Structural, conductivity and DFT studies of L-Histidinium phosphite – Ferroelectric phosphite single crystal

Highlights: • L-HPI serves as a good NLO active material at room temperature. • Histidine forms a cis-position in HPI crystal with carbonyl group. • Ferroelectric to paraelectric transition takes place at 270K. • Energy gap of L-HPI is about 0.61eV. • Non-Debye relaxation process is attested from the modulus plot. L-Histidinium phosphite [C₆N₃O₂H₁₀]⁺. [HPO₃H]^- abbreviated as HPI, is a semi-organic nonlinear optical material. In the present work HPI crystals were grown from the aqueous solution of HPI by slow evaporation technique. Single crystal XRD (SXRD) reveals that the resulting crystals predominantly exhibit monoclinic structure with space group P2₁^. Sharp and well-defined peaks of the powder XRD pattern attested the good crystallinity of HPI and the pattern is in agreement with SXRD results. The different modes of vibrations of molecular groups and functional groups present in the HPI crystal was investigated using IR spectra. It is evident from the UV–Vis spectrum that HPI is transparent in the examined frequency regime. The TG-DTA studies ascertain that the crystal is thermal stable till 230°C. A.C. and D.C. conduction mechanism in the grown crystals were studied from 119K to 380K for 1kHz to 1MHz frequency range. The pattern suggests that there is ferroelectric to paraelectric transition at 270K. This transition temperature is higher than the glycine phosphite crystals. Detailed insight about the conduction mechanism in HPI crystals was analyzed by complex impedance and modulus studies. Density functional theory was applied to know in detail about the structure and non-linear optical characteristics of the grown crystal and it attested that HPI is NLO active at room temperature.