Process Optimization of Er₂O₃ Coating by Reactive Magnetron Sputtering for DEMO-Relevant Blanket Modules

India has proposed to develop and test the Lead-Lithium–cooled Ceramic Breeder Test Blanket Module (In-LLCB-TBM) in ITER. This concept, unlike some others, may need a high-performance ceramic coating on the inner wall to meet dual requirements such as high insulation to mitigate magnetohydrodynamic effects and a tritium permeation barrier to avoid tritium in the structural material. We deposit Er₂O₃ coatings using a direct-current magnetron reactive sputter deposition technique. As part of optimizing the coating from the application point of view, we carried out a series of deposition experiments. These included investigating the effects of substrate temperature in the range 165°C to 360°C, the effects of postannealing, and the effects of oxygen-to-argon gas flow ratio, keeping all other process parameters constant. Primarily, a densely packed film is required to grow in the most stable cubic crystal structure, with very high resistivity, in the range of gigaohm-centimeters to teraohm-centimeters. The results indicate that erbia films of thicknesses in the range 270 to 1000 nm are formed in amorphous, monoclinic, and cubic phases, where the cubic phase content is enhanced in a narrow window of the flow ratio at 360°C. Both crystalline phases seem to grow in a preferred crystalline direction. Post-vacuum-annealing at 500°C for 2 h largely transforms the monoclinic phase into the cubic phase.