  While nature provides a plethora of perovskite materials, only a few exhibits
large ferroelectricity and possibly multiferroicity. The majority of perovskite
materials have the non-polar CaTiO$_3$(CTO)structure, limiting the scope of
their applications. Based on effective Hamiltonian model as well as
first-principles calculations, we propose a general thin-film design method to
stabilize the functional BiFeO$_3$(BFO)-type structure, which is a common
metastable structure in widespread CaTiO$_3$-type perovskite oxides. It is
found that the improper antiferroelectricity in CTO-type perovskite and
ferroelectricity in BFO-type perovskite have distinct dependences on mechanical
and electric boundary conditions, both of which involve oxygen octahedral
rotation and tilt. The above difference can be used to stabilize the highly
polar BFO-type structure in many CTO-type perovskite materials.
