Mesoscopic-scale transformation processes in Bi-based perovskite-type ferroelectric solid solutions
Experimental Condensed Matter Physics
Final Report Abstract
The goal of project was to explore the mesoscopicscale aspects of the mechanism of formation of polar order in Bi-based solid solutions with morphotropic phase boundary (MPB) and its dependence on the degree and type of doping. For this purpose a pair-distribution-function analysis along with reverse Monte-Carlo modeling as well as Raman spectroscopy was applied to (1-x)PbTiO3-xBiB’0.5B”0.5O3 (PTxBB’B”) with B’0,5B”0.5=Mg0.5Ti0.5, Ni0.5Ti0.5, Ni0.5Zr0.5 and (1-x)Na0.5Bi0.5TiO3-xBaTiO3 (NBTxBT) with x < 0.1. The compositional dependence of the intermediate-range atomic structure and dynamics at room temperature revealed the key role of three main factors for the enhanced piezoelectric response at the MPB of both PT-xBB’B” and NBT-xBT: (i) suppressed anisotropy in the local potentials at both A and B sites; (ii) high degree of orientation disorder, consisting in a reduction of the correlation length of the local dipoles within the same cationic sublattice; (iii) dynamical synchronization of adjacent A-site and B-site dipoles. The in situ studies of the temperature-driven transformation processes of PT-xBB’B” revealed that: (i) the room-temperature structure of PT-based solid solutions at the MPB is a chemically-stabilized analogue of the high-temperature state of PT, which comprises local ferroic distortions; (ii) the incorporation of BB’B” into the PT host matrix introduces a new energetic state of the A-site cations and strongly enhances the order-disorder phenomena above and across TC; (iii) The MPB is distinct by the unchanged correlation length among coherent off-centred displacements of the A-site cations at TC and competing local-scale polar and antiferodistortive orders related to the B-site sublattice below TC, i.e. the paraelectric-ferroelectric phase transition at the MPB does not involve any dynamical instability driven by a soft mode but it should be a result of thermodynamic instability in a heavily inhomogeneous system comprising competing types of ferroic distortions and a high level of orientation disorder. The in situ studies of NBT-xBT single crystals at different temperatures and electric fields E showed that: (i) the formation of ferroelectric state on cooling is a pure manifestation of increasing correlation length among coupled local polar shifts; (ii) the structural state between the paraelectric and ferroelectric zones in the x-T diagram is weak ferrielectric in nature; (iii) the enhanced longitudinal piezoelectric coefficient in alkali-Bi based solid solutions with a pseudocubic structure near MPB is related to the composition-driven reduction of the local strains and the consequent enhancement of the structural flexibility under external stimuli.
Publications
- (2018): Multistep coupling of preexisting local ferroic distortions in PbTiO3 above the Curie temperature, J. Phys.: Condens. Matter, 30, 435401/1-8
Margaritescu, I., Datta, K., Mihailova, B.
(See online at https://doi.org/10.1088/1361-648X/aae344) - (2018): Stochastic polarization instability in PbTiO3. Phys. Rev. Lett., 121, 137602/1-6
Datta, K., Margaritescu, I., Keen, D.A., Mihailova, B.
(See online at https://doi.org/10.1103/PhysRevLett.121.137602) - (2019): Local-scale structural response of (1- x)Na0.5Bi0.5TiO3-xBaTiO3 to external electric fields, Appl. Phys. Lett., 114, 042901/1-5
la Flor, G., Gorfman, S., Mihailova, B.
(See online at https://doi.org/10.1063/1.5070118) - (2020): Distinct temperature behavior of the local structure of (1-x)PbTiO3-xBiNi0.5Ti0.5O3 at the morphotropic phase boundary, J. Raman Spectrosc., 1-10
Margaritescu, I., Datta, K., Chen, J., Mihalova, B.
(See online at https://doi.org/10.1002/jrs.5885)
