Determining the appropriate water-soluble sacrificial layer is crucial for fabricating large-scale free-standing oxide membranes.Here,we introduce a new water-soluble sacrificial layer called"super tetragonal"Sr₄Al₂O₇.In contrast to Sr₃Al₂O₆,the low-symmetry crystal structure demonstrates excellent resilience to epitaxial strain,allowing for a wide range of lattice constant tunability.The defect-free interfaces within the heterogeneous structure of encapsulated crystalline ABO₃/Sr₄Al₂O₇effectively mitigate crack formation in the free-standing oxide film during water release.Additionally,this new material exhibits a faster rate of water dissolution.Furthermore,its higher interfacial bonding energy and excellent chemical stability enable the preparation of high-quality and high-integrity free-standing oxide films 。