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Bi5Ti3FeO15 (pentabismuth trititanium iron pentadecaoxide), which is a multiferroic four‐layer Aurivillius phase compound, has received much attention in recent years. However, three mutually inconsistent orthorhombic space groups, i.e. A21am, Fmm2 and Pnn2, have been reported for the room‐temperature phase of Bi5Ti3FeO15 by X‐ray and neutron diffraction investigations. Here, electron diffraction results are presented and discussed for the first time to unambiguously clarify the room‐temperature space group of ceramic Bi5Ti3FeO15. It has been found that all the observed reflections from the ceramic agree with those expected in A21am, while the observed reflections 011, 013 and 015 should be forbidden in the case of Fmm2, and no 107 and 109 reflections were observed although allowed for Pnn2. The present study has demonstrated that the space group of Bi5Ti3FeO15 ceramic is A21am rather than Fmm2 or Pnn2, an identification that proved to be a challenge for X‐ray diffraction. On the basis of the space group A21am, the lattice parameters of the Bi5Ti3FeO15 ceramic were calculated from its X‐ray diffraction data. [ABSTRACT FROM AUTHOR]

[Display omitted] • As-synthesized Bi 5 Ti 3 FeO 15 naturally contains moderate concentration of oxygen vacancies. • Bi 5 Ti 3 FeO 15 is highly active in piezocatalytic degradation of AO7, MO, RhB, MB and their mixture. • Bi 5 Ti 3 FeO 15 shows superior environmental adaptability and stability. • Real textile wastewater can be efficiently degraded by Bi 5 Ti 3 FeO 15. Piezocatalyst with high and stable efficiency for multiple pollutants degradation shows great promise for practical applications but remains a challenge. Herein, a self-modified oxygen-deficient piezoelectric Bi 5 Ti 3 FeO 15 catalyst is synthesized via a facile method, which demonstrates outstanding piezocatalytic properties. Investigations reveal that an optimal concentration of oxygen vacancies could increase carrier concentration, reduce the electronic impedance and enhance carrier's separation efficiency under ultrasonic vibration, leading to superior piezocatalytic performance. As a result, the typical pollutants acid orange 7, methyl orange, rhodamine B and methylene blue dyes can be efficiently degraded by 98, 95, 94 and 94 %, respectively, within 30 and 50 min (for the latter three dyes), and the acquired degradation efficiencies are higher than most of the previously reported piezocatalysts. Moreover, Bi 5 Ti 3 FeO 15 displayed excellent degradation efficiency for mixed dyes solution with a high first-order rate constant k (0.072 min−1), which is higher than most of the reported piezocatalysts for just single dye degradation. In addition, the Bi 5 Ti 3 FeO 15 catalyst possesses superior environmental adaptability and highly efficient degradation ability for real textile wastewater. This work provides a novel and comprehensive strategy for designing high performance oxygen-deficient piezocatalysts that can be further extended to other Bi-based oxides, and also demonstrates that Bi 5 Ti 3 FeO 15 is a promising eco-friendly and superior piezocatalyst for complex wastewater purification by harvesting mechanical energy. [ABSTRACT FROM AUTHOR]