Polycrystalline Yttrium Aluminum Garnet 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.

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.

Formation of Yttria Aluminium Garnet by Microwave Sintering

Polycrystalline yttrium aluminium garnet (YAG) ceramic has been prepared using microwave sintering. Micron-sized of Al2O3 and Y2O3 powders were mixed through in house fabrication mixer for 24 hours before calcined at 1100 °C and palletization process. The effect of sintering parameters on the microstructures was observed at various and holding times. X-ray diffraction (XRD) analysis was carried out to determine and quantify phase transformation with respect to these parameters. It was found that three phases namely YAM (Y4Al2O9), YAP (YAlO3) and YAG have been identified. While both grain sizes and density of sintered samples were found increased from 1.4 μm to 2.46 μm and 90% to 98%, respectively. Therefore, microwave sintering has a significant effect on the densification behavior of YAG.

Polishing characteristics of Nd:YAG ceramics with various Nd-dopant concentrations

Neodymium-doped polycrystalline yttrium aluminum garnet (Nd:YAG) ceramics require nanometer-scale surface roughness when used as laser gain media to minimize light scattering. Variations in grain size and crystallographic orientation can result in uneven material removal between grains and excessive material removal at the grain boundaries, hindering the smoothing of this material. The introduction of rare earth ion dopants, necessary for laser oscillation, can influence these parameters. This paper explores the effects of varying dopant concentration on grain structure and those effects on the polishing characteristics of polycrystalline Nd:YAG ceramics.

The effects of ball milling time on the rheological, optical, and microstructural properties of YAG transparent ceramics

AbstractStable slurries dispersed mixture of commercial Al2O3 and Y2O3 powders, ammonium poly meta acrylate (Dolapix CE64) as the dispersant, and tetraethyl orthosilicate (TEOS) as the sintering aid were prepared by ball milling process. The effects of the milling time on the fabrication of transparent polycrystalline yttrium aluminum garnet (YAG) ceramics were investigated by slip casting and vacuum sintering. The results showed that the best milling time for the deagglomeration of the powder mixture was 16 hours and the slurry prepared during this time showed a near‐Newtonian behavior due to the better deagglomeration and lower viscosity. X‐ray patterns also showed that all samples were pure YAG phase. The results also revealed that the sample prepared by 16 hours ball milling time suspensions exhibited higher relative green and final density, as well as the maximum transmittance at 1064 nm (≈ 77%). These samples had a more uniform microstructure too.

Static recrystallization of transparent polycrystalline yttrium aluminum garnet (YAG)

Cold deformation was realized in the transparent polycrystalline yttrium aluminum garnet (YAG) using Vickers indentation. Following this, annealing at 1500 °C for 2 h led to a grain refinement from 4.8 to 0.49 μm in the plastically deformed region, indicating the occurrence of recrystallization. It is supported by transmission electron microscope characterization that plastic deformation-induced dislocations are annihilated and rearranged, resulting in the formation of new grain boundaries during annealing.

Nucleation of the Plasticity at Nanodeformation of the Y3Al5O12 Yttrium-Aluminum Garnet

The nanoindentation in the continuous stiffness measurement (CSM) mode was used to study the nucleation of the plasticity at the nanodeformation of the yttrium-aluminium garnet (YAG) having a low ((111) YAG single crystal after the annealing at the temperature of 1300°C) and a high (polycrystalline yttrium-aluminium garnet with a grain size of ~ 20 μm after the mechanical polishing) density of dislocations. For a sample having a high dislocations density a smooth elastoplastic transition was observed in the nanocontact as a result of the motion and multiplication of dislocations that are already present in the sample. For (111) YAG single crystal after annealing at the temperature of 1300°C an abrupt elastoplastic transition (pop-in) caused by a homogeneous nucleation of dislocations in the region under the contact was observed.

Nanometer-scale characteristics of polycrystalline YAG ceramic polishing

Polycrystalline yttrium aluminum garnet (YAG) ceramics used as laser gain media require nanometer-scale surface geometries to minimize light scattering. Generally, uneven material removal between grains and excessive material removal at the grain boundaries retards smoothing of the ceramic surfaces. This paper describes the effects of the mechanical properties and polishing tool structures on the tool contact against the target surface during polishing. This, in addition to the abrasive type and size, influences the polishing characteristics, especially the material removal at the grain boundaries, the grain enhancement, the grain dislodgement, and the resulting nanometer-scale geometries of the polished surfaces.

Polishing Characteristics of Transparent Polycrystalline Yttrium Aluminum Garnet Ceramics Using Magnetic Field-Assisted Finishing

Transparent polycrystalline yttrium aluminum garnet (YAG) ceramics have garnered an increased level of interest for high-power laser applications due to their ability to be manufactured in large sizes and to be doped in relatively substantial concentrations. However, surface characteristics have a direct effect on the lasing ability of these materials, and a lack of a fundamental understanding of the polishing mechanisms of these ceramics remains a challenge to their utilization. The aim of this paper is to study the polishing characteristics of YAG ceramics using magnetic field-assisted finishing (MAF). MAF is a useful process for studying the polishing characteristics of a material due to the extensive variability of, and fine control over, the polishing parameters. An experimental setup was developed for YAG ceramic workpieces, and using this equipment with diamond abrasives, the surfaces were polished to subnanometer scales. When polishing these subnanometer surfaces with 0–0.1 μm mean diameter diamond abrasive, the severity of the initial surface defects governed whether improvements to the surface would occur at these locations. Polishing subnanometer surfaces with colloidal silica abrasive caused a worsening of defects, resulting in increasing roughness. Colloidal silica causes uneven material removal between grains and an increase in material removal at grain boundaries causing the grain structure of the YAG ceramic workpiece to become pronounced. This effect also occurred with either abrasive when polishing with iron particles, used in MAF to press abrasives against a workpiece surface, that are smaller than the grain size of the YAG ceramic.

High-pressure circular dichroism spectroscopy up to 400 MPa using polycrystalline yttrium aluminum garnet (YAG) as pressure-resistant optical windows

Circular dichroism (CD) spectroscopy at high pressure (≤400 MPa) was accomplished by using polycrystalline yttrium aluminum garnet (Y3Al5O12, YAG) as pressure-resistant optical windows.

Development of polycrystalline yttrium aluminum garnet (YAG) fibers

Polycrystalline yttrium–aluminum garnet (YAG) fibers are attractive for high-power lasers and for high-temperature structural materials. Processing methods for <30μm diameter polycrystalline YAG fibers suitable for single-mode laser operation are presented. The methods use extrusion of classified YAG powders with binders. Extrusion rheologies and rates, and heat-treatment temperatures, times, and environments that yield the most dense, defect-free fibers were explored. Fiber tensile testing, followed by fractography, was used to identify defects and to guide determination of optimal processing conditions. The effects of processing variables on fiber microstructures and properties are discussed. Advantages and disadvantages of processing methods are compared.

Polycrystalline Yb3+–Er3+-co-doped YAG: Fabrication, TEM-EDX characterization, spectroscopic properties, and comparison with the single crystal

Abstract

Structure formation in yttrium aluminum garnet (YAG) fibers

Abstract Polycrystalline yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) fibers were prepared from aqueous solutions of aluminum chlorohydrate and yttrium chloride. Fiber processing was accomplished via dry spinning. Poly(vinylpyrrolidone) (PVP) was used as spinning aid. Polycrystalline YAG fibers were obtained by pyrolysis of the green fibers followed by sintering at defined temperatures in air. Ceramic fibers were 9–16 μm in diameter. Differential scanning calorimetry/thermogravimetric analysis coupled with mass spectrometry (DSC/TGA-MS) showed an exothermic peak at 920 °C assigned to the crystallization of YAG and an overall ceramic yield of 38% at 1400 °C. X-ray diffraction (XRD) analysis showed that phase-pure YAG can be obtained at 1600 °C after intermediate formation of Y 2 O 3 and monoclinic yttrium aluminum oxide (YAM, Y 4 Al 2 O 9 ) phases.

Creep of polycrystalline yttrium aluminum garnet (YAG) at elevated temperature in air and in steam

Compressive creep of high-purity polycrystalline yttrium aluminum garnet (YAG, Y3Al5O12) was investigated at 1300°C and 50–200MPa in air and in steam. Compressive creep behavior of silica-doped polycrystalline YAG (Y3Al5O12–0.14wt% SiO2) was also studied. Creep specimens were microstructurally characterized by optical microscopy and TEM before and after creep. Steam slightly increased creep rates of material with grain size less than 1μm (the undoped YAG), but otherwise had little effect. The flow stress exponent was n≈1 for both SiO2-doped YAG and undoped YAG. Creep rates and microstructural observations are consistent with the Nabarro-Herring creep mechanism, with creep rate limited by lattice diffusion of yttrium cations (Y3+). Silica-doped YAG had a larger grain size of 2.41μm and lower creep rates than undoped YAG with 0.92μm grain size. However, creep rates normalized by grain size for Nabarro-Herring creep were higher in SiO2-doped YAG. Possible effects of SiO2 doping and steam on creep of YAG are discussed.

Efficient Graphene Q-Switching of an In-Band Pumped Polycrystalline Er:YAG Ceramic Laser at 1617 nm

An erbium-doped polycrystalline yttrium aluminum garnet ( Er:Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> , and Er:YAG) ceramic laser is passively Q-switched by a few-layer graphene at 1617 nm. When in-band is pumped by a continuous-wave Er,Yb fiber laser at 1532 nm, the laser produces a continuous and stable train of Q-switched pulses with pulse energy of as much as 12.2 μJ, pulse repetition rate of 54.4 kHz, and average output power of 662 mW.

Correlation of the atomic and electronic structures and the optical properties of the Σ5(2 1 0)/[ 0 01] symmetric tilt grain boundary in yttrium aluminum garnet

A series of atomic models of the Σ5(210)/[001] symmetric tilt grain boundary in yttrium aluminum garnet (YAG) are constructed according to the coincident site lattice theory. Calculations performed using empirical potentials show that the O-termination configurations, namely G(1) and G(2), are the most energetically favorable boundary structures. First-principles density functional theory calculations have been further performed to understand the atomic and electronic structures, effective charge, potential distributions and optical properties of G(1) and G(2) grain boundaries. The simulated high-resolution transmission electron microscopy images of G(1) and G(2) are generally in good agreement with the experimental micrographs of the Σ5(210)/[001] grain boundaries. Results show that the effective charges of the atoms in the grain boundary region are related to their coordination numbers and bonding lengths. Moreover, the overall total density of states of G(1) and G(2) has been found to have similar features with the bulk YAG, with the exception of some defect states being introduced at the top of the valence band, resulting in the reduction of the band gap. The calculated optical properties show that the refractive indices of both grain boundary models are slightly larger than those of the bulk YAG. This is in agreement with the experimental observation that the refractive index of the polycrystalline YAG is higher than that of its single crystalline counterpart.

Simultaneous synthesis and densification of transparent, photoluminescent polycrystalline YAG by current activated pressure assisted densification (CAPAD)

Abstract We report a method for the synthesis and processing of transparent bulk polycrystalline yttrium aluminum garnet (YAG) and photoluminescent Ce-doped YAG ceramics via solid-state reactive-current activated pressure assisted densification (CAPAD). The process uses commercially available γ-Al 2 O 3 , Y 2 O 3 , and CeO 2 nanopowders. The nanopowders were reacted and densified simultaneously at temperatures between 850 °C and 1550 °C and at a maximum pressure of 105 MPa. The solid-state reaction to phase pure YAG occurs in under 4 min at processing temperatures 1100 °C which is significantly faster (on the order of tens of hours) and occurs at much lower temperatures (∼600 °C) compared to conventional reaction sintering. We found that the reaction significantly improves densification – the shrinkage rate of reaction-produced YAG was three times higher than that of YAG using pre-reacted powder. The Ce additions were found to retard the reaction driven shrinkage kinetics by a factor ∼3, but are still faster (by a factor ∼1.6) than those associated with direct densification (no synthesis). Densities >99% were achieved in both pure YAG and Ce doped YAG (Ce:YAG). Results of optical measurements show good transparency in the visible and photoluminescence (PL) in the Ce:YAG. The PL peak is broad and appears white when excited using blue light confirming that the ceramics can be used in solid state lighting to produce white light.

The effect of precipitant on co-precipitation synthesis of yttrium aluminum garnet powders

Polycrystalline yttrium aluminum garnet (Y3Al5O12, YAG) powders were prepared by the co-precipitation method from a mixed solution of aluminum and yttrium nitrates (Y(NO3)3·6H2O, Al(NO3)3·9H2O) using ammonium carbonate ((NH4)2CO3, AC) and ammonium hydrogen carbonate (NH4HCO3, AHC) as precipitants. The effect of precipitant and pH on the preparation of pure-phase YAG powders was mainly studied. Phase evolution of the precursors during calcination and sinterability of the resultant YAG powders were compared for the two precipitants. The composition of YAG precursor, the phase formation process of YAG and the properties of the powders were investigated by means of DTA–TG, XRD, and TEM. AC as precipitant could produce a hydroxide precursor, which transformed to a YAG and Y2O3 mixture at about 1300K. AHC as precipitant could produce a loosely agglomerated carbonate precursor. The resultant YAG powders showed good dispersity and excellent sinterability. The precursor directly converted to pure YAG via YAlO3 (YAP) phase at about 1300K.

Densification of transparent yttrium aluminum garnet (YAG) by SPS processing

Nano-size YAG powder co-mixed with 0.25 wt.% LiF was used to fabricate transparent polycrystalline YAG specimens by means of the Spark Plasma Sintering (SPS) technique. The presence of the LiF additive in the initial nano-powder allows obtaining fully dense disc shaped (up to 4 mm thick) transparent specimens at the outcome of a 2 h treatment at 1300 °C. The presence of LiF plays a key role in the mass transport related effects during the densification of YAG to full density and also in the elimination of the residual carbon contamination, allowing reaching a level of optical transmittance close to the theoretical value.

Mechanism for the development of anisotropic grain boundary character distributions during normal grain growth

Grain boundaries in polycrystalline magnesia-doped alumina and yttrium aluminum garnet were classified as growing in area or shrinking in area on the basis of topology and curvature considerations. Measurements of dihedral angles at grain boundary thermal grooves were used to determine that the energies of the growing boundaries are, on average, lower than the energies of the shrinking boundaries. The observations also show that the length of a boundary is inversely correlated to its energy. The findings suggest that anisotropic grain boundary character distributions, which influence the properties of polycrystals, develop because higher-energy grain boundaries are preferentially eliminated from the network during grain growth.