YCN - Research in Spot: New opportunities in transparent ceramic by Guangran Zhang

Transparent ceramic has been developed as an alternative of single crystal in 1960s for its superior mechanical strength, lower processing temperature and comparable optical transparency.

It is now widely used as transparent amor, laser gain media, led phosphor etc.  To make it possible, full densification must be achieved in bulk ceramics with limited scattering centers like pores, grain boundaries, secondary phases and anisotropic refractive index change in different grains. Most of the recent reports of transparent ceramic are still talking about well-studied systems like YAG, Y2O3, MgAl2O4, ALON, Al2O3 etc. using very traditional sintering methods. 

Thus, research in this field needs to find new opportunities. During my doctoral studying, I find that additives manufacturing provides a lot of opportunities for us to reconsider these old material systems with more efficient way to shape transparent ceramics. So far, our group has successfully demonstrated transparent YAG and Al2O3 ceramic by material extrusion. The optical transmittance of these printed and sintered ceramics is comparative but less than some traditional approaches. However, it has some much potential in the miniaturization and customization of fabrication transparent ceramic. I believe additive manufacturing could be optimized to deliver the same grade optical ceramics compared to some tradition approaches within the next few years.

Another opportunity is originated from the relatively new concept of high-entropy alloy. By introducing more elements, researchers found it is more like to from single phase solid solution inside alloy system. It was explained by the fact that addition elements could increase structural configuration entropy and serve as additional driving force to stabilize system and lead to single phase. This might be helpful in transparent ceramic because it could help eliminating secondary phases formation which can act as scattering centers and cause decrease in transmittance. The image shows our initial trial of making high entropy transparent ceramics possible. This demonstration brought complexity in the transparent ceramic’s studies.  

High transparent ceramic (Lu0.2Y0.395Gd0.2Yb0.2Tm0.005)2O3 when excited by 980nm laser that exhibited blue up-conversion (left up), the appearance of transparent ceramic (left down), up-conversion mechanism (center), SEM of microstructure exposed by vibrational polishing (right). Reprinted from Scripta Materialia, 186, Zhang, G., Milisavljevic, I., Zych, E. and Wu, Y., High-entropy sesquioxide X2O3 upconversion transparent ceramics, Pages 19-23., Copyright (2020), with permission from Elsevier.

Guangran Zhang
Kazuo Inamori School of Engineering
New York State College of Ceramics
Alfred University
2 Pine Street, Alfred, NY 14802-1296, USA
Email: gz1@alfred.edu