Mechanochemical synthesis and electrical conductivity of nanocrystalline delta-Bi2O3 stabilized by HfO2 and ZrO2

A powder mixture of alpha-Bi2O3 and HfO2, in the molar ratio 2:3, was inechanochemically treated in a planetary ball mill under air, using zirconium oxide vials and balls as the milling medium. After 50 h of milling, the mechanochemical reaction led to the formation of a nanocrystalline delta-Bi2O3 phase (fluorite-type solid solution Bi0.78Hf0.59Zr0.63O3.61), with a crystallite size of 20 nm. The mechanochemical reaction started at a very beginning of milling accompanied by an accumulation of ZrO2 arising from the milling tools. The samples prepared after various milling times were characterized by X-ray powder diffraction and DSC analysis. The electrical properties of the as-milled and pressed Bi0.78Hf0.59Zr0.63O3.61 powder were Studied using impedance spectroscopy in the temperature range from 100 to 700 degrees C under air. The electrical conductivity was determined to be 9.43 x 10(-6) and 0.080 S cm(-1) for the temperatures of 300 and 700 degrees C, respectively.