Long-lasting, fast-switchable photochromism in Na0.5Bi0.5TiO3 induced by photocatalytic memory effect, and its subsequently enhanced piezoelectric response and catalytic performances

A ferroelectric ceramic material of Na0.5Bi0.5TiO3 was found to possess a pronounced, long-lasting, and fast-switchable photochromic behavior responsive to visible light. The working mechanism of its photochromism could be attributed to an interesting photocatalytic memory effect, during which photogenerated electrons were trapped by Bi3+/Ti4+ and oxygen vacancies generated in Na0.5Bi0.5TiO3. The release kinetics of trapped electrons could be modulated by controlling environment conditions to make its photochromism phenomenon both long-lasting and fast-switchable to meet various application requirements. In the meantime, the photochromism process changed its inner electronic structure, resulting in stronger oxidation capability, increased piezoelectric response, improved charge carrier separation and transfer, and more active oxygen species production. Thus, its photocatalytic, piezocatalytic and photopiezocatalytic performances were all significantly enhanced as demonstrated by its TC-HCl degradation performances. This work offered a novel approach to search for and design inorganic photochromic materials with good reversibility for various technical applications.