Yttria Nanopowders Research Articles

Structural and opto-electrical properties of Y2O3 nanopowders synthesized by co-precipitation method

The synthesis-dependent structural-optical characteristics of nanomaterials have induced the critical optimization of parameters for nanoparticle synthesis. Considering the potential applications of yttria (Y2O3) in high-temperature IR windows and electro-optic devices, the present study describes the preparation of yttria nanopowders (YNPs) through co-precipitation method. Some special morphological and opto-electrical properties have been observed with a change in the precipitating agent concentration (R = NH5CO3/Y3+ = 1.5–5.5) without using any surfactant. Rietveld refinement confirmed the body-centered cubic (Ia-3 space group) structure of YNPs. Surface functionalities have been determined by Fourier transform infrared (FTIR) spectroscopy. Electron microscopy results confirmed the formation of agglomerated YNPs with R-dependent morphological modifications from flake-like shape to pseudo-spherical and rod-like particles. UV–visible and fluorescence (FL) spectroscopy confirmed the R-dependent optical absorption and emission (indigo, blue and green) characteristics. The dielectric measurement also confirmed the R-dependent variation in the dielectric constant values in the lower frequency range.

Synthesis of yttria nanopowder with poly acrylic acid as dispersant for highly transparent yttria ceramics

AbstractHighly pure and well‐dispersed yttria nanocrystalline powders were synthesized with a modified coprecipitation method that uses mixed ammonium hydroxide‐carbonate solution as the precipitant and poly acrylic acid (PAA) as the dispersant. Comparing with the yttria powders synthesized using the same route but without PAA dispersant, the PAA‐assisted powders exhibit lower level of agglomeration and better sinterability. Sintering trajectories of the powders with and without PAA dispersant were investigated. Y2O3 ceramics sintered with the PAA‐assisted powders exhibited smaller grain size, homogeneous microstructure, and higher in‐line optical transmittance. The result suggests that the polymer‐assisted coprecipitation could be used to synthesize yttria nanopowders for fabricating high optical quality transparent ceramics.

Yttria nanopowders with low degree of aggregation by a spray precipitation method

Highly sinterable Y2O3 nano-powder with low degree of agglomeration was synthesized by using a spray precipitation technology, without the use of any additives and dispersants. Compared with the precursor made by using the dripping method (D-precursor), the precursor made by the spraying method (S-precursor) had much lower degree of hard agglomeration. So did the resultant calcined Y2O3 powder (S-Y2O3 powder) as compared with the D-Y2O3 powder. Sintering behaviors of the two powders were studied. Ceramics made from the S-Y2O3 powder (S-Y2O3 ceramics) showed much higher densification rate and final density. After vacuum sintered at 1650 °C for 5 h, relative density of the D-Y2O3 ceramics was merely 97.3%, while that of the S-Y2O3 ceramics reached 99.5%. In addition, the D-Y2O3 ceramics cannot be sintered to 98% relative density by using the vacuum sintering technique, due to the high degree of agglomeration of the D-Y2O3 powder. Moreover, the S-Y2O3 ceramic exhibited homogeneous microstructure and an in-line optical transmittance of 81.6% at 1200 nm after HIP treatment. The spray precipitation method should be applicable to synthesizing other oxide powders.

Size and Morphology of Yttria Nanopowders Obtained by Solution Combustion Synthesis

Size and Morphology of Yttria Nanopowders Obtained by Solution Combustion Synthesis

Determining the phase composition of yttrium oxide nanopowders by means of luminescence

The possibility of developing a luminescence technique for phase composition analysis is demonstrated via the example of bi-phase yttria nanopowders doped with neodymium ions. The deviation from X-ray diffraction reference values is ±2%. It is found that the results depend on the inhomogeneity of the crystalline phase distribution within a sample’s bulk, rather than on the luminescence scattering by powder nanoparticles. A luminescence coefficient that determines the phase inhomogeneity in nanopowders is introduced.

Preparation of yttria nanopowders for use in transparent ceramics by dry ball-milling technique

To evaluate the effectiveness of dry ball-milling, yttria powders were ball-milled, and the optimal sample was spark plasma sintered to fabricated transparent yttria ceramics. The characterization of the powders and pellets were analyzed using XRD, FESEM, UV/VIS/NIR and FTIR spectrometer throughout the whole experimental process. The results indicated that ball-milling can significantly decrease yttria particle size and enhance the specifice surface area. The best duration is 20h ball-milling with average particle size and specifice surface area of 64nm and 20.4m2/g, respectively. Transparent yttria ceramic was made up of grains in the size range of approximately 0.67μm and the relative density was 99.8%. The in-line transmittance of the SPS-sintered yttria ceramic (2.5mm thick) reached 83% in the infrared region, which is very close to the theoretical value of yttria.

Color tunable up-conversion emission from Er3+:Y2O3 nanoparticles embedded in PMMA matrix

Yttria (Y2O3) nano-powders doped with various concentrations of Er3+ were synthesized using thermal decomposition method and annealed at 800°C. Annealed powders were doped in PMMA with 2.0 weight% of MMA by free radical polymerization. The crystalline structures of the powders and those embedded in PMMA matrix were identified as the cubic (BCC) Y2O3 phase using X-ray diffraction technique. According to the Scherer equation, the average crystallite sizes were found to be 32 ±3nm and 20 ±3nm for the powders and those embedded in the PMMA matrix, respectively. The transmission electron micrographs of samples were also taken and found to be consistent with the results obtained using X-ray diffraction measurements. Upconversion emission spectra of the Y2O3:Er3+ powders were measured in the 400–850nm wavelength range under the excitation of a diode laser operated at 975nm and, compared with the results obtained for Y2O3:Er3+ in PMMA. Spectral profiles of the emissions remain unchanged for different Er3+ concentrations and excitation powers. The doping of the nanopowders into the PMMA matrix did also not change the spectral profile, but only enhanced the intensity of the upconversion emission. Measurements of the emission intensity dependence on the pumping power under atmospheric conditions were performed to provide a possible explanation for the mechanisms responsible for the upconversion luminescence. Relative intensities for all the luminescence transitions were found to vary with Er3+ concentration resulting in the possible control of both color tuning and the color quality parameters.

Fabrication of 5 at.%Yb:(La0.1Y0.9)2O3 transparent ceramics by chemical precipitation and vacuum sintering

Yttria (Y2O3) nanopowders were synthesized by a normal precipitation method using (NH4)2SO4 as dispersing agent. Pure Y2O3 powders without any other phase can be achieved by calcining the precursor at 600 °C for 4 h. The precursor and Y2O3 powders were characterized by TG-DTA, XRD, SEM and BET. In this work, 5 at.%Yb:(La0.1Y1.9)2O3 transparent ceramics were made by vacuum sintering at 1650 °C for 10 h. The in-line transmittance of the 5 at.%Yb:(La0.1Y0.9)2O3 ceramics is 81.3% at the wavelength of 1031 nm. The absorption cross-sections of the sample are calculated to be 1.20 × 10−20 cm2, 5.74 × 10−21 cm2 and 4.18 × 10−21 cm2 at 976, 951 and 906 nm, respectively. The emission cross-sections of the emission peak located at around 1031 and 1073 nm are 1.13 × 10−20 and 0.42 × 10−20 cm2, respectively.

Synthesis of yttria nano-powders by the precipitation method: The influence of ammonium hydrogen carbonate to metal ions molar ratio and ammonium sulfate addition

Yttria (Y2O3) nano-powders were synthesized by the normal-strike precipitation method. The influences of R (NH4HCO3/M3+, molar ratio) and ammonium sulfate addition were studied throughout the preparation process. Several analytic techniques such as XRD, TG/DSC, SEM and FTIR were used to determine the characteristics of the precursors and Y2O3 powders. It was found that morphologies and phases of the precursors were evidently influenced by the R value. The phases of the precursors were Y2(CO3)3·2.79H2O when R was 3–4, while the composition of the precursors with R = 4–5 was (NH4)aY(OH)b(CO3)c·xH2O. Homogeneous needle-flake shaped particles composed of coadjacent grains with diameters of about 70 nm were obtained as the R = 3–4. The rhombohedral flake-shaped particles were the products with R = 5–6. The mechanism of the influence of R value on the precipitation of the precursor was also investigated in this work. Pure Y2O3 nano-powders were obtained by calcining the precursors at 1000 °C for 4 h regardless of what the R value was. Sulfate ions affect not only dispersion of nanopowders, but also their grain size. Results obtained in this work are contributed to the controllable synthesis of yttria powders.

Synthesis and Characterization of Yttria Nanopowders by Precipitation Method

In this investigation, yttria nanopowder was synthesized by precipitation method using yttria micro powder and ammonium hydrogen carbonate as precursor materials. The most important parameters, aging time and calcination temperature, have been reviewed in detail. The effects of aging time (3, 6, 12 and 24 h) and calcination temperature (700o, 800o, 900o, 1000o and 1100oC) were studied. Disk samples were fabricated from nanopowder at 1800oC and 50 Mpa via SPS method. Synthesized phases, thermal behaviour and particle size were shown by X-ray diffraction pattern, thermogravimetry and differential thermal analysis, and field emission scanning electron microscopy, respectively. Fourier transform infrared spectroscopy was used for bonding study before and after heat treatment at different temperatures.

Synthesis of Yttria Nanopowders by Two Precipitation Methods and Investigation of Synthesis Conditions

Yttrium oxide nanopowder was successfully synthesized by two precipitation methods, through which Y2O3 nanopowder was prepared by ammonium hydroxide and ammonium hydrogen carbonate as precipitants. Hydroxide and carbonate precursors of Y2O3 with approximate composition of Y(OH)3 and Y2(CO3)3, respectively, were synthesized using yttrium nitrate as the starting salt. XRD results show cubic yttrium oxide phase for annealed samples. SEM and TEM images show that samples are composed of agglomerated and nonagglomerated nanoparticles with different shapes and sizes. Optimal conditions for synthesis of nanoparticles were defined as 3‐h aging time, ammonium hydrogen carbonate as precipitant, and calcination temperature of 1000°C.

Fabrication of YAG transparent ceramics using carbonate precipitated yttria powder

Well-dispersed yttria nanopowders were synthesized by a precipitation method from yttrium nitrate solution using ammonium hydrogen carbonate as a precipitant. Needle-like precursor Y2(CO3)3·2.79 H2O undergoes fragmentation and decomposition into isolated quasi-spherical Y2O3 particles upon calcination in air. Highly transparent YAG ceramics were fabricated from the as-synthesized Y2O3 powder and the commercial α-Al2O3 powder by vacuum sintering. Phase transformation, morphology evolution, and sinterability of Y2O3 powders, microstructure and optical properties of YAG ceramics were investigated in detail. The densification, grain growth, linear shrinkage and phase transformation of the as-sintered ceramics were also explored. The activation energy for grain growth in the ceramic sample is 881kJ/mol. With optimized preparation conditions, YAG ceramics with the average grain size of about 20μm were fabricated by sintering at 1780°C for 20h, whose in-line transmittance reached 83.7% and 80.3% at the wavelength of 1064nm and 400nm, respectively.

Raman scattering and luminescence of yttria nanopowders and ceramics

We have studied Raman scattering in yttria nanopowders and ceramics that was excited by radiation at wavelengths of 514.5 and 632.8 nm. We show that, in undoped nanopowders and cubic phase of doped yttria ceramics, only the Raman scattering by phonons is observed, with no other Raman scattering centers having been revealed. In nanopowders of the monoclinic phase, we have observed an additional Raman line with a Raman shift of 1093 ± 4 cm−1. If all the objects under investigation are excited by the radiation at a wavelength of 514.5 nm, their spectra exhibit four series of photoluminescence lines, two of which (at λ = 521–523 and 538–564 nm) are emitted by Er3+ ions, “impurity” dopants, while the other two lines (at λ = 607–635 and 644–684 nm) are emitted by intrinsic centers. Under excitation by the radiation at a wavelength of 632.8 nm, only a series of bands at λ = 644–684 nm is emitted. In addition to these photoluminescence bands, neodymium-doped ceramics show photoluminescence bands of Nd3+ ions. We have shown that intrinsic luminescence centers, which occur in all the examined specimens, are capable of acting as acceptors with respect to neodymium ions excited to the upper laser level.

Low-agglomerated yttria nanopowders via decomposition of sulfate-doped precursor with transient morphology

The fabrication peculiarities of low-agglomerated yttria (Y2O3) nanopowders via thermal decomposition of sulfate-doped precursor with transient morphology were studied. It was determined that Y2(OH)5(NO3)x(CO2)y(SO4)z·nH2O (n=1-2) crystalline precursor underwent fragmentation and decomposition into isolated quasi-spherical Y2O3 particles upon calcination. Effect was connected with minimizing the free energy of the plate-like crystallites via reducing the contact surface until to the moment of spheroidization and attainment of isolation that occurred at T=1100 °C. Residual sulfate ions slowed down the surface diffusion during heat treatment thus retaining quasy-spherical morphology and low aggregation degree of Y2O3 nanopowders. Sulfate-doped yttria nanopowders with medium particle size of 53±13 nm possessed improved sinterability in comparison with undoped ones arising from finer particle size, narrower particle distribution and lower agglomeration degree.

Synthesis of neodymium doped yttria nanopowders by microwave-assisted glycine combustion method and the powder characteristics

Trivalent neodymium ion doped yttria (Nd3+:Y2O3) nanopowders were synthesized by using a glycine combustion method. The characteristics of the Nd3+:Y2O3 nanopowders with different calcination temperatures and Nd3+ ion doping concentrations were analyzed to determine the optimum synthesis conditions of the samples. Thermo-gravimetry and differential scanning colorimetry (TG/DSC), XRD and FTIR analysis showed that the novel glycine-gel microwave combustion method can provide an effective reaction to form yttria nanopowders. The peak positions of the emission spectra of Nd3+ ion in yttria host did not differ with the neodymium ion concentration or the calcination temperatures, whereas the luminescence intensities were heavily dependent on the ion concentration and calcination temperatures.

Fabrication and spectral investigation of Y2O3:Nd3+ nanoparticles

In this study we have synthesized Y2O3 (yttria) nanopowders with 1 % Nd3+ concentration by using a thermal decomposition method and investigated the effect of annealing temperature on the particle sizes and the effect of particle sizes on the spectroscopic properties of these systems. The particle sizes were effectively controlled by synthesis and annealing temperatures; the sizes were found to vary in the 15–290 nm range. The particle sizes and cubic phase of the yttria were determined by using XRD patterns and confirmed by SEM and TEM measurements. We note that the particle sizes increase by increasing the synthesis and annealing temperatures. Temperature dependence of the width and position of a selected spectral line were successfully fitted with the theoretical expressions. We studied thoroughly the behavior of the samples under pulsed excitation and give plausible explanations of the measured effects.

Synthesis of nanostructured Nd:Y2O3 powders by carbonate-precipitation process for Nd:YAG ceramics

Abstract Neodymium doped yttria (Nd:Y 2 O 3 ) nanopowders were synthesized by a co-precipitation method, and the effect of thermal decomposition behavior of the precursors were studied. Nonlinear and linear heating schedules (NHS and LHS) were adopted during the calcination processes. The results show that as compared to the LHS the NHS can not only lower the crystallization temperature substantially, but also decrease the mean particle size and lighten the particle agglomeration in the obtained Nd:Y 2 O 3 nanopowders. Using the obtained well-dispersed Nd:Y 2 O 3 and commercial Al 2 O 3 powders, transparent Nd:YAG ceramics were fabricated at 1750 °C in vacuum. Better transparency can be obtained by using the Nd:Y 2 O 3 powders calcined in the NHS instead of the LHS.

Mechanism of ammonium sulfate regulation effect on microstructure of Y2O3 nanopowders via urea precipitation method

In the preparation of transparent ceramics and ultrafine oxide nanopowders, ammonium sulfate ((NH4)2SO4) has been widely used as the control agent. However, the mechanism of its regulation effect has not been well studied. In the present work, precursors of yttria (Y2O3) nanopowders with controlled morphology were synthesized via a urea precipitation method using ammonium sulfate as the additive. The effect of (NH4)2SO4 is discussed throughout the preparation process. Two opposite morphology transformation modes were noticed for the precursor samples made with and without (NH4)2SO4 during the calcination process. Flocculent precursors and flowers assembled by the plate-shaped particles were obtained in the systems without and with (NH4)2SO4. By calcination, the aggregated 200–400 nm particles with massive defects and 100 nm particles with homogeneous crystalline structure were obtained, respectively. The mechanism of (NH4)2SO4 as a regulator that could mediate the nucleation and growth of the precursors as well as its decomposition behavior is verified.

Effect of complexing agents on the powder characteristics and sinterability of neodymium doped yttria nanoparticles

Abstract We report the synthesis of neodymium doped cubic yttria (Nd:Y 2 O 3 ) nanopowders by microwave assisted combustion method using citric acid, urea and l -alanine as complexing agents as well as fuels. FTIR and XRD of powders calcined at 1000 °C for 3 h in oxygen atmosphere demonstrated formation and phase purity of Nd:Y 2 O 3 respectively. Varied morphologies of as prepared precursor and calcined oxide (from polyhedral to spheroidal) due to different complexing agents were observed by SEM and TEM. Sintering of these nanopowders with different morphologies after compaction by cold isostatic press at 400 MPa at 1700 °C for 10 h under 10 − 5 mbar vacuum gave maximum densification with 32.5% transmission by using l -alanine compared to 20% and 8% transmission obtained for urea and citric acid respectively. Thus l -alanine gave highly sinterable nanopowders with narrow size range of 25–40 nm with close to spherical morphology.

Ammonium sulfate regulation of morphology of Nd:Y2O3 precursor via urea precipitation method and its effect on the sintering properties of Nd:Y2O3 nanopowders

Ammonium sulfate has been widely used as a control agent in the preparation of yttrium-aluminium-garnet (YAG) transparent ceramics, however, research of its application in the preparation in transparent ceramic yttria has not been intensively studied. Neodymium–doped yttria (Nd:Y2O3) nanopowders with controlled morphology and size were synthesized via a urea precipitation method using ammonium sulfate as the additive. The effect of ammonium sulfate was intensively studied throughout the preparation process. Morphology of precursors was found to be evidently affected by the [(NH4)2SO4]/[Nd:Y2O3] ratio (measured by weight). Uniform spheres of Nd:Y2O3 precursor were obtained without the addition of ammonium sulfate. With increasing amounts of ammonium sulfate added, the scale of the Nd:Y2O3 precursors diminished which results in the aggregation of the Nd:Y2O3 precursor. Aggregates of coral like particles after precipitation and uniform well dispersed particles after calcinations were obtained as the dosage of ammonium sulfate reached 20 wt%. It was considered to be the optimum state for the preparation of highly sinterable Nd:Y2O3 nanopowders. Ammonium sulfate was proved to be a regulator that could mediate the nucleation and growth of the precursor as well as its decomposition behaviour. Results of this paper can contribute to the controllable synthesis of transparent ceramic yttria.