Greater functionality of bismuth and lead based perovskites
Novel Bi and Pb-based perovskite oxide chemistries have been investigated through bulk solid-state synthesis methods with a goal of increasing the dielectric, ferroelectric, and magnetic functionality of these materials. Although the Pb+2 and Bi+3 canons are chemically similar, Pb-based perovskites have historically received greater commercial and scientific attention. However, recent experimental and theoretical progress in studies of Bi containing systems has prompted a renewed interest in their potential. As such, particular focus was given to the Bi+3 containing systems in the current work. An investigation of the Bi-based perovskite compounds, emphasizing multiferroic BiFeO3 and related solid solutions, has explored the limitations of bulk synthesis methods for these systems. Numerous cation and anion substitution routes are experimentally studied and a comprehensive review of previous work examining B′ site cation substitution in Bi-based perovskites is performed. This has resulted in an improved understanding of phase competition within these systems. These findings were used to engineer new chemistries, particularly those of mixed cation site occupancy, with improved perovskite stability. New low tolerance factor Bi-based perovskites with mixed B ′ site cation chemistries have been used to induce morphotropic phase boundary (MPB) formation in solid solutions with PbTiO3. Moreover, a new qualitative relationship correlating the tolerance factor of Bi and Pb-based end members in PbTiO3 solid solutions to the compositional position of the system's MPB has been developed and experimentally validated. This relationship has been used to explore novel end members with very low tolerance factors including (Pb1/2Th1/2)ScO 3, for PbTiO3-based MPB solid solutions. A new category of Bi-based chemistries which enhance tetragonality and Curie temperature (Tc) in solid solutions with PbTiO3 has been identified. This effect is particularly dramatic for the (x)PbTiO 3-(1 − x)Bi(Zn1/2Ti1/2)O 3 solid solution. The x = 0.6 composition of this system exhibits a high c/a ratio of 1.11 and a TC greater than 700°C. Detailed structural analysis of this system was performed by powder neutron diffraction. It is postulated that such unique behavior is driven by A′ site Bi canons, but is effective only when the B′ site positions are fully occupied by ferroelectrically active canons. These TC and tetragonality enhancing Bi-based chemistries are used as additives to modify the structural, ferroelectric, and piezoelectric properties of well known PbTiO3-based MPB systems.
Suchomel, Matthew R, "Greater functionality of bismuth and lead based perovskites" (2005). Dissertations available from ProQuest. AAI3179819.