Phase evolution and electrical behaviour of samarium-substituted bismuth ferrite ceramics

Bi1-xSmxFeO3 (x = 0.15-0.18) ceramics with high density were produced using spark plasma sintering. The effects of composition, synthesis conditions and temperature on the phase evolution were studied, using XRD, TEM and dielectric spectroscopy. The coexistence of the ferroelectric R3c, antiferroelectric Pnam and paraelectric Pnma phases was revealed, with relative phase fractions affected by both calcination conditions and Sm concentration. Experiments on powdered samples calcined at different temperatures up to 950 °C suggest higher calcination temperatures promote Sm diffusion, allowing samples to reach compositional homogeneity. The structural transitions from the Pnam and R3c phases to the Pnma phase were comprehensively investigated, with phase transition temperatures clearly identified. The dielectric permittivity, electrical resistivity and breakdown strength were increased upon Sm-substitution, while ferroelectric switching was suppressed. The polarization-electric field loop became increasingly narrow with increasing Sm-content, but double hysteresis loops, which may reflect a reversible antiferroelectric to ferroelectric transformation, were not observed.