Operando single crystal neutron diffraction reveals insight into the field response mechanisms in the hydrogen-bonded KH2PO4 ferroelectric

C M Fancher,L L Daemen,A J Schultz,C M Hoffmann,X P Wang

doi:10.1063/5.0035866

Abstract

The mechanism that facilitates polarization reorientation in KH2PO4 (KDP) was investigated using operando single-crystal neutron diffraction. Diffraction data were measured from a KDP single crystal during the application of alternating electric fields and were then binned into 40 increments to enable field-dependent single-crystal structure refinements. The field-dependent structures are compared with an as-grown crystal to determine how the lattice and atomic sites evolve in response to the applied electric fields. These analyses provide evidence that the reorientation of the macroscopic polarization is facilitated through a cooperative change in hydrogen bonding, which results in the reversal of the spontaneous dipole. In addition, a decrease in secondary extinction near the coercive field indicates that the inversion of the macroscopic polarization is achieved through the nucleation and subsequent growth of new domains.

Highlights

Since the initial discovery of ferroelectricity in Rochelle salt,1 researchers have leveraged the functional properties of electroactive materials, e.g., dielectric, pyroelectric, electrocaloric, piezoelectric, and ferroelectric, to enable device miniaturization.2 BaTiO3 and PbZrxTi1-xO3 based ceramics have become the dominant piezoelectric materials used in applications
The crystallographic refinement of data measured at 95 K without the application of electric fields is summarized in Tables I and II
Beyond KDP or hydrogen-bonded ferroelectric materials, the present study shows promise for studying the electric-field dependent crystallography of electroactive materials, in particular materials that are prone to degradation when subjected to ionizing radiation

Summary

INTRODUCTION

Since the initial discovery of ferroelectricity in Rochelle salt, researchers have leveraged the functional properties of electroactive materials, e.g., dielectric, pyroelectric, electrocaloric, piezoelectric, and ferroelectric, to enable device miniaturization. BaTiO3 and PbZrxTi1-xO3 based ceramics have become the dominant piezoelectric materials used in applications. Enabling efficient and reliable applications that utilize Hbonded ferroelectric materials requires insight into the underlying mechanisms for inverting the polarization in these systems and how H-bonded materials respond to an applied external stimulus in operando conditions. Measured diffraction data were binned into specific segments related to the driving stimulus to enable a full structural analysis to determine field-dependent crystallographic information (lattice parameters, atomic coordinates, and displacement parameters). These data provide evidence that polarization reversal in KDP is mediated through a cooperative interchange of domains with opposite spontaneous polarization directions by a rotation of the PO4 cage

Sample preparation

Single crystal diffraction

Structure refinement

As-grown crystal

Operando Analysis

CONCLUSIONS