Disclosed is provision of a ceramic coat having an excellent low-particle generation as well as a method for assessing the low-particle generation of the ceramic coat. A composite structure including a substrate and a structure which is formed on the substrate and has a surface, wherein the structure includes a polycrystalline ceramic and the composite structure has luminance Sa satisfying a specific value calculated from a TEM image analysis thereof, can be suitably used as an inner member of a semiconductor manufacturing apparatus required to have a low-particle generation.

Disclosed is provision of a ceramic coat having an excellent low-particle generation as well as a method for assessing the low-particle generation of the ceramic coat. A composite structure including a substrate and a structure which is formed on the substrate and has a surface, wherein the structure includes a polycrystalline ceramic and the composite structure has luminance Sa satisfying a specific value calculated from a TEM image analysis thereof, can be suitably used as an inner member of a semiconductor manufacturing apparatus required to have a low-particle generation.

A coating material containing an oxyfluoride of yttrium and having a Fisher diameter of 1.0 to 10 m and a tap density TD to apparent density AD ratio, TD/AD, of 1.6 to 3.5. The coating material preferably has a pore volume of pores with a diameter of 100 m or smaller of 1.0 cm.sup.3/g or less as measured by mercury intrusion porosimetry. A coating containing an oxyfluoride of yttrium and having a Vickers hardness of 200 HV0.01 or higher. The coating preferably has a fracture toughness of 1.010.sup.2 Pa.Math.m.sup.1/2 or higher.

A coating material containing an oxyfluoride of yttrium and having a Fisher diameter of 1.0 to 10 m and a tap density TD to apparent density AD ratio, TD/AD, of 1.6 to 3.5. The coating material preferably has a pore volume of pores with a diameter of 100 m or smaller of 1.0 cm.sup.3/g or less as measured by mercury intrusion porosimetry. A coating containing an oxyfluoride of yttrium and having a Vickers hardness of 200 HV0.01 or higher. The coating preferably has a fracture toughness of 1.010.sup.2 Pa.Math.m.sup.1/2 or higher.

A positive-electrode active material contains a compound represented by the following composition formula (1):

Li.sub.xMe.sub.yO.sub.X.sub.(1) where Me denotes one or more elements selected from the group consisting of Mn, Ni, Co, Fe, Al, Sn, Cu, Nb, Mo, Bi, Ti, V, Cr, Y, Zr, Zn, Na, K, Ca, Mg, Pt, Au, Ag, Ru, Ta, W, La, Ce, Pr, Sm, Eu, Dy, and Er, X denotes two or more elements selected from the group consisting of F, Cl, Br, I, N, and S, and x, y, , and satisfy 0.75x2.25, 0.75y1.50, 1<3, and 0<2, respectively. A crystal structure of the compound belongs to a space group Fm-3m.

A positive-electrode active material contains a compound represented by the following composition formula (1):

Li.sub.xMe.sub.yO.sub.X.sub.(1) where Me denotes one or more elements selected from the group consisting of Mn, Ni, Co, Fe, Al, Sn, Cu, Nb, Mo, Bi, Ti, V, Cr, Y, Zr, Zn, Na, K, Ca, Mg, Pt, Au, Ag, Ru, Ta, W, La, Ce, Pr, Sm, Eu, Dy, and Er, X denotes two or more elements selected from the group consisting of F, Cl, Br, I, N, and S, and x, y, , and satisfy 0.75x2.25, 0.75y1.50, 1<3, and 0<2, respectively. A crystal structure of the compound belongs to a space group Fm-3m.

An yttrium oxyfluoride is represented by YOF and is stabilized by a fluoride represented by CaF.sub.2. Preferably, the number of moles of Ca with respect to 100 mol of yttrium is from 8 to 40 mol. A powder material is made of a first powder mixture including a calcium fluoride powder represented by CaF.sub.2 and an yttrium oxyfluoride powder represented by YOF, or a second powder mixture including a calcium fluoride powder represented by CaF.sub.2, an yttrium fluoride powder represented by YF.sub.3, and an yttrium oxide powder represented by Y.sub.2O.sub.3. A production method involves firing a molded product of the first or second powder mixture under predetermined conditions.

An yttrium oxyfluoride is represented by YOF and is stabilized by a fluoride represented by CaF.sub.2. Preferably, the number of moles of Ca with respect to 100 mol of yttrium is from 8 to 40 mol. A powder material is made of a first powder mixture including a calcium fluoride powder represented by CaF.sub.2 and an yttrium oxyfluoride powder represented by YOF, or a second powder mixture including a calcium fluoride powder represented by CaF.sub.2, an yttrium fluoride powder represented by YF.sub.3, and an yttrium oxide powder represented by Y.sub.2O.sub.3. A production method involves firing a molded product of the first or second powder mixture under predetermined conditions.

An article comprises a body having a coating. The coating comprises a M-O-F coating having a molar O/F ratio that is customized to future processing that the article may be exposed to.

An article comprises a body having a coating. The coating comprises a M-O-F coating having a molar O/F ratio that is customized to future processing that the article may be exposed to.