Coating

At least one layer in a coating located on a surface of a substrate is a domain structure layer constituted of two or more domains different in composition. The average value of the size of each of first domains, defined as the diameter of a virtual circumcircle in contact with each first domain, is 1 nm to 10 nm. The average value of the nearest neighbor distance of each first domain, defined as the length of the shortest straight line connecting the center of the circumcircle with the center of another circumcircle adjacent to the circumcircle, is 1 nm to 12 nm. 95% or more of the first domains has a size within ±25% of the average value of the size, and 95% or more of the first domains has a nearest neighbor distance within ±25% of the average value of the nearest neighbor distance.