Progress Towards Ferroelectric Thin Films from Host-Guest Dielectric Materials of Hexagonal Tris (o-phenylenedioxy) cyclotriphosphazene Host and Polar Guest Molecules

We will report on thin films of host-guest organic inclusion compounds using a hexagonal Tris (o-phenylenedioxy) cyclotriphosphoazene (TPP) host and included molecular dipoles. The goal is a ferroelectric phase driven by dipole-dipole interactions. We need dipole-dipole interaction energies which exceed k_BT as well as small rotational barriers. We have grown films of TPP with xylenes (xylene@TPP) and pyridazine (pyridazine@TPP) as inclusion compounds and are investigating more complicated pyridazine-based molecules in inclusion compounds with TPP. X-ray diffraction on films of xylene@TPP and pyridazine@TPP show hexagonal structure, to have a preferred (0001) orientation normal to the substrate, and hexagonal in-plane lattice spacing of about 11.6Å and c-axis spacing of about 9.9Å, consistent with x-ray powder patterns of similar inclusions. Optical ellipsometry has shown the films to be flat with an optical index of 1.5-1.6. Films co-deposited on interdigital capacitors allow us to measure dielectric properties of the dipole system. Dielectric spectroscopy suggests a dielectric constant at 300K of 3 for monoclinic TPP, and 6-7 for xylenes@TPP and pyridazine@TPP. Dielectric loss peaks are observed near 100K for these simple inclusion compounds.