Ramamoorthy Boomishankar

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.

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.

Organic–inorganic hybrid halides offer a versatile platform for programmable multimodal functionalities, through structural softness and lattice‐charge coupling, despite the challenge of balancing the competing ferroic order, carrier transport, and thermal stability requirements. We present a composition‐driven lattice engineering strategy in a 1D iodide series based on 1,6‐diaminohexane (HDA), comprising orthorhombic non‐centrosymmetric phases of HDABiI ₅ (HBI) and HDASbI ₅ (HSI) together with a lower‐symmetry non‐centrosymmetric monoclinic phase of HDABi _0.5 Sb _0.5 I ₅ (HBSI) identified by its birefringent response, allowing systematic control of symmetry, lattice dynamics, and coupled transport phenomena. Through variable‐temperature crystallography and ¹ H NMR, multi‐perturbation Raman spectroscopy, scanning probe microscopy, photophysical measurements, and electronic structure calculations, we demonstrate a progression from a rigid Bi‐dominated lattice exhibiting strong piezoelectric and ferroelectric coupling to a softer Sb‐rich framework with enhanced anharmonicity, pyroelectricity, and photonic activity, while HBSI combines efficient thermal robustness and phonon transport. Density functional theory calculations show that Bi/Sb substitution tunes the electronic structure from indirect to direct bandgap, modulates oscillator strength, spontaneous polarization, pressure‐dependent electronic properties, thermoelectric and piezoelectric responses, while preserving low iodine‐vacancy formation energies. A trilayer HBI‐HSI‐HBSI architecture couples piezoelectric, triboelectric, pyroelectric, thermoelectric, ferroelectric, and photonic effects, showing 5.1‐fold synergistic enhancement in current generation through interfacial polarization and multimodal coupling.

A chiral Cu( ii ) complex prepared from a chiral pybox ligand crystallized in a non-centrosymmetric space group and displayed ferroelectric properties.

The development of ferroelectric materials is fundamentally constrained by the stringent requirement for crystallization within polar space groups. Moreover, integrating multiple functionalities, such as ferroelectricity, piezoelectricity, and negative thermal expansion (NTE), into a single‐component organic material remains a significant challenge, despite the demand for sustainable, wearable, high‐precision electronics. In this study, we report a symmetry‐breaking strategy to transform para‐halogenated 3‐oxo‐2‐phenylhydrazineyline indolines from centrosymmetric to polar space groups via controlled oxidation. The novel isostructural oxo‐derivatives exhibit robust ferroelectricity ( P _s and E _c ranging from 1.3 to 6.3 µC .cm ⁻² and 4 to 9.6 kV.cm ⁻¹ , respectively), supported by quantum‐mechanical calculations. Detailed crystal structure analysis reveals the mechanisms governing their polarization and ferroelectric domain switching. Leveraging its superior polarization, the chloro‐analog‐based device demonstrated high‐performance memristive behavior with stable bipolar resistive switching at minimal bias (∼1 V). The piezoelectric nanogenerators demonstrated superior energy‐harvesting capabilities, including rapid charging and high power density (up to 4.23 µW.cm ⁻² ). Additionally, bromo‐ and iodo‐analogs experienced moderate to colossal axial NTE, and all three analogs displayed minimal volumetric expansion. This study represents the first demonstration of single‐component organic materials that unite ferroelectric, piezoelectric, and NTE properties, providing a blueprint for multifunctional, high‐precision micro‐ and nanoelectronics.

Organic ferroelectrics have emerged as a promising class of functional materials owing to their lightweight nature, structural flexibility, low processing temperatures, and environmentally benign composition. In this study, we report the synthesis and comprehensive characterization of guanidinium croconate , a new two‐component organic salt obtained via acid–base neutralization of croconic acid and guanidine. Single‐crystal x‐ray diffraction reveals a polar crystal structure stabilized by an extensive three‐dimensional N─H···O hydrogen‐bonded network that supports long‐range polar order. Macroscopic ferroelectricity is confirmed through polarization–electric field ( P–E ) hysteresis loops and positive‐up‐negative‐down (PUND) measurements, yielding a remnant polarization of 3.5 µC/cm ² . Piezoresponse force microscopy (PFM) demonstrates clear ferroelectric domain structures, reversible 180° phase switching, and a converse piezoelectric coefficient ( d ₃₃ ) of 10–13.5 pm/V. Kurtz–Perry second‐harmonic generation (SHG) measurements show an efficiency of 0.11 relative to KDP at room temperature. Variable‐temperature SHG and differential scanning calorimetry reveal a strongly hysteretic ferroelectric‐to‐paraelectric phase transition at 510 K. Density functional theory calculations indicate a large molecular dipole moment of 12.56 D, arising from enhanced ionic charge separation. These results highlight ionic assembly as an effective strategy for designing hydrogen‐bond‐driven organic ferroelectrics.

Halide substitution provides a compelling yet underexplored route to engineer polar, noncentrosymmetric solids with emergent ferroelectric functionality. Herein, we report a new ammonium-based mixed-halide halogenometallate, [BTMA]2CdBr2I2, that crystallizes in the polar P21 space group and exhibits coupled ferroelectric and piezoelectric responses. The noncentrosymmetric nature of the structure is confirmed by its pronounced second harmonic generation (SHG) activity. Bulk ferroelectricity is evidenced by a well-saturated, rectangular polarization–electric field (P–E) hysteresis loop with a polarization of 4.43 μC cm–2, while piezoresponse force microscopy (PFM) directly visualizes switchable ferroelectric domains, confirming intrinsic polarization at the microscale. Beyond these fundamental properties, we further demonstrate device-level functionality by integrating [BTMA]2CdBr2I2 into flexible thermoplastic polyurethane (TPU) composites. The optimized 10 wt % composite delivers a high piezoelectric nanogenerator output voltage of 15.9 V, a power density of 10.24 μW cm–2, and an output work efficiency (OWE) of 23.7%. These results not only establish mixed halide engineering as a viable strategy to access polar molecular materials but also position halogenometallate-based hybrids as promising candidates for flexible, high-performance energy harvesting technologies.

Metal‐oxide‐based resistive switching (RS) memristors have been extensively investigated, but their practical application is often hindered by complex fabrication processes and high‐power consumption. Metal halide perovskites have emerged as promising alternatives due to their low‐cost fabrication, high defect tolerance, and large I–V hysteresis. Their intrinsic ion migration makes them suitable for resistive switching and artificial synaptic devices. In particular, low‐dimensional hybrid‐halide perovskites (LHPs) have attracted considerable attention because their electronic properties can be tuned by engineering the organic spacer cations. Compared with their three‐dimensional counterparts, they offer improved stability and design flexibility. Moreover, ferroelectric LHPs provide intrinsic nonvolatility beneficial for neuromorphic computing applications. In this perspective, we examine the molecular engineering, synthetic strategies, and operating mechanisms of memristors based on LHPs and their applications in neuromorphic computing. We comparatively analyze the ferroelectric and nonferroelectric variants, highlighting the superior stability and nonvolatility of ferroelectric types versus the faster switching and simpler fabrication of nonferroelectric ones. We provide a systematic four‐stage experimental protocol for unambiguously identifying ferroelectric RS (FeRS) in LHPs, benchmarking key performance parameters and variability challenges for device engineering. We finally conclude with a forward‐looking outlook on materials design, multimodal stimulus response, multiterminal architectures, and hardware security applications.

Amino-phosphate-based ferroelectrics exhibit strong ionic conductivity, biocompatibility, high dielectric constants, and pronounced ferroelectric properties. Considering these attributes, we propose a strategy to enhance ferroelectric performance through angle strain engineering in a six-membered cyclic anionic phosphate ferroelectric, benzylammonium chlorophenyl cyclohexyl-dimethyl-phosphate (BzA• ^ClPh-Cy-DMP), with the chemical formula(BzNH₃).[O₂(cyclo-POC( ClPh)CMe₂CH₂O)]. The compound crystallizes in the monoclinic P2^₁ space group. Its non-centrosymmetric structure was confirmed by second-harmonic generation (SHG) measurements. Ferroelectricity in BzA• ^ClPh-Cy-DMP was validated by a well-defined rectangular P-E hysteresis loop, yielding a saturated polarization (Ps) of 2.95 μC cm^⁻² at an applied field of 9 kV cm^-1. Piezoresponse force microscopy (PFM) analysis visualized the presence of ferroelectric polar domains in BzA• ^ClPh-Cy-DMP. The observed amplitude-bias butterfly curves and phase-bias hysteresis loops provided clear evidence of a reversible polarization switching mechanism. Furthermore, polycaprolactone (PCL) polymer composites of BzA• ^ClPh-Cy-DMP enabled the fabrication of piezoelectric nanogenerators (PENGs) with advanced piezoelectric energyharvesting performance. The top-performing 15 wt% BzA• ^ClPh-Cy-DMP-PCL device achieved a peak output voltage of 23.6 V at an optimized force of 30 N. Furthermore, the device's output work efficiency (OWE) parameter, calculated at room temperature, was found to be 29.0%. Additionally, we present a novel investigation of the effect of temperature on piezoelectric energy harvesting. As temperature increases from 293 K to 315 K, the voltage rises from 23.6 V to 26.3 V, then decreases to 16.9 V at 333 K, with temperature coefficient rates of + 0.15 V K⁻¹ and -0.52 V K⁻¹, respectively. The device exhibits a rapid response time of 22.1 ms, enabling precise periodic mechanical sensing, and demonstrates its potential for wind speed estimation through a prototype piezoelectric-based wind sensor. This work offers a strategic framework for enhancing ferroelectric properties, exploring the effects of temperature on piezoelectric energy harvesting, and advancing the applications of piezoelectric materials.