Abstract
High Tc superconductor YBa2Cu3Oy, having various oxygen contents have been examined by a.c. susceptibility, d.c. conductivity and Raman spectrum measurements. The Tc is greatly affected by the oxygen content, being lowered by decreasing oxygen content. Particularly, the Tc drops markedly when the compound takes a tetragonal form. To confirm the y vs temperature relation, the compound was reexamined by thermogravimetry. The new results cast doubt on our previous y value (6.5>y>5.8).