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Abstract 5 at.% Yb:Y 2 O 3 transparent ceramics were fabricated using vacuum sintering plus HIP. The ceramics doped with 1 at.% ZrO 2 as the sintering additive were densified at 1700 °C in vacuum followed by HIPing at 1775 °C, while those without sintering additives were densified at 1520 °C in vacuum followed by HIPing at 1450 °C. After sintering, both ceramics had relatively high in-line transmittance. However, during laser experiments, the ZrO 2 -doped Yb:Y 2 O 3 (Zr-YbY) ceramics were photodarkened when irradiated by 940 nm pump light. The discoloration might be attributed to the formation of Zr3+ color centers during lasing. In contrast, no photodarkening effect was detected in the pure Yb:Y 2 O 3 ceramics without sintering additives (P-YbY). The P-YbY ceramics exhibited much higher lasing efficiency (17%) than the Zr-YbY ceramics (9%). To our best knowledge, it is the first time that the photodarkening effect was detected in rare-earth doped sesquioxide laser ceramics. [ABSTRACT FROM AUTHOR]

Abstract Highly sinterable Y 2 O 3 nano-powder with low degree of agglomeration was synthesized by using a spray precipitation technology, without the use of any additives and dispersants. Compared with the precursor made by using the dripping method (D-precursor), the precursor made by the spraying method (S-precursor) had much lower degree of hard agglomeration. So did the resultant calcined Y 2 O 3 powder (S-Y 2 O 3 powder) as compared with the D-Y 2 O 3 powder. Sintering behaviors of the two powders were studied. Ceramics made from the S-Y 2 O 3 powder (S-Y 2 O 3 ceramics) showed much higher densification rate and final density. After vacuum sintered at 1650 °C for 5 h, relative density of the D-Y 2 O 3 ceramics was merely 97.3%, while that of the S-Y 2 O 3 ceramics reached 99.5%. In addition, the D-Y 2 O 3 ceramics cannot be sintered to 98% relative density by using the vacuum sintering technique, due to the high degree of agglomeration of the D-Y 2 O 3 powder. Moreover, the S-Y 2 O 3 ceramic exhibited homogeneous microstructure and an in-line optical transmittance of 81.6% at 1200 nm after HIP treatment. The spray precipitation method should be applicable to synthesizing other oxide powders. [ABSTRACT FROM AUTHOR]

This paper reports on the influence of rapid rate sintering (RRS) on densification and microstructure evolution of yttria transparent ceramics by using vacuum sintering. The presence of temperature gradient has been confirmed during the RRS process. The higher the heating rate (HR), the larger the temperature gradient in the samples would be. By using RRS, e.g., HR = 40°C/min, the samples could be densified very fast to a relative density of 99.6%. However, these samples could not be further densified, due to the presence of difference in densification caused by a heating rate-induced temperature gradient. By using a two-step RRS with an intermediate-temperature thermal treatment, this problem has been successfully addressed. The intermediate-temperature treatment allowed for the particle neck growth, so that effective thermal conductivity of the compacts was increased greatly. Therefore, the temperature gradient and differentiate densification were effectively prevented. Samples sintered using the two-step RRS process could be fully densified and excellent in-line optical transmittance was achieved. It is believed this strategy is applicable to other transparent ceramics, as well as other engineering ceramics. [ABSTRACT FROM AUTHOR]

Highly transparent 0.5 at.% Tm:Y2O3 ceramics were prepared by using solid-state reaction combined with vacuum sintering method, with ZrO2 and Al2O3 as sintering aids. Doping amount of ZrO2 was fixed at 1 at.%, while the effect of Al2O3 on densification, microstructure evolution, and transmittance of the Y2O3 ceramics was carefully studied. It was found that the addition of Al2O3 was very effective in improving densification of Y2O3, due to the formation of an Al-rich eutectic phase Y4Al2O9 ( YAM) during the sintering process. As the content of Al2O3 was increased from 0 to 81.8 wt ppm, porosity of the ceramics was decreased and transmittance was increased. However, when the content of Al2O3 was increased to 137 wt ppm, a secondary phase began to segregate at grain junctions. Further increase in the amount of Al2O3 led to an increase in both amount and size of the secondary phase. At the optimized content of Al2O3 with 81.8 wt ppm, the Tm:Y2O3 ceramics sintered at 1860°C for 13 h exhibited an in-line transmittance of 83.0% at 2000 nm and 76.5% at 600 nm. It is expected that this finding can be readily applied to other transparent ceramics. [ABSTRACT FROM AUTHOR]

Highly transparent Y2O3 ceramics were successfully fabricated with CaO as sintering aid. The microstructure evolution, optical transmittance, hardness and thermal conductivity of the Y2O3 ceramics were investigated. It was found that doping a small amount (0.01–0.15 wt.%) of CaO could greatly improve the densification rate of Y2O3. With an optimized CaO dosage of 0.02 wt.% combined with the low temperature vacuum sintering plus hot isostatic pressing (HIP-ing), Y2O3 ceramics with in-line transmittance of 84.87% at 1200 nm and 81.4% at 600 nm were obtained. [ABSTRACT FROM AUTHOR]

Highly transparent 5 at.% Yb:Y 2 O 3 ceramics were fabricated by using a combination method of vacuum sintering and hot isostatic pressing (HIP). Co-precipitated Yb:Y 2 O 3 powders, with 1 at.% ZrO 2 as the sintering aid, were used as the starting material. The Yb:Y 2 O 3 ceramics, vacuum sintered at 1700 °C for 2 h and HIPed at 1775 °C for 4 h, exhibited small grain size of 1.9 μm and highly dense microstructure. In-line optical transmittance of the ceramics reached 83.4% and 78.9% at 2000 and 600 nm, respectively. As the ceramic slab was pumped by a fiber-coupled laser diode at about 940 nm, a maximum output power of 0.77 W at 1076 nm was achieved, with a corresponding slope efficiency of 10.6%. [ABSTRACT FROM AUTHOR]