Damping and Resonance Correlations in OH···O Bonded Ferroelectrics

The prototypic ferroelectric KH 2 PO 4 (KDP) and most other OH···O bonded ferroelectric crystals transform to paraelectric phase above the critical temperature ( T c ), which decreases at high pressure. The negative ∂ T c /∂ p in KDP and in antiferroelectric squaric acid (C 4 H 2 O 4, H 2 SQ) is generally connected to the compressed O···O distance. The ferroelectric croconic acid (C 5 H 2 O 5 ) does not transform to the paraelectric phase until it decomposes at 450 K, and our high-pressure X-ray diffraction structural and Raman spectroscopy studies have not detected the paraelectric phase up to 5.3 GPa, either. This striking behavior of croconic acid can be explained by somewhat longer OH···O bonds as well as by the damping correlations of H-sites with atomic displacements in the structure, preventing the H-dynamics in hydrogen bonds. This structure–property relation combines the features of supramolecular aggregation and ferroelectric ordering in OH···O and NH···N bonded chemical compounds and reveals new structural factors significant in the search for new functional materials.