## 2 Synthesis of Yttrium
### Precipitation Method  
Due to the perspective applications and properties of Y\({}_{2}\)O\({}_{3}\), the preparation of Y\({}_{2}\)O\({}_{3}\) has emerged as a widely increasing trend. However, a series of preparation methods have been reported in a few decades--these include precipitation [51] and sol-gel practice [52]. Precipitation is a popularly used technique, and is simple for the synthesis of Y\({}_{2}\)O\({}_{3}\) NPs (Table 3) and yttria powder for large-scale industrial production with low cost to regulate the size of particles. Y\({}_{2}\)O\({}_{3}\) NPs can be synthesized using a simple co-precipitation method in a distillate pack, followed by calcination of the precursor, yttrium oxalate (Y\({}_{2}\)(C\({}_{2}\)O\({}_{4}\))\({}_{3}\)) in a furnace with the reaction varied between room temperature (RT) and 100 \({}^{\circ}\)C for various reaction durations ranging (0.5 to 3) h. The results proved that pure Y\({}_{2}\)O\({}_{3}\) was synthesized using the processing parameters, which were in good agreement with the thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Raman analysis results for co-precipitation reaction at 40 \({}^{\circ}\)C for 1 h, followed by calcination at 650 \({}^{\circ}\)C for 4 h. This method yielded semispherical Y\({}_{2}\)O\({}_{3}\) nanoparticles with crystallite sizes ranging (7-21) nm, and a large specific surface area of 7.40 m\({}^{2}\)/g [53].  
[PERSON] and [PERSON] et al. [54] synthesized this familiar yttrium compound and doped it with bismuth and zinc oxide, as they have been shown to have an extended bandgap, and tested their optical properties. As a result, the wet chemical method is  
Figure 1: Scheme for the preparation of Y\({}_{2}\)O\({}_{3}\) cubes and flowers [50].  
prompt and easy to synthesize Bi and Zn co-doped yttrium oxide nanoparticles for various phosphor utilities. Another study conducted by [PERSON] et al. [55] revealed that Y\({}_{2}\)O\({}_{3}\) stability could be improved, and appreciable absorption selectivity was achieved by adding ZnO\({}_{3}\) to form Y\({}_{2}\)O\({}_{3}\) ZnO complex using the precipitation method. The complexes proved to be acting as a photocatalyst.  
Yttrium hafnate (Y\({}_{2}\)Hf\({}_{2}\)O\({}_{7}\)) precursor was prepared by mixing yttrium nitrate and hafnium (IV) chloride with ammonium oxalate aqueous solution using the oxalate co-precipitation method at 800 \({}^{\circ}\)C for 4 h. Platelet, rod, and spherical shape Y\({}_{2}\)Hf\({}_{2}\)O\({}_{7}\) powders were obtained by controlling the concentration of the surfactant PEG6000, and it played a vital role in the morphology of the particles [56]. [PERSON] et al. [41] synthesized yttria nanopowders with a narrow size distribution using a precipitation method. In this process, the pH value at the end has a significant effect on the size and morphology of the precursor and the yttria powders; under the same calcination condition, the yttria powders made from the precursor obtained at a pH of 8 are smaller in mean particle size and narrower in size distribution than those made from the precursor obtained at a pH of 10 with the optimum calcination temperature of 1000 \({}^{\circ}\)C. The nanopowder was obtained at 30 nm size and was well dispersed. Using this yttria nanopowder, transparent yttria ceramics were produced by vacuum sintering at 1700 \({}^{\circ}\)C for 4 h without any additives.