconductors with a bandgap of approximately 2.1 eV. The calculation of the transition dipole moment demonstrates two significant aspects: the electronic transition is direct and allowed, and its enhancement is evident in the Sm sample. Overall, this study provides valuable insights into the crystal structure, magnetic properties and optical behavior of RFeO3 perovskites, synthesized via the EDTA-citrate method.

Impact of Ln cation on the oxygen ion conductivity of Ln14W4O33 (Ln = Nd, Sm, Gd, Dy, Ho, Er, Tm, Yb) tungstates

Tungstates Ln14W4O33 (Ln = Nd, Sm, Gd, Dy, Ho, Er, Tm, Yb) with a pseudorhombohedral structure have been synthesized by a short high temperature annealing (1450–1600 °С) from mechanically activated mixtures of oxides. The resulting ceramics were studied by X-ray diffraction, Raman and SEM analyses. The conductivity of ceramics was measured by the 4-probe direct current method in dry and wet atmospheres (oxidizing and reducing) and by impedance spectroscopy. In order to estimate the ionic and electronic contributions to the total conductivity, the dependences of the conductivity on the oxygen partial pressure (pO2) were determined at temperatures between 700 and 900 °C. Ln14W4O33 (Ln = Nd, Sm, Gd) tungstates have a wide electrolytic range (10−15–1 atm) above 700 °C. It should be noted that under oxidizing conditions the contribution of hole conductivity is absent in these compounds. Among the pseudorhombohedral phases of Ln14W4O33 (Ln = Nd, Sm, Gd), Nd14W4O33 exhibits the highest oxygen-ion conductivity (4 × 10−4 S/cm at 700 °C). The electrolytic domain of the second half of the REE Ln14W4O33 (Ln = Dy, Ho, Er, Tm, Yb) series becomes narrower (10−10–10−5 atm) and at the same time has a slight slope indicating the presence of impurity electronic charge carriers. Investigations in a reducing atmosphere confirmed that the reduction tendency increases with decreasing lanthanide ionic radius in the Ln14W4O33 tungsten series. The variations of the total conductivity in the series of pseudorhombohedral phases Ln14W4O33 (Ln = Dy, Ho, Er, Tm, Yb) are associated with local changes in the short-range order structure (Raman spectroscopy). When Ln14W4O33 (Ln = Nd, Gd) is exposed to water at room temperature for an extended period of time, the total conductivity decreases due to the diffusion of the Nd and Gd cations into the water.

Role of Lanthanide in the Electronic Properties of RbLn 2Fe4As4O2 (Ln = Sm and Ho) Superconductors

We focus on the effect of ionic radius of lanthanides and the number of electrons in 4f orbitals on the superconducting temperature in 12442-type iron-based superconductors RbLn 2Fe4As4O2 (Ln = Sm and Ho). Electronic properties of RbSm2Fe4As4O2 and RbHo2Fe4As4O2 with the largest differences of ionic radii and numbers of electrons in 4f orbital, and the largest difference of superconducting temperatures by using first-principles calculations. We predict that the ground state of RbLn 2Fe4As4O2 is spin-density-wave-type in-plane striped antiferromagnet, and the magnetic moment around each Fe atom is about 2μ B. RbSm2Fe4As4O2 has a great influence on the energy band near the Γ point, and a Dirac-like dispersion energy band appears. This band is mainly contributed by the orbital of Fe, which proves that RbSm2Fe4As4O2 has a stronger three-dimensionality. At the same time, this extra Fermi surface appears at the Γ point, which also shows that Sm can effectively enhance the coupling strength within Fe2As2 bilayers. This is also confirmed by the charge density difference ρ(RbHo2Fe4As4O2) −ρ(RbSm2Fe4As4O2). It increases the internal coupling strength of the bilayer Fe2As2 layers, which in turn leads to a higher T c of RbSm2Fe4As4O2 than RbHo2Fe4As4O2. Determining the details of their electronic structure, which may be closely related to superconductivity, is crucial to understanding the underlying mechanism. Such microscopic studies provide useful clues for our further research of other high-temperature superconductors.

A ribozyme that uses lanthanides as cofactor.

To explore how an early, RNA-based life form could have functioned, in vitro selection experiments have been used to develop catalytic RNAs (ribozymes) with relevant functions. We previously identified ribozymes that use the prebiotically plausible energy source cyclic trimetaphosphate (cTmp) to convert their 5'-hydroxyl group to a 5'-triphosphate. While these ribozymes were developed in the presence of Mg2+, we tested here whether lanthanides could also serve as catalytic cofactors because lanthanides are ideal catalytic cations for this reaction. After an in vitro selection in the presence of Yb3+, several active sequences were isolated, and the most active RNA was analyzed in more detail. This ribozyme required lanthanides for activity, with highest activity at a 10:1 molar ratio of cTmp : Yb3+. Only the four heaviest lanthanides gave detectable signals, indicating a high sensitivity of ribozyme catalysis to the lanthanide ion radius. Potassium and Magnesium did not facilitate catalysis alone but they increased the lanthanide-mediated kOBS by at least 100-fold, with both K+ and Mg2+ modulating the ribozyme's secondary structure. Together, these findings show that RNA is able to use the unique properties of lanthanides as catalytic cofactor. The results are discussed in the context of early life forms.