The present application provides a method for preparing lanthanide fluoride two-dimensional porous nanosheets and belongs to the field of novel materials. In the present application, mixing a water-soluble lanthanide metal salt and an aqueous solution of sodium acetate in a nitrogen atmosphere to obtain a mixed solution, and adding an aqueous solution of fluorine-containing salt to the mixed solution obtained for precipitation reaction to produce lanthanide fluoride two-dimensional porous nanosheets. In the preparation process provided by the present application, no additional surfactant or template agent needs to be added, the pollution of the surfactant to the surface of the prepared material is avoided and the tedious after-treatment steps to template agent are reduced. Accordingly, the large-scale production can be realized, and the lanthanide fluoride two-dimensional porous nanosheets constructed by nanoparticles are prepared in large scale by one step. Moreover, no other organic solvents are required, and the pollution to the environment during the preparation process is avoided.

A sprayed coating having a multilayer structure including a lower layer made a sprayed coating containing a rare earth oxide, and a surface layer made of another sprayed coating containing a rare earth fluoride and/or a rare earth oxyfluoride, the multilayered sprayed coating having a volume resistivity at 23 C. and a volume resistivity at 200 C., the volume resistivity at 23 C. being 110.sup.9 to 110.sup.12 .Math.cm, and a temperature index of the volume resistivities defined by the ratio of the volume resistivity at 200 C. to the volume resistivity at 23 C. being 0.1 to 10.

A method of fluorinating a solid compound of a rare earth metal to produce a fluorinated rare earth metal compound in solid form includes reacting, in a reaction zone, a solid compound of the rare earth metal and gaseous hydrofluoric acid, thus producing the fluorinated rare earth metal compound in solid form. The reaction takes place, in the reaction zone, in the presence of exogenous water, which is water that is exogenous to water that is produced in the reaction zone as water of reaction due to the reaction of the solid compound of the rare earth metal and the hydrofluoric acid. Conditions of temperature and pressure in the reaction zone avoid condensation of the exogenous water, the water of reaction when present, and the hydrofluoric acid.

Fluoride-based nanocomposite materials, optical articles made therefrom, and methods of making the fluoride-nanocomposite materials and optical articles. In certain examples, a fluoride-based nanocomposite material includes two or more interspersed fluoride-based nanograin materials with grains having one, two, or three dimensions that are less than 1 micrometer.

An yttrium oxyfluoride sprayed coating contains Y.sub.5O.sub.4F.sub.7 as a main component. In the yttrium oxyfluoride sprayed coating, when the total intensity of all peaks attributable to yttrium oxyfluoride in a diffraction spectrum obtained by X-ray diffractometry is assumed to be 100, the total intensity of all peaks attributable to yttrium fluoride and yttrium oxide is less than 10. Furthermore, in an yttrium oxyfluoride-containing sprayed coating, when the total intensity of all peaks attributable to yttrium oxyfluoride and yttrium fluoride in a diffraction spectrum obtained by X-ray diffractometry is assumed to be 100, the total intensity of all peaks attributable to yttrium oxide is less than 1.

A spray coating containing a rare earth fluoride and/or a rare earth acid fluoride contains, carbon at 0.01-2% by mass or titanium or molybdenum at 1-1000 ppm. When an acid fluoride is not contained, the spray coating is gray to black in which, in terms of the L*a*b* chromaticity, L* is 25-64, a* is 3.0 to +5.0, and b* is 4.0 to +8.0. When an acid fluoride is contained, the spray coating is white or gray to black in which, in terms of the L*a*b* chromaticity, L* is equal to or greater than 25 and less than 91, a* is 3.0 to +5.0, and b* is 6.0 to +8.0. By forming this coating on a plasma resistant member, a partial color change is reduced, thus, a member that is capable of reliably realizing the original longevity is obtained.

A spray coating containing a rare earth fluoride and/or a rare earth acid fluoride contains carbon at 0.01-2% by mass or titanium or molybdenum at 1-1000 ppm. When an acid fluoride is not contained, the spray coating is gray to black in which, in terms of the L*a*b* chromaticity, L* is 25-64, a* is ?3.0 to +5.0, and b* is ?4.0 to +8.0. When an acid fluoride is contained, the spray coating is white or gray to black in which, in terms of the L*a*b* chromaticity, L* is equal to or greater than 25 and less than 91, a* is ?3.0 to +5.0, and b* is ?6.0 to +8.0. By forming this coating on a plasma resistant member, a partial color change is reduced, thus, a member that is capable of reliably realizing the original longevity is obtained.

A spray coating containing a rare earth fluoride and/or a rare earth acid fluoride contains carbon at 0.01-2% by mass or titanium or molybdenum at 1-1000 ppm. When an acid fluoride is not contained, the spray coating is gray to black in which, in terms of the L*a*b* chromaticity, L* is 25-64, a* is ?3.0 to +5.0, and b* is ?4.0 to +8.0. When an acid fluoride is contained, the spray coating is white or gray to black in which, in terms of the L*a*b* chromaticity, L* is equal to or greater than 25 and less than 91, a* is ?3.0 to +5.0, and b* is ?6.0 to +8.0. By forming this coating on a plasma resistant member, a partial color change is reduced, thus, a member that is capable of reliably realizing the original longevity is obtained.

A sprayed coating having a multilayer structure including a lower layer made a sprayed coating containing a rare earth oxide, and a surface layer made of another sprayed coating containing a rare earth fluoride and/or a rare earth oxyfluoride, the multilayered sprayed coating having a volume resistivity at 23 C. and a volume resistivity at 200 C., the volume resistivity at 23 C. being 110.sup.9 to 110.sup.12 .Math.cm, and a temperature index of the volume resistivities defined by the ratio of the volume resistivity at 200 C. to the volume resistivity at 23 C. being 0.1 to 10.

A sprayed coating having a multilayer structure including a lower layer made a sprayed coating containing a rare earth oxide, and a surface layer made of another sprayed coating containing a rare earth fluoride and/or a rare earth oxyfluoride, the multilayered sprayed coating having a volume resistivity at 23 C. and a volume resistivity at 200 C., the volume resistivity at 23 C. being 110.sup.9 to 110.sup.12 .Math.cm, and a temperature index of the volume resistivities defined by the ratio of the volume resistivity at 200 C. to the volume resistivity at 23 C. being 0.1 to 10.