Synthesis of the high dielectric permittivity perovskite (Na1/3Ca1/3 Bi1/3Cu3Ti4O12) by different routes

Abstract

A high dielectric permittivity perovskite (Na1/3Ca1/3 Bi1/3Cu3Ti4O12) or NCBCTO was successfully synthesized by three different routes: solid state (SSS), solution combustion (SCS) and polymeric precursor (PPS). Wide angle x-rays (WAXD) and scanning electron microscopy (SEM) were used as control characterization techniques. A pure NCBCTO phase was obtained straightforward by the SSS method; by the SCS synthesis, however, only after a calcination at 800 °C was the resultant powder converted into the pure NCBCTO. The PPS samples maintained the same initial level of impurities (probably CuO), even after the calcination step. Further sintering of all the samples at 1000 and 1080 °C and characterization of their microstructures by SEM, their density and porosity by immersion tests and dielectric permittivity by impedance spectroscopy were done. Grain size increase and porosity decrease with the increase of the sintering temperature were observed. The samples produced by the PPS method, calcined at 800 °C and sintered at 1080 °C displayed the highest dielectric permittivity (above 20 000), but also the highest dielectric loss (tan δ = 0.35) at 1 kHz. However, the highest ε’/tan δ ratio (160 400 at 1 kHz, with ε’ = 9500 and tan δ = 0.059) was observed in samples produced by the SCS route, calcined at 800 °C and sintered at 1080 °C; these samples had also the smallest and sharpest grain size of all the samples. Thus, this last material was considered the best perovskite to be used as a high k ceramic in dielectric nanocomposites.