Strain-Gradient-Controlled Disorder Dynamics in Chemically Substituted Ferroelectrics

Correlated disorder, a type of crystallographic state, widely exists in complex material systems and is beneficial for the improvement of material properties. The strain gradient del S, caused by structural heterogeneity, controls the features of correlated disorder. However, the exact mechanism whereby del S controls the disorder dynamics, especially in bulk materials, is still largely unknown, hindering property optimization. We design and achieve a macroscopic del S in the KTa1-X NbXO3 (KTN) single crystal by the coupling effect of the Nb-composition gradient del X and 180 degrees domains near the Curie temperature T-C. The electricfield dependences of the electro-optic (EO) effect are investigated to reveal the del S-controlled disorder dynamics. The EO characteristics indicate that the flexoelectric field E-flexo caused by del S is sufficiently strong to control the local correlated dipoles. Further, it is demonstrated by dielectric, Raman, and absorption spectroscopies that the del S in the KTN sample plays a dominant role in the disorder dynamics. At the nanoscale, the large local del S, approximately 10(-3)-10(-2) nm(-1) in magnitude, caused by random substitutions of B cations, can determine the local structure and dynamics, deeply influencing the properties of materials. This work reveals how del S acts on the disorder dynamics and local dipole behaviors, which provides the basis for the understanding and harnessing of disordered ferroelectrics.