Effect of equivalent and aliovalent doping on dielectric properties and relaxation of BaBi4TiO15 ceramics

The equivalent and aliovalent ions (Zr4+, Al3+ and Nb5+) doped (BaBiTi4O15)-Ti-4 ceramics were prepared by a solid-state reaction method. X-ray diffraction patterns showed that the ceramics have a tetragonal structure with space group of 14/intrun at room temperature. The plate -like morphology was observed by scanning electron microscope (SEM) and the anisotropy of grains weakens after doping. The dielectric properties and complex impedance spectra of all samples were studied. The results showed that the dielectric properties demonstrate strong dependence on the type of doping element. Al doping decreases the dielectric constant for limiting the vibration space of Ti ions in small cell volume. Nb doping as a donor induces the formation of Ti3+ and the increase of dielectric constant and loss; simultaneously, it decreases the temperature of dielectric constant maximum obviously and the temperature stability of dielectric constant. Doping leads to the increase of diffuseness of phase transition, due to the increasing distribution disorder of cations. Through Arrhenius fitting, the activation energy was estimated to be 0.81-1.18 eV, which could be attributed to the thermal motion of oxygen vacancy and grain distortion.