Fig. 1: Optical detection of the 90°-domain twinning in crystalline striped ferroelectric and ferroelastic domains in the RPPs with n > 1.

a Schematic illustration of angle-resolved polarized optical microscopy setup for measurement on domains. b A visual representation of color intensity contrast between adjacent ferroelectric domain A and B in n = 2 Br-RPP relative to the polarized light angle. c A visual representation of color intensity contrast between adjacent ferroelastic domain A and B in n = 2 I-RPP relative to the polarized light angle. d The plot of contrast intensity change (IA - IB) between adjacent ferroelectric domains as a function of polarized angle from 0° to 360°. e The plot of contrast intensity change (IA - IB) between adjacent ferroelastic domains as a function of polarized angle from 0° to 360°. f, Two types of configurations for 90°-domain wall separation within striped ferroelectric or ferroelastic domains.