# Progress in Transparent Nano-Ceramics and Their Potential Applications
## 7 Outlook  
Transparent nano-ceramics are a new class of materials, and various preparation strategies have been developed, especially using nano-powders, to obtain them with various compositions and properties to meet the needs of different applications. Here, we reviewed the research progress and potential applications of mainstream transparent nano-ceramics. In the future, the development of transparent nano-ceramics and their potential applications are anticipated as follows:  
1. For the preparation of transparent nano-ceramics, high-purity and high-quality nano powder is very important, especially the average particle diameter of nano powder. At present, in the existing literature, many studies use the nano powder of commercial companies to prepare them, and the average particle diameter ranges from 50 to 100 nm (the average of 150 nm). However, in order to prepare high-quality transparent nano-ceramics, it is necessary to pretreat the existing nano powders, such as further improving the sintering activity of nano powders and reducing the average diameter of particles through laser processing or other methods, so that the light transmittance can be improved after the subsequent fabricating process. 2. The preparation of transparent nano-ceramics via new sintering technologies, such as spark plasma sintering and laser sintering, is still in the exploratory stage. The existing research on these sintering technologies is mainly based on experiments, and there is a lack of theoretical research to clarify the action mechanism of micro defects in the sintering process, especially to establish the thermodynamics and kinetics of sintering reaction. In addition, with the background of carbon peak and carbon neutralization, reducing the sintering temperature and sintering in a lower temperature range to obtain transparent nano-ceramics with excellent properties is still an important research direction in the future. 3. The preparation of transparent nano-ceramics via new sintering technologies, such as spark plasma sintering and laser sintering, is still in the exploratory stage. New sintering processes, such as spark plasma sintering and laser sintering, are continuously being investigated for the preparation of transparent nano-ceramics. Especially, the laser-induced plasma process, with the advantages of high-power plasma and an ultrafast laser, has potential for the fabrication of transparent nano-ceramics [125]. However, there is a shortage of theoretical studies to explain the action mechanism of micro defects in the sintering process and especially to establish the thermodynamics and kinetics of the sintering reaction in current studies. Furthermore, in consideration of the carbon peak and carbon neutralization, lowering the sintering temperature and sintering in a lower temperature range to create transparent nano-ceramics with good characteristics appears to be an important research direction. 4. Transmittance is one of the most important indicators for transparent nano-ceramics, and the microstructure is the most important component determining it. Transparent nano-ceramic samples supplemented with sintering aids have low porosity, allowing the grains to tightly fill the space and achieve an excellent microstructure. Different varieties of transparent nano-ceramics, in general, need different sintering aids. Furthermore, the doping ratio of sintering aids impacts the sintering process, affecting the transmittance for the same type of transparent ceramics. In the future, not only will trials be used to determine the best sintering aid, but computer simulations will also be used to save time and cost. 5. The powder particle size, sintering temperature, sintering duration, sintering environment, sintering pressure, and sintering aids are the primary elements impacting the sintering of transparent nano-ceramics. Aside from the standard light transmittance and physical properties, the indicators for evaluating transparent nano-ceramics must also take into account the manufacturing cost and environmental impact.