Rare-earth Radius Research Articles

Apatite and garnet stability in the Al–Ca–Mg–Si–(Gd/Y/Yb)–O systems and implications for T/EBC: CMAS reactions

AbstractThis work advances the understanding of the influence of rare earth (RE) ion radius on the stability and extent of the garnet solid solution phase in the (ytterbia/yttria/gadolinia)‐calcia‐magnesia‐alumina‐silica systems. Guided by the crystal chemistry and charge neutrality constraints, selected compositions in the notional garnet stability field were synthesized, equilibrated at 1400°C, and characterized to determine the equilibrium phases and their compositions. The results show a significant reduction in the stability of the silicate garnet relative to apatite with increasing RE ion radius. Apatite was not observed for any composition in the Yb‐containing system, the Y‐containing system formed both garnet and apatite, and there was no evidence of silicate garnets in the Gd‐containing system. However, despite the apparent differences in stability relative to apatite, the extent of the garnet solid solution increases only slightly for the Yb‐ compared to Y‐containing systems. The quantitative microchemical analysis suggests that Mg2+ prefers the octahedral site over the dodecahedral site in the garnet structure, and that the solubility of Mg2+ in the dodecahedral site increased in the system containing Yb3+ compared to Y3+. The results are discussed for their relevance to reactions between RE‐containing thermal and environmental barrier coatings and CMAS‐type silicate deposits.

Preparation, microstructures, and mechanical properties of directionally solidified Al2O3/Lu3Al5O12 eutectic ceramics

AbstractAl2O3/Lu3Al5O12 (LuAG) directionally solidified eutectic (DSE) ceramics with two solidification rates were prepared utilizing optical floating zone (OFZ) technique. The microstructures (eutectic morphology, preferred growth direction and interface orientation) of Al2O3/LuAG were characterized, and the mechanical properties (Vickers hardness and fracture toughness) were compared with those of Al2O3/REAG (RE = Y, Er, and Yb). Results show that Al2O3/LuAG with solidification rate of 30 mm/h has established preferred growth direction in both Al2O3 and LuAG phases with cellular eutectic structures. While Al2O3/LuAG with solidification rate of 10 mm/h only shows preferred growth direction in Al2O3 phase and presents degenerate irregular eutectic microstructures. Besides, Al2O3/LuAG exhibits higher hardness compared with Al2O3/REAG (RE = Y, Er, and Yb). In addition, a special attention is focused on the relations among rare earth ionic radius, eutectic microstructures, and mechanical properties of these DSE ceramics. It is demonstrated that a smaller rare earth ionic radius could lead to larger eutectic interspacing as well as higher Vickers hardness of DSE Al2O3/REAG, revealing the possibility and feasibility of microstructure control and mechanical properties optimization for DSE Al2O3/REAG ceramics by tailoring the rare earth elements.

Hydrofluorocarbon Diluent for CMPO Without Third Phase Formation: Extraction of Uranium(VI) and Lanthanide(III) Ions

ABSTRACT The extraction behaviors of trivalent lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and hexavalent uranium with octylphenyl(,-diisobutylcarbamoylmethyl)phosphine oxide (CMPO) from a nitric acid medium were studied using hydrofluorocarbon (1,1,1,2,2,3,4,5,5,5- decafluoropentane: HFC-43) as a nonflammable diluent. It was revealed that HFC-43 exhibits high solubility of CMPO even in the absence of tributylphosphate (TBP), which has typically been necessary to prevent third-phase formation in the conventional TRUEX process using -dodecane as a diluent. Distribution ratios have been studied as a function of aqueous HNO concentrations, CMPO concentrations, and ionic radii of lanthanide(III) ions. The stoichiometry of the extracted coordination complex was examined based on the slope analysis, and it was determined that two to three CMPO molecules are coordinated to one lanthanide or uranium ion. The feasibility of the process is indicated by the distribution ratio, which is comparable to the conventional system using -dodecane as diluent. In addition, the safety benefits of applying the nonflammable solvent HFC to the TRUEX process are also presented.

Molten-salt synthesis of rare-earth nickelate electronic transition semiconductors at medium high metastability

The metastable rare-earth nickelates (RENiO3) exhibit exceptional complex electronic phase diagram and widely tunable metal to insulator transition (MIT) properties among the correlated oxide semiconductors. Unlike the synthesis of PrNiO3, NdNiO3, and SmNiO3 at low metastability, the material growth of RENiO3 with small rare-earth radius and large metastability yet requires harsh conditions. Herein, we demonstrate the molten-salt synthesis of EuNiO3 and GdNiO3 powders that reduces the oxygen pressure from the previous 90 MPa magnitude to 10 MPa utilizing their heterogeneous nucleation with KCl. The KCl behaves as seed crystal that triggers heterogeneous growth of metastable RENiO3 via interfacial energy, as confirmed by density functional theory (DFT) calculations. Apart from extending the widely adjustability in their MIT temperature (TMIT), we highlight the much smaller electronic resistivity of the insulating phase of RENiO3 compared to conventional thermistor materials, and this may cater for special thermistor applications such as inrush current limiting.

The effect of substituting of rare earth elements (R = Ho, Yb) on energetic characteristics of doped barium cerates

The barium cerates doped by holmium, ytterbium and indium (BaCe0.7Ho0.2In0.1O2.85, BaCe0.7Yb0.2In0.1O2.85) as perspective ionic conductor materials for fuel cells with increased thermodynamic stability have been synthesized by solid state reactions. The study of energy characteristics with emphasis on determination of basic thermodynamic characteristics such as standard formation enthalpies and lattice enthalpies was carried out using reaction calorimetry. On the basis of experimental data it was shown that standard formation enthalpies and lattice enthalpies are increasing in absolute value from BaCeO3 doped by holmium and indium to BaCeO3 doped by ytterbium and indium. The dependences of energetic characteristics on radii of rare-earth elements were constructed; and explanation of dependences based on the Kapustinski formula was presented. Based on our studies, we can conclude that barium cerate doped by indium and ytterbium is the most promising compound for practical application from thermodynamic point of view.

Preparation and dielectric properties of co-contained unfilled tungsten bronze ceramics Ba4RCo0.5Nb9.5O30

In this study, Ba4RCo0.5Nb9.5O30 (R = La, Nd, Sm, Eu) (BRCN) ceramics were synthesized using a high-temperature solid-state reaction. The XRD refinement results show that ceramic samples are tetragonal tungsten bronze (TTB). As the radius of rare-earth ions decreases, the unit cell volume of BRCN ceramics decreases, and the radius difference between Ba2+ and R ions increase, which results in BO6 octahedral distortion and the Raman peaks shift to high frequency. In addition, as the radius of rare-earth ions decreases, the ionic displacements increase and thus the dielectric constant peak temperature goes up. The high-temperature impedance results show that there exists n-type electronic conduction in the samples. The remanent polarization of the P–E curve at low frequencies increases from 0.470 to 1.038 μC cm−2 as the rare-earth ion radius decreases.

First-principles study of electron and hole doping effects in perovskite nickelates

Rare-earth nickelates ${R}^{3+}{\mathrm{Ni}}^{3+}{\mathrm{O}}_{3}$ ($R=\mathrm{Lu}\text{\ensuremath{-}}\mathrm{Pr}$, Y) show a striking metal-insulator transition in their bulk phase whose temperature can be tuned by the rare-earth radius. These compounds are also the parent phases of the newly identified infinite layer $R\mathrm{Ni}{\mathrm{O}}_{2}$ superconductors. Although intensive theoretical works have been devoted to understand the origin of the metal-insulator transition in the bulk, there have only been a few studies on the role of hole and electron doping by rare-earth substitutions in $R\mathrm{Ni}{\mathrm{O}}_{3}$ materials. Using first-principles calculations based on density functional theory (DFT) we study the effect of hole and electron doping in a prototypical nickelate $\mathrm{SmNi}{\mathrm{O}}_{3}$. We perform calculations without Hubbard-like $U$ potential on Ni $3d$ levels but with a meta--generalized gradient approximation better amending self-interaction errors. We find that at low doping, polarons form with intermediate localized states in the band gap resulting in a semiconducting behavior. At larger doping, the intermediate states spread more and more in the band gap until they merge either with the valence (hole doping) or the conduction (electron doping) band, ultimately resulting in a metallic state at 25% of $R$ cation substitution. These results are reminiscent of experimental data available in the literature and demonstrate that DFT simulations without any empirical parameter are qualified for studying doping effects in correlated oxides and exploring the mechanisms underlying the superconducting phase of rare-earth nickelates.

Promoting electron transfer of surface oxygen vacancies in Pd/CeO2-RE via doping engineering for enhancing catalytic activity in Suzuki coupling reaction

Doping engineering is considered as a facile and effective method for improving the physical and chemical properties of CeO2. Herein, rare earth (RE) ions (La and Nd) doped Pd/CeO2 with the coaxial double-nanotube structure were manufactured by the electrospinning and high-temperature calcination. Through the doping engineering, the original morphologies of Pd/CeO2 were not destroyed and all the elements were uniformly distributed on the surface of nanotubes. XRD, Raman and UV–vis characterizations revealed that La3+ and Nd3+ ions were incorporated into the CeO2 lattice, while the cubic fluorite structure of CeO2 was maintained. Moreover, it has been proved that there were oxygen vacancies existed on the surface of CeO2 and the concentration of oxygen vacancies increased significantly as the radius of RE ions increases. In addition, an electron transfer pathway between CeO2 and Pd nanoparticles was proposed based on the experimental data and Density Functional Theory (DFT) calculations. The Pd/CeO2-La catalyst with abundant oxygen vacancies showed a high catalytic performance for Suzuki coupling reaction under mild conditions without any phase-transfer reagent, toxic solvent and inert protective atmosphere, which realizing the green catalysis.

The insights into the catalytic performance of rare earth metal ions on lactic acid formation from biomass via microwave heating

• Ln 3+ showed special activity for lactic acid formation from biomass. • The activity increased monotonically with the atomic number of Ln 3+ . • Smaller ionic radius of Ln 3+ led to stronger interaction with glucose. • Ln 3+ with smaller ionic radius exhibited higher electron-withdrawing ability. • The orbital-stabilization ability of transition state increased with atomic number. The unique properties of rare earth metal offer attractive potentials for the application as catalyst in biomass valorization. In present work, we found that rare earth metal ions exhibited specific catalytic activity for lactic acid production from biomass, giving 75.9% and 71.0% carbon molar yield of lactic acid from glucose and furfural residue, respectively. The activity of lanthanide(III) ions increased monotonically with the atomic number, as well as the decreasing ionic radius, from La 3+ to Lu 3+ . The increasing oxidation potential with atomic number might facilitate the disproportionation reaction in glucose conversion via an intramolecular H-shift. DFT calculation further revealed that smaller ionic radius of lanthanide(III) ions led to stronger interaction between lanthanide(III) ions and glucose/fructose, as well as the less composition of 4 f in LUMO that enabled more activation of glucose. More importantly, lanthanide(III) with smaller ionic radius exhibited higher electron-withdrawing ability from the oxygen atom in -C = O. This enhanced the electrophilicity of C2, C3, and C4 atoms, and led to the more exposure especially for C4 atom, thereby significantly weakening C3-C4 bond. In addition to the increasing orbital-stabilization ability at the bond-breaking site in the corresponding transition state with atomic number, the energy barrier for C3-C4 cleavage in fructose was greatly reduced by heavy lanthanide(III) ions. These factors contributed to the special activity for lactic acid formation from biomass. The insights in this work might give some useful clues for the widespread application of rare earth metal in biomass valorization.

A Facile One-Pot Approach to the Synthesis of Gd-Eu Based Metal-Organic Frameworks and Applications to Sensing of Fe3+ and Cr2O72- Ions.

Gadolinium metal-organic frameworks (Gd-MOFs) and Eu-doped Gd-MOFs have been synthesized through a one-pot green approach using commercially available reagents. The 1,4-benzenedicarboxylic acid (H2-BDC) and 2,6-naphthalenedicarboxylic acid (H2-NDC) were chosen as ditopic organic linkers to build the 3D structure of the network. The Gd-MOFs were characterized using powder X-ray diffraction (XRD), FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM) and N2 adsorption–desorption analysis. The Gd-MOF structures were attributed comparing the XRD patterns, supported by the FT-IR spectra, with data reported in the literature for Ln-MOFs of similar lanthanide ionic radius. FE-SEM characterization points to the effect of the duration of the synthesis to a more crystalline and organized structure, with grain dimensions increasing upon increasing reaction time. The total surface area of the MOFs has been determined from the application of the Brunauer–Emmett–Teller method. The study allowed us to correlate the processing conditions and ditopic linker dimension to the network surface area. Both Gd-MOF and Eu-doped Gd-MOF have been tested for sensing of the inorganic ions such as Fe3+ and Cr2O72−.

Structural and Magnetic Tuning of LaFeO3 Orthoferrite Substituted Different Rare Earth Elements to Optimize Their Technological Applications

Lanthanum partially substituted rare earth (RE) elements to form RE0.7La0.3FeO3; RE = Ce, Pr, Nd, Sm and Gd) nanoparticles. They were synthesized using the citrate–nitrate auto-combustion method. The crystal structure and microstructure were refined by applying Rietveld profile refinements using the Maud Program. The morphology, magnetic and optical properties of the inspected samples have been explored using HRTEM, VSM, and UV–Vis diffuse reflectance, respectively. The prepared-samples distortion increases as the substituted RE ionic radius decreases. Iron spins of RE orthoferrite samples are known to be ordered Anti-ferromagnetically (AFM). They also possess weak ferromagnetism due to the Dzyaloshinskii-Moriya interaction. This feeble ferromagnetism is reflected in their soft behavior, whereas Sm0.7La0.3FeO3 sample exhibits the butterfly shape hysteresis loop. The remnant magnetization, saturation magnetization, and coercivity are relatively small, but sometimes impressively, enhanced through Lanthanum-rare-earth substitution. Introducing rare earth ions into LaFeO3 decreases the Fe–O–Fe angle and the consequent reduction of the super exchange interaction. In particular, the coercivity of Sm0.7La0.3FeO3 is remarkably improved relative to the parent sample. It has the largest coercivity of all the prepared nanoparticles. Due to the aforementioned substitution, a slight reflectance edge red shift is observed in the spectra. The relation between the magnetic properties of the investigated samples and the ionic radii of RE was investigated and discussed. The experimental results of this work can provide fundamental support for the research and development of multiferroic materials.

Phase Diagrams of Lead Difluoride Systems with Rare-Earth Fluorides

Phase equilibria in the PbF2–RF3 (R = La–Nd, Sm, Gd–Lu, Y, and Sc) systems were studied by X-ray powder diffraction in samples annealed under a fluorinating atmosphere and then quenched and by differential thermal analysis (DTA) under an inert atmosphere using unlidded thin-walled graphite crucibles. Stability areas were elucidated for Pb1 – xRxF2 + x fluorite solid solutions, for R1 – yPbyF3 – y solid solutions having the tysonite LaF3 structure, and for ordered phases of idealized composition Pb4R3F17 having trigonally distorted cubic unit cells. The topological evolution of the systems in response to the changing rare-earth ionic radius was considered.

Towards efficient oxygen separation from air: Influence of the mean rare-earth radius on thermodynamics and kinetics of reactivity with oxygen in hexagonal Y1-xRxMnO3+δ

It is documented that the mean radius r¯ of rare-earth cations occupying Y1-xRx sublattice in Y1-xRxMnO3+δ hexagonal oxides plays a decisive role in terms of thermodynamics and kinetics of reactivity of the materials with oxygen, and consequently, influences strongly the oxygen storage performance in thermal swing processes conducted in oxygen and air. Y1-xRxMnO3+δ samples with designed r¯ being close to the critical one, at the border of stability between hexagonal- and perovskite-type phases, can reversibly incorporate/release significant amounts of oxygen in pure O2 or air atmospheres, at the moderate temperatures on the order of 200–300 °C. Characteristic temperatures of oxidation and reduction are dependent on r¯, therefore, it is possible to adjust conditions of the temperature swing operation by the chemical doping in Y1-xRxMnO3+δ with larger rare-earth elements. Crucial from a practical point of view, an increase of the oxidation temperature in such compounds greatly enhances the speed of the oxidation process (20 °C increase can reduce half-time of oxidation twice), which is found to be the limiting factor concerning the performance. Based on the comprehensive studies of the physicochemical properties of Y1-xRxMnO3+δ, the optimized Y0.95Pr0.05MnO3+δ composition is proposed, doped only with a small amount of more expensive praseodymium. The material exhibits excellent oxygen storage-related properties and is able for the effective production of oxygen in air by the thermal swing process, utilizing medium-/low-temperature industrial waste heat.

Effect of the nature of lanthanide on intramolecular C-F→Ln dative interactions in hexafluoroisopropoxide complexes

Electronic structures of a series oflanthanide complexes with hexafluoroisopropoxide ligands [Ln(OCH(CF3)2)2(μ2-OCH(CF3)2)(DME)]2 (Ln = Ce, Sm, Tm, Yb; DME is dimethoxyethane) were studied by quantum chemical calculations at the density functional theory (DFT) level. Intramolecular C-F→Ln interactions are present in all these compounds. A decrease in the ionic radius of lanthanide in the series from Ce to Yb leads to an increase in the degree of filling of the coordination sphere from 92.9(2) to 97.3(2)%, resulting in a systematic decrease in the delocalization index between lanthanide and fluorine atoms. An experimental-theoretical study of the complexes using a molecular invariom provided an estimate of the energy of Ln⋯F interactions, which also decreases for the complexes of the late lanthanides (Tm, Yb) compared with the complexes of the early lanthanides (Ce, Sm). Geometry optimization of the isolated molecule leads to an increase in the number of non-covalent interactions involving fluorine atoms (F⋯F, F⋯H, and F⋯O) and in their energy compared to the molecular invariom. The topological characteristics of electron density in the coordination sphere of lanthanide atoms determined by quantum chemical calculations are in good agreement with those estimated using the molecular invariom.

Synthesis, structural and physical properties of some rare-earth doped nickel chromites

A systematic investigation of structural, magnetic and transport properties of NiCr1.9R0.1O4 (R = Eu, Dy and Ho) has been undertaken. Rietveld analysis of powder X-ray diffraction data revealed that all the compounds crystallize in the cubic symmetry with space group having small volume fraction of orthorhombic phase RCrO3. Both a and V decreases with the substitution of heavier rare earth ion which is consistent with the decrease in ionic radius of rare earth ion. Temperature dependent magnetization studies showed that all our investigated compounds have negative value of Weiss constant (Θ) indicating the dominance of anti-ferromagnetic interactions in the samples. The phases are semi-conductors and the conduction mechanism was dominated by Arrhenius model in the high temperature paramagnetic semiconducting region.

Petrogenesis of the peralkaline Dutsen Wai and Ropp complexes in the Nigerian younger granites: implications for crucial metal enrichments

ABSTRACT The Dutsen Wai and Ropp complexes are parts of the over 50 within-plate alkaline ring complexes in north-central Nigeria. These complexes consist mainly of A-type granites that were emplaced between 175 Ma (in Dutsen Wai) and 149 Ma (in Ropp). They are characterized by moderately negative zircon ԑHf(t) values (–9.8 to – 5.86) with Paleoproterozoic (1597–1884 Ma) crustal model ages (TDMc), suggesting the mantle-derived parental magmas have been substantially modified by assimilation of crustal materials. The granites exhibit elevated HFSEs (e.g., Nb and Zr) and LILE (e.g., Rb and REE) concentrations, with higher values in the peralkaline than in the aluminous granites, but are depleted in compatible elements (e.g., CaO, MgO, Ba and Sr). This is typical of highly differentiated granites associated with rare metal mineralization. The peralkaline plutons show REE patterns with strong negative Eu anomalies, significant M-type lanthanide tetrad effect (TE1,3 = 1.16–1.32), and non-CHarge and Radius Controlled (CHARAC) behaviour of some HFSEs. The positive correlation of Na2O vs. Nb (r2 = 0.92) and Nb vs. TE1,3 (r2 = 0.7), increasing degree of albitization and shift in eutectics of granite minimum towards Ab-Qtz sideline indicate that Na-rich fluid plays an important role in the complexation between F and other incompatible elements in open system processes. Fluorine also favoured the retention of these crucial metals in the peralkaline melt until late magmatic-stage during which the breakdown of the F-HFSEs and F-REE complexes was accompanied by crystallization of pyrochlore and REE-bearing accessory minerals. We proposed that the emplacement of these A-type granites was probably linked to the prevailing transtension regime before the fragmentation of Gondwana during the Mesozoic period which reactivated some deep-seated Pan-African transcurrent faults. This, in turn, caused pressure release and channelled fluid, which triggered partial melting of the lower part of the lithospheric mantle.

Structural, photophysical and nonlinear optical limiting properties of sandwich phthalocyanines with different rare earth metals

Four sandwich phthalocyanines with different rare earth metals (La, Y, Yb and Sc) are synthesized to investigate the influence of aggregation on nonlinear optical limiting effect. Hyperchem fitting results show that the distance between the phthalocyanine rings of the four phthalocyanine compounds is 2.81, 2.69, 2.56 and 2.38 Å for LaPc (Tetra-β-(4-nitro) lanthanum phthalocyanine), YPc (Tetra-β-(4-nitro) yttrium phthalocyanine), YbPc (Tetra-β-(4-nitro) ytterbium phthalocyanine) and ScPc (Tetra-β-(4-nitro) scandium phthalocyanine), respectively. As the radius of rare earth ions decreases, the interlayer spacing between phthalocyanine rings decreases, which greatly increases the degree of aggregation between phthalocyanine rings. As a result, the photophysical and nonlinear absorption coefficients of different rare-earth phthalocyanines also show regular changes. The nonlinear absorption coefficients of the four rare-earth phthalocyanines were LaPc (β = 1.86ⅹ10−10 m/W), YPc (β = 9.78ⅹ10−11 m/W), YbPc (β = 6.63ⅹ10−11 m/W), ScPc (β = 7.43ⅹ10−11 m/W), respectively, indicating that the degree of aggregation between phthalocyanine rings gradually increases as the radius of rare earth metals changes from La, Y, Yb, to Sc, which inhibits the reverse saturable absorption process of the triplet states, resulting in a gradual decrease of the nonlinear absorption coefficient. The experimental results fully reveal the effect of the aggregation effect between phthalocyanine rings on photophysical and nonlinear optical properties, and would provide a theoretical basis for the design of high-performance nonlinear optical materials.

Weak ferromagnetism in perovskite oxides

Weak ferromagnetism has been widely found in antiferromagnetic systems, including the technically important orthorhombic perovskites $R\mathrm{Fe}{\mathrm{O}}_{3}$ ($R=\mathrm{rare}\phantom{\rule{0.16em}{0ex}}\mathrm{earth}$) owing to spin canting associated with crystal symmetry. Antisymmetric exchange interaction (AEI) and single-ion anisotropy (SIA) are the essential mechanisms responsible for the development of noncollinear structures in antiferromagnetic systems. AEI and SIA share the same structural restriction to facilitate the spin canting. While both AEI and SIA originate from the spin-orbit coupling effect, they have sharply different dependences on the local structure. Consideration of the structural dependence of a canted spin motivates us to revisit the orthoferrite family. The spin canting along the $c$ axis measured on precisely oriented crystals increases monotonically from $\mathrm{La}\mathrm{Fe}{\mathrm{O}}_{3}$ to $\mathrm{Lu}\mathrm{Fe}{\mathrm{O}}_{3}$. Based on Moriya's model, AEI is sensitive to the octahedral-site distortion in the perovskite structure. However, the site distortion does not exhibit a monotonic change with the rare-earth substitution. Instead, a linear relationship has been found in both the octahedral rotation and the spin canting angle versus the rare-earth ionic radius, which indicates that SIA plays a significant role leading the spin canting in orthoferrites.

Crystal structure, spectra analysis and dielectric characteristics of Ba4M28/3Ti18O54 (M= La, Pr, Nd, and Sm) microwave ceramics

High dielectric constant Ba4M28/3Ti18O54 (M = La, Pr, Nd, and Sm) ceramics were synthesized via standard solid-state reaction route. All the samples possessed single-phase orthorhombic tungsten-bronze structure, and the unit cell volumes decreased monotonously when rare-earth ion changed from La to Sm. With the decreasing radius of rare-earth ions, the dielectric constant (εr) gradually decreased, which was correlated with the decrease of total ionic polarizability and blue shift of Raman vibration modes. The increase of the quality factor (Q × f) was associated with the increase of packing fraction and the decrease of FWHM of Raman vibration modes (Ag and B1g). The temperature coefficient of resonant frequency (TCF) shifted in the negative direction, which was highly related to the decrease of the TiO6 octahedral tilt angle. Infrared reflection (IR) spectroscopy analysis indicated that the infrared vibration modes between TiO6 octahedron and A-site cation (M3+ and Ba2+) at low frequency dominated microwave dielectric polarization in the Ba4M28/3Ti18O54 ceramics.

Novel complex ceramic oxides, Ln2TiO5 (Ln = La, Sm, Gd, Tb, Dy, Ho, Er, and Yb), for polyphase nuclear waste‐forms

AbstractAs part of a broader study of ceramic nuclear waste‐forms, four different lanthanide titanates were fabricated; La0.1Sm0.1Gd0.1Tb0.1Dy0.3Ho0.1Er0.2YbTiO5, Sm0.3Gd0.3Dy0.3Yb1.1TiO5, Sm0.1Gd0.4Dy0.4Yb1.1TiO5, and Sm0.2Gd0.2Dy0.2Yb1.4TiO5. The aim was to produce single‐phase novel materials with cubic symmetry, capable of incorporating a wide variety of cations and with acceptable radiation tolerance. The chemistry flexibility and radiation tolerance are some of the major desirable properties for nuclear waste‐form materials. By using multiple lanthanides the average lanthanide radius can be controlled and consequently the structure, along with properties such as radiation tolerance. The radiation tolerance was assessed using in situ 1 MeV krypton irradiation and transmission electron microscopy characterization. Those materials for which cubic symmetry was achieved displayed better radiation tolerance; a greater critical fluence of ions (Fc) was required for the crystalline to amorphous transition, and a lower temperature was required to maintain crystallinity (Tc) during irradiation.