An investigation of the influence of grain boundaries on the electrical behavior of polycrystalline ZrO2-CaO

The dielectric behavior of polycrystalline zirconium oxide with calcium concentrations ranging from 12 to 19 mole per cent as investigated as a function of frequency, from 100 Hz to 500 KHz, temperature, from 300 C to 900 C, and partial pressure of oxygen, from 10-5 atm. to 1 atm. Specimens having various grain sizes, electrode materials, and degrees of sintering were also considered in order to determine the influence of grain boundaries on the electrical conduction. The a.c. dielectric data were analyzed with the aid of impedance plotting technique. This allowed an equivalent circuit representation of the specimen. The a.c. impedance of ZRO2-CaO exhibited a general three loop behavior. At high temperatures, space charge polarization due to ionized oxygen vacancies being partially blocked at the specimen electrodes seems responsible for a major portion of the dielectric behavior.