Ferroelectric properties of PbxSr1−xTiO3 and its compositionally graded thin films grown on the highly oriented LaNiO3 buffered Pt∕Ti∕SiO2∕Si substrates

Thin films of ferroelectric PbxSr1−xTiO3 (PST) with x=0.3–0.7 and graded composition were fabricated on LaNiO3 buffered Pt∕Ti∕SiO2∕Si substrates by a sol-gel deposition method. The thin films crystallized into a single perovskite structure and exhibited highly (100) preferred orientation after postdeposition annealing at 650°C. The grain size of PST thin films systematically decreased with the increase of Sr content. Dielectric and ferroelectric properties were investigated as a function of temperature, frequency, and dc applied field. Pb0.6Sr0.4TiO3 films showed a dominant voltage dependence of dielectric constant with a high tunability in a temperature range of 25–230°C. The compositionally graded PST thin films with x=0.3–0.6 also showed the high tunability. The graded thin films exhibited a diffused phase transition accompanied by a diffused peak in the temperature variations of dielectric constants. This kind of thin films has a potential in a fabrication of a temperature stable tunable device.