Yttrium Aluminum Research Articles

Thermal stability and crystallisation behaviour of amorphous alumina-yttria synthesised by co-precipitation and combustion synthesis

Amorphous alumina-yttria powders with 20, 25, 30 and 37.5 mol% yttria were synthesised by a co-precipitation method using the respective nitrates as precursors for identifying a composition with the best amorphous phase stability. Thermal analysis showed that calcination to yield amorphous oxides completed at around 800 °C. Crystallisation behaviour investigated by x-ray diffraction (XRD) showed that Al2O3–25 mol% Y2O3 (25Y) had the highest crystallisation temperature of 900 °C. Crystallisation involved the appearance and disappearance of metastable hexagonal yttrium aluminate (H-YAlO3) below 1000 °C. The phase evolution sequences for all the compositions were studied in detail. All the phases were nanocrystalline, establishing the efficacy of amorphous phase crystallisation as a viable route for the synthesis of nanocrystalline ceramics. Solution combustion synthesis (SCS) was selected to synthesis 25Y with enhanced amorphous phase stability using different proportions of citric acid and ethylene glycol. Thermal analysis revealed that the powder was free of organic residue after heat treating at 650 °C. The powder produced with 10 vol% of fuel (citric acid + ethylene glycol) yielded the highest crystallisation temperature of 925 °C and the appearance and disappearance of H-YAlO3 between 950 and 1100 °C. Fourier transform infrared (FT-IR) spectroscopy revealed that the co-precipitation synthesis might have residual NH4+ and NO3- radicals whereas SCS did not contain any residual carbonate above 700 °C.

Eu3+-doped highly thermal-stable barium yttrium aluminate as a red-emitting phosphor for UV based white LED

A series of novel Eu3+ activated aluminate Ba2Y1−xEuxAlO5 (x = 0.02–0.40) red-emitting phosphors were synthesized through a high-temperature solid-state route at 1380 °C. The phosphors were well crystallized in the space group P21/c (No. 14). Their photoluminescence emission (PL) and excitation (PLE) spectra were investigated. The results indicate that the Ba2YAlO5:Eu3+ phosphor can be excited effectively under 394 nm irradiation, which is suitable for UV LED chip. The obtained Ba2YAlO5:Eu3+ phosphor shows four peaks, corresponding to the 5D0–7FJ (J = 0, 1, 2, 3 and 4) transitions of Eu3+ upon 394 nm excitation. The optimal doping concentration of Eu3+ in Ba2YAlO5:xEu3+ was determined at 30 mol%. By temperature dependent emission spectra, the quenching temperature for Ba2YAlO5:0.30Eu3+ was found to be over 500 K. And the CIE chromaticity coordinates of Ba2YAlO5:0.30Eu3+ are very close to the National Television System Committee (NTSC) standard red.

Synthesis and characterization of pure and Mn-substituted YAl1.15(CO3)yO3+δ: A variation from the classical hexagonal “YAlO3”

Recent works describing the existence of an intense-blue color within the YIn1-xMnxO3 solid solution due to the presence of Mn3+ cations in trigonal-bipyramidal sites have led to the interest to prepare Al-analogues with the same 5-fold non-centrosymetric coordination. In this framework, YAlO3 structure has been recently re-examined, concluding the aluminate is indeed an oxycarbonate with the Y3Al3O8CO3 stoichiometry. In this work, we observed that pure yttrium aluminate is not only obtained for fast thermal treatments below 1000 °C but with higher Al:Y ratio than 1:1. YAl1.15(CO3)yO3+δ. The corresponding YAl1.15-xMnx(CO3)yO3+δ solid solutions were successfully prepared showing dull brown colors for the low Mn-content in comparison to Yin1-xMnxO3 series, confirming that the TBP coordination is lost in the aluminate, partly due to the presence of carbonate groups in the structure.

Investigating the role of solvent formulations in temperature-controlled liquid-fed aerosol flame synthesis of YAG-based nanoparticles

Abstract Key effects of solvent formulations on the structure and morphology of optical-quality yttrium-aluminum nanocomposites using liquid-fed aerosol flame synthesis are investigated. Employing a temperature-controlled flat flame burner with inexpensive nitrates as multi-component precursors, three different solvent formulations, i.e., ethanol, ethanol/2-ethylhexanoic acid (EHA), and butanol, are studied. Adding EHA into ethanol in a 1:1 volume ratio dramatically changes the flame-made yttrium-aluminum oxides from hollow inhomogeneous powders that contain non-uniform large particles to homogeneous nanopowders around 10 nm. As characterized by in-situ phase Doppler anemometry, droplet size with increasing burner height for the EHA/ethanol case remains constant at the beginning, whereas those for both ethanol and butanol cases reduce immediately. EHA likely causes a shift from the droplet-to-particle precipitation route to the gas-to-particle route because of the formed low-boiling-point 2-ethylhexanoates from nitrates via ligand exchange. By replacing ethanol with butanol, hollow particles are produced with better crystallinity because of its high calorific value that helps to heat precursors at the droplet surface. In-situ diagnostics using phase-selective laser-induced breakdown spectroscopy, which tracks only atomic emission from the nanoparticle phase. The result shows that the Al atomic emissions in the EHA/ethanol mixture case gradually increase along the burner height, while those for both ethanol and butanol cases fluctuate, further verifying the favoring of the gas-to-particle route for producing uniform, ultrafine solid multi-oxide particles by adding EHA in solvents.

Effects of Y2O3 and yttrium aluminates as sintering additives on the thermal conductivity of AlN ceramic substrates

AlN ceramic substrates are prepared by tape casting and presureless sintering at 1850 °C for 10 h, with 8 wt% Y2O3 and yttrium aluminates of Y3Al5O12 (YAG), YAlO3 (YAP), and Y4Al2O9 (YAM) as sintering additives. The effects of the sintering additives on the phase assemblage, microstructure, thermal conductivity, and bending strength of the sintered AlN ceramics are discussed. With Y2O3, YAG, YAP, and YAM as sintering additives, the secondary phases in the sintered AlN ceramics are YAM, YAG, YAP + YAG, and YAM + YAP, and the average sizes of AlN grains are 5.5, 3.6, 4.4, and 4.9 µm, respectively. In the order of sintering additives with decreasing Y2O3/Al2O3 ratio, viz. Y2O3 > YAM > YAP > YAG, both the thermal conductivity and bending strength of the sintered AlN ceramics decrease. With Y2O3 as the sintering additive, the sintered AlN sample shows the maximum thermal conductivity of 205 W/(m K) and bending strength of 295 MPa.

Sol-gel synthesis of yttrium aluminum garnet (YAG): effects of the precursor nature and concentration on the crystallization

The sol–gel synthesis of yttrium aluminum garnet (YAG) was performed using different metal precursors (salts and alkoxides of aluminum and yttrium) and metal concentrations (up to a concentration factor of 7.4). The cross-reactivity of the aluminum and yttrium precursors is not clear, and generally, the sol–gel process leads to polyphasic samples consisting of hexagonal YAlO3 and a monoclinic yttrium-aluminum oxide. Nevertheless, the high reactivity of the yttrium precursor can be offset by the use of an aluminum alkoxide and yttrium salt as the precursors, which results in the synthesis of pure-phase YAG at 1000 °C. The effects of the metal concentration in the sol–gel synthesis on the crystallite size of the resulting YAG are reported for the first time and are found to be significant with the crystallite size varying from 55 to 123 nm. Repeated experiments demonstrate that the proposed synthesis protocol is relatively robust.

Quantitative description of yttrium aluminate ceramic composition by means of Er+3 microluminescence spectrum

The composition of erbium-doped yttrium aluminate ceramics was analyzed by means of confocal luminescence spectroscopy, EDX, and X-ray diffraction. A well-defined linear correlation was found between a proposed estimator computed from the luminescence spectrum and the proportion of ceramic phases coexisting in different samples. This result shows the feasibility of using erbium luminescence spectroscopy to perform a quantitative determination of different phases of yttrium aluminates within a micrometric region in nanograined ceramics.

Influence of Transient Liquid Phase Promoting Additives upon Reactive Plasma Spraying of AlN Coatings and Its Properties

The feasibility of using a transient liquid phase promoting agent upon reactive plasma spraying (RPS) of AlN coatings in atmospheric ambient is successfully investigated. Several sprayable fine AlN–Al2O3–Y2O3 mixtures with different compositions are prepared by spray‐drying. Upon plasma spraying in N2/H2 plasma, thick and homogeneous AlN based coatings (h‐AlN, c‐AlN, γ‐Al2O3, Al5O6N, α‐Al2O3, and YAG) are fabricated. Fine Y2O3 acts as transient liquid phase promoting additive, and reacts with Al2O3 phase (from feedstock mixture and on AlN particles surface) to create wetting agent of yttrium aluminate Y–Al–O around solid AlN particles. However, due to rapid solidification rates of plasma, it is difficult to react with the interspersed oxygen in AlN grains. The Y2O3 addition significantly reduces the coatings oxide content due to the consumption of starting Al2O3 to form the YAG. Influence of Y2O3 significantly observes with increasing AlN feedstock and high AlN content coatings with small oxides are fabricated by RPS of 80AlN–10Al2O3–10Y2O3 mixture. Thermal conductivity is improved with using Y2O3 and increasing AlN feedstock. However, the conductivity is not so high compared to the AlN compacts, due to increased porosity, incomplete sintering of the formed initial liquid phase state, remaining oxide content, and low density of the coatings.

Solution-processed ternary alloy aluminum yttrium oxide dielectric for high performance indium zinc oxide thin-film transistors

In this study, we evaluated the structural, chemical, and electrical properties of ternary alloy aluminum yttrium oxide (Al2-xYxO3) films prepared by employing a low-cost spin-cast technique. Al2-xYxO3 films annealed at 400 °C were found to possess smooth and excellent insulating characteristics compared to their binary Al2O3 or Y2O3 film counterparts. This superior performance of the Al2-xYxO3 films as a gate insulator can be explained based on structure stabilization from the cation alloying mixing effect. The amorphous indium zinc oxide (a-IZO) thin-film transistor (TFT) with the ternary alloy Al0.45Y1.55O3 film exhibited a high mobility of 52.9 cm2/V, a low subthreshold gate swing of 0.19 V/decade, a threshold voltage of −0.51 V, a high ION/OFF ratio of 4 × 106, and good hysteresis-free stability, suggesting that the solution-based Al0.45Y1.55O3 dielectric film is an attractive candidate as a gate dielectric for high-performance and low-cost a-IZO TFTs.

Temperature Dependence of the Thermal, Electrical Resistivity, Dielectric and Piezoelectric Properties of CaYAl3O7 Crystal

Calcium yttrium aluminate (CaYAl3O7) crystal was grown and characterized in detail for high temperature piezoelectric sensors for the first time. The thermal properties of the CaYAl3O7 (CYAM) crystal were investigated systematically. In particular, the CYAM crystal exhibits considerably high resistivity along X- and Z- direction in the order of 6.96 × 107 Ω·cm and 2.86 × 108 Ω·cm at 600 °C, respectively. The temperature dependence of the electromechanical properties of CYAM crystal were investigated over the temperature range of 25–500 °C. The high thermal stability of piezoelectric properties together with its high electrical resistivity, makes CaYAl3O7 crystal a promising candidate for high temperature piezoelectric applications.

Crystallization kinetics of yttrium aluminate glasses

Yttrium aluminate glasses with eutectic AY-E and near-eutectic composition AY-NE were prepared in the form of glass microspheres. Their basic characterization was carried out by XRD, optical microscopy and SEM. In DSC records of both samples, two exothermic peaks in temperature interval 940–1027 °C were observed. In both samples, YAG phase crystallized in two steps, as determined by HT XRD. DSC experiments conducted in the temperature interval 35–1200 °C at heating rates 2, 4, 6, 8 and 10 °C min−1 were performed, and the kinetic parameters of crystallization were determined with the use of the JMAK model. Crystallization in both samples was controlled by diffusion flow with linear nucleation rate time dependence. One-dimensional growth and formation of needle-like (dendritic) YAG crystals was observed in AY-E glass crystallized at 932 °C corresponding to the first exothermic maximum at the DSC curve. Two-dimensional growth and the presence of plate-like YAG crystals were observed in AY-NE glass crystallized at 996 °C. For the second exothermic effect, plate-like crystals crystallized at higher temperatures (996 and 1020 °C) in both compositions. The results of SEM analysis are in agreement with the results of kinetic calculations in the prepared systems.

Pulsed laser deposition of crystalline garnet waveguides at a growth rate of 20 μm per hour

We report pulsed laser deposition of high-quality crystalline yttrium aluminium oxide and yttrium gallium oxide with a growth rate approaching 20μm per hour by using an excimer laser operating at a repetition rate of 100Hz. This result demonstrates the capability of PLD at 100Hz for upscaling deposition speeds to a rate that is industrially relevant. In addition, we show that use of this high repetition rate can cause additional heating of the substrate, which in turn affects the film composition. This effect is used as an additional control parameter on the composition, and thus refractive index, of the grown material.

Phase, microstructure and sintering of aluminum nitride powder by the carbothermal reduction-nitridation process with Y2O3 addition

Aluminum nitride powders were synthesized by carbothermal reduction-nitridation method using Al(OH)3, carbon black and Y2O3 as raw materials. The change of phase, microstructure and densification during the AlN synthesis and sintering process were investigated and the effects of Y2O3 was discussed. The results showed that Y2O3 reacted with Al2O3 to form yttrium aluminates of YAlO3 (orthorhombic and hexagonal phases), Y4Al2O9 and Y3Al5O12 at the low temperature of 1350°C. YAlO3 could firstly be transformed into Y2O3 and then completely into YN when the firing temperature and holding time increased. However, YN could be oxidized into Y2O3 again after the carbon removal at 700°C in the air atmosphere. There were two ways generating AlN when adding Y2O3 and the possible mechanism was proposed. Y2O3 from YN oxidation favored the densification of AlN ceramics because the liquid had better flowability and distribution in the sintering process at 1800°C.

Low-Temperature Steam Annealing of Metal Oxide Thin Films from Aqueous Precursors: Enhanced Counterion Removal, Resistance to Water Absorption, and Dielectric Constant

Aqueous solution deposition has emerged as a potentially scalable, high-throughput route to functional metal oxide thin films. Aqueous routes, however, generally require elevated processing temperatures to produce fully condensed films that are resistant to water absorption. Herein, we report a low-processing-temperature method for preparing more fully condensed, stable metal oxide films from aqueous precursors. We show that a steam anneal at ≤200 °C reduces residual nitrates in zinc oxide, yttrium aluminum oxide, and lanthanum zirconium oxide (LZO) films. An in-depth study on LZO dielectric films reveals steam annealing also reduces residual chloride content, increases resistance to post-anneal water absorption, eliminates void formation, and enhances the dielectric constant. This investigation demonstrates that steam annealing directly affects the decomposition temperatures and chemical evolution of aqueous precursors, suggesting a general means for producing high-quality films at low processing tempera...

Crystallization kinetics of glass microspheres with yttrium aluminium garnet (YAG) composition

A combination of sol–gel Pechini method and flame synthesis was used to prepare yttrium aluminate glass microspheres with the garnet composition (YAG, 62.5 mol% aluminium oxide, 37.5 mol% yttrium oxide). Prepared glass microbeads were studied by optical microscopy, SEM, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-temperature (HT) XRD analysis. Formation of YAG as the only crystalline phase was observed during HT XRD experiment in the temperature interval (750–1200 °C), with the onset of YAG phase crystallization in the temperature interval 860–870 °C and most prominent increase in the YAG phase content between 905 and 910 °C. The experimental data obtained by DSC analysis and the Johnson–Mehl–Avrami–Kolmogorov model were used for determination of crystallization behaviour of the studied system. The frequency factor A = 5.2 × 1048 ± 9.6 × 1048 min−1, apparent activation energy E app = 1100 ± 10 kJ mol−1 and the Avrami coefficient m = 4 were determined. The linear temperature dependence of nucleation rate, reaction-controlled crystal growth interface and a 3-D crystal growth were confirmed in the studied system.

Hot corrosion behaviour of plasma sprayed alumina + YSZ particle composite coating

Hot corrosion is one of the damage mechanisms in thermal barrier coatings (TBCs) due to the molten salt effects as a result of combustion of low quality fuel. In this study, the hot corrosion behaviour of alumina–yttria stabilized zirconia particle composite coatings produced by thermal spraying for use as a thermal barriers on industrial gas turbines and in jet engines was evaluated. Plasma sprayed coatings with three different amounts of alumina- yttria stabilized zirconia particle composite have been exposed to 50 wt % Na2SO4 + 50 wt % V2O5 corrosive molten salt temperatures at 1050°C for 60 hours. Damages in the coatings surface and cross section after hot corrosion tests have been studied by using a scanning electron microscope to observe the microstructure and x-ray diffraction techniques to analyze the phase composition. The results have shown that the amount of YVO4 crystals on the surface of YSZ coatings decrease while Al2O3 increases in YSZ + Al2O3 composition, therefore, the hot corrosion resistance of TBC improves with the addition of Al2O3.

Rapid solution combustion synthesis of sponge like mesoporous Ce3+ doped yttrium aluminium oxide

We present here an effective and facile method to synthesize hierarchical sponge-like mesoporous trivalent cerium (Ce3+) doped cubic (YAG (Y3A5O12)) and monoclinic (YAM (Y4A2O9)) yttrium aluminium oxide (YAlO) by a single step self propagating low temperature combustion technique without any post heating. The X-ray diffraction study revealed the formation of YAG and YAM structures and optimum incorporation of dopant is confirmed through precipitated secondary phase at higher Ce3+ concentration. Raman spectra of undoped and Ce3+ doped YAlO shows the characteristics peaks of YAG and YAM structure. The field emission scanning electron micro graphs (FESEM) reveal highly porous sponge-like surface with individual pore size of about 12–15 nm. The photoluminescence studies show efficient single band emission spectra centered at 568 and 550 nm for Ce3+ doped YAG and YAM respectively due to intra-shell transitions of the rare earth atom, compared to negligible emission in visible region for undoped YAlO due to defects present in the host lattice. Influence of dopant and the changes observed in structural, morphological and luminescence studies due to differences in crystal field environment (cubic and monoclinic) are explained in detail. Such highly stable mesoporous material with luminescence in visible region is suited for applications in illumination devices like white LEDs for indoor and outdoor lighting and also high end biomedical applications such as tumor targeting.

Synthesis and sintering of submicron Nd:YAG particles prepared from carbonate precursors

Using high-temperature X-ray diffraction, differential scanning calorimetry, and electron microscopy, we have studied the formation of yttrium aluminates and Nd:YAG (YAG) activated garnet nanoparticles during the thermal decomposition of a poorly crystallized carbonate precursor prepared in the NH4Al(OH)2CO3–(Y,Nd)(ОН)CO3 nanosystem and the development of the morphological structure of powders during heating to a temperature of 1350°C. The results demonstrate that heat treatment in the temperature range 850–950°C leads to the formation of metastable nonstoichiometric YAlO3 with a garnet-like structure, which reacts with Al2O3 at a temperature of 1000°C to form YAG. The cubic cell parameter a and X-ray density of YAG crystals with the composition Y2.97Nd0.03Al5O12 synthesized at 1200°C are 1.2009 nm and 4.565 g/cm3, respectively, and the average particle size is 108 nm. Using carbonate route, we prepared transparent Nd:YAG ceramics with a relative density of 99.7%, X-ray density of 4.562 g/cm3, and crystallite size in the range 1–7 μm.

Preparation and characterization of Yttrium based luminescence phosphors

Abstracts Ce doped Yttrium aluminate modified by replacing different molar part of aluminium or gallium (Y3Al5−xGaxO12) and Yttrium silicate phosphors activated with Ce and Tb (Y2SiO5:Ce3+,Tb3+) were synthesized by solid state reaction and a gel combustion method, respectively. X-ray diffraction and Scanning electron microscope (SEM) techniques are used to identify their structures and morphologies. Luminescence characteristics are measured and spectroscopic data confirm that Y2SiO5:Ce3+, Tb3+ phosphors can be effectively excited upon UV excitation light and X-ray irradiation, resulting in intense blue and green emissions, respectively. This energy transfer takes place by means of a non-radiative process inside Ce3+-Tb3+ clusters formed in the host matrix. Tb3+ doped Y2SiO5 yields both blue emission 5D3 → 7Fj (j = 3,4,5,6) and green emission 5D4 → 7FJ (J = 3,4,5,6) of Tb3+. Y3Al5−xGaxO12:Ce3+ phosphors exhibit a broad blue emission band originating from allowed 5d-4f transition of the Ce3+ ions under different excitation sources but the broad emission band shifts with increasing of Ga3+ content. This work presents a quantitative understanding of host material's on dopant's luminescence properties and thereby provides an optimization guideline, which is extremely demanding for the development of new luminescent materials.

Effect of the ion-beam bombardment and annealing temperature on sol-gel derived yttrium aluminum oxide film as liquid crystal alignment layer

We demonstrated a homogeneous liquid-crystal (LC) alignment state on yttrium aluminum oxide (YAlO) films, where the alignment was induced by ion-beam (IB) irradiation. Topographical analysis was performed by atomic force microscopy as a function of annealing temperature. Higher annealing temperatures yielded a smoother surface, accompanied by reduced light scattering. Transparency in the visible region increased on the surface fabricated at higher annealing temperatures. LC alignment mechanism was determined by X-ray diffraction (XRD) analysis. Moreover, IB-irradiated YAlO films annealed at temperatures greater than 200 °C exhibited good thermal stability and low capacitance–voltage hysteresis. The IB-irradiated YAlO films are suitable as alternative alignment layers in advanced LC display applications.