A substrate for mounting a light-emitting element according to the present disclosure contains a crystal particle of aluminum oxide and is composed of an alumina-based ceramic that contains 97% by mass or more of Al as a value of an Al.sub.2O.sub.3 equivalent among 100% by mass of all components thereof. An average value of an equivalent circle diameter of the crystal particle is 1.1 μm or greater and 1.8 μm or less and a standard deviation of an equivalent circle diameter thereof is 0.6 μm or greater and 1.4 μm or less.

A method of producing a core-shell particle includes introducing a barium titanate-based base powder and an additive to a reactor, and exposing the barium titanate-based base powder and the additive to a thermal plasma torch to obtain core-shell particles including a core portion having barium titanate (BaTiO.sub.3) and a shell portion including the additive and formed on a surface of the core portion.

A polycrystalline diamond (PCD) construction has a first region of a first grade of PCD material; and a second region of a second grade of PCD material, the first region being at least partially peripherally surrounded by the second region, the first and second regions being bonded to each other by direct inter-growth of diamond grains to form an integral PCD structure and a substrate bonded to the first and/or second region(s) along an interface. The first grade of PCD differs from the second grade in one or more of diamond and metal network compositional ratio, metal elemental composition, or average diamond grain size, the first grade of PCD material having a larger average diamond grain size than the second grade of PCD material, and/or a smaller volume percentage of residual catalyst and/or binder in interstitial spaces between interbonded diamond grains than the PCD material of the second region.

Provided are an aluminum-silicon-carbide composite having high thermal conductivity, low thermal expansion, and low specific gravity and a method for producing the composite. Provided is an aluminum-silicon-carbide composite formed by impregnating a porous silicon carbide molded body with an aluminum alloy. The ratio of silicon carbide in the composite is 60 vol % or more, and the composite contains 60-75 mass % of silicon carbide having a particle diameter of 80 m or more and 800 m or less, 20-30 mass % of silicon carbide having a particle diameter of 8 m or more and less than 80 m, and 5-10 mass % of silicon carbide having a particle diameter of less than 8 m.

A shower plate according to the present disclosure includes a ceramic sintered body, the ceramic sintered body comprising a first surface, a second surface facing the first surface, and a through hole positioned between the first surface and the second surface. An inner surface of the through hole includes a protruding crystal grain which protrudes more than an exposed part of a grain boundary phase existing between crystal grains. In addition, a semiconductor manufacturing apparatus according to the present disclosure includes the shower plate mentioned above.

A method for producing an alumina sintered body, including: a step of applying an alkaline earth metal compound onto a surface of an alumina raw material which is an unsintered alumina compact or an alumina sintered body; and a step of subjecting the alumina raw material to which the alkaline earth metal compound has been applied to heat treatment at a temperature of 1200 C. or more for 5 minutes or more and 300 minutes or less.

A ceramic electronic component includes a body including a dielectric layer and an internal electrode, and an external electrode disposed on the body and connected to the internal electrode. The dielectric layer includes a plurality of dielectric grains, and at least one of the plurality of dielectric grains has a core-dual shell structure having a core and a dual shell. The dual shell includes a first shell surrounding at least a portion of the core, and a second shell surrounding at least a portion of the first shell, and a concentration of a rare earth element included in the second shell is more than 1.3 times to less than 3.8 times a concentration of a rare earth element included in the first shell.

A ceramic electronic device includes: a multilayer structure; and a cover layer, wherein a concentration of Mn of the cover layer with respect to a main component ceramic is larger than a concentration of Mn of the dielectric layers with respect to a main component ceramic in a capacity section, wherein an average crystal grain diameter of a first dielectric layer is smaller than that of a second dielectric layer, and a concentration of Mn of the first dielectric layer with respect to the main component ceramic is larger than a concentration of Mn of the second dielectric layer with respect to the main component ceramic, in the capacity section.

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 method for producing an alumina sintered body, including: a step of applying an alkaline earth metal compound onto a surface of an alumina raw material which is an unsintered alumina compact or an alumina sintered body; and a step of subjecting the alumina raw material to which the alkaline earth metal compound has been applied to heat treatment at a temperature of 1200 C. or more for 5 minutes or more and 300 minutes or less.