Crystal structure and electrical properties of (1 -x)BiFeO ₃-xBiCoO₃ thin films prepared by pulsed laser deposition

BiFeO₃ (BFO) has attracted much attention because of its room-temperature multiferroic properties with a ferroelectric Curie temperature of T_c~-830 °C and an antiferromagnetic Néel temperature of T_N~370 °C. Concerning the electrical properties, although its spontaneous polarization is as large as ~100μC/cm², the piezoelectric constant (d₃₃~60pm/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-xcBiCoO₃ (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.