Effects of K nonstoichiometry in bismuth layer-structured K0.5+xBi4.5Ti4O15 ceramics

The effects of K nonstoichiometry on phase formation, grain morphology, dielectric and piezoelectric properties of K0.5+xBi4.5Ti4O15 (KBT) were studied in the range of excess up to +2mol% and deficient down to −8mol% of K0.5. The relative densities of the sintered KBT ceramics with various K contents prepared by a solid state reaction method were all higher than 95%. In all samples, a bismuth layer-structured phase was confirmed, although a secondary phase appeared as K deficiency became larger than −6mol%. Piezoelectric coefficient (d33) increased, showing a high of 16pC/N at x=−3mol%, and then decreased with further K deficiency while Curie temperature (TC) decreased showing a low of 540°C at x=−8mol% from 551°C at x=0mol%. Mechanical quality factor (Qm) of all samples was in the range of 900–1860.