Local structural mechanism for phase transition and ferroelectric polarization in the mixed oxide K0.5Na0.5NbO3

J. Kong, J. Liu, F. Marlton, M. R.V. Jørgensen, A. Pramanick

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13 Scopus citations

Abstract

(KxNa1-x)NbO3 (KNN) and its solid solutions are considered as potential alternatives to traditional Pb-based piezoelectric materials. Recent investigations indicated that the local structure in KNN is much more complex than its long-range average structure. Here, we have undertaken a systematic investigation of the temperature-dependent evolution of local and average structures of KNN5 [(KxNa1-x)NbO3,x=0.5] using time of flight neutron scattering. Rietveld analysis of neutron diffraction patterns indicated that the average structure of KNN5 changes from monoclinic to tetragonal to cubic upon heating from 100 to 773 K. In contrast, analysis of neutron pair distribution function (PDF) indicated that the local structure stays monoclinic within the above temperature range. Based on comparative analysis of local and average structures, it is proposed that the average structural phase transitions in KNN5 are partly derived from a local ordering of the polar units, which are correlated over a length of 10 15 Å. A clear indication of order-disorder type transition at 473 K is evident from the temperature-dependent PDF patterns. Additionally, based on local structural analysis, it is shown that large electrical polarization in KNN5 can be attributed to displacements of both A-site and B-site atoms. These structural insights may help in further optimization of electrical properties of Pb-free KNN piezoceramics.

Original languageEnglish
Article number184104
JournalPhysical Review B
Volume103
Issue number18
DOIs
StatePublished - May 11 2021

Funding

Funding support from CityU (Projects No. 7005121 and No. 6000688) and Research Grants Council of HK (Project No. 9043039) are gratefully acknowledged. F.M and M.R.V.J. thank the Danish Agency for Science, Technology, and Innovation for funding the instrument center DanScatt. Affiliation with the Center for Integrated Materials Research (iMAT) at Aarhus University is gratefully acknowledged. J.K. and F.M. gratefully acknowledge Michelle Everett for assisting with measurements at the NOMAD instrument. Research conducted at the NOMAD beamlines at ORNL's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Sciences, U.S. Department of Energy.

FundersFunder number
Office of Basic Sciences
Research Grants Council of HK9043039
Scientific User Facilities Division
U.S. Department of Energy
City University of Hong Kong6000688, 7005121
Danish Agency for Science and Higher Education

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