Depoling phenomena in Na0.5Bi0.5TiO3-BaTiO3: A structural perspective

Das Adhikary, G and Mahale, B and Rao, BN and Senyshyn, A and Ranjan, R (2021) Depoling phenomena in Na0.5Bi0.5TiO3-BaTiO3: A structural perspective. In: Physical Review B, 103 (18).

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Abstract

The structural complexities of the lead-free piezoelectric system (1-x)Na0.5Bi0.5TiO3-xBaTiO3 (NBT-BT) continues to pose challenge regarding understanding the mechanisms underlying several interesting phenomena. Issues like (i) whether thermal depoling across compositions is triggered by a structural transformation event or not, (ii) what causes the average Cc structure to partially transform to R3c at x0.03 in unpoled specimens, (iii) what makes complete depoling of the compositions 0.03�x�0.05 occur in a considerably small temperature interval as compared to those for x<0.03, (iv) what makes the R3c-P4bm transition temperature (T2) abruptly become smaller than the depolarization temperature (Td) at x=0.06, etc., have remain unresolved. Here, we offer structural insights on these issues by carrying out a detailed investigation using a set of complementary tools involving temperature-dependent X-ray powder diffraction, neutron powder diffraction, dielectric, ferroelectric, piezoelectric, and thermally induced depoling current measurements. We show that onset of thermal depoling in NBT (x=0) well below its depolarization temperature is caused by abrupt reduction of intrinsic polarization in the ferroelectric R3c phase, triggered by the appearance of the P4bm phase. Our study suggests that partial conversion of the Cc average structure to R3c in unpoled NBT-BT at x0.03 (more precisely in the range 0.03�x�0.05) is catalyzed by the appearance of P4bm phase. The overlap of Td and T2 for this composition range is correlated with the collapse of the tetragonality of the P4bm phase and significantly reduced kinetic barrier associated with the R3c�P4bm transformation. We show that the abrupt crossover between Td and T2 at x=0.06 is due to takeover of the thermal depoling process by an emergent tetragonal (P4mm)-like ferroelectric distortion. We present updated phase diagrams of poled and unpoled specimens which highlight all the subtle details needed to explain the temperature-dependent properties of this complex piezoelectric alloy system. © 2021 American Physical Society.

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:	Barium titanate; Depolarization; Diffraction; Ferroelectricity; Piezoelectricity; X ray powder diffraction, Depolarization temperature; Ferroelectric distortion; Lead-free piezoelectrics; Structural complexity; Structural transformation; Temperature dependent; Temperature intervals; Temperature-dependent properties, Ferroelectric materials
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	18 Aug 2021 05:48
Last Modified:	18 Aug 2021 05:48
URI:	http://eprints.iisc.ac.in/id/eprint/69170

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