Ferroelectric and piezoelectric properties of high temperature (Bi,La)FeO3–Bi(Zn1/2Ti1/2)O3–PbTiO3 ceramics at rhombohedral/tetragonal coexistent phase

In this article, some high Curie temperature ferroelectric piezoceramics of perovskite-structured BiFeO3–Bi(Zn1/2Ti1/2)O3–PbTiO3 (BF–BZT–PT) solid solutions were prepared using fine-ball milling and solid state reaction method. X-ray diffraction measurements exhibited those BF–BZT–PT ceramics being crystallized in rhombohedral/tetragonal coexistent phase while scanning electron microscopy showed their microstructure grain size about 200 nm. It was found that the ferroelectric Curie temperature increases up to 630 °C with increasing BF content in those BF–BZT–PT ceramics and that their ferroelectric and piezoelectric properties were strongly dependent on compositions and sintering temperature. A good combination of ferroelectric and piezoelectric property of remanent polarization Pr = 18 µC/cm2, coercive field Ec = 64 kV/cm, piezoelectric constant d33 = 41 pC/N, dielectric constant , loss tan δ = 0.023, and Curie temperature TC = 582 °C was obtained for 0.59BF–0.15BZT–0.26PT ceramics sintered at 780 °C for 10 h and poled under 8.4 kV/mm at 120 °C for 20 min. In comparison with tetragonal 0.50BF–0.15BZT–0.35PT ceramics reported previously by the author group, rhombohedral/tetragonal-coexistent-phased 0.59BF–0.15BZT–0.26PT ceramics exhibited a higher piezoresponse, and contemporarily, La-substitution was found playing the same role of enhancing piezoresponse and reducing Curie temperature. Of most interest, a good piezoelectric property of d33 = 24 pC/N, er = 217, tan δ = 0.020, and TC = 630 °C was obtained for 0.66BF–0.15BZT–0.19PT ceramics prepared by two-step sintering with 850–750 °C for 10 h and poled under 9.0 kV/mm at 120 °C for 20 min, which is better than that of commercial K-15 bismuth titanate ceramics with d33 = 18 pC/N, , tan δ = 0.03, and TC ~ 620 °C. Like the case of Pb(Zr,Ti)O3, BF–BZT–PT perovskites are becoming important to design high temperature high performance ferroelectric piezoceramics through adjusting composition and crystallographic structure.