Abstract
The fabrication of transparent polycrystalline Y3Al5O12 (YAG) is still a challenge, requiring the achievement of highly pure and fully dense, homogeneous materials. An important role is played by the powder characteristics: pure, fine and unagglomerated powders are essential for achieving full density and the required microstructural features. Keeping in mind these requirements, the aim of this work was to investigate the role of different synthesis parameters during co-precipitation, which is widely used to prepare YAG powders for transparent devices. The key role of the precipitant solution is here illustrated, by comparing the effect of aqueous ammonia (AA) versus ammonium hydrogen carbonate (AHC). This latter allowed the preparation of softly agglomerated powders, characterized by a very good sinterability. However, when AHC is used, attention should be paid to its concentration. By comparing the effect of two AHC precipitant solutions (at 0.5 M and 1.5 M, respectively), only the former one allowed the preparation of pure YAG powders, free from secondary phases. In this last condition, by using both chlorides and nitrates as YAG precursors, pressureless sintering at 1500–1600 °C/3 h gave rise to pure materials, highly dense and characterized by a fine and homogeneous microstructure.
Highlights
Dense polycrystalline Y3Al5O12 (YAG) can be used as a structural material, in particular for high-temperature applications, due to the high melting point, resistance to corrosive conditions [2,3] and low creep rate [4].In addition, due to its cubic structure, YAG is suitable for transparent devices
We investigated the role of the precipitant concentration, by using ammonium hydrogen carbonate (AHC) at 0.5 M and 1.5 M
We investigated the role of the previously mentioned synthesis parameters on the phase evolution, dispersability, sinterability and final microstructures, with the aim of preparing pure YAG
Summary
Dense polycrystalline Y3Al5O12 (YAG) can be used as a structural material, in particular for high-temperature applications, due to the high melting point (about 1940 °C [1]), resistance to corrosive conditions [2,3] and low creep rate [4]. Due to its cubic structure, YAG is suitable for transparent devices. First fabricated a transparent polycrystalline YAG material (doped with Nd) for laser applications. This material, with nearly the same optical characteristics as those of single crystal, was prepared by solid-state reaction method, reaching 99.98% density and grain size of about 50 μm. Techniques for producing polycrystalline transparent YAG have evolved ever since. Unlike other transparent ceramics such as alumina, YAG is a monorefringent material due to the cubic structure
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