Enhanced dielectric relaxations in spark plasma sintered CaCu3Ti4O12 ceramics

Abstract

Dense CaCu3Ti4O12 ceramics were prepared by spark plasma sintering method. The microstructure and dielectric properties, especially the dielectric responses, were systematically investigated and compared to solid state sintering process. The spark plasma sintered CaCu3Ti4O12 ceramics with much smaller grain size represent a higher dielectric constant than ceramics sintered by traditional solid state sintering process at room temperature and below 10 kHz. This difference is proposed to be the results of the enhanced dielectric responses in spark plasma sintered CaCu3Ti4O12 ceramics. Two dielectric relaxations in low temperature range (150–212 K) with the activation energy of 0.174 eV and 95.8 meV respectively are detected in spark plasma sintered CaCu3Ti4O12 ceramics at low and high frequency respectively, which are caused by the intrinsic mechanisms in grain associated with ionization of oxygen vacancies (VO2+) and aliovalences of Ti and Cu ions clusters. The more distinct mid-temperature dielectric relaxation in spark plasma sintered CaCu3Ti4O12 ceramics is suggested to be the result of enhanced domain boundary effects, while the high-temperature dielectric relaxation is related to the grain boundaries. The enhanced dielectric constant and weakened temperature stability in spark plasma sintered CaCu3Ti4O12 ceramics were supposed to be the mutual function of dielectric relaxations at domain boundary and grain boundary, which can be due to the increased defects and barrier layers generated by the fast and low oxygen partial pressure of spark plasma sintering process.