Nanopowders containing nanoparticles having a core particle with a thin film coating. The core particles and thin film coatings are, independently, formed from at least one of a rare earth metal-containing oxide, a rare earth metal-containing fluoride, a rare earth metal-containing oxyfluoride or combinations thereof. The thin film coating may be formed using a non-line of sight technique such as atomic layer deposition (ALD). Also disclosed herein are nanoceramic materials formed from the nanopowders and methods of making and using the nanopowders.

Rare earth compound particles are prepared by a step of heating an aqueous solution containing rare earth metal ions and urea to form a rare earth compound by a reaction of a hydrolysis product of urea, and the rare earth metal ions. In the heating step, heating the aqueous solution into which an acetylene glycol-ethylene oxide adduct is added.

Rare earth compound particles are prepared by a step of heating an aqueous solution containing rare earth metal ions and urea to form a rare earth compound by a reaction of a hydrolysis product of urea, and the rare earth metal ions. In the heating step, heating the aqueous solution into which an acetylene glycol-ethylene oxide adduct is added.

Provided is a slurry for suspension plasma spraying, which is a spray material used for suspension plasma spraying in an atmosphere including an oxygen-containing gas, contains 5-40 mass % of rare earth fluoride particles having a maximum particle diameter (D100) of 12 μm or less, and contains one or more types of solvent selected from among water and organic solvents. A rare earth acid fluoride-containing sprayed film, in which process shift and particle generation hardly occur, can be stably formed on a base material by carrying out suspension plasma spraying in an atmosphere including an oxygen-containing gas. A spraying member provided with this sprayed film exhibits excellent corrosion resistance to halogen-based gas plasma.

A plasma-resistant member that includes a base material and a layer structural component is provided, wherein the layer structural component includes an yttria polycrystalline body, is formed at a surface of the base material, and has plasma resistance; crystallites that are included in the yttria polycrystalline body included in the layer structural component are not bonded to each other via a heterogenous phase; the yttria polycrystalline body included in the layer structural component has a crystal structure including only cubic, or a crystal structure in which cubic and monoclinic coexist; and an average value of a proportion of monoclinic to cubic inside the yttria polycrystalline body included in the layer structural component is greater than 0% and not more than 60%.

A plasma-resistant member that includes a base material and a layer structural component is provided, wherein the layer structural component includes an yttria polycrystalline body, is formed at a surface of the base material, and has plasma resistance; crystallites that are included in the yttria polycrystalline body included in the layer structural component are not bonded to each other via a heterogenous phase; the yttria polycrystalline body included in the layer structural component has a crystal structure including only cubic, or a crystal structure in which cubic and monoclinic coexist; and an average value of a proportion of monoclinic to cubic inside the yttria polycrystalline body included in the layer structural component is greater than 0% and not more than 60%.

A sintered rare earth oxyfluoride compact is composed of Ln.sub.aO.sub.bF.sub.c (wherein Ln is a rare earth element; and a, b, and c each independently represent a positive number, provided that they are not equal to each other) or Ca-stabilized LnOF as a primary phase and LnOF unstabilized with Ca as a secondary phase. The intensity ratio of the XRD peak of the (018) or (110) plane of the unstabilized LnOF to the highest XRD peak of Ln.sub.aO.sub.bF.sub.c is preferably 0.5% to 30%.

A material synthesis method may comprise: adding at least one liquid precursor solution to an atomizer device; generating by the atomizer device an aerosol comprising liquid droplets; transporting the aerosol to a reactive zone for evaporating one or more solvents from the aerosol; and collecting particles synthesized from at least evaporating the aerosol.

A material synthesis method may comprise: adding at least one liquid precursor solution to an atomizer device; generating by the atomizer device an aerosol comprising liquid droplets; transporting the aerosol to a reactive zone for evaporating one or more solvents from the aerosol; and collecting particles synthesized from at least evaporating the aerosol.

A film-forming material of the present invention contains an oxyfluoride of yttrium represented by YO.sub.XF.sub.Y (X and Y are numbers satisfying 0<X and X<Y) and YF.sub.3, wherein a ratio I.sub.2/I.sub.1 of a peak height I.sub.2 of the (020) plane of YF.sub.3 to a peak height I.sub.1 of the main peak of YO.sub.XF.sub.Y as analyzed by XRD is from 0.005 to 100. It is preferable that a ratio I.sub.4/I.sub.1 of a peak height I.sub.4 of the main peak of Y.sub.2O.sub.3 to the peak height I.sub.1 of the main peak of YO.sub.XF.sub.Y as analyzed by XRD is 0.01 or less.