Sc2O3 Powders Research Articles

Alternative alloy to increase bandgap in gallium Oxide, β-(ScxGa1-x)2O3, and rare earth Stark luminescence

β-Ga2O3 is an emergent ultrawide bandgap material, which has been recently studied with respect to alumina alloying in order to tailor the bandgap for thin film or bulk applications. In this work, bulk Czochralski and vertical gradient freeze crystals of 6 – 8 mol.% Sc2O3 alloyed β-Ga2O3 (SGO) – β-(Sc0.06Ga0.94)2O3 to β-(Sc0.08Ga0.92)2O3 – were obtained, which showed a nominal + 0.07 eV increase in the optical bandgap compared to unintentionally doped (UID) β-Ga2O3. SGO was characterized for structure (X-ray diffraction, rocking curve, nuclear magnetic resonance, Raman microscopy), purity (glow discharge mass spectrometry, X-ray fluorescence), optical transmission (200 nm – 25,000 nm), resistivity, and luminescence (laser induced luminescence microscopy, photoluminescence). Structural measurements indicate successful incorporation of Sc, although overall lower quality than UID and β-(Al0.1Ga0.9)2O3 (AGO) material. Purity and optical measurements demonstrated few acceptor impurities and a widened band gap, although not wide enough for some donors to become deep enough to promote insulating behavior. Bulk SGO crystals demonstrated intense Stark luminescence transitions characteristic of Nd3+, presumably an impurity in the Sc2O3 powder, with some areas of the crystal showing highly concentrated Nd3+. Despite demonstrating an enlarged bandgap, scandia alloyed β-Ga2O3 retained electrical conduction similar to UID β-Ga2O3, unlike alumina alloyed β-Ga2O3 which was electrically insulating.

Fabrication and properties of 10 at.% Yb:Y3Sc1.5Al3.5O12 transparent ceramics

10 at.% Yb:Y3Sc1.5Al3.5O12 (Yb:YSAG) transparent ceramics were fabricated by the solid state reactive of high-purity Y2O3, α-Al2O3, Yb2O3 and Sc2O3 powders, utilizing MgO and tetraethoxysilane (TEOS) as the sintering aids. The Yb:YSAG ceramic sample sintered at 1820 °C for 10 h has a dense and homogenous microstructure with average grain size of 26.9 μm, whose in-line transmittance reaches 83.2% at 1100 nm (2 mm thick). The absorption and emission cross sections are calculated to be 5.09 × 10−21 cm2 at 941 nm and 12.33 × 10−21 cm2 at 1031 nm, respectively. The full width at half maximum (FWHM) of the main emission peak centered at 1031 nm is 12.4 nm, which is about 1.3 times larger than that of the 10 at.% Yb:YAG ceramics. By using the three-mirror resonator, the Yb:YSAG ceramic laser output power of 1.67 W at 1031 nm and slope efficiency of 13.1% were obtained with an output coupler (OC) of T = 5%.

Fabrication and laser oscillation of Yb:Sc2O3 transparent ceramics from co-precipitated nano-powders

Ytterbium doped scandium oxide (Yb:Sc2O3) transparent ceramics were fabricated by a co-precipitation and vacuum sintering method. The characteristics of the precursor and the calcined powders were investigated by BET, XRD, and SEM. Ultra-fine and low agglomerated 5at%Yb:Sc2O3 powders with the average particle size about 65.4nm were obtained after calcined at 1100°C for 5h. Using the synthesized powders as starting materials, 5at%Yb:Sc2O3 transparent ceramics with the in-line transmittance of 71.1% at 1100nm and average grain size of 145μm were fabricated by vacuum sintering at 1825°C for 10h. Quasi-CW laser oscillation of Yb:Sc2O3 ceramics was obtained at 1040.6nm. A maximum output power as high as 2.44W with a corresponding slope of 35% was achieved. Finally, the tunability of the ceramic was explored measuring a tuning range up to 55nm.

Fabrication of Yb:Sc2O3 laser ceramics by vacuum sintering co-precipitated nano-powders

Ytterbium doped scandium oxide (Yb:Sc2O3) nano-powders were synthesized by a co-precipitation method. Ammonium hydrogen carbonate (NH4HCO3) and ammonia sulfate ((NH4)2SO4) were used in the precipitation process as the precipitant and dispersing agent, respectively. Structural properties and morphology of the precursor and nano-powders were investigated by BET, XRD, and SEM measurements. Ultra-fine and low agglomerated 5 at%Yb:Sc2O3 powders with the average particle size of 86 nm were obtained after calcination of the precipitate at 1100 °C for 5 h, that was found to be the optimal temperature for preparation of 5 at%Sc2O3 powders for further sintering. 5 at%Yb:Sc2O3 transparent ceramics with in-line transmittance of 73.9% at 1100 nm and average grain size of 182 μm were fabricated by vacuum sintering of the optimal powder at 1850 °C for 10 h. The microstructure, the spectroscopic properties and the gain characteristics of obtained 5 at%Yb:Sc2O3 ceramics were also studied and discussed.

Intrinsic luminescence centers in scandia, yttria, and their solid solutions

Pulsed cathodoluminescence (PCL) of Y2O3 and Sc2O3 powders, as well as of ceramic samples of binary (11 mol % Sc2O3–ZrO2 and 10 mol % Y2O3–ZrO2) and ternary (xSc2O3–(10–x)Y2O3–ZrO2) (x = 5, 6, 7, 8 mol %) solid solutions are studied in the range of 300–850 nm at room temperature. In Y2O3 and Sc2O3, series of strong narrow luminescence bands emitted by surface bound radicals ...0...0>-Y=O and ...0...0>-Sc=O are found. The PCL spectra of xSc2O3–(10–x)Y2O3–ZrO2 ceramic samples showed the same series of narrow bands at 543, 551, 555, 572, 583, 594, 614, and 639 nm as the yttrium oxide spectra. The existence of these luminescence bands, which correspond to the emission of the ...0...0>-Y=O radical, and the absence of the emission lines of the ...0...0>-Sc=O radical indicate that yttrium ions, due to their larger radius, are the first that are displaced to the surface of crystallites in these systems, which is accompanied by the formation of the second phase in subsurface layers.

Zigzag Sc2C2 Carbide Cluster inside a [88]Fullerene Cage with One Heptagon, Sc2C2@Cs(hept)-C88: A Kinetically Trapped Fullerene Formed by C2 Insertion?

A non-isolated pentagon rule metallic carbide clusterfullerene containing a heptagonal ring, Sc2C2@Cs(hept)-C88, was isolated from the raw soot obtained by electric arc vaporization of graphite rods packed with Sc2O3 and graphite powder under a helium atmosphere. The Sc2C2@Cs(hept)-C88 was purified by multistage high-performance liquid chromatography (HPLC), cocrystallized with Ni-(octaethylporphyrin), and characterized by single-crystal X-ray diffraction. The diffraction data revealed a zigzag Sc2C2 unit inside an unprecedented Cs(hept)-C88 carbon cage containing 13 pentagons, 32 hexagons, and 1 heptagon. Calculations suggest that the observed nonclassical fullerene could be a kinetically trapped species derived from the recently reported Sc2C2@C2v(9)-C86 via a direct C2 insertion.

Effect of Sc2O3 particles on the microstructure and properties of tungsten alloy prepared by spark plasma sintering

W–Sc2O3 composite powders (W, W–0.5vol%Sc2O3, and W–2vol%Sc2O3) doped with highly uniform Sc2O3 particles were successfully synthesized by mechanical alloying followed by hydrogen reduction with Sc2O3 and WO3 powders. The reduced powders were then consolidated by spark plasma sintering at 1700°C to suppress grain growth during sintering. Field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy analyses, as well as tensile tests and thermal conductivity measurements, were used to characterize the samples. The results showed that the Sc2O3 particles were uniformly distributed in the tungsten grains and grain boundaries. The W–2vol%Sc2O3 composite possess the best relative density and Vickers micro-hardness up to 98.6% and 683.2Hv, respectively. The Sc2O3 particles significantly refine the grain size and increase the density of tungsten alloy. With increased Sc2O3 content, the thermal conductivity decreased while tensile strength of the samples respectively increased at 700 and 800°C.

Sintering of nanostructured Sc2O3 ceramics from sol–gel-derived nanoparticles

Sol–gel route was used to synthesize scandium oxides nanopowders. Oxohydroxide nanoparticles were first prepared in solution using ScCl3·xH2O as precursor. The influence of pH and reflux time on particle size and shape was studied. Sc2O3 nanoparticles were then obtained after water dialysis and ScOOH sol drying. Depending on pH, 40–1000nm size ScOOH particles can be obtained. At a given pH, reflux time also influences the ScOOH particles size, which can vary from a few nanometers to 1µm.The ScOOH sol can be used to prepare very pure Sc2O3 nanopowders. Results indicate a strong relation between nanoparticle size and the transformation temperature of γ-ScOOH to Sc2O3. A direct correlation between the Sc2O3 powder and the original ScOOH nanoparticle shapes has also been observed. From the TEM studies, it is likely that the crystallization from the phase ScOOH into Sc2O3 one is isomorphic.Spark plasma sintering test highlights a very good sinterability of the Sc2O3 powder. Nearly fully dense ceramics can be obtained at 1400°C. Microstructure is very homogeneous with ultrafine grains, with size in the range of 25–225nm.

Synthesis of Sc2O3 nanopowders and fabrication of transparent, two-step sintered Sc2O3 ceramics

Synthesis of Sc2O3 nanopowders using a wet chemical approach and fabrication of transparent polycrystalline Sc2O3 ceramics via a two-step sintering procedure (vacuum sintering plus hot isostatic pressing) have been investigated. A hydrated basic sulphate precursor powder [Sc(OH)(3−2x)(SO4)x.nH2O] is synthesised from the scandium sulphate, hexamethylenetetramine and ammonia water solution at room temperature. Phase transformation processes of the precursor upon calcination are studied via differential scanning calorimetry/thermogravimetry, Fourier transform infrared spectroscopy and X-ray diffractometry. Nanocrystalline Sc2O3 powder is obtained by calcining the precursor at 1100°C for 4 h. The resultant Sc2O3 powder is highly pure, ultrafine (12 nm in average size), of narrow particle size distribution and spherical. Hexamethylenetetramine plays an important role in Sc2O3 particle properties. The transparent Sc2O3 ceramics fabricated by two-step sintering have a highly inline transmittance. The two-step sintering mechanism is discussed.

Sc2S@Cs(10528)-C72: A Dimetallic Sulfide Endohedral Fullerene with a Non Isolated Pentagon Rule Cage

A non isolated pentagon rule metallic sulfide clusterfullerene, Sc(2)S@C(s)(10528)-C(72), has been isolated from a raw mixture of Sc(2)S@C(2n) (n = 35-50) obtained by arc-discharging graphite rods packed with Sc(2)O(3) and graphite powder under an atmosphere of SO(2) and helium. Multistage HPLC methods were utilized to isolate and purify the Sc(2)S@C(72). The purified Sc(2)S@C(s)(10528)-C(72) was characterized by mass spectrometry, UV-vis-NIR absorption spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the C(72) fullerene cage violates the isolated pentagon rule, and the cage symmetry was assigned to C(s)(10528)-C(72). The electrochemical behavior of Sc(2)S@C(s)(10528)-C(72) shows a major difference from those of Sc(2)S@C(s)(6)-C(82) and Sc(2)S@C(3v)(8)-C(82) as well as the other metallic clusterfullerenes. Computational studies show that the Sc(2)S cluster transfers four electrons to the C(72) cage and C(s)(10528)-C(72) is the most stable cage isomer for both empty C(72)(4-) and Sc(2)S@C(72), among the many possibilities. The structural differences between the reported fullerenes with C(72) cages are discussed, and it is concluded that both the transfer of four electrons to the cage and the geometrical requirements of the encaged Sc(2)S cluster play important roles in the stabilization of the C(s)(10528)-C(72) cage.

Synthesis of nanocrystalline Sc2O3 powder and fabrication of transparent Sc2O3 ceramics

Synthesis of nanocrystalline Sc2O3 powder via a homogeneous precipitation method and fabrication of transparent Sc2O3 ceramics with vacuum sintering has been investigated here. Hydrated basic carbonate–sulphate precursor was synthesised from scandium sulphate and urea solution. Phase transformation processes of the precursor upon calcination were analysed. The resultant Sc2O3 powder is highly pure, ultrafine (50 nm), well dispersed, narrow particle size distribution, spherical and highly sinterable. Transparent Sc2O3 ceramics were fabricated using the excellent powder. The final pH value of the solution has a significant influence on sintering properties of the powder, which directly affects the transmittance of the ceramics. The sulphate system also plays an important role in powder properties.

Ab initio study of the EFG tensor at Cd impurities in Sc2O3 semiconductor

We present an ab initio study of diluted Cd impurities localized at both cation sites of the semiconductor Sc2O3. The electric-field-gradient (EFG) tensor at Cd impurities located at both cationic sites of the host structure was determined from the calculation of the electronic structure of the doped system. Calculations were performed with the full-potential augmented-plane wave plus local orbitals (APW+lo) method within the framework of the density functional theory. We studied the atomic structural relaxations and the perturbation of the electronic charge density induced by the impurities in the host system in a fully self-consistent way. We showed that the Cd impurity introduces an increase of 8% in the nearest oxygen neighbors bond-lengths, changing the EFG sign for probes located at the asymmetric cation site. The APW+lo predictions for the charged state of the Cd impurity were compared with EFG results existent in the literature, coming from time-differential γ–γ perturbed-angular-correlations experiments performed on 111Cd-implanted Sc2O3 powder samples. From the excellent agreement between theory and experiment, we can strongly suggest that the Cd acceptor impurities are ionized at room temperature. Finally, we showed that simple calculations like those performed within the point-charge model with antishielding factors do not correctly describe the problem of a Cd impurity in Sc2O3.

Impedance Spectroscopy Analysis of Zirconia:10 mol% Scandia Solid Electrolytes During and After Sintering

ZrO2:10 mol%Sc2O3 (10ScSZ) powders were synthesized by the polyacrylamide technique (route I) and the polymeric precursor technique (route II). Attrition milling was used to break up powder agglomerates. The evolution of the distribution of particle size upon attrition milling was evaluated by laser scattering. Impedance spectroscopy measurements were carried out in cold-pressed powders in the 500oC-1400oC range during sintering and in the 300-500oC range after sintering. Upon sintering, the decrease of the total electrical resistivity of the specimens prepared with both powders is similar. Nanosize ZrO2:10 mol% Sc2O3 powders synthesized by route I are less sinteractive than powders synthesized by route II due to formation of agglomerates, which produce, upon sintering, pellets with intragranular pores. Sintered pellets using powders prepared by route I have lower electrical conductivity than pellets using powders prepared by route II.

Nanocrystalline Scandia Powders Via Oxalate Precipitation: The Effects of Solvent and Solution pH

Nanocrystalline Sc2O3 was synthesized via precipitation with scandium nitrate as the scandium source and oxalic acid as the precipitant, with investigations into the influences of solution pH and solvent type on powder properties. Three types of scandium precursors (normal oxalate, double oxalate, and oxyhydroxide) have been obtained from aqueous media by adjusting pH of the precipitant solution with ammonia water. All the precursors, however, yield severely aggregated Sc2O3 powders of low surface areas. Replacing water with pure ethanol as the solvent was shown to be able to yield Sc2O3 nanopowders of high specific surface area (35.7 m2/g) and good dispersion. The mechanisms of solution pH and solvent type on precursor properties were also discussed.

Preparation of Yb-Doped Sc2O3 Transparent Ceramics for Laser Applications

AbstractPolycrystalline transparent Yb:Sc2O3 ceramics were obtained in the best conditions by a solid-state reaction route using high purity Sc2O3 and Yb2O3 powders with TEOS as a sintering aid. The as-prepared powders containing various ytterbium content were characterized by BET measurements, XRD and FEG-SEM. The sintering behaviour of the powders was investigated by dilatometry. The sintered materials microstructures were observed by FEG-SEM. EPMA allowed to characterize the repartition of the dopant Yb3+ in the Sc2O3 matrix.

Fabrication of Transparent, Sintered Sc2O3Ceramics

We report here the fabrication of transparent Sc2O3ceramics via vacuum sintering. The starting Sc2O3powders are pyrolyzed from a basic sulfate precursor (Sc(OH)2.6(SO4)0.2·H2O) precipitated from scandium sulfate solution with hexamethylenetetramine as the precipitant. Thermal decomposition behavior of the precursor is studied via differential thermal analysis/thermogravimetry, Fourier transform infrared spectroscopy, X‐ray diffractometry, and elemental analysis. Sinterability of the Sc2O3powders is studied via dilatometry. Microstructure evolution of the ceramic during sintering is investigated via field emission scanning electron microscopy. The best calcination temperature for the precursor is 1100°C, at which the resultant Sc2O3powder is ultrafine (∼85 nm), well dispersed, and almost free from residual sulfur contamination. With this reactive powder, transparent Sc2O3ceramics having an average grain size of ∼9 μm and showing a visible wavelength transmittance of ∼60–62% (∼76% of that of Sc2O3single crystal) have been fabricated via vacuum sintering at a relatively low temperature of 1700°C for 4 h.

Solution-Based Processing of Sc2O3 Nanopowders Yielding Transparent Ceramics

A basic sulfate precursor [Sc(OH)SO4·2H2O] for well-sinterable Sc2O3 powders was precipitated from mixed solutions of scandium nitrate [Sc(NO3)3] and ammonium sulfate [(NH4)2SO4] at room temperature and which was subsequently converted to Sc2O3 via dehydroxylization and desulfurization at temperatures ≥900 °C. With the reactive powders synthesized in this work, polycrystalline Sc2O3 ceramics showing high inline transmittances of approximately 70% in the visible wavelength region (corresponding to ∼90% of the theoretical value of single crystals) have been fabricated via vacuum sintering at a relatively low temperature of 1700 °C.

Wet‐Chemical Routes Leading to Scandia Nanopowders

Two wet‐chemical routes have been used to synthesize Sc2O3 nanopowders from nitrate solutions employing ammonia water (AW) and ammonium hydrogen carbonate (AHC) as the precipitants. The precursors and the resultant oxides are characterized by elemental analysis, X‐ray diffractometry, differential thermal analysis/thermogravimetry, high‐resolution scanning electron microscopy, and Brunauer‐Emmett‐Teller analysis. Crystalline γ‐ScOOH·nH2O (n≈ 0.5) is the only phase obtained by the AW method. This phase dehydrates to Sc2O3 at ∼400°C, yielding hard aggregated nanocrystalline Sc2O3 powders. Three types of precursors have been synthesized by the AHC method, depending on the AHC/Sc3+ molar ratio (R): amorphous basic carbonate [Sc(OH)CO3·H2O] at R≤ 3, crystalline double carbonate [(NH4)Sc(CO3)2·H2O] at R≥ 4, and a mixture of the two phases at 3 < R < 4. Among these precursors, only the basic carbonate shows spherical particle morphology, ultrafine particle size (∼50 nm), and weak agglomeration. Sc2O3 nanopowders (∼28 nm) with high surface area (∼49 m2/g) have been prepared by calcining the basic carbonate at 700°C for 2 h.

Fabrication of transparent Sc2O3 ceramics with powders thermally pyrolyzed from sulfate

Scandia (Sc2O3) is a ceramic material that shows interesting thermal and optical properties, but is difficult to grow as single crystals. As an alternative, in this work we fabricated polycrystalline Sc2O3 transparent ceramics via vacuum sintering, using powders thermally pyrolyzed at 1200 °C from a scandium sulfate salt, Sc2(SO4)3 · 7.8H2O, that we prepared. Characterization of the powders was achieved by differential thermal analysis/thermogravimetry, x-ray diffractometry, Brunauer–Emmett–Teller analysis, and field-emission scanning electron microscopy. Sintering behaviors of the Sc2O3 powders were studied in air via dilatometry. The sulfate salt transforms to oxide at temperatures ≥1000 °C, and the best pyrolysis temperature for transparent ceramics fabrication is 1200 °C, at which the resultant Sc2O3 powder is good in dispersion, ultrafine in particle size (∼80 nm), and almost free from residual sulfur. Transparent ceramics were fabricated from this powder via vacuum sintering at 1625 °C or above. The ceramics sintered at 1700 °C for 4 h exhibit an in-line transmittance of approximately 56–58% in the visible light region at a sample thickness of 1.0 mm.

Monodispersed Sc2O3 precursor particles via homogeneous precipitation: Synthesis, thermal decomposition, and the effects of supporting anions on powder properties

Monodispersed Sc2O3 precursor particles were synthesized by the urea-based homogeneous precipitation method, with an investigation into the effects of supporting anions (NO3−, Cl−, and SO4 2−) on powder properties. Characterizations of the powders were achieved by elemental analysis, x-ray diffractometry, Fourier transform infrared, differential thermal analysis/thermogravimetry, high-resolution scanning electron microscopy, and the Brunauer-Emmett-Teller method. Unlike other rare earths, Sc3+ does not precipitate as basic carbonate but instead forms hydrated γ-ScOOH from either nitrate or chloride solution. Particles of the hydrated γ-ScOOH are pumpkin-shaped (approximately 1.0 μm) and are made up of thin-platelike crystallites emanating from a common axis. The presence of complexing SO42− changes the reaction chemistry toward Sc2O3 powders, leading to basic sulfate [Sc(OH)1.6(SO4)0.7 η H2O] precursor particles having hexagonal morphology (approximately 10 μm in diameter and 0.5 μm in thickness). The hydrated γ-ScOOH directly converts to Sc2O3 by calcination at 400 °C or above, while the basic sulfate transforms to oxide at temperatures ≥ 900 °C via an amorphous state and a Sc2(SO4)3 intermediate. The effect of SO42− on powder morphologies and reaction chemistry is discussed. Nanocrystalline Sc2O3 powders comprising monodispersed particles were obtained via thermal decomposition of the precursors.