“…2 For example, in YBa 2 Cu 3 O 7−y , according to chemistry calculation oxygen, the amount of O should be 6.5 (Y is +3, Ba +2, and Cu +2), thus when 7 − y must be bigger than 6.5, that is, 0 < y < 0.5, YBa 2 Cu 3 O 7−y has superconductivity, and the oxygen in 7 − y > 6.5 parts is called overstep chemistry calculation oxygen. Two postures exist in YBa 2 Cu 3 O 7−y : positive cross posture and square posture.…”