Effects of strontium and calcium simultaneous substitution on electrical and structural properties of Pb1-x-y Ca x Sr y TiO3 thin films

Ferroelectric Pb1-x-y Ca (x) Sr (y) TiO3 thin films (denoted by PCST90, PCST70, and PCST30) were deposited on the Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. Their properties were investigated from the viewpoint of crystal structure, microstructure, dielectric, and ferroelectric properties. X-ray diffraction patterns revealed the formation of PCST90, PCST70, and PCST30 thin films without any secondary phases. Infrared and Raman spectroscopy results show that a gradual phase transition from tetragonal to pseudocubic or cubic perovskite structure may occur in PCST thin films with the simultaneous increase of Ca2+ and Sr2+ contents. Both substitution of isovalent Ca2+ and Sr2+ at Pb2+-site enhanced the dielectric constant and reduced the remnant polarization. In addition, ferroelectric test analyses show that the PCST thin films undergo a ferroelectric-to-paraelectric phase transformation with an amount of Pb2+, Ca2+, and Sr2+ at 30%, 35%, and 35% mol, respectively. Hence, the absence of ferroelectric property may be attributed to a decreasing of the octahedron distortion in the perovskite structure accompanied by a weakening of long-range ferroelectric order.