| Yttrium aluminum garnet(Y3Al5O12,YAG)transparent ceramics have relatively good optical properties and sufficient chemical and physical stabilities.It has been widely applied as laser host material,infrared windows and so on.Hot-pressing?HP?is a very common sintering method for transparent ceramics,because of its significant effect on increasing the density with less complex sintering technique.In this work,we focused on YAG ceramics.YAG transparent ceramics were fabricated by hot-pressing,using YAG powder synthesized by co-precipitation method.Impedance spectroscopy analysis was applied to the study of YAG ceramic.Specific studies were as follows:YAG powder was synthesized by co-precipitation methods,using ammonium hydroxide as precipitant.The effect of the pH of the reaction system on the properties of YAG powder was discussed.When the pH was 7.58,a single YAG phase could be synthesized at 900°C.The composition of the precursor could be expressed as Al?OH?3?0.3[Y2?OH?5?NO3??3H 2O]and the nucleus grew sufficiently.Ammonium sulfate was added to improve the dispersion of powder.And to reduce the agglomeration of the precursor,the method of filtration was improved.The powder calcinated at 1000?showed good dispersity with semispherical shape.The effects of sintering atmosphere?vacuum and nitrogen?,sintering temperature,heating rate,holding time and pressure mode on YAG ceramics sintered by HP were investigated.When the sintering temperature was 1450°C with a heating rate of 10°C/min,and a holding time of 1h under one-step pressure mode?50MPa?,the samples showed the best optical properties with densified uniform microstrcture.The in-line transmittance of the sample was 58%at the wavelength of 400 nm,68%at the wavelength of 1100 nm and75%at the wavelength of 2500 nm.The effects of vacuum and nitrogen atmosphere on the impedance spectroscopy of YAG ceramics were studied.The results showed that the bulk and grain boundary resistance of samples sintered in vacuum was smaller than that of samples sintered in nitrogen.Vacuum was benefit to the reduction of porosity and the diffusion of oxygen,which would increase the density of YAG ceramics.Compared with nitrogen,vacuum was better for improving the properties of YAG transparent ceramics.The effects of LiF on optical properties,microstructure and impedance spectroscopy of YAG ceramics were investigated.LiF promoted the growth of grains and improved the density of ceramics by liquid phase sintering.At the same time,it could avoid carbon contamination by forming?CF?n.The results of impedance spectroscopy showed that LiF could purify the grain boundary and remove the carbon contamination inside the sample,thus promote the optical properties of YAG ceramic sintering. |
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