The origin of the modulated structure in Sr 2 CuO 3+ δ ( δ  = 0.4): [CuO 2 ] in‐plane oxygen vacancy or apical oxygen vacancy?

We propose the question of the modulated structures of copper oxide is caused by the [CuO 2 ] in‐plane oxygen vacancy or apical oxygen vacancy. Sr 2 CuO 3+ δ single‐crystal samples were prepared using high‐temperature and high‐pressure methods. The major phase of Sr 2 CuO 3+ δ ( δ = 0.4) single‐crystal system is found to be constituted by the 5 a modulated structure with the Fmmm space group, which originates from the [CuO 2 ] in‐plane oxygen vacancy appearing in octahedral Cu‐O. Besides, the presence of the [CuO 2 ] in‐plane oxygen vacancy may obliterate the superconductivity of the system. Experimental results deduce that the oxygen vacancy may appear in the apical oxygen sites in high‐temperature copper oxide superconductors.