Aminophosphonium Dihydrogen Phosphate: A Structurally Modified KDP Analogue With Room‐Temperature Ferro‐ and Piezoelectric Properties

Potassium dihydrogen phosphate is well‐known to exhibit ferroelectricity, while ammonium dihydrogen phosphate is an antiferroelectric material, with both of them exhibiting a phase transition to paraelectric phase below room temperature. In this work, we report the synthesis and room‐temperature ferroelectric behavior of an aminophosphonium dihydrogen phosphate of formula, [{P(NHPh) 4 (H 2 PO 4 )·(CH 3 OH) 0.5 ] ( TAPDP·(CH 3 OH) 0.5 ) that exhibits a three‐dimensional pillared‐layered hydrogen bonding network. (TAPDP·(CH 3 OH) 0.5 crystallizes in the polar monoclinic P 2 1 space group, and its non‐centrosymmetric structure was confirmed by second‐harmonic generation (SHG) measurements. The ferroelectric behavior was further verified through polarization–electric field ( P–E ) loop measurements, with a saturation polarization of 21.40 µC cm −2 . Structural analysis combined with preliminary density functional theory calculations indicates a ferrielectric‐type ordering in which the adjacent layers exhibit different polarization directions but with unequal dipole moments. Furthermore, the electromechanical energy‐harvesting properties of TAPDP·(CH 3 OH) 0 . 5 were explored in its composites with the polydimethylsiloxane (PDMS) polymer. The 10 wt% TAPDP·(CH 3 OH) 0 . 5 – PDMS device exhibited a maximum peak‐to‐peak open‐circuit voltage (𝑉 oc ) of 10.69 ± 0.04 V and the output work efficiency parameter (OWE) of 9.63%. Owing to the superior signal sensitivity of this device, a contact‐type sensor was developed to measure a motor's revolutions per minute (RPM) at both low and high speeds.