Structure and electrical properties of intergrowth bismuth layer-structured Bi₄Ti₃O₁₂-CaBi₄Ti₄O₁₅ ferroelectric ceramics

Pb-free ferroelectric Bi₄Ti₃O₁₂-CaBi₄Ti₄O₁₅ (BIT-CBT) ceramics were manufactured using a solid-state reaction method. Structural analysis by using X-ray diffraction confirmed the presence of a second phase of Bi₂Ti₂O₇, and the surface depth X-ray diffraction analysis revealed that this phase existed only on the surface. This second phase appears to have been caused by the volatilization of Bi ions at high sintering temperatures. For resolution of the issue of volatilization of Bi ions and manufacture of BIT-CBT ceramics with a single phase, Bi₂O₃ powder was added to the BIT-CBT mixture, and a powder-bed method, in which pellets were covered with BIT-CBT powder, was used to manufacture the ceramic. The piezoelectric coefficient of the single-phase BIT-CBT ceramics was 12.4 pC/N while the residual polarization and the coercive electric field were 11.3 μC/cm², and 125 kV/cm, respectively. The results suggest that single-phase BIT-CBT ceramics are suitable for the manufacture of elements incorporating these electrical characteristics.