PZT-like structural phase transitions in the BiFeO₃–KNbO₃ solid solution

Abstract

Despite the high prominence of the perovskites BiFeO(3) and KNbO(3) the solid solution between the two has received little attention. We report a detailed neutron and synchrotron X-ray powder diffraction, and Raman spectroscopy study which demonstrates an R3c→P4mm→Amm2 series of structural phase transitions similar to that exhibited by the PbZrO(3)-PbTiO(3) solid solution.

Chemical heterogeneity and approaches to its control in BiFeO3–BaTiO3 lead-free ferroelectrics

“…It has been suggested that chemical heterogeneity in the form of core-shell structures can introduce internal stresses and lead to broad asymmetric peaks. 62,63 Similar observations were made previously by Lennox et al 64 on the basis of neutron diffraction studies on BiFeO 3 -KNbO 3 solid solutions. It was suggested that regions consisting of different A-site and B-site ion ratios, as a consequence of chemical inhomogeneity, can lead to peak broadening.…”

Photoresponse of KNbO3–AFeO3 (A = Bi3+ or La3+) ceramics and its relationship with bandgap narrowing

“…Nevertheless, those peaks are clearly asymmetric, ruling out a simple cubic symmetry, as also corroborated by the Raman spectra in Fig. 2 [8]. Similarly, for KNLF x=0.16, a secondary tetragonal phase is also present, which appears to be in broad agreement with the work by Kakimoto and co-workers [9].…”

Crystal Structure, Phase Transitions and Photoferroelectric Properties of KNbO3-Based Lead-Free Ferroelectric Ceramics: A Brief Review

“…In 2003, Kakimoto et al (2005) investigated the (1-x)KNbO 3 -xLaFeO 3 system and found the crystal symmetry to change from orthorhombic to tetragonal at x = 0.02 and to cubic at x = 0.20. In 2015, Lennox et al (2015) investigated the (1-x)KNbO 3 -xBiFeO 3 system and found a Orthorhombic (Amm2) → Tetragonal (P4mm) → Rhombohedral (R3c) series of structural phase transitions, as shown in Figure 7D, similar to that exhibited by the PbZrO 3 -PbTiO 3 solid solution. In this system, the orthorhombic symmetry is maintained at least up to 20% mol BiFeO 3 as inferred from neutron diffraction data (Lennox et al, 2015).…”

“…In 2015, Lennox et al (2015) investigated the (1-x)KNbO 3 -xBiFeO 3 system and found a Orthorhombic (Amm2) → Tetragonal (P4mm) → Rhombohedral (R3c) series of structural phase transitions, as shown in Figure 7D, similar to that exhibited by the PbZrO 3 -PbTiO 3 solid solution. In this system, the orthorhombic symmetry is maintained at least up to 20% mol BiFeO 3 as inferred from neutron diffraction data (Lennox et al, 2015). KN crystals exhibit unusual large mechanical coupling factors, k t , which presents a maximum value of 0.69 at 40.51 • away from the polar axis.…”