Ca 2+ substitution induced phase coexistence and synergistic regulation of Ti 3+ defects to improve piezoelectric–photocatalytic water splitting performance of BaTiO 3

BaTiO 3 -Ca 0.2 photoanode with a coexisting tetragonal-orthorhombic phase involving Ti 3+ defects boosts piezo-photocatalytic water splitting performance via enhanced built-in piezoelectric field and shallow energy levels from orbital modulation.