Abstract
BiFeO3 (BFO) has attracted much attention because of its room-temperature multiferroic properties with a ferroelectric Curie temperature of TC～830 ˚C and an antiferromagnetic Néel temperature of TN～370 ˚C. Concerning the electrical properties, although its spontaneous polarization is as large as ～100 µC/cm2, the piezoelectric constant (d33～60 pm/V) is far smaller than those of lead containing piezoceramics, such as Pb(Zr,Ti)O3 (PZT). An improved piezoelectric response is expected in the solid solution of rhombohedral BFO and tetragonal BiCoO3, (1− x)BiFeO3 – xBiCoO3 (BFCO), owing to the presence of morphotropic phase boundary (MPB)1) similar to PZT. In this study,epitaxial thin films of BFCO with x = 0 − 0.1 were prepared on SrRuO3(SRO)(001)/SrTiO3(STO)(001) substrates by pulsed laser deposition, and their crystal structure and electrical properties were investigated. We successfully obtained single phase of epitaxial BFCO thin films with well-saturated polarization-electric field hysteresis loops at room temperature. Sharp BFCO/SRO and SRO/STO interfaces without intermixing and a good quality of BFCO were found by transmission electron microscopy. The effective d33 estimated from the slope of the displacement-electric curve of the BFO film was ～60 pm/V, which is comparable to that reported by other investigators. The d33 value of the BFCO thin film increased with increasing Co content and reached ～100 pm/V at x = 0.1.
