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 +2 mol% and deficient down to −8 mol% 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 −6 mol%. Piezoelectric coefficient (d33) increased, showing a high of 16 pC/N at x = −3 mol%, and then decreased with further K deficiency while Curie temperature (TC) decreased showing a low of 540 °C at x = −8 mol% from 551 °C at x = 0 mol%. Mechanical quality factor (Qm) of all samples was in the range of 900–1860.