We introduce experimental investigations on the high T_c superconductivity at 80 K in the bilayer nickelate La₃Ni₂O₇ under a 14 GPa pressure. The superconductivity emerges coincidently with a structural transition from Amam to I4/mmm. Both zero resistance and diamagnetic response, which are essential for superconductivity, were observed. A multislice electron ptychography technique was employed to visualize the oxygen. The results confirm the superconducting phase is the bilayer phase of La₃Ni₂O₇ with low oxygen vacancies.

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