Preparation and characterisation of compositionally graded BaxSr1-xTiO3 thin films

BaxSr1-xTiO3 thin films with a compositional gradient of x=0.3 to 1 (in 0.1 mole fraction increments) were fabricated on Pt/Ti/SiO2/Si substrates using a modified sol--gel technique. The graded film crystallised in a perovskite structure and consists of a uniform microstructure with comparatively larger grains. The room-temperature relative dielectric constant (*er) and dielectric loss (cos*d) at 100 kHz were found to be 305 and 0.03 respectively. Dielectric peaks were not observed in the temperature range from -20 C to 120 C. The dielectric constant and dielectric loss were almost independent of temperature. Polarisation--electric field measurements at room temperature revealed a saturated but slim hysteresis loop with a remanent polarisation (Pr) of 0.6 *mC/cm and a coercive field (Ec) of 2.4 kV/mm. The graded film behaves as a stack of BaxSr1-xTiO3 capacitors connected in series and hence the dielectric Curie peaks are removed.