Structure-property relationships were investigated to reveal the generic influence of various substituents on ferroelectric BaTiO3. Compositional modifications of ferroelectric BaTiO3 were systematically investigated for La3+ and Nb5+ substituents. A generic influence of charged point defects in breaking down the ferroelectric domains into polar clusters was demonstrated. In both types of modified BaTiO3, relaxor ferroelectric behavior was induced for higher concentrations of substituents.