Abstract: Metal oxide particles have p-type semiconductivity. The metal oxide particles have a volume-based particle size distribution having a first local maximum value and a second local maximum value. The first local maximum value is in a range of 0.1 ?m or more and less than 5 ?m, and the second local maximum value is in a range of 5 ?m or more and less than 50 ?m. A ratio of the second local maximum value to the first local maximum value is 0.5 or more and less than 2.0. 99% by volume or more of the metal oxide particles have a particle diameter in a range of from 0.1 to 50 ?m.