Title: Piezoelectric polar nanoregions and relaxation-coupled resonances in relaxor ferroelectrics

Abstract

It is a generally accepted fact that the unique dielectric properties of relaxor ferroelectrics are related to the formation of polar nanoregion (PNRs). Less well recognized is the corollary that, because they are polar and therefore lack inversion symmetry, PNRs are also piezoelectric at the nanoscale and can therefore behave as nanoresonators. Using the particular relaxor ferroelectric K_1–xLi_xTaO₃ (KLT), we show that, when electrically excited into oscillation, these piezoelectric nanoresonators can drive macroscopic electromechanical resonances. Unexpectedly, however, pairs of coupled resonances corresponding to a particular type of oscillation are observed, with one of the resonance exhibiting a characteristic Fano-like line shape. The complex resonance spectra can be described equally well by two alternative but complementary models both involving two resonances coupled through a relaxation: a purely classical one based on two coupled damped harmonic oscillators and a semiclassical based on two discrete excitations coupled to each other through a continuum. Together, they provide complementary perspectives on the underlying physics of the system. Both reproduce the rapid evolution of the resonance spectrum across three wide temperature ranges, including a phase transition range. In the high-temperature range, the coupling between modes is due to the collective π relaxation of the lithium ionsmore » within PNRs and, in the phase transition range, to “heterophase relaxation” of the surrounding lattice between its high-temperature cubic and low-temperature tetragonal phases, both coherent effects. Here, the coupling is suppressed in the intermediate range of the collective π/2 relaxation of the lithium ions. Incidentally, the measured dielectric spectra are shown to bear a surprising but justifiable resemblance to the optical spectra of certain atomic vapors exhibiting electromagnetically induced transparency.« less

Authors:

Cai, Ling ^[1]; Pattnaik, Radha ^[1]; Lundeen, Joel ^[1]; Toulouse, Jean ^[1]

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+ Show Author Affiliations

1. Lehigh Univ., Bethlehem, PA (United States)

Publication Date:

Thu Oct 25 00:00:00 EDT 2018

Research Org.:

Lehigh Univ., Bethlehem, PA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1609755

Alternate Identifier(s):

OSTI ID: 1479135

Grant/Contract Number:  

FG02-06ER46318

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review B

Additional Journal Information:

Journal Volume: 98; Journal Issue: 13; Journal ID: ISSN 2469-9950

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; materials science; physics; dielectric properties; ferroelectricity; phase transitions; piezoelectricity; relaxor ferroelectrics; single crystal materials