The starting LiF raw powder was sup

The starting LiF raw powder was supplied by Aladdin Chemical Reagent Co., LTD (99.99 %). Prior to weighing, LiF powder was dried at 150 ◦C for 12 h in a vacuum oven to remove potential moisture. The dried powder was then weighed and uniformly mixed with 10 wt.% of deionized water. The moist powder was placed into a metal die with a diameter of 12.7 mm and then pressed under a uniaxial pressure of 250 MPa. Along with the holding pressure, the die was heated from room temperature to 150 ◦C with a heating rate of 5 ◦C/min and then held for 60 min. Finally, the die was cooled to room temperature, and pellets with dimensions of 12.7 mm in diameter and 5 mm in height were successfully obtained. Further post-annealing of the as-prepared pellets was carried out between 650 ◦C and 800 ◦C for 3 h with a heating rate of 5 ◦C/min and then cooled to room temperature within the furnace.