Superior dielectric tunability of high-valence W6+-doped Na0.5Bi0.5TiO3 thin films

Na0.5Bi0.5TiO3 (NBT) and Na0.5Bi0.5Ti1-xWx O3+delta (NBTWx, x = 0.005, 0.010, 0.020) thin films were successfully fabricated on indium tin oxide (ITO)/glass substrates via a modified sol-gel method annealed at 600 degrees C. The effects of W6+ doping content on crystalline structure, surface morphology and electrical properties were studied in detail. All the films can be crystallized into phase-pure perovskite structures and possess smooth surfaces without any cracks. Compared with the NBT, each NBTWx thin film exhibits an obvious decrease of leakage current density and enhanced dielectric properties. A large dielectric tunability (62 %) which is comparable to that of lead-based ones (such as PZT) is achieved in NBTW0.010 sample at the frequency of 100 kHz, which can be attributed to the inhibition effect of the appropriate concentration of W6+ on the formation of oxygen vacancies. These results suggest that high-valence-ion substitution of W6+ ion for Ti4+ ion can significantly optimize the electrical properties of NBT-based thin films.