Yttrium oxyfluoride

Yttrium oxyfluoride may be formed in the decomposition of crystalline hydrate of yttrium fluoride upon heating to 900 °C in a vacuum:

${\displaystyle {\mathsf {2YF_{3}\cdot 1/2H_{2}O\ {\xrightarrow {\tau ,900^{o}C}}\ YOF+YF_{3}+2HF}}}$

Yttrium oxyfluoride can also be made by hydrolysis of yttrium fluoride with superheated steam at 800 °C:

${\displaystyle {\mathsf {2YF_{3}+H_{2}O\ {\xrightarrow {800^{o}C}}\ YOF+2HF}}}$

Yttrium oxyfluoride forms colorless crystals of tetragonal crystal system; its cell parameters are: a = 0.3910 nm, c = 0.5431 nm. According to hexagonal crystal family, the cell parameters are: a = 0.38727 nm, c = 1.897 nm, Z = 6.

Stable yttrium oxyfluoride material is used for inner walls of plasma process equipment.[3][4]