Structural insights into electric field induced polarization and strain responses in K0.5Na0.5Nb O3 modified morphotropic phase boundary compositions of Na0.5Bi0.5Ti O3 -based lead-free piezoelectrics

Das Adhikary, G and Jafo Muleta, G and Abebe Tina, G and Sharma, D and Mahale, B and Da Silva, LL and Hinterstein, M and Senyshyn, A and Ranjan, R (2023) Structural insights into electric field induced polarization and strain responses in K0.5Na0.5Nb O3 modified morphotropic phase boundary compositions of Na0.5Bi0.5Ti O3 -based lead-free piezoelectrics. In: Physical Review B, 107 (13).

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Abstract

K0.5Na0.5NbO3 (KNN)-modified morphotropic phase boundary (MPB) compositions of the two Na0.5Bi0.5TiO3-based lead-free piezoelectrics, namely, 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-6BT) and 0.80Na0.5Bi0.5TiO3-0.20K0.5Bi0.5TiO3 (NBT-20KBT) are model systems exhibiting large (>0.4%) electric-field-driven strain. There is a general perception that (i) increasing KNN concentration monotonically weakens the direct piezoelectric response (d33), and (ii) maximum electrostrain occurs when KNN pushes the system in the fully ergodic relaxor state. We have examined these issues using various complementary techniques involving electrostrain, piezoelectric coefficient (d33), ferroelectric switching-current measurements, and field-driven structural studies on the global and local scales using laboratory and synchrotron x-ray diffraction, neutron powder diffraction, and Eu+3 photoluminescence techniques. Our investigations revealed the following important features: (i) In the low-concentration regime, KNN induces a tetragonal ferroelectric distortion, which improves the weak signal piezoresponse. (ii) Beyond a threshold concentration, in-phase octahedral tilt sets in and weakens the long-range ferroelectric order to partially stabilize an ergodic state. (iii) The maximum electrostrain (∼0.6%) is achieved in the mixed (nonergodic + ergodic) state. (iv) The mixed state invariably exhibits a less-known phenomenon of field-driven ferroelectric-to-relaxor transformation during bipolar field cycling. (v) The enhanced electrostrain in the mixed state is associated with the electric field increasing the correlation lengths of the short-ranged tetragonal and rhombohedral ferroelectric regions without overall transformation of one phase to the other. We summarize the findings of this work in a comprehensive electric field composition (E-x) phase diagram. The findings reported here are likely to be true for other NBT-based MPB systems.

Item Type:	Journal Article
Publication:	Physical Review B
Publisher:	American Physical Society
Additional Information:	The copyright for this article belongs to American Physical Society.
Keywords:	Ferroelectric materials; Ferroelectricity; Phase diagrams; Piezoelectricity; Polarization; Ternary alloys, Electric field induced; Electrostrain; Ergodics; Induced polarization; Induced strain; Lead-free piezoelectrics; Mixed state; Morphotropic phase boundaries; Phase boundary composition; Structural insights, Barium titanate
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	15 Jun 2023 08:00
Last Modified:	15 Jun 2023 08:00
URI:	https://eprints.iisc.ac.in/id/eprint/81961

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