We report the characteristic domain wall (DW) patterns observed in rare-metal-free plastic/ferroelectric films of $\left[\mathrm{MDABCO}\right]\left[{\mathrm{PF}}_6\right]$, where ${\left[\mathrm{MDABCO}\right]}^{+}$ is a cage-like molecular ion with a protrusion. In its paraelectric plastic phase, $\left[\mathrm{MDABCO}\right]\left[{\mathrm{PF}}_6\right]$ adopts a cubic lattice. However, in the ferroelectric phase, the lattice undergoes significant distortion into a right prism (pseudocube) with a kite-shaped quadrilateral base. This distortion results from the alignment of the ${\left[\mathrm{MDABCO}\right]}^{+}$ protrusions parallel to the base planes of the prism lattice, with spontaneous polarization along the $\langle 110\rangle$ direction of the pseudocubic $\left(pc\right)$ lattice. This leads to multiaxial ferroelectricity with six possible polarization directions. We demonstrate that two distinct types of thin films, each with unique crystal orientations, can be fabricated depending on the film growth method, resulting in different DW patterns. Films grown from a confined solution layer between top and bottom substrates exhibit the pseudocubic ${\left\{100\right\}}_{pc}$ plane nearly parallel to the substrate, producing a DW pattern corresponding to two possible in-plane polarization orientations. In contrast, blade-coated films show the diagonal ${\left\{110\right\}}_{pc}$ plane of the pseudocubic lattice aligned parallel to the substrate surface. These films predominantly feature polarized domains with in-plane polarization components, while thin, streak-like domains with out-of-plane polarization components intersect at a consistent angle of approximately 54°. Furthermore, blade-coated films allow for polarization switching across the entire film surface, generating out-of-plane polarization components. These findings advance our understanding of polarization domain control in plastic/ferroelectrics and highlight their potential for use in printable ferroelectric-based devices.

Close

PrevNext

View figure in article

• Electric polarization
• Electrical properties
• Ferroelectricity