Nonferroelectric Lead-Free Ceramics and Thick Films with High Dielectric Permittivity - Synthesis, Sintering and Properties

摘要

This work was focused on preparation and comparison of properties of the developed nonferroelectric lead-free high permittivity materials. Eight compounds of perovskite structure with compositions: Bi_(1/2)Cu_(1/2)(Fe_(2/3)W_(1/3))O_3, Ca(Fe_(2/3)W_(1/3))O_3, Bi_(1/2)Cu_(1/2)(Fe_(1/2)Nb_(1/2))O_3, Ca(Fe_(1/2)Nb_(1/2))O_3, Bi_(1/2)Cu_(1/2)(Fe_(1/2)Ta_(1/2))O_3, Ca(Fe_(1/2)Ta_(1/2))O_3, Bi_(2/3)Cu_3Ti_4O_(12) and Cu_2Ta_4O_(12) were synthesized. The obtained powders were used for fabrication of ceramic samples and pastes destined for dielectrics of plate and thick film capacitors. Capacitance and dissipation factor were measured at frequencies 10 Hz- 1 MHz in the temperature range from -55 to 700 °C and -55° to 400 °C for plate and thick film capacitors, respectively. Dc resistivity of the samples was investigated as a function of temperature in the range 20 – 500 °C. Microstructure and chemical homogeneity of the ceramics and layers were studied using scanning electron microscopy and X-ray microanalysis. High permittivity values exceeding 10000, observed especially at low frequencies for all the developed ceramic samples and some of the thick films, are supposed to originate from the formation of internal barrier layer capacitors. Broad maxima of dielectric permittivity and dissipation factor versus temperature plots, shifting towards higher temperatures with increasing frequency, as well as a distinct dependence of dielectric properties on frequency were characteristic of the investigated materials. In view of their lead-free composition and relatively simple preparation procedure, yielding high capacitance and miniaturization, the developed ceramics seem to be promising dielectric materials for capacitive elements.