Rare-earth Size Research Articles

Influence of Rare-Earth Doping Content and Type on Phase Transformation and Transport Properties in Highly Doped CeO2.

Rare-earth doped CeO2 materials find extensive application in high-temperature energy conversion devices such as solid oxide fuel cells and electrolyzers. However, understanding the complex relationship between structural and electrical properties, particularly concerning rare-earth ionic size and content, remains a subject of ongoing debate, with conflicting published results. In this study, we have conducted comprehensive long-range and local order structural characterization of Ce1-xLnxO2-x/2 samples (x ≤ 0.6; Ln = La, Nd, Sm, Gd, and Yb) using X-ray and neutron powder diffraction, Raman spectroscopy, and electron diffraction. The increase in the rare-earth dopant content leads to a progressive phase transformation from a disordered fluorite structure to a C-type ordered superstructure, accompanied by reduced ionic conductivity. Samples with low dopant content (x = 0.2) exhibit higher ionic conductivity in Gd3+ and Sm3+ series due to lower lattice cell distortion. Conversely, highly doped samples (x = 0.6) exhibit superior conductivity for larger rare-earth dopant cations. Thermogravimetric analysis confirms increased water uptake and proton conductivity with increasing dopant concentration, while the electronic conductivity remains relatively unaffected, resulting in reduced ionic transport numbers. These findings offer insights into the relationship between transport properties and defect-induced local distortions in rare-earth doped CeO2, suggesting the potential for developing new functional materials with mixed ionic oxide, proton, and electronic conductivity for high-temperature energy systems.

On the Lanthanide Effect on Functional Properties of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 Ceramic.

The beneficial effects of lanthanide incorporation into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-BT) matrix on its functional properties were investigated. The conventional solid-state method was used for synthesizing samples. The structural refinement revealed that all samples crystallized in R3c rhombohedral symmetry. Raman spectroscopy study was carried out using green laser excitation and revealed that no clear perceptible variation in frequency is observed. Dielectric measurements unveiled that the introduction of rare earth obstructed the depolarization temperature promoted in BNT-BT, the diffusive phase transition decreasing with increasing lanthanide size. Only dysprosium addition showed comparable diffusion constant and dielectric behavior as the unmodified composition. Further, the comparison of the obtained ferroelectric hysteresis and strain-electric field loops revealed that only Dy-phase exhibited interesting properties comparing parent composition. In addition, the incorporation of lanthanides Ln3+ into the BNT-BT matrix led to the development of luminescence characteristics in the visible and near infrared regions, depending on the excitation wavelengths. The simultaneous occurrence of photoluminescence and ferroelectric/piezoelectric properties opens up possibilities for BNT-BT-Ln to exhibit multifunctionality in a wide range of applications.

Tiny Sc Allows the Chains to Rattle: Impact of Lu and Y Doping on the Charge-Density Wave in ScV6Sn6.

The kagome metals display an intriguing variety of electronic and magnetic phases arising from the connectivity of atoms on a kagome lattice. A growing number of these materials with vanadium-kagome nets host charge-density waves (CDWs) at low temperatures, including ScV6Sn6, CsV3Sb5, and V3Sb2. Curiously, only the Sc version of the RV6Sn6 materials with a HfFe6Ge6-type structure hosts a CDW (R = Gd-Lu, Y, Sc). In this study, we investigate the role of rare earth size in CDW formation in the RV6Sn6 compounds. Magnetization measurements on our single crystals of (Sc,Lu)V6Sn6 and (Sc,Y)V6Sn6 establish that the CDW is suppressed by substituting Sc by larger Lu or Y. Single-crystal X-ray diffraction reveals that compressible Sn-Sn bonds accommodate the larger rare earth atoms within loosely packed R-Sn-Sn chains without significantly expanding the lattice. We propose that Sc provides extra room in these chains crucial to CDW formation in ScV6Sn6. Our rattling chain model explains why both physical pressure and substitution by larger rare earth atoms hinder CDW formation despite opposite impacts on lattice size. We emphasize the cooperative effect of pressure and rare earth size by demonstrating that pressure further suppresses the CDW in a Lu-doped ScV6Sn6 crystal. Our model not only addresses why a CDW only forms in the RV6Sn6 materials with tiny Sc but also advances our understanding of why unusual CDWs form in the kagome metals.

Rare-earth control of phase transitions in infinite-layer nickelates.

Perovskite nickelates RNiO3 (R = rare-earth ion) exhibit complex rare-earth ion dependent phase diagram and high tunability of various appealing properties. Here, combining first- and finite-temperature second-principles calculations, we explicitly demonstrate that the superior merits of the interplay among lattice, electron, and spin degrees of freedom can be passed to RNiO2, which recently gained significant interest as superconductors. We unveil that decreasing the rare-earth size directly modulates the structural, electronic, and magnetic properties and naturally groups infinite-layer nickelates into two categories in terms of the Fermi surface and magnetic dimensionality: compounds with large rare-earth sizes (La, Pr) closely resemble the key properties of CaCuO2, showing quasi-two-dimensional (2D) antiferromagnetic (AFM) correlations and strongly localized orbitals around the Fermi level; the compounds with small rare-earth sizes (Nd-Lu) are highly analogous to ferropnictides, showing three-dimensional (3D) magnetic dimensionality and strong dispersion of electrons at the Fermi level. Additionally, we highlight that RNiO2 with R = Nd-Lu exhibit on cooling a structural transition with the appearance of oxygen rotation motion, which is softened by the reduction of rare-earth size and enhanced by spin-rotation couplings. The rare-earth control of dispersion and structural phase transition might be the key factors differentiating the distinct upper critical field and resistivity in different compounds. The established original phase diagram summarizing the temperature and rare-earth controlled structural, electronic, and magnetic transitions in RNiO2 compounds provides rich structural and chemical flexibility to tailor the superconducting property.

Impact of the lanthanide size on the polymorphism and electrical properties of Ln5.4MoO11.1 (Ln = Nd, Sm and Gd)

Mixed proton-electronic conductors are of great interest for high temperature electrochemical devices, such as hydrogen separation membranes. In this contribution, ceramics with composition Ln5.4MoO11.1 (Ln = Nd, Sm and Gd) were prepared by a freeze-drying precursor method. The resulting powders were sintered at 1500 °C and cooled down at different rates to investigate the different polymorphic forms: quenching (rapid cooling), 5 and 0.5 °C min−1. The ceramics were characterized by different techniques: X-ray diffraction, scanning and transmission electron microscopies and X-ray photoelectron and impedance spectroscopies. X-ray diffraction studies confirmed that all materials are single phase regardless of the cooling rate used. Those cooled by quenching present a simple cubic fluorite structure. At lower rates, 5 and 0.5 °C min−1, the cubic symmetry is stabilized as the size of the lanthanide decreases. However, electron diffraction studies indicated the formation of domains with superstructure ordering. Furthermore, XPS analysis showed the presence of mixed Mo6+ and Mo5+ for all compositions, which explains the electronic conduction in an oxidizing atmosphere. All materials are stable in reducing atmosphere and the ionic and electronic conductivities show opposite trends as the ionic radii of the lanthanide element becomes smaller, where the former decreases and the latter increases.

Structural and Spectroscopic Features of the Bixbyite-Type Yttrium Scandate Doped by Rare-Earth Ions

Yttrium scandate crystal fiber has been obtained through laser-heated pedestal growth. The crystal belongs to a bixbyite crystal structure and crystallizes in Ia3¯ space group. X-ray diffraction method shows a lattice parameter of a = 10.228(1) Å. Factor-group analysis of YScO3 Raman spectra points to high degree of disorder in crystal structure of the new compound. Spectral-kinetic investigation of the crystal fibers doped by rare-earth ions points to the presence of two independent active optical centers of rare-earth ions. Moreover, the character of rare-earth impurities’ distribution is independent on a rare-earth ionic radius size.

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Competing dynamical and lattice instabilities in RVO4 rare-earth vanadium oxides under high pressure

Zircon-type ${R\mathrm{VO}}_{4}$ compounds (where R = rare-earth atom) constitute a family of ternary oxides which are abundant in both nature and the industrial field. Their structural systematics upon compression has been widely studied. According to the observed systematics, the high-pressure crystal structure is determined by the rare-earth cation size. Nonetheless, the mechanisms involved in the phase transitions remain relatively unexplored. Thus, we gathered the experimental data reported in the literature and compared it to our ab initio calculations, including not only enthalpy, but also the frequency of lattice modes and the value of elastic constants. Our study reveals systematic trends, where high-pressure phases appear only if they are thermodynamically stable and are always preceded by a mechanical or dynamical instability, which counteracts the effects of kinetic barriers in the zircon-to-monazite or -scheelite phase transition, respectively.

Fabrication of different rare earth incorporated ZnCo2O4 matrix via chemical-mechanical hybrid mechanism and study their charge carrier dynamics by Motts VRH model

This work reports how microstructural and electrical property varies with different rare-earth (Nd, Sm, Gd, Dy and Y) incorporation in spinel structured ZnCo2O4 nano-cobaltite. These materials have been synthesized using a combination of both chemical and physical methods. Host spinel material was prepared through chemical co-precipitation method and mechanical milling was used to reinforce the rare earth oxides into the spinel structure. Structural, microstructural, elemental and optical characterization has been carried out using XRD, FTIR, FESEM, EDX and UV-Vis spectroscopy. XRD confirms the formation of the nanocrystalline materials. Different microstructural parameters like lattice parameters, microstrain, crystallite size and x-ray density have been estimated from Rietveld analysis, which shows particle size of the doped samples depends on size of the dopant rare earth. Positions of different bonds have been confirmed from FT-IR analysis. FESEM micrographs confirm particle dimensions of the agglomerated spherical grains are in good agreement with Rietveld output. Optical band gap increases with decreasing dopant radii from 3.48 eV to 3.99 eV. Impedance plots show highest conductivity achieved was 1.151 × 10−3 Ω−1cm−1 at 433 K for Yttrium doped ZnCo2O4 nano-composition with lowest activation energy of 0.34 eV. Temperature dependent frequency exponent explains small polaron hopping transaction. Impedance master curves obey time-temperature superposition principle. Motts VRH model applied to electrical properties to get an insight about electrical conduction mechanism of the prepared samples.

Performance of the layered cobaltites in membrane mediated oxygen separation from air and methane partial oxidation

The performance of dense ceramics LnBaCo2–xAlxO6–δ, where Ln = Pr, Sm, and Gd, and x = 0.025 and 0.1, was studied at oxygen separation from the air and membrane-mediated catalytic partial oxidation of methane. The best oxygen permeability was observed for PrBaCo2–xAlxO6–δ at x =0.025. The increase of aluminum content and the decrease of the rare-earth size resulted in a fast decline of the oxygen separation efficiency. The oxygen flux is found to improve more than ten times at partial oxidation of methane (POM) with the selectivity for CO near 90%. The energy-dispersive X-ray spectroscopy (EDX) analysis gives evidence to phase separation effects in the membrane material after 800 h of the POM run.

Strain tuning of interorbital correlations in LaVO3 thin films

$3{d}^{2}$ vanadate perovskites exhibit an unusual phase diagram where the low temperature orbital and spin orders are strongly dependent upon the rare-earth cation size. Here, we demonstrate the delicate role of strain in epitaxial ${\mathrm{LaVO}}_{3}$ films by performing low-energy muon spin spectroscopy and ellipsometry measurements. The electronic structure is revealed by the measurement of the multipeak structure of the charge excitations. The analysis highlights the independent roles of the ${d}_{xy}$ band confinement and the ${d}_{zx},{d}_{zy}$ doublet polarization for the orbital ordering to establish.

X-ray absorption and x-ray magnetic circular dichroism in bulk and thin films of ferrimagnetic GdTiO3

Perovskite rare-earth titanates are prototypical Mott insulators in which ${\mathrm{Ti}}^{3+}$ ions with $3{d}^{1}$ electronic configuration exhibit ferromagnetic or antiferromagnetic spin order, depending on the rare-earth size. This peculiar magnetic behavior has, however, been barely studied with element-specific probes, either in bulk or in thin films. The recent finding of fingerprints of ferromagnetism in two-dimensional electron gases at oxide interfaces involving rare-earth titanates has produced a surge of the interest in these complex materials. Harnessing the interfacial magnetic states in these heterostructures calls for a better understanding of their insufficiently explored magnetic states in bulk and especially in thin film form. In this paper, we combine high-resolution transmission electron microscopy with x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) to determine the structural, electronic, and magnetic structure of $\mathrm{GdTi}{\mathrm{O}}_{3}$ in bulk and thin film form. In both cases, we find that the sample surface is strongly overoxidized but a few nm below, Ti is mostly 3+ and shows a large XMCD. We provide evidence for the ferrimagnetic nature of $\mathrm{GdTi}{\mathrm{O}}_{3}$ with antialigned Gd and Ti sublattices and show that, just as in antiferromagnetic $\mathrm{LaTi}{\mathrm{O}}_{3}$ or ferromagnetic $\mathrm{YTi}{\mathrm{O}}_{3}$, Ti carries no orbital moment.

Structural evolution across the metal-insulator transition of strongly distorted Lu1−xScxNiO3 perovskites (x = 0, 0.1, 0.2)

RNiO3 perovskites have been described to present thermally driven metal-insulator transitions (at TMI) as a function of the rare-earth ion size (R = Pr to Lu). Aiming to extend the stability range of RNiO3 for smaller R3+ ions, we prepared Lu1−xScxNiO3 (x = 0, 0.1, 0.2) perovskites, being Sc3+ ions substantially smaller than Lu3+, by using a multi-anvil high-pressure synthesis device at 10 GPa. We have studied the structural evolution of Lu0.9Sc0.1NiO3 by synchrotron x-ray diffraction (SXRD) from room temperature to 350 °C. The symmetry of the lattice evolves from monoclinic (P2 1 /n) to orthorhombic (Pbnm) upon heating across TMI (≈320 °C), with the existence of two chemically and crystallographically distinct nickel sites in the insulating, monoclinic regime, whereas the metallic phase has a single NiO6 environment. A simultaneous structural and electronic transition implies an abrupt evolution of the lattice parameters and size of the NiO6 octahedra upon entering the metallic regime, leading to the merging of the disproportionated Ni-O bond lengths. The magnetic properties correspond to the establishment of antiferromagnetic correlations at the Ni sublattice; a decrease of the TN ordering temperature from 122 K (x = 0) to 113 K (x = 0.2) is observed as the Sc content increases, which is concomitant with a more distorted perovskite structure.

Electrical conductivity and thermal expansion of Ln-substituted SrTiO3 for solid oxide cell electrodes and interconnects: The effect of rare-earth cation size

The present work aims to evaluate relevant effects of the size of substituting rare-earth cation on electrical conductivity and thermal expansion of donor-doped SrTiO3 as ceramic components of electrochemical solid electrolyte cells. A series of strontium titanate-based ceramics with a moderate doping level and different cation stoichiometry, Sr0.90Ln0.10TiO3±δ and Sr0.85Ln0.10TiO3±δ (Ln = La–Yb), are prepared under identical conditions with the final reductive treatment in 10%H2–N2 atmosphere at 1500 °C for 10 h. The solubility of rare-earth cations in the strontium sublattice of perovskite-type SrTiO3 is found to decrease with reducing ionic radius leading to a segregation of secondary pyrochlore-type Ln2Ti2O7 phase in the case of smaller rare-earth cations (Ln = Dy–Yb). The results of electrical, dilatometric and thermogravimetric studies suggest that the size of donor Ln3+ cation and cation stoichiometry have no evident impact on the electrical conductivity or thermal expansion behavior as long as the content of Ln3+ is within the solubility limits. All reduced donor-doped titanate ceramics (except Yb-doped) show a similar level of electrical conductivity, 100–155 S cm−1 at 800 °C, determined by the content of Ln3+ in the strontium sublattice, and moderate thermal expansion coefficients, 11.9–12.1 ppm K−1 at 25–1100 °C, compatible with that of conventional solid electrolytes.

High-Pressure, High-Temperature Synthesis and Characterization of Polar and Magnetic LuCrWO6.

A new polar and magnetic oxide, LuCrWO6, was synthesized under high pressure (6 GPa) and high temperature (1673 K). LuCrWO6 is isostructural with the previously reported polar YCrWO6 (SG: Pna21, no. 33). The ordering of CrO6 and WO6 octahedra in the edge-shared dimers induce the polar structure. The effective size of rare earth, Ln cation does not seem to affect the symmetry of LnCrWO6. Second harmonic generation measurements of LuCrWO6 confirmed the noncentrosymmetric character and strong piezoelectric domains are observed from piezoresponse force microscopy at room temperature. LuCrWO6 exhibits antiferromagnetic behavior, TN, of ∼18 K with a Weiss temperature of -30.7 K.

Rare earth barium cobaltites: potential candidates for low-temperature oxygen separation

Oxygen storage materials with low operating temperatures have gained attraction in oxygen separation and enrichment applications. Herein, $$\hbox {YBaCo}_{2}\hbox {O}_{6-x}$$ , $$\hbox {Dy}_{0.5}\hbox {Y}_{0.5} \hbox {BaCo}_{2}\hbox {O}_{6-x}$$ and $$\hbox {DyBaCo}_{2}\hbox {O}_{6-x}$$ are explored for low-temperature oxygen enrichment. These oxides were synthesized through solid-state reaction and the oxygen separation properties at various temperatures were studied using a home-built volumetric setup. The oxygen intake temperatures of the sample were found to vary depending upon the rare-earth cation size. The lowest absorption temperature of 523 K was observed for $$\hbox {DyBaCo}_{2}\hbox {O}_{6-x}$$ . Interestingly, $$\hbox {DyBaCo}_{2}\hbox {O}_{6-x}$$ had the largest saddle point radii through which oxide ion migration occurs. The effect of the synthesis method and microstructure on the oxygen holding capacity of $$\hbox {DyBaCo}_{2}\hbox {O}_{6-x}$$ has also been analyzed. For this, $$\hbox {DyBaCo}_{2}\hbox {O}_{6-x}$$ was synthesized through a combination of solution combustion synthesis followed by calcination and sintering at different temperatures. The particle size was found to have a profound effect on the oxygen intake of $$\hbox {DyBaCo}_{2} \hbox {O}_{6-x}$$ .

Supramolecular assembly of lanthanide-2,3,5,6-tetrafluoroterephthalic acid coordination polymers via fluorine⋯fluorine interactions: a platform for luminescent detection of Fe3+ and nitroaromatic compounds

F⋯F interactions stabilize {[Ln(TFTA)1.5(H2O)2]·H2O}n 2D coordination polymers which selectively detect Fe3+ and p-nitrophenols.

Interface exchange coupling controlled electronic transport in (La,Nd)NiO3/La0.7Sr0.3MnO3 multilayer thin films

Abstract The hetero-structures of different correlated electronic and magnetic oxides have created fresh hope for the emerging class of oxide electronics. Here, we present a detailed investigation on structural, electrical, and magnetic properties of two such hetero-structures of perovskite nickelates and manganites; i.e., NdNiO3/La0.7Sr0.3MnO3 (NL) which exhibits metal-insulator (M-I) transition and LaNiO3/La0.7Sr0.3MnO3 (LL) sans MIT. The interfacial properties of these two heterostructures are scaled and compared as a function of the number of stacking layer periodicity (x) and the layer thickness (n). For NL series, we found a pronounced dependence of M-I transition on ‘x’ but for LL series, in contrast, we observed a different electronic transition: from a non-Fermi liquid to a Fermi liquid behavior upon reduction of layer thickness. A significant difference in magnetic properties of these two SL series reveals that the rare-earth cation size and/or magnetic order exceptionally control the charge redistribution at the interface of these two different SL series. Overall, this study brings out a broad range of electronic phases that can be realized in nickelate based heterostructures in which the rare-earth cation size can act as an effective controlling parameter.

Wettability and Interfacial Tension Alteration of Rare-Earth Doped Yttrium Iron Garnet under Influence of Electromagnetic Waves

Yttrium Iron Garnet (YIG) doped with rare-earth elements have shown to alter the magnetic properties of garnet nanoparticles (NPs), which is believed to have direct influence on the wettability, interfacial tension and viscosity alteration of garnet nanofluids. In this study, Y2.8R0.2Fe5O12 (R = Lanthanum (La), Neodymium (Nd) and Samarium (Sm)) NPs were synthesized by using the sol gel auto-combustion method followed by annealing treatment at 1000°C for 3 hours. The Y2.8R0.2Fe5O12 nanoparticles synthesized had grain size ranging from 100 to 200nm with high crystallinity properties. X-ray Diffraction peaks showed varying shifting with the size of the rare-earth ions in the Y2.8R0.2Fe5O12 crystal system, suggesting that structural distortion is due to replacement of bigger ions. Sm-YIG exhibited the highest magnetization saturation among all samples, with the value of 23.54 emu/g. Wettability data of Y2.8R0.2Fe5O12 (RE-YIG) nanofluids showed that oil-wetting contact angle has an overall reduction under the influence of electromagnetic wave. Whereas the interfacial tension and viscosity data showed that doped garnet nanofluids has lower value than that of garnet nanofluids, but the magnitude of interfacial tension and viscosity value decreased with the rare-earth ionic size. Sm-YIG also has the highest interfacial tension across all samples, as the stronger magnetization saturation may contribute to higher surface tension exerted on the oil-nanofluid interface.

Thermoluminescence spectra of rare earth doped magnesium orthosilicate

Thermoluminescence (TL) spectra of undoped and rare earth doped magnesium orthosilicate, Mg2SiO4: RE3+ (RE = Yb, Tm, Er, Dy, Tb, Eu, Sm, Nd, Pr, Ce) samples, were recorded from room temperature to 450 °C. The rare earth dopants mostly suppress signals from the host material. The glow peak temperatures are a function of rare earth size relative to the magnesium ions. The patterns differ between glow peaks, and this is interpreted as evidence for rare earth ions on the two possible magnesium lattice sites. Further, the peak TL temperatures can vary between the transition wavelengths of the same dopant, which is consistent with close association of the rare earth and charge trapping sites. Overall, this large body of spectrally resolved thermoluminescence data indicate systematic changes with the size of the dopants. Powder formation introduces lattice damage which lowers the peak temperatures relative to single crystals, and inherent temperature sensitive spectral complexity of the data emphasis that energy analyses of polychromatic signals are inappropriate.