Direct Determination of Pyroelectric Coefficients in Molecular Crystals by X-ray Quantum Crystallography

Organic molecular crystals with piezoelectric and pyroelectric responses are emerging as soft, biocompatible materials for next-generation energy harvesting. However, quantifying crystal polarity in such materials—and its variations under mechanical or thermal stimuli—on a structural basis remains challenging. Here, we estimate pyroelectric coefficients directly from high-resolution X-ray quantum crystallography (QCr) via accurate modelling of hydrogen positions and electron densities. QCr modelling of a series of piezoelectric crystals reveals in-crystal molecular dipole moments (μ) and spontaneous polarization (P S ) at variable temperatures (~100 and ~298 K) with pronounced crystal-field effects, including enhanced μ relative to isolated molecules and elevated P S . Temperature-dependent variations in P S (∆P S /∆T) predict pyroelectric behaviour, corroborated by variable-temperature voltage-output measurements in γ-glycine. The pyroelectric coefficients (p) and P S values thus estimated agree well with experimental measurements. The results demonstrate QCr as a powerful route to elucidating the molecular and electronic level origins of pyroelectric phenomena in crystalline materials, with potential extension to piezoelectric and ferroelectric properties.