# Progress in Transparent Nano-Ceramics and Their Potential Applications
## 3 Magneto-Optical Transparent Nano-Ceramics
### Tag  
TAG transparent nano-ceramics have the same garnet structure and similar optical and thermal properties as TGG transparent nano-ceramics, but their Verdet constant is about 30-50% higher than that of TGG transparent nano-ceramics. Therefore, TAG transparent nano-ceramics have better magneto-optical properties and can be used in Faraday magneto-optical materials in visible and near-infrared bands. In 2011, [PERSON] et al. [49] prepared TAG transparent nanoceramics for the first time by solid-phase reaction and vacuum sintering (depicted in Figure 8a) and studied the optical quality and microstructure of the samples. The samples sintered at 1650 \({}^{\circ}\)C had relatively good optical transparency between 400 nm and 1600 nm (up to 70%, as shown in Figure 8b). The experimental data demonstrated that the thermal conductivity of the prepared TAG transparent nano-ceramics was 6.5 W/m\(\cdot\)K (at room temperature), and the Verdet constant could reach \(-\)172.72 rad/T\(\cdot\)m (at 632.8 nm) with the best quality, which was 28.9% larger than that (\(-\)134 rad/T\(\cdot\)m) of the TGG single crystal [50]. This indicates that TAG transparent nano-ceramics have better magneto-optical properties than TGG single crystals and have potential commercial values. In 2015, [PERSON] et al. [51] found that by optimizing the sintering aid, TEOS combined with MgO as a sintering aid could improve the optical quality of TAG transparent ceramics but had no effect on the magneto-optical properties. The study found that when the addition of TEOS was 0.4 wt.% and the addition of MgO was 0.1 wt.%, the optical transmittance of the obtained TAG ceramics exceeded 80% in the 500-1500 nm band, and the optical quality was  
Figure 7: Experimental results of depolarization as a function of laser power (red and blue circles represent results for TGG ceramics with and without magnetic field, respectively; squares represent calculated results for TGG single crystals; solid lines represent theoretical curves) [48]. Reprinted with permission from Ref. [48]. Copyright 2014, copyright Optical Society of America. greatly improved. Moreover, in 2017, [PERSON] et al. [52] adopted the reaction sintering method combining muffle furnace pre-sintering and HIP sintering and obtained TAG transparent ceramics with ideal optical quality for the first time without vacuum sintering. After ball milling, the raw material powders were uniformly mixed, wherein the particle size of Al\({}_{2}\)O\({}_{3}\) was 260 nm, and the particle size of Tb\({}_{4}\)O\({}_{7}\) was 1.15 \(\upmu\)m. The experimental results confirmed that the optical transmittance of the prepared 0.4 wt.% TEOS:TAG transparent nano-ceramics in the visible and near-infrared regions could reach more than 80%, which was very close to the theoretical limit. In addition, some researchers found that the Verdet constant of TAG transparent nano-ceramics could be changed by adding rare earth elements [38; 53; 54]. In 2012, [PERSON] et al. [53] adopted solid-state reaction and vacuum sintering methods to prepare Y\({}^{3+}\) and Ce\({}^{3+}\) rare earth element-doped TAG transparent nano-ceramics. They found that the Verdet constant of Y\({}^{3+}\)-doped TAG transparent nano-ceramics was \(-\)108.79 rad/T\(\cdot\)m at 632.8 nm, which was smaller than that of TAG transparent ceramics. This indicated that diamagnetic ion (Y\({}^{3+}\)) doping would have an adverse effect on the magneto-optical properties of TAG transparent ceramics. However, the magneto-optical properties of the Ce\({}^{3+}\)-doped TAG transparent nano-ceramics were greatly improved, and its Verdet constant, measured as \(-\)199.55 rad/T\(\cdot\)m at 632.8 nm, was about 16% higher than that of TAG transparent ceramics. A year later, [PERSON] et al. [54] continued to study the relationship between the  
Figure 8: Optical quality of TAG transparent nano-ceramics; (**a**) samples and (**b**) optical transmittance of polished TAG transparent nano-ceramics [49]. Reprinted with permission from Ref. [49]. Copyright 2011, copyright ELSEVIER.