Abstract The stability of various amounts of Ba3Cu3In4O12 (334) or BaTbO3 (BTO) in a sintered YBa2Cu3Oy (YBCO) matrix was examined. Samples with added 334 or BTO exhibited critical temperatures (Tc) above 90 K for up to 20 vol.% addition and improved critical current densities (Jc) under a magnetic field. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis indicated that 334 and BTO did not react with the YBCO matrix under the sintering conditions used. The normalized Jc under a magnetic field of 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 increasing BTO content. YBCO films with added 334 showed a constant Tc of 87 K up to a 334 content of 4 vol.%.