EFFECT OF A-SITE VACANCY ORDER-DISORDER STATES ON DIFFUSE PHASE-TRANSITION OF THE MORPHOTROPIC PHASE-BOUNDARY PB1-XBAXNB2O6 FERROELECTRICS

The effect of A-site vacancy order-disorder states on diffuse phase tr ansition (DPT) of tungsten bronze Pb1-xBaxNb2O6 (PEN) ferroelectrics h as been investigated. The A-site vacancy disordered PEN ceramics exhib it notable variations of the Curie temperatures (i.e., the temperature s at the dielectric maximum permittivities) up to 12 degrees C in resp onse to frequency changed from 0.1 KHz to 100 KHz. The largest frequen cy dispersion occurred at the morphotropic phase boundary of 1 - X = 0 .63, along with the lowest Curie point. In contrast, the A-site vacanc y ordered PEN ceramics present little frequency dispersion in the rang e of 2 degrees C from 0.1 KHz to 100 KHz. Dielectric constants of the disordered PEN ceramics were generally higher than those of the ordere d ones. In comparison with the ordered PEN ceramics, the Curie points of the disordered ceramics were shifted from lower to higher temperatu re as the Pb2+ cation percentage was decreased; i.e., the Curie temper atures of the disordered PEN ceramics were lower than those of the ord ered ones when 1 - X greater than or equal to 0.70, but higher when 1 - X less than or equal to 0.65. These differences are suggested to inh erently result from the A-site vacancy order-disorder stares. The rela tionship between the A-site vacancy order-disorder states and the diel ectric properties has also been confirmed with studies of thermal hyst eresis.