Ferroelectricity Driven by Orbital Resonance of Protons in CH3NH3Cl and CH3NH3Br

The β and γ phases of methylammonium chloride CH3NH3Cl and methylammonium bromide CH3NH3Br are identified to be ferroelectric via pyroelectric current and dielectric constant measurements. The magnetic susceptibility also exhibits...

Pyroelectric Nanogenerator Based on an SbSI–TiO2 Nanocomposite

For the first time, a composite of ferroelectric antimony sulfoiodide (SbSI) nanowires and non-ferroelectric titanium dioxide (TiO2) nanoparticles was applied as a pyroelectric nanogenerator. SbSI nanowires were fabricated under ultrasonic treatment. Sonochemical synthesis was performed in the presence of TiO2 nanoparticles. The mean lateral dimension da = 68(2) nm and the length La = 2.52(7) µm of the SbSI nanowires were determined. TiO2 nanoparticles served as binders in the synthesized nanocomposite, which allowed for the preparation of dense films via the simple drop-casting method. The SbSI–TiO2 nanocomposite film was sandwiched between gold and indium tin oxide (ITO) electrodes. The Curie temperature of TC = 294(2) K was evaluated and confirmed to be consistent with the data reported in the literature for ferroelectric SbSI. The SbSI–TiO2 device was subjected to periodic thermal fluctuations. The measured pyroelectric signals were highly correlated with the temperature change waveforms. The magnitude of the pyroelectric current was found to be a linear function of the temperature change rate. The high value of the pyroelectric coefficient p = 264(7) nC/(cm2·K) was determined for the SbSI–TiO2 nanocomposite. When the rate of temperature change was equal dT/dt = 62.5 mK/s, the maximum and average surface power densities of the SbSI–TiO2 nanogenerator reached 8.39(2) and 2.57(2) µW/m2, respectively.

Manipulating electron redistribution to achieve electronic pyroelectricity in molecular [FeCo] crystals

Pyroelectricity plays a crucial role in modern sensors and energy conversion devices. However, obtaining materials with large and nearly constant pyroelectric coefficients over a wide temperature range for practical uses remains a formidable challenge. Attempting to discover a solution to this obstacle, we combined molecular design of labile electronic structure with the crystal engineering of the molecular orientation in lattice. This combination results in electronic pyroelectricity of purely molecular origin. Here, we report a polar crystal of an [FeCo] dinuclear complex exhibiting a peculiar pyroelectric behavior (a substantial sharp pyroelectric current peak and an unusual continuous pyroelectric current at higher temperatures) which is caused by a combination of Fe spin crossover (SCO) and electron transfer between the high-spin Fe ion and redox-active ligand, namely valence tautomerism (VT). As a result, temperature dependence of the pyroelectric behavior reported here is opposite from conventional ferroelectrics and originates from a transition between three distinct electronic structures. The obtained pyroelectric coefficient is comparable to that of polyvinylidene difluoride at room temperature.

Manipulating electron redistribution to achieve exotic electronic pyroelectricity in dynamic [FeCo] crystals

Pyroelectricity plays a crucial role in modern sensors and energy conversion devices. However, obtaining materials with large and nearly constant pyroelectric coefficients over a wide temperature range for the practical uses remains a formidable challenge, because in conventional ferroelectric materials the pyroelectric effect promptly declines upon cooling from the transition temperature. Attempting to discover a solution to this obstacle, we combined molecular design of labile electronic structure with the crystal engineering of the molecular orientation in lattice resulting in the electronic pyroelectricity of purely molecular origin. Here, we report a polar crystal of an [FeCo] dinuclear complex exhibiting a peculiar pyroelectric behavior (a substantial sharp pyroelectric current peak and an unusual continuous pyroelectric current at higher temperatures) which is caused by a combination of Fe spin transition and redistribution of electron density between redox isomers of high-spin Fe through a charge transfer between the Fe atom and redox active ligand. As a result, temperature dependence of the pyroelectric behavior reported here is opposite and originates from the interconversion between three distinct electronic states. The obtained pyroelectric coefficient is comparable to that of polyvinylidene difluoride at room temperature.

Electro-Optical Properties of Sputtered Calcium Lead Titanate Thin Films for Pyroelectric Detection

We report the deposition and characterization of calcium lead titanate (PCT) thin films for pyroelectric detectors. PCT films of thicknesses ranging from ~250 to 400 nm were deposited on both silicon and Si/SiN/Ti/Au substrates at 13 mTorr pressure by 200W radio frequency sputtering in an Ar + O2 environment. Substrates were kept at variable temperatures during the deposition. The PCT films were annealed at various temperatures in an O2 environment for 15 min. X-ray diffraction results confirm the polycrystalline nature of these films. Energy dispersive spectroscopy function of scanning electron microscope showed that the films are stoichiometric (Ca0.43Pb0.57) TiO3 (Ca/Ti = 0.5, Pb/Ti = 0.66). Temperature dependence of capacitance, pyroelectric current, and pyroelectric coefficient was investigated for different PCT films. Our results show that films deposited at 550 °C and 600 °C demonstrate better quality and larger values of the pyroelectric coefficient. On the other hand, the capacitance fabricated on the PCT films at 550 °C showed the highest value of pyroelectric current and pyroelectric coefficient which were 14 pA and at 30 °C was ~2 µC/m2K respectively at a higher temperature. In addition, we used density functional theory to determine the atomic and band structure, real and imaginary parts of dielectric constant and refractive index, and absorption and reflection constants with energy.

Simulation of Nonlinear Pyroelectric Response of Ferroelectrics near Phase Transition: Fractional Differential Approach

The paper is devoted to mathematical modeling pyroelectric current of ferroelectric single crystal under the conditions of intensive light heating in view of fractal behavior of these materials. The proposed approach is based on numerical simulation of thermal distribution in a ferroelectric sample using time fractional operator as well as computation of pyroelectric response. The simulation results for typical TGS ferroelectric crystal were described in one-dimensional case of the model in comparison with experimental data. Pyroelectric signals depending on temperature pyroelectric coefficient and thermal physical characteristics were also analyzed.

Pyroelectricity and field-induced spin-flop in (4-(Aminomethyl)pyridinium) 2 MnCl 4 · 2H 2 O

Large single crystals of (4-(Aminomethyl)pyridinium) 2 MnCl 4 · 2H 2 O ( 1 ) were grown by slow evaporation of solution. The crystal structure was solved to be Pī, which belongs to the central symmetric space group. But small pyroelectric current was detected, as well as a ferroelectric hysteresis loop. The pyroelectric and the ferroelectric properties were attributed to the strain caused by defects. Temperature-dependent magnetic curves and the M – H curve show that 1 is antiferromagnetic ordering below 2.5 K. A field-induced spin-flop is observed in the antiferromagnetic ordering state.

Особенности пироэффекта в эпитаксиальных слоях нитрида алюминия, полученных на Si-подложках

The pyroeffect was studied in quasi-bulk AlN layers with a thickness of 10-170 μm obtained by the technology of chloride-hydride vapor phase epitaxy on standard Si sub-strates. The pyroelectric current was measured by the method of thermal exposure to non-stationary (me-ander type) laser radiation, that together with the data of independent non-contact measure-ment of the active layer surface temperature dynamics made it possible to determine the value of the pyroelectric coefficient AlN in the composition of the bimorph AlN / Si structure for different thicknesses of AlN layers. It was found that the mean values are less than those that correspond to the material obtained by the same technology, but on SiC substrates; so, in or-der to achieve the pyrocoefficients of comparable magnitude with those in the case of “AlN on Si”, an increase in the thickness of AlN layers by 60 -70% is re-quired. At the same time, when the thickness of the AlN layer is large (110 μm, 170 μm) after the removal of the silicon substrate, the pyroelectric coefficient increased and reached ~8.6-9.0μC/(m2·K).