Enhancing polarization by electrode-controlled strain relaxation in PbTiO3 heterostructures

A large remanent polarization close to theoretical value 80 μC/cm2 of bulk PbTiO3 is achieved in epitaxial heterostructures of (120–600)-nm-thick PbTiO3 films grown by pulsed laser deposition on (001) SrTiO3 substrate using a 100-nm-thick SrRuO3 bottom electrode layer. The heterostructures employing a 50-nm-thick electrode exhibit a significantly smaller polarization of ≤60 μC/cm2. A detailed x-ray diffraction analysis of the crystal structure allows for relating this large polarization to electrode-controlled relaxation of epitaxial strain in PbTiO3. Based on the observed results, we anticipate that the electrode-promoted strain relaxation can be used to enhance polarization in other epitaxial ferroelectric films.