Structure, impedance and conduction mechanisms of tape-casting (Bi0.44Nd0.01Sr0.02Ca0.02)Na0.5TiO2.965 ceramic film

Bi0.5Na0.5TiO3 (BNT)-based complexes, one of the most promising piezoelectric materials, have been recently raised as potential ionic conductors. Although the property modification of BNT-based materials was studied intensively, the influence of the preparation process on the structure and conduction mechanism has not received the attention it deserves since its particular sensitivity to the conductive performance. Herein, (Bi0.44Nd0.01Sr0.02Ca0.02)Na0.5TiO2.965 (BNSCNT) ceramics were prepared by tape-casting (TC) and conventional solid-state reaction (SR) method, respectively. Despite the pure perovskite phase with rhombohedral distortion of BNSCNT ceramics prepared by SR, the rutile titanium dioxide phase can be identified for TC. The ac impedance spectra reveal a discernible bulk response with appreciable oxide ion conductive capacity in SR, while the contribution from each physical origin becomes obscure due to the superposition in the Nyquist plots of TC. Combined with the activation energy deduced from the thermally dependent conductivity, which is significantly less than the dielectric BNTs, the dominated ionic conductive nature with non-negligible electron contribution is proposed. The grain boundary and electrodes/interfaces response, and their conduction mechanism in the intermediate frequencies range are disclosed by employing the dc bias field and atmospheres. The field-induced inverse variation is recognized of which the dissociation of defect clusters is responsible for SR, whereas the trapping of conduction electrons on the sample surface and the second phase will play the key role for TC, in determining their impedance. This work raises the great importance of the preparation route on the structure and conduction mechanisms of BNT-based oxide ionic conductive materials.