A Polar Magnetic Tetrachloroferrate Hybrid Crystal Enabling Piezoelectric Energy Harvesting and Nonlinear Optical...

In this work, we report a polar organic-inorganic hybrid single crystal, 2-chloroethyltrimethylammonium tetrachloroferrate (III), [C₅H₁₃ClN][FeCl₄], that distinctly integrates piezoelectric, nonlinear optical, and paramagnetic properties within an ammonium tetrachloroferrate framework. The [C₅H₁₃ClN][FeCl₄] single crystal belongs to the polar non-centrosymmetric space group Cmc2₁. The non-centrosymmetric structure is evidenced by the second harmonic generation (SHG) response. The crystal exhibits a quasi-static piezoelectric charge coefficient (d₃₃) of 4.1 pC N^-1, further supported by local piezoresponse force microscopy (PFM) showing characteristic amplitude butterfly and phase hysteresis loops. The Piezoelectric generator (PEG) fabricated using [C₅H₁₃ClN][FeCl₄] generates an electrical output voltage corresponding to the applied periodic mechanical force, demonstrating the energy-harvesting capability. Magnetic measurements performed using SQUID magnetometry indicate paramagnetic behavior arising from tetrahedrally coordinated high-spin Fe^{3 +} centers. These findings establish that discrete [FeCl₄]^- tetrahedra can be incorporated into a polar ammonium lattice to promote magnetic functionality without disrupting symmetry-dependent piezoelectric and nonlinear optical properties.