Order‐Disorder Phase Formation in the Complex Perovskite Compounds Ba(Ni1/3Nb2/3)O3 and Ba(Zn1/3Nb2/3)O3

The order‐disorder phase formation of the complex perovskite compounds Ba(Ni 1/3 Nb 2/3 )O 3 (BNN) and Ba(Zn 1/3 ‐Nb 2/3 )O 3 (BZN) was investigated using X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, and energy‐dispersive spectroscopy. The BNN and BZN samples were sintered over a temperature range of 1200° to 1500°C in air for 2 h. X‐ray diffraction and transmission electron microscopy showed that these compounds exhibited a 1:2 ordering on the B‐site within a narrow temperature range. When BNN and BZN were sintered above 1400° and 1350°C, respectively, a liquid phase formed in the grain boundary which was accompanied by disordering. The composition of the liquid phase resembled that of pyrochlore, with a small amount of nickel for BNN or zinc for BZN. The disordering with the formation of the liquid phase was attributed to the increase in defect concentration.