Yttrium Aluminum Garnet Ceramics Research Articles

Rapid, Micron-Resolution 3D Printing of Nd:YAG Ceramic with Optical Gain.

Polycrystalline yttrium aluminum garnet (YAG) ceramic doped with neodymium (Nd), referred to as Nd:YAG, is widely used in solid-state lasers. However, conventional powder metallurgy methods suffer from expenses, time consumption, and limitations in customizing structures. This study introduces a novel approach for creating Nd:YAG ceramics with 3D free-form structures from micron (∼70µm) to centimeter scales. Firstly, sol-gel synthesis is employed to form photocurable colloidal solutions. Subsequently, by utilizing a home-built micro-continuous liquid interface printing process, precursors are printed into 3D poly(acrylic acid) hydrogels containing yttrium, aluminum, and neodymium hydroxides, with a resolution of 5.8µm pixel-1 at a speed of 10µm s-1. After the hydrogels undergo thermal dehydration, debinding, and sintering, polycrystalline Nd:YAG ceramics featuring distinguishable grains are successfully produced. By optimizing the concentrations of the sintering aids (tetraethyl orthosilicate) and neodymium trichloride (NdCl3), the resultant samples exhibit satisfactory photoluminescence, emitting light concentrated at 1064nm when stimulated by a 532nm laser. Additionally, Nd:YAG ceramics with various 3D geometries (e.g., cone, spiral, and angled pillar) are printed and characterized, which demonstrates the potential for applications, such as laser and amplifier fibers, couplers, and splitters in optical circuits, as well as gain metamaterials or metasurfaces.

SiC ceramics production by spark plasma sintering from a coal fly ash residue after high-pressure NH4HSO4-and-H2SO4 leaching

In this article, a novel method for SiC production from a residue of coal fly ash (CFA) after high-pressure leaching with a mixture of NH4HSO4 + H2SO4 is proposed. A thermodynamic analysis showed that SiC can be obtained at >1500 °C, and titanium carbide (TiC) and ferrosilicon (FeSi) can form as byproducts. Carbothermal reduction of the CFA residue with carbon in the range 1300–1500 °C with holding time 1–3 h was investigated. X-ray phase analysis (XRD) indicated that SiC forms at >1425 °C. Iron compounds in the form of Fe3Si and Fe5Si3 were detected by Mössbauer spectroscopy in a sample sintered at 1500 °C. The possibility of SiC production by a two-step procedure was demonstrated. First, a SiC powder was obtained from the CFA residue and carbon at 1500 °C, then SiC was mixed with yttrium aluminum garnet Y3Al5O12 and processed by spark plasma sintering at 1750–2000 °C, holding time 5 min, and pressure 50 MPa. Ceramic samples obtained at 1850 and 1900 °C with compressive strength of 350 ± 17.5 & 416 ± 20.8 MPa and Vickers hardness of 17.89 ± 0.89 & 15.97 ± 0.79 GPa, respectively, proved to be comparable to the best reported SiC + yttrium aluminum garnet ceramics. Thus, this study presents an original method for ceramics production from solid waste of coal-fired power plants; this approach will allow to create a comprehensive technology for utilizing 100 % of CFA.

Dodecahedron lattice of rattling phenomenon, and microwave dielectric properties of yttrium aluminum garnet ceramics and its application verification for Wifi6E/7 patch and 6G resonant antennas

In garnet phase ceramics Y2.9M0.1Al4.9Si0.1O12 (M = Mg2+, Co2+, Zn2+, Mn2+, Ca2+, Sr2+, Ba2+), rattling effects occur when M = Mg2+, Co2+, Zn2+, Mn2+ ions with smaller ionic radius (<1Å) occupy the dodecahedron lattice lattices. This results in an abnormally high dielectric constant, in contrast to the larger ionic radius (>1 Å) of M = Ca2+, Sr2+ and Ba2+, which deviate from the theoretical values calculated using the Clausius-Mosotti formula according to each ion’s polarizability. The optimal microwave dielectric properties for Y2.9Mg0.1Al4.9Si0.1O12 was obtained by sintering at 1575 °C for 5 h (Q×f = 51,382 GHz, εr = 9.74, and τf = −30.12 ppm/°C). Additionally, a thermal stable Y2.9Mg0.1Al4.9Si0.1O12-6 wt%TiO2 composite ceramic was developed. Based on this composite, a Wifi6E/7 patch antenna operating at 6.3 GHz and a millimeter-wave resonant antenna functioning at 27.1 GHz were designed and validated. This indicates the potential application prospects of garnet ceramics in 5G/6G radio communication technologies.

Fabrication of YAG ceramics surface without damage and grain boundary steps using catalyzed chemical wet etching

Achieving an atomically smooth surface without damage or grain boundary steps is crucial for yttrium aluminum garnet (YAG) ceramics to deliver high-power laser oscillation and stable output. We propose a wet etching method that utilizes a thin-film catalyst, enabling the topmost crystal grain to be selectively removed through a catalyzed chemical reaction. This study demonstrates the effectiveness of the proposed method by polishing Nd- and Yb-doped YAG ceramic substrates. We realized damage-free surfaces having steps with a height of less than 1.0 nm. Such surfaces can effectively deliver high-power laser oscillation with high output stability.

Surface fracture behavior and subsurface damage of polycrystalline yttrium aluminum garnet ceramics in Vickers indentation

In this paper, the Vickers indentation experiments were carried out under different loads on the polished surface of polycrystalline yttrium aluminum garnet (YAG) ceramics to investigate the surface fracture behavior and subsurface damage under quasi-static conditions. The surface of polycrystalline YAG ceramic was corroded for intuitively observing the surface fracture behavior under quasi-static load, and the method of section polishing combined with chemical corrosion was used to examine the subsurface damage. The Johnson-Holmquist (JH-2) material model of polycrystalline YAG ceramics was established and imported into Abaqus software to simulate the process of Vickers indentation, so as to predict surface fracture behavior and subsurface damage depth under quasi-static load. The results show that the surface fracture behavior was divided into two stages with the increase of loads, that is, the fracture toughness value increased gradually and the fracture behavior was mainly transgranular fracture in the loading range of 0.05–0.3kgf. The fracture toughness value decreased obviously and fracture behavior was mainly intergranular fracture when the load range was 0.3-1kgf. The simulation values of surface fracture length and subsurface damage depth under different loads are highly consistent with the experimental results of Vickers indentation, the accuracy of the established simulation model was verified, which has an important guiding value for predicting the surface fracture behavior and subsurface damage in ultra-precision grinding of polycrystalline YAG ceramics.

Phase Composition, Crystal Structure and Microwave Dielectric Properties of Nb-Doped Yttrium Aluminum Garnet Ceramics

The Y3Al5-xNbxO12 (0 ≤ x ≤ 0.06) garnet ceramics were prepared by solid-state reaction method. The effects of Nb5+ substitution on the phase composition, microstructure and microwave dielectric properties were investigated. All samples retained the yttrium-aluminum garnet solid solution form until x up to 0.06 at which YNbO4 secondary phase precipitated. The doping of Nb2O5 improved the grain development and enhanced the physical properties of the ceramics under the sintering condition of 8 h at 1700 °C. Specifically, with the substitution of Nb5+, the degree of micromorphology improvement and quality factor first increased and then decreased, with a maximum value at x = 0.015. Finally, the best combination of microwave dielectric properties was obtained, i.e., εr = 10.79, Q×f = 165,478 GHz, τf = -31.7 ppm/°C. This study provides a theoretical basis for the further expansion and application of yttrium aluminum garnet in the microwave field. Keywords: Yttrium Aluminum Garnet ceramics, Nb2O5, microwave dielectric properties.

Study of sintering mechanisms of Ca-doped yttrium aluminum garnet ceramics: From nanostructure to macroscopic behaviour

This paper aims at elucidate the role of calcium as sintering aid for YAG ceramics elaborated by a reaction-sintering process. From structural and microstructural analyses, the solubility limit of calcium was found to be close to 0.065 ± 0.015 at% at 1700 °C. For calcium content higher than this value up to 1 at%, CaAl12O19 crystallized precipitates with a melting temperature close to 1850 °C were observed. Whatever its content, calcium segregates at grain boundaries as evidenced by STEM and NanoSIMS chemical analyses at nanometric scale, and strongly decreases densification and grain growth kinetics of YAG ceramics. This result was explained by a solute-drag mechanism due to the segregation of complex Ca2+-VO.. clusters with low mobility at grain boundaries. Finally, calcium appears as a very efficient sintering additive to limit grain growth in YAG, thus avoiding the formation of intragranular porosity that is a critical point for the manufacturing of highly transparent ceramics.

Fabrication of Yb:YAG Transparent Ceramic by Vacuum Sintering Using Monodispersed Spherical Y2O3 and Al2O3 Powders

In the present work, Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated using monodispersed spherical Y2O3, Al2O3 powders and commercial Yb2O3 nano-powder as raw materials, adding 0.5 wt% tetraethyl orthosilicae (TEOS) through the solid-state method and vacuum sintering technology. The prepared monodispersed Y2O3 and Al2O3 powders adopted by homogeneous co-precipitation showed improved mixing uniformity and lead to the reduced defect of the YAG powders. After sintering in vacuum at 1700 °C for 10 h, the (Y1−xYbx)AG (x = 0, 0.01, 0.10) ceramics with high transparency were obtained. Analysis of the densification rate, micromorphology, and optical properties of the ceramics suggests that the performance of the Yb:YAG ceramics is independent of the doping amount of Yb. Moreover, when the Y2O3, Al2O3, and Yb2O3 mixtures were laid aside for some time in the air after milling and drying, the performances of the as-prepared Yb:YAG ceramics would be affected distinctively. It is likely because the Y2O3 is easily hydrolyzed to Y(OH)3, Y(OH)2+ and Y2(OH)24+, which impinged the sintering activity of the powder mixture.

Phase composition, crystal structure, and microwave dielectric properties of Nb-doped and Y-deficient yttrium aluminum garnet ceramics

Nb-doped and Y-deficient yttrium aluminum garnet ceramics were designed and synthesized using the solid-state reaction method according to the chemical equation Y3−xAl5NbxO12+x (0 ≤ x ≤ 0.16). The phase composition, sintering behavior, microstructure, and microwave dielectric properties were investigated as functions of the composition and sintering temperature. A single-phase solid solution of yttrium aluminum garnet structure formation was observed in the range of 0 ≤ x ≤ 0.1. Further increments in x prompted the precipitation of the YNbO4 secondary phase at the grain boundary of Y3Al5O12. The complexity of the phase composition degrades the micromorphology and dielectric properties of the ceramics to varying degrees. Transmission electron microscopy results show that the lattice exhibits additional symmetry, which is closely related to the ultrahigh Q×f values of the ceramics. Effectively improving the sintering behaviour and suppressing the secondary phase by simultaneously doping with Nb5+ and reducing the yttrium stoichiometry. Finally, excellent microwave dielectric properties of εr ~ 10.99, Q×f ~ 280,387 GHz (13.5 GHz), and τf ~ − 34.7 ppm/°C can be obtained in x = 0.1 (Y2.9Al5Nb0.1O12.1) sintered at 1700 °C for 6 h.

Synthesis and robocasting of YAG xerogel: one-step conversion of ceramics

An optimized sol–gel protocol was carried out to produce an yttrium aluminum garnet (YAG) xerogel from aluminum alkoxide and an yttrium salt on a semi-pilot scale. This xerogel was successfully used without prior pyrolysis as a solid load with the aid of additives in the preparation of pastes. Thermal treatment of the green bodies, obtained by robocasting of the paste, led to cohesive single-phase YAG ceramics. Manufacturing ceramic pieces by additive methods will allow shaping complex forms, while the single step conversion/consolidation would simplify the technological process, reducing global energy costs. Since YAG possesses high strength and good creep behavior at high temperatures, these refractory pieces could replace the metal alloys used in turbine blades for deep space exploration. Structural, thermal and chemical characterizations were performed on xerogel powders, pastes, and YAG ceramics.

Improved optical properties of BN powder shielded Ce:YAG ceramics prepared by hot pressing

Yttrium aluminum garnet (YAG) phosphor transparent ceramics prepared via vacuum hot pressing (HP) suffer from carbon contamination owing to the graphite mould used in the HP system. The conventional method was to dope LiF as a decarburizing agent, but carbon contamination cannot be effectively prevented when preparing Ce:YAG ceramics via a solid-phase reaction combined with HP sintering. In this study, we report the fabrication of highly transparent Ce:YAG ceramics via HP sintering with a flexible hexagonal boron nitride (BN-h) wrapping, which prevents carbon contamination of the samples caused by the graphite mould used in the process. High-transmittance Ce:YAG ceramics were prepared at a medium temperature of 1600 °C and a low vacuum pressure of 10−1 Pa.

Luminescence efficiency of cerium-doped yttrium aluminum garnet ceramics formed by radiation assisted synthesis

The variety of applications of yttrium-aluminum garnet (YAG)-based luminescent materials and the morphology necessary for these purposes required the development of many technologies for their synthesis. All synthesis technologies used are complex. The structural phase of yttrium-aluminum garnet is formed with any technology, at temperatures exceeding 1,500 °C. The starting materials for the synthesis are metal oxides of aluminum, yttrium and other oxides for activation and modification. It seems possible to use hard radiation to form a new phase. Radiation synthesis of ceramics is realized in less than 1 s, without the use of any additives and influences. The synthesis was carried out at the electron accelerator of the Institute of Nuclear Physics (Novosibirsk). In this work, we studied the spectral-kinetic and quantitative characteristics of luminescence for the first time obtained by the method of radiation synthesis of ceramic samples of yttrium-aluminum garnet doped with cerium with statistical processing of their values. The dependences of the reproducibility of the spectral characteristics of the luminescence of the samples on the preliminary preparation of the charge for synthesis have been investigated. Several cycles of luminophore brightness studies have been performed. It is shown that the obtained ceramics based on yttrium-aluminum garnet doped with cerium possesses the required spectral-kinetic properties, and the efficiency of conversion of the chip radiation into luminescence is achieved, which is comparable to that available in commercial phosphors. The maximum measured values of the position of the bands are from 553.5 to 559.6 nm. Brightness values range from 4,720 to 1,960 cd/m2. It was found that the main reason for the scatter in the characteristics of the luminescent properties of ceramics of yttrium-aluminum garnet, activated by cerium obtained by radiation assisted synthesis is the high rate of synthesis and, especially, the high rate of cooling of the samples.

Phase composition, microstructure, and microwave dielectric properties of non-stoichiometric yttrium aluminum garnet ceramics

A series of Y3+xAl5O12 (−0.12 ≤ x ≤ 0.12) ceramics were prepared via a solid-state reaction under a vacuum sintering environment to investigate the impact of variations in different cation composition on the phase composition, microstructure, and microwave dielectric properties of yttrium aluminum garnet (Y3Al5O12; YAG) ceramics. X-ray diffraction analyses revealed that Al2O3 precipitates in the Al-excess samples. In contrast, the YAlO3 secondary phase appeared in the Y-excess samples, and variations in the content of both contributed to an increase in lattice parameters. The Rietveld refinement results showed that the lattice parameters and unit cell volume increased as the |x| value increased. The secondary phases of granular Al2O3 and YAlO3 crystallized at the extended grain boundaries in samples with excess Al and Y were visible in the scanning electron microscopy images. The electron diffraction patterns confirmed that a small amount of Y2O3 promoted continuous phase boundaries and facilitated the release of internal stresses. Ultimately, after sintering at 1750 °C for 12 h and at x = 0.03, the microwave dielectric properties of the non-stoichiometric YAG ceramic sample were εr = 11.18, Q×f = 236936 GHz, and τf = −35.9 ppm/℃.

Effect of Ca2+ and Mg2+ ions on the sintering and spectroscopic properties of cr‐doped yttrium aluminum garnet ceramics

AbstractIn this work, we investigated the effects of Ca2+ and Mg2+ ions and annealing temperature on the spectroscopic parameters of chromium‐doped yttrium aluminum garnet ceramics (Cr:YAG). Samples were obtained with either a separate or a simultaneous addition of calcium and magnesium oxides. To achieve this, aqueous suspensions were prepared using Y2O3, Al2O3, Cr2O3, MgO, and CaO high‐purity powders as raw materials. The obtained suspensions were freeze‐granulated, pressed into pellets, debinded, and subjected to reactive sintering in vacuum at 1715°C for 6 h. Each material was annealed in air with temperatures between 1300 and 1700°C. Samples were also compared to Cr:YAG ceramics with the addition of silica as a sintering aid. All the materials obtained were then exposed to 445 nm excitation, and emission spectra in the visible and infrared wavelengths were recorded. The results showed that the emission spectra of Cr:YAG ceramics varied according to the annealing conditions: as‐sintered samples exhibited strong emissions of around 680 nm and, after air annealing, of around 1400 nm. This phenomenon is attributed to the Cr3+→Cr4+ transition. Samples doped solely with MgO exhibited the highest emission intensity in the infrared region. Thus, Mg2+ ions provided the best conversion efficiency of chromium ions.

Effect of heat treatment of green bodies on the sintering and optical properties of large-size and thick transparent YAG ceramics

Large-size and thick yttrium aluminum garnet (YAG) transparent ceramics with complex shapes were successfully fabricated by solid-state reaction and vacuum sintering using commercial high-purity oxide powders as starting materials. Before sintering in vacuum, green bodies were calcined at different temperatures in a muffle furnace. The effects of heat treatment temperature on the particle size of green bodies as well as the compressive strength, densification, phase transformation and optical transparency of YAG ceramics were examined. After calcination at 1000 °C, the compressive strength of the green bodies reached 81.7 MPa. Using this calcinating procedure, large-size and thick YAG transparent ceramic dome (120 mm diameter, 15 mm thickness) was successfully obtained by sintering at 1750 °C for 30 h, without any apparent defects including microcracks. The in-line optical transmittance of the as-prepared ceramic was 83.1% and 76.8% at wavelengths of 1000 nm and 400 nm, respectively. Such transparent ceramic domes can be used as missile domes or transparent protective covers for submersibles, and detection equipment at full ocean depth (maximum depth of 11,000 m).

3D printed transparent ceramic YAG laser rods: Matching the core-clad refractive index

Abstract Yttrium Aluminum Garnet (YAG) solid state laser gain media rods with an active Neodymium-doped core and an optically-clear cladding region were additively manufactured via direct-ink-writing (DIW), followed by sintering and hot isostatic pressing to form fully dense optical ceramics. Lutetium and Gadolinium were chosen as optically-inert co-doping ions in the clad to match the increase in refractive index caused by the Neodymium in the core. Either 11.6% Lutetium or 3.8% Gadolinium can be used to match the index change from 2% neodymium; however, differences in diffusion distances across the core-clad interface lead to large fluctuations in index in that region. These index fluctuations can be minimized either by matching dopants with similar diffusion distances, or by implementing a gradual gradient in the doping profile, possible through DIW, rather than a sharp compositional interface attainable via more standard fabrication methods. This improvement in index homogeneity resulted in a 40% improvement in lasing performance compared with that of a core-clad rod fabricated with a sharp interface between the doped and undoped regions.

Manufacturing of Large Size and Highly Transparent Nd:YAG Ceramics by Pressure Slip-Casting and Post-Sintering by HIP: An Experimental and Simulation Study.

This study reports the fabrication of Nd:YAG (i.e., Neodymium-doped Yttrium Aluminum Garnet: Y3-xNdxAl5O12) transparent ceramics of a large size by the pressure slip-casting forming technique. Colloidal suspensions of primary oxides (i.e., Y2O3, Al2O3, Nd2O3, and SiO2 used as sintering aid) were cast under pressure through a porous membrane. Cakes with a good microstructural homogeneity and mean pore diameter of 90 nm were obtained. Modeling of the pressure slip-casting process at the millimetric to centimetric scale based on a computational fluid dynamics simulation showed good agreement with experimental results in terms of the casting kinetics (i.e., cake thickness and fluid flow as a function of time) and cake permeability. As a result, it was possible to better manage pressure casting parameters in order to obtain large size and homogeneous green parts. Finally, transparent Nd:YAG ceramics sintered by vacuum sintering, followed by post-sintering treatment by Hot Isostatic Pressing (HIP), demonstrated laser slope efficiency (51.7%) and optical-to-optical efficiency (44%) with 130 mJ of output laser energy at 1064 nm equivalent to commercial single crystals.

Photoluminescence of Doped YAG Transparent Ceramics Fabricated by Spark Plasma Sintering

AbstractDoped transparent ceramics have potential for a wide range of optical applications derived from their easily controllable fluorescence properties. The aim of this contribution is to present and discuss an effective fabrication method for doped transparent yttrium aluminum garnet ceramics. The powder synthesis route was adapted from common co‐precipitation methods and the powder densification was performed by spark plasma sintering. Parameters of the fabrication process were optimized for different lanthanide dopants in order to obtain highly transparent single‐ and multi‐doped ceramics. The photoluminescence properties of the samples were measured and discussed. The use of lithium fluoride as a sintering additive was confirmed to be favorable and post‐sintering heat treatments were shown to be necessary for certain dopants. Finally, the photoluminescence lifetime of dopants in a multi‐doped sample were measured and the energy transfer efficiency between dopants was determined.

Preparation of translucent YAG glass/ceramic at temperatures below 900 °C

The work presented here deals with the preparation of bulk yttrium aluminium garnet (YAG) glass-ceramics and YAG ceramics from glass microspheres with a YAG composition. Sol-gel prepared YAG powder was fed into a high temperature methane-oxygen flame where the particles melted and glass microspheres, with a YAG composition, were formed. Viscous flow sintering of the microspheres was then performed to prepare bulk YAG glass-ceramics or ceramics in a hot press.Rapid crystallization of YAG glass was traced during hot pressing through a change in the heating rate slope due to release of latent (crystallization) heat. This allowed control of crystallization and enabled preparation of YAG-based materials with different amounts of residual glass. YAG ceramic with relative density of 94.2 % was prepared at 891 °C without isothermal heating; additionally, YAG glass-ceramic reached relative density > 99 % at temperature 815 °C without isothermal heating.

Influence of Yb and Si on the fabrication of Yb:YAG transparent ceramics using spherical Y2O3 powders

Abstract Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated by the solid-state method using monodispersed spherical Y2O3 powders as well as commercial Al2O3 and Yb2O3 powders. Pure YAG phase was obtained at low temperature due to homogeneous mixing of powders. Under the same sintering conditions, the Yb:YAG ceramics with different doping contents of Yb3+ had similar morphologies and densification rates. After being sintered at 1700 °C in vacuum, the ceramic samples had high transparencies. The Yb:YAG ceramics doped with 0.5 wt% SiO2 formed Y–Si–O liquid phase and nonstoichiometric point defects that enhanced sintering. Compared with Nd doping, Yb doping hardly affected the YAG grain growth, sintering densification or optical transmittance, probably because Yb3+ easily entered the YAG lattice and had a high segregation coefficient.