Phase transition, ferroelectric behaviors and domain structures of (Na1/2Bi1/2)1−xTiPbxO3 thin films

The phase transition, ferroelectric behaviors and domain structures of ferroelectric thin films of perovskite (Na1/2Bi1/2)1−xTiPbxO3 have been investigated over the composition range 0 < x < 0.9. In contrast to previously reported results for (Na1/2Bi1/2)1−xTiPbxO3 bulk ceramics, the films exhibit a rhombohedral–tetragonal structure change at x = 0.4–0.5, together with a long-range tetragonal symmetry at x ⩾ 0.8. The unique phase transition behaviors are discussed in relation to the growth of Pb2+TiO3 clusters upon substitution of Pb2+ for Na+/Bi3+ cations. The effect of compositional fluctuation in the films is also reflected in their ferroelectric behaviors, where unusual double hysteresis loops are shown by the films for x > 0.5. The polarization behaviors were studied by means of domain imaging using piezoresponse force microscopy. The coexistence of ferroelectric domains and polar nanosized regions in the films and their response under different electric field magnitudes are responsible for the occurrence of the double hysteresis loops.