Stable barium compounds in YBa2Cu3Oy superconductors

► YBCO sintered samples with added 334 or BTO exhibited Tc above 90 K for up to 20 vol% addition and improved Jc under a magnetic field. ► The normalized Jc at 1 T reached a maximum at 14 vol.% of 334 addition and 20 vol% BTO addition. ► YBCO thin films with added BTO showed a gradual decrease in the Tc with BTO content. ► YBCO films with added 334 showed a constant Tc of 87 K up to a 334 content of 4 vol.%.