Dielectric relaxations in Ba0.85Sr0.15TiO3 thin films deposited on Pt/Ti/SiO2/Si substrates by sol–gel method

This paper presents an extended analysis of dielectric relaxations in ferroelectric Ba0.85Sr0.15TiO3 thin films deposited by a sol–gel technique on Pt/Ti/SiO2/Si substrates. By means of dielectric, impedance and ac conductivity analysis, it is revealed that both temperature and film thickness modify strongly the resulting behavior under small ac signal. Indeed a ferroelectric-to-paraelectric transition is observed at Tc = 75 °C. Moreover, low frequency dispersion is observed caused by the interfacial polarization in film/electrode and/or in grain boundary interfaces. Simultaneously, above Tc one marks the presence of broad peaks in the permittivity at high temperatures. This can be attributed to the possible existence of polar nanoregions due to oxygen vacancies migration. The effect of ferroelectricity on admittance is also discussed. It is revealed that, dielectric properties of the MIM structures are thickness independent in the ferroelectric state. Whereas, in the paraelectric state it depends strongly on thickness as well as frequency.