The dielectric relaxation behavior of (Na0.82K0.18)0.5Bi0.5TiO3 ferroelectric thin film

(Na1-xKx)(0.5)Bi0.5TiO3 (NBT-KBT-100x) thin films were deposited on Pt/Ti/SiO2/Si(100) by metal organic decomposition, and the effects of potassium content (x = 0.15, 0.18, 0.20, 0.25) on ferroelectric, piezoelectric, dielectric properties of the thin films, and the temperature dependence of dielectric permittivity of NBT-KBT-18 thin film were investigated in detail. NBT-KBT-18 thin film is of the largest effective piezoelectric coefficient d(33eff), remnant polarization 2P(r), spontaneous polarization 2 P-s, dielectric constant epsilon(r), and the lowest dielectric loss among the thin films. The dielectric constants decrease steeply with the increase of frequency, and there are a series of resonance peaks with Debye-like relaxation. In dielectric temperature spectra, two abnormal peaks corresponding to depolarization temperature and Curie temperature are at the range of 75-90 degrees C and 295-320 degrees C, and they are associated with the phase transitions. Based on the dielectric relaxation theory, Debye-like relaxation and diffused phase transition/frequency dispersion are interpreted by space charge polarization and polar nanoregions. Because of the centrosymmetric paraelectric phase, the 2 P-s and epsilon(r) of NBT-KBT-100x thin film are responsible for the d(33eff) according to phenomenological equation. The improved d(33eff) may make NBT-KBT-18 thin film a promising candidate for piezoelectric thin film devices, and the enhanced Curie temperature will offer useful guidelines of safe working temperature for potential application in micro-electro-mechanical system. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3665389]