Properties Of Rare Earth Oxides Research Articles

Structure and cryogenic magnetocaloric effects of NaREO2 (RE = Er, Ho) compounds

Rare-earth (RE) based oxides have presented great application prospects in low-temperature magnetic refrigeration technology. Thus far, studies on magnetic and especially magnetocaloric properties of alkali-metal RE oxides are limited, largely due to the difficulty in synthesizing these oxides. In this work, NaREO2 (RE = Er, Ho) compounds with both the rhombohedral (R3‾m space group) and cubic (Fm3‾m space group) structures were prepared by a facile ball-milling-aided sintering approach. The cubic structural compounds exhibit a spherical microstructure composed of vertically-grown irregular hexahedra, which sharply contrast with a loose lamellar microstructure of the rhombohedral structural compound. The as-prepared NaHoO2 or NaErO2 compound exhibits an antiferromagnetic ordering of RE3+ moments at a temperature of 2.4 K or lower than 2 K respectively. An excellent comprehensive magnetic refrigeration performance at cryogenic temperatures in a low magnetic field change of 0–20 kOe was obtained in these compounds, including a complete reversibility of the magnetocaloric effect, a maximal magnetic-entropy change ΔSM at 2 K of 12 J/kg·K for the rhombohedral NaErO2 and a relative cooling power (RCP) of 79.7 J/kg for the cubic NaHoO2.

The modification and strengthening dual functionality of rare-earth oxide in La2O3-BaO-SiO2 glass for high temperature sealing application

In this paper, the modification and strengthening dual functionality of rare-earth oxide is authenticated by the effect La2O3/BaO on composition-structure-property correlations of new type La2O3-BaO-SiO2 (LBS) glass-ceramics sealing material with high softening point, high coefficient of thermal expansion and excellent high temperature resistivity. As the network modifier, the La2O3 can create more non-bridging oxygen than the BaO, resulting in the increase of Q0 and Q1 units and the decrease of Q2 and Q3 units in the La2O3-BaO-SiO2 glass according to Raman and 29Si Solid-State Nuclear Magnetic Resonance. The strengthening functionality of La2O3 is declared by Static 139La WURST-QCPMG NMR spectra that La3+ ions form La-O bonds with O2- ions in the glass structure and La3+ spectra widens slightly with the increasing of La2O3. Correspondingly, physical properties including Tg, Tc, ρ, and MV of La2O3-BaO-SiO2 glass gradually increase with increasment of effective cation field strength. The main crystal phase of LBS glass-ceramic transforms from Ba2Si3O8 to Ba5Si8O21 and furthur to Ba3Si5O13 phase with high coefficient of thermal expansion and there is not lanthanum-contained phase precipitation. The coefficients of thermal expansion (CTE) of LBS glass-ceramic increases from 12.48 × 10−6/℃ to 13.18 × 10−6/℃ (30–1000 ℃) and the softening temperature are between 1231.1 ℃ and 1305.1 ℃. The direct-current (DC) resistivity of the LBS glass-ceramics is higher 106 Ω·cm at a high temperature of 700 °C, which has good high-temperature electrical insulation. All in all, the high CTE, high Ts and high electrical insulation “Tri-high” properties of rare-earth oxide La2O3-BaO-SiO2 glass-ceramic will be an excellent candidate for solid oxide fuel cell, solid oxide electrolysis cell, oxygen sensors, and so on.

Analyzing the tribological and mechanical performance of Al-6061 with rare earth oxides: An experimental analysis

This article aims to evaluate the effect of ceria oxide as rare earth oxides (REOs) on the tribological properties of aluminum hybrid composites with varied concentrations of reinforcing elements such as silicon carbide, aluminum oxide, and ceria oxide. In order to accomplish this, composites were produced by varying the percentage of SiC/Al2O3 in the Al-6061 matrix from 2.5 to 7.5 wt% and the quantity of CeO2 from 0.5 to 2.5 wt%. The formation of the intermetallic phase (Al4Ce3) as a result of the integration of cerium oxide into aluminum composites at concentrations between 0.5 and 2.5 wt% results in a wear rate improvement of up to 87.28%. The objective of developing Levenberg-Marquardt algorithm (LMA) neural networks is to forecast how the tribological behavior of hybrid composites would be altered by the addition of REOs based on data acquired from wear testing. The correlation value (R) and mean square error are found to be 0.987 and 4.3424e−10, respectively, which is an indication of good fit for the model with high significance. The findings indicate that the LMA neural network models accurately forecast the tribological properties of REOs–aluminum hybrid composites.

Effect of rare earth oxide additive in coating deposited by laser cladding: A review

In this paper, the effect of rare earth oxide additive on coating material deposited by laser cladding process on various engineering materials has been discussed. The purpose of rare earth oxide additive in the coating composition is to improve the various properties like mechanical, tribological, and chemical properties. The main rare earth oxides are La2O3, CeO2 and Y2O3, which are generally used in laser cladded coatings. The limited amount of addition of these rare earth oxide compound may leads to improvement in hardness, wear and corrosion resistance of coating. The attractive properties of rare earth oxide is grain refinement, conversion of coarse structure to fine dendritic structure, creating grain boundary movement hindrance of dislocation in the material which leads to its application as nutrients in the coating material. The main purpose of coating is to enhance the surface properties of material like hardness, corrosion resistance and wear resistance. When rare earth oxide are added to the coating then it creates extra enhancement in the above properties. The laser cladding is widely used in modern manufacturing technology due to its very attractive properties like good metallurgical bonding with substrate, less dilution, minimum distortion, less heat affected zone and fast solidification and high cooling rate. In this review article the coating developed by laser cladding on various conventional engineering materials like ferrous materials, magnesium alloys, titanium alloys, aluminium alloys and nickel based super alloys with rare earth oxide addition are described.

Measurement of dielectric properties of rare earth oxides by resonance cavity perturbation method

The dielectric properties and thermostable characteristics of 15 rare earth oxides are systematically investigated in microwave fields. Results indicate that the Pr6O11 of the light and Tb4O7 of the heavy rare earth oxides show excellent responsiveness to microwaves, both start to surge after 500 °C, with dielectric constant values of 10.814 and 10.157 (F/M) at 800 °C, respectively, meaning that it takes only 8.8 min for Pr6O11 and Tb4O7 to be heated from 150 to 800 °C. The dielectric properties of rare earth oxides are related to their thermostable characteristics, mainly affected by crystal transformation. Moreover, the Ln2O3-type rare earth oxides have no crystal transformation within the range of microwave heating to 800 °C, and the changes in dielectric properties and heating curve are attributed to lattice distortion of the particles. This work provides guidance for applications of microwave technology to the rare earth oxides.

Interfacial Structure and Physical Properties of High-Entropy Oxide Coatings Prepared via Atmospheric Plasma Spraying

The feasibility of using a high-entropy rare-earth oxide (REO) as a top coating material for thermal barrier coatings was explored using the atmospheric plasma spray technique. The microstructure and Vickers hardness of the coating layer were compared to those of an 8 mol % yttria-stabilized zirconia (8YSZ) top coating material. Macroscopic observations revealed the formation of a well-coated surface with no surface defects or delamination. Scanning electron microscopy images showed the presence of several parallel and vertical microcracks in the REO and 8YSZ coating layers. The origin of these cracks is attributed to differences in the coefficient of thermal expansion, very fast cooling, and process parameters. X-ray diffraction demonstrated the high phase stability and excellent thermal properties of REO due to the absence of phase transformation after plasma spray processing. The measured Vickers hardness of REO was 425 HV, which is lower than that of sintered REO powder and the 8YSZ coating.

Morphology-controlled synthesis of CeO2 nanocrystals and their facet-dependent gas sensing properties

Abstract Recently, the influence of polar facets on the gas sensing performance of metal oxides has drawn much attention, yet the facet-dependent gas sensing properties of rare earth oxides have not been reported so far. In this work, taking CeO2 as an example, uniform single-crystalline nanopolyhedra, nanorods and nanocubes of cubic CeO2 were selectively prepared by a hydrothermal method at different temperatures and NaOH concentrations, using Ce(NO3)3 as the cerium source. According to X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis, these CeO2 nanocrystals possess different exposed crystal planes: {111} and {100} for nanopolyhedra, {110} and {100} for nanorods, and {100} for nanocubes. Abundant defects were confirmed on the surface of three CeO2 nanocrystals by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and photoluminescence (PL). Notably, gas sensors based on these three CeO2 nanocrystals exhibited distinct response values towards dimethylamine vapor in the following order: nanocubes > nanorods > nanopolyhedra, while excluding the effects of characteristic dimension and specific surface area. The response order of CeO2 nanocrystals is primarily ascribed to the different content of surface defects and {100} polar facets instead of {111} and {110} nonpolar facets.

Influence of frequency and gamma irradiation on the electrical characteristics of Er2O3, Gd2O3, Yb2O3, and HfO2 MOS-based devices

The unique physical, chemical, and electronic properties of rare earth oxides have been of immense interest to replace SiO2 as a dielectric material in metal–oxide–semiconductor (MOS)-based sensors applications to accurately measure the radiation dosage and increase sensor sensitivities in as diverse applications as space radiation, nuclear physics, medical diagnostics, radiation cancer therapy, and personal dosimetry devices. Hence, the electrical characteristics of oxides prior to and after irradiation of MOS-based devices are needed since they are the backbone of the devices such as MOSFETs and ICs. In addition, an understanding of the behaviour of high-k dielectric oxides in an MOS configuration is necessary since the radiation-induced damage occurs in the bulk oxide film and/or near the oxide–semiconductor interface resulting in creation of lattice defects. Hence, MOS structures with the rare earth oxides of Er2O3, Gd2O3, Yb2O3, and a transition metal oxide of HfO2 were produced by RF magnetron sputtering to determine (a) the structure of the films, (b) dielectric constants, (c) capacitance versus voltage behaviour of Er2O3, Gd2O3, Yb2O3, and HfO2 prior to and after irradiation of the devices in the dose range of 0–76 Gy. The experimental results were analysed with a theoretical framework on the energy band diagram and the radiation effects on the electrical characteristics of the MOS capacitors. The characteristics of the devices were evaluated by using effective oxide charge density ( $$ Q_{\text{EFF}} $$ ), variation in the oxide trapped charge density ( $$ \Delta N_{\text{ox}} $$ ), and interface trapped charge density ( $$ \Delta N_{\text{it}} $$ ). In addition, barrier height ( $$ \phi_{\text{b}} $$ ), image force barrier lowering ( $$ \Delta \phi_{\text{b}} $$ ), acceptor concentration ( $$ N_{\text{a}} $$ ) were calculated before and after irradiation and examined the nature of interface states. The radiation responses of the Er2O3 and HfO2 MOS capacitors did not show a stable behaviour with an increase in radiation dose due to possible neutral electron trap centres. Contrary to expectations, we infer that more negative charges are trapped in Gd2O3-based device than positive charges with an increase in radiation dose. The C–V curves of the Yb2O3 MOS capacitor shifted in the same direction at both 100 kHz and 1 MHz, and as expected, positive charge traps in the structure are more efficient than negative charges. The observed sensitivities of Yb2O3 MOS capacitors are 4–7 times higher than those of SiO2, and the sensitivities of the Yb2O3 MOS capacitors with a total radiation dose of 70 Gy were found to be around 28.08 mV/Gy at both 100 kHZ and 1 MHz frequencies. The Yb2O3 appears to be a promising dielectric candidate for developing a new generation of radiation sensors with an excellent interface quality when compared to rare earth mixed oxides such as silicates, transition metal oxides, and the silicates based on transition metals, Al2O3, and BiFeO3. Our review of the literature suggests that while the radiation damage has been assessed comprehensively based on the C–V characteristics, microstructural characterization of the irradiated films and their interfaces is lacking even though the quality of oxide/Si interface is the most important feature of the devices. The electrical data should be correlated with the inferences from XPS, AFM, TEM, XRD, and other techniques. Further progress requires selection and validation of material properties based on theoretical calculations and predications, utilization of diverse thin film processing and characterization techniques, determining the effect of thickness on the properties of MOS capacitors, a thorough understanding of the interfaces, effect of frequency on the MOS capacitors and the interface characteristics, effect of radiation on the physical, interfacial, and electrical characteristics of MOS capacitors, and preparation and characterization of sensors based on thin films of novel mixed oxides and silicates of different chemistries.

Oxide Based Dilute Magnetic Semiconductor- A Brief Review

Dilute magnetic semiconductors (DMS) play an important role in interdisciplinary materials science. Out of this oxygen based DMS this system has been the subject of intense research for Enhancement of magnetic property as well as the Curie temperature. In this system the charge and spin degrees of freedom are accommodated into single matter and their interplay is expected to explore novel physics and new devices. Rare earth oxides have become a interesting field of study for their interesting properties as well as their versatile applications in different fields. Recently the various physical properties, viz., optical (absorption spectra, IR spectra, Raman spectra), magnetic, thermal and hyperfine properties of rare earth oxides have been reported. The various 3d transition metal ion (e.g., Fe, Ni, Co etc) which has also high value of magnetic moment, has been doped in different rare earth oxides, in recent years and it is reported that there is an enhancement in the magnetization. Doping of 3-d metal ion in different rare earth oxide and other semiconducting oxide system can be interesting for the enhancement of magnetization. From the viewpoint of DMS, there may be strong ferromagnetic exchange coupling between localized spins due to carrier induced ferromagnetism and double exchange interaction when localized spin is introduced in the oxide semiconductor.

Role of surface oxygen-to-metal ratio on the wettability of rare-earth oxides

Hydrophobic surfaces that are robust can have widespread applications in drop-wise condensation, anti-corrosion, and anti-icing. Recently, it was shown that the class of ceramics comprising the lanthanide series rare-earth oxides (REOs) is intrinsically hydrophobic. The unique electronic structure of the rare-earth metal atom inhibits hydrogen bonding with interfacial water molecules resulting in a hydrophobic hydration structure where the surface oxygen atoms are the only hydrogen bonding sites. Hence, the presence of excess surface oxygen can lead to increased hydrogen bonding and thereby reduce hydrophobicity of REOs. Herein, we demonstrate how surface stoichiometry and surface relaxations can impact wetting properties of REOs. Using X-ray Photoelectron Spectroscopy and wetting measurements, we show that freshly sputtered ceria is hydrophilic due to excess surface oxygen (shown to have an O/Ce ratio of ∼3 and a water contact angle of ∼15°), which when relaxed in a clean, ultra-high vacuum environment isolated from airborne contaminants reaches close to stoichiometric O/Ce ratio (∼2.2) and becomes hydrophobic (contact angle of ∼104°). Further, we show that airborne hydrocarbon contaminants do not exclusively impact the wetting properties of REOs, and that relaxed REOs are intrinsically hydrophobic. This study provides insight into the role of surface relaxation on the wettability of REOs.

Role of Rare Earth Oxide Nanoparticles (CeO2 and La2O3) in Suppressing the Photobleaching of Fluorescent Organic Dyes

Aqueous solutions with Rhodamine dye, and fluorescently labeled polymer samples of fibrin and collagen were mixed with aqueous dispersions of cerium oxide, lanthanum oxide, iron (II) oxide nanoparticles, and OxyFluor, a commonly used reagent for suppressing photobleaching. From time dependent studies of the fluorescence from these samples, we observed that the dyes in samples containing rare earth oxide nanoparticles exhibited significantly slower rates of fluorescence decay compared to control samples without additives, or containing OxyFluor or iron oxide nanoparticles. We posit that this may be related to the oxygen free radical scavenging properties of rare earth oxides.

Electrical and dielectric properties of rare earth oxides coated LiCoO2 particles

Pure and rare earth oxides (Sm2O3, La2O3) coated LiCoO2 nanoparticles were prepared by acrylamide-assisted polymeric citrate and resin-coating processes, respectively. The prepared powders were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and impedance spectroscopy. Powder X-ray diffraction patterns confirmed the formation of phase pure LiCoO2 with nanocrystallite size. X-ray fluorescence spectra confirm the presence of Sm2O3 and La2O3 in coated samples. The conductivity, dielectric and electric modulus studies of the samples were carried out at room temperature. Dielectric spectra of the samples show the decrease in dielectric constant with an increase in frequency of the applied field. The modulus studies indicate the non-Debye behavior of the samples, which is due to long-time slow polarization and relaxation of hopping charges.

Optical, mechanical and tribological properties of Y2O3, Er2O3 and Nd2O3 doped polycrystalline silicon nitride ceramics

Y2O3, Er2O3 and Nd2O3 doped polycrystalline silicon nitride ceramics were prepared by hot press sintering method at 1850°C and 30 MPa pressure. 1 wt.% of each rare earth oxides (REO) were sintered with 3 wt.% MgO, 9 wt.% AlN and 87 wt.% α-Si3N4.The optical, mechanical and tribological properties of REO doped polycrystalline silicon nitride ceramics were investigated. Optical transmittance was measured in visible and near infrared region and found to be 54% transmittance for Y2O3 doped Si3N4 ceramics. β- phase transformation was suppressed with REO addition. High hardness and high fracture toughness were achieved by addition of REO. Adding REO shows good mechanical properties as high strength and toughness. Coefficient of friction of the REO doped silicon nitride ceramics was lower than that of without REO doped silicon nitride ceramics.

Basic properties of rare earth oxides

Abstract Basic properties of rare earth oxides (REOs) calcined at different temperatures were investigated. During the calcination process, the crystal structures of Lu, Yb, Tm, Er, Y, Ho, and Dy oxides transformed from monoclinic to cubic with increasing calcination temperature, while those of Sc, Ce, La, Pr, Nd, Sm, Eu, Gd, and Tb oxides showed no change at temperatures below 1100 °C. No acidic sites were observed in the measurement of NH 3 adsorbed on the REOs at 25 °C. CO 2 was adsorbed on the REOs: CO 2 desorption peaks were observed depending on the strength of the basic sites. Light REOs, such as La 2 O 3 , Pr 6 O 11 , Nd 2 O 3 , and Sm 2 O 3 , had surface basic sites from which CO 2 desorbed at temperatures below 500 °C, as well as structural carbonate that decomposed above 500 °C. Heavy REOs, such as Dy 2 O 3 , Ho 2 O 3 , Y 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 , and Lu 2 O 3 , had weak basic sites. The basic properties of REOs are attributed to lanthanide contraction: the strength of the basic sites decreases with decreasing radius of the rare earth cation.

Catalytic reaction of 1,3-butanediol over rare earth oxides

Abstract Vapor-phase reaction of 1,3-butanediol was investigated over rare earth oxide (REO) catalysts. In the reaction of 1,3-butanediol, dehydration and decomposition of 1,3-butanediol occurred simultaneously at 325 °C. The formation of unsaturated alcohols such as 3-buten-2-ol and trans -2-buten-1-ol was predominant over CeO 2 , Sc 2 O 3 , and Tm 2 O 3 , while 1,3-butanediol was preferentially decomposed over the other REOs. Especially, light REOs such as La 2 O 3 , Pr 6 O 11 , Nd 2 O 3 , and Sm 2 O 3 , catalyzed decomposition of 1,3-butanediol into 2-propanol, propanone, methanol, and ethanol. Basic and acidic properties of REOs were measured with temperature-programmed desorption (TPD) of adsorbed CO 2 and NH 3 , respectively. The surface character of REOs was basic but not acidic. Both strength and number of basic sites of REOs increased with increasing ionic radius of rare earth cation in the REO except CeO 2 : light REOs were more basic. The decomposition of 1,3-butanediol would be attributed to the basicity of catalyst. In the reaction of 1,3-butanediol as well as 1,4-butanediol, the catalytic function of REOs will be discussed in connection with lanthanide contraction.

Tribological properties of rare earth oxide added Cr 3C 2–NiCr coatings

A novel supersonic plasma spraying was used to prepare rare earth oxide added Cr 3C 2–NiCr coatings. X-ray diffractometer, contact surface profiler, hardness tester, micro-friction and -wear tester, environmental scanning electron microscope equipped with energy dispersive spectroscopy were employed to investigate the phase structure, surface morphology, microhardness, and friction properties of deposited coatings, respectively. The results show that surface roughness, microhardness, brittle fracture, friction extent and wear resistance of rare earth oxide added Cr 3C 2–NiCr coatings are effectively improved compared with that of unadded one. The friction and friction mechanism are also discussed.

Sensing properties of rare earth oxide doped In2O3 by a sol–gel method

The powders of pure In2O3 and Eu3+, Gd3+, Ho3+-doped In2O3 with the structure of bixbyite-type were synthesized by a sol–gel method in the citric acid system. The structure and crystal phase of the powders were characterized by using an X-ray diffractometer. The gas sensing characteristics were obtained by measuring the response magnitude as a function of various controlling factors like dopant, operating temperature, concentrations of the test gases and the response time. The results showed that pure In2O3 had poor selectivity, while the In2O3 sensors doped with 5wt.% Eu2O3, 5wt.% Gd2O3, and 5wt.% Ho2O3 increased the gas-sensing performance towards H2S as a reducing gas, but decreased gas towards Cl2 as an oxidizing gas at 195°C. Namely, doping of the rare earth oxides remarkably improved the selectivity for H2S. In addition, it was found that among the dopants, 5wt.% Ho2O3 gave the highest the response value, selectivity, stability and the most excellent response and recovery characteristics to H2S at 195°C. Thus, the Ho2O3-doped In2O3 is a promising candidate for detection of H2S in environments.

Structural and optical properties of polycrystalline thin films of rare earth oxides grown on fused quartz by low pressure MOCVD

We report the structural and optical properties of oriented polycrystalline thin films of rare earth oxides (REO), namely Er 2O 3, Gd 2O 3, Eu 2O 3, and Yb 2O 3 grown on fused quartz by low-pressure metalorganic chemical vapour deposition (MOCVD) in the temperature range of 450–800 °C, using adducted β -diketonate complexes of rare earth metals as precursors. The films were characterized by X-ray diffraction (XRD) and UV–visible spectrophotometry. While the films grown at low temperatures (∼500 °C) are poorly crystalline, those grown on or above 525 °C display a significant (1 1 1) texture. Growth of textured cubic REO in (1 1 1) direction on amorphous substrate is interpreted in terms of minimization of surface energy at the film–substrate interface. The degree of misfit between the interatomic distances in the disordered fused quartz substrate and those in the crystalline REO is invoked to explain the presence (absence) of low-intensity reflections other than (1 1 1). The incorporation of carbon (from the precursor) into the films affects the optical properties of REO, as examined by UV–visible spectroscopy.

Properties of rare earth oxide doped translucent polycrystalline alumina

This paper presents the results of an investigation into the properties of rare earth oxide doped translucent polycrystalline alumina (PCA). Materials containing very high concentrations of dopant with 50% translucency have been fabricated in less than 30 min. Fully dense translucent aluminas have a number of applications such as in electric discharge tubes for lighting applications, dental brackets and electrical insulators. The sintering of translucent PCA traditionally requires prolonged high temperatures and a hydrogen atmosphere to encourage grain growth and reduce porosity. Using a liquid-doping technique involving the introduction of the rare earth metal nitrate into the partially sintered powder compact, the dopant is located at the grain boundaries. Also, with the introduction of relatively large amounts of rare earth oxide dopant the sintering behaviour is modified, both to increase the required firing temperatures and to affect porosity and its distribution. The effects of two rare earth oxides are reported in terms of sintering behaviour, density, grain size and component translucency.

Electrorheological Properties of Rare Earth Oxide and Rare Earth Hydroxide

The electrorheological (ER) behaviors of 31 kinds of ER suspensions, 16 kinds of rare earth oxide and 15 kinds of rare earth hydroxide [RE(OH)3] are tested systematically under electric field. The microscopy shows that only Gd2O3, Pr6O11 from rare earth oxides and RE(OH)3 · nH2O (RE = La, Y, Pr, Gd, Sm, Lu) from rare earth hydroxides dispersed in silicone oil produce fibrous chains in the direction of the ac field vector. The viscosities of ER suspensions with Gd2O3. Pr6O11, RE(OH)3 · nH2O (RE = La, Y, Gd, Pr) dispersed in hydrocarbon oil are determined under different field strength (dc field). The results show that the ER activity of the materials is not influenced by the coordinated water with the rare earth ion, and it is related with the microstructure of the molecule.