Manifestation of strong magneto-electric dipolar coupling in ferromagnetic nanoparticles−FLC composite: evaluation of time-dependent memory effect

Rod-shaped 5 wt.% copper-doped ZnO (ZnO:Cu²⁺) ferromagnetic nanoparticles (NPs), prepared by hydrothermal method, were dispersed in ferroelectric liquid crystal (FLC) named Felix 17/100. The effect of ferromagnetic NPs on the physical properties of FLC material (Felix 17/100) has been investigated by dielectric, electro-optical and polarising optical microscopic methods. A noteworthy time-dependent memory has been observed in the NPs-dispersed FLC composite attributed to the coupling of magnetic field associated to NPs with the director orientation of FLC. Improvement in spontaneous polarisation and dielectric susceptibility of FLC material has been ensued with the addition of ferromagnetic NPs. Faster electro-optic response, at lower applied voltage, has also been observed in NPs-dispersed FLC composite. These changes are accredited to the magneto-electric dipolar coupling existing due to the interactions between magnetic-dipole and electric-dipole moments of magnetic NPs and FLC material, respectively. The formation of periodic domains capable to show memory effect has been observed in composite. The observed time-dependent memory was confirmed by dielectric and electro-optical methods. FLC material enriched with the properties of ferromagnetic NPs can be utilised in advanced multifunctional optical devices, time-dependent memory-based security devices and computational purposes.     

Alloying n‐Butylamine into CsPbBr3 To Give a Two‐Dimensional Bilayered Perovskite Ferroelectric Material

Cesium‐lead halide perovskites (e.g. CsPbBr₃) have gained attention because of their rich physical properties, but their bulk ferroelectricity remains unexplored. Herein, by alloying flexible organic cations into the cubic CsPbBr₃, we design the first cesium‐based two‐dimensional (2D) perovskite ferroelectric material with both inorganic alkali metal and organic cations, (C₄H₉NH₃)₂CsPb₂Br₇ ( 1 ). Strikingly, 1 shows a high Curie temperature (T_c=412 K) above that of BaTiO₃ (ca. 393 K) and notable spontaneous polarization (ca. 4.2 μC cm^?2), triggered by not only the ordering of organic cations but also atomic displacement of inorganic Cs⁺ ions. To our knowledge, such a 2D bilayered Cs⁺‐based metal–halide perovskite ferroelectric material with inorganic and organic cations is unprecedented. 1 also shows photoelectric semiconducting behavior with large “on/off” ratios of photoconductivity (>10³).     

Experimental Evidence for a Triboluminescent Antiperovskite Ferroelectric: Tris(trimethylammonium) catena‐Tri‐μ‐chloro‐manganate(II) Tetrachloromanganate(II)

The perovskite structure is rich in ferroelectricity. In contrast, ferroelectric antiperovskites have been scarcely confirmed experimentally since the discovery of M₃AB‐type antiperovskites in the 1930s. Ferroelectricity is now revealed in an organic–inorganic hybrid X₃AB antiperovskite structure, which exhibits a clear ferroelectric phase transition 6/mmmF6mm with a high Curie point of 480 K. The physical properties across the phase transition are obviously changed along with the symmetry requirements, providing solid experimental evidence for the ferroelectric phase transition. More interestingly, the discovered antiperovskite shows intense photoluminescence and triboluminescence properties. The confirmation of the triboluminescent ferroelectric antiperovskite will open new avenues to explore excellent optoelectronic properties in the antiperovskite family.     

Ferroelectric PZT Thin Films by Sol-Gel Deposition

Sol-gel spin coating has a low thermal budget, is cheap compared to vacuum-based techniques and is now routinely used to produce dense, pore-free ferroelectric films. PbZrx Ti(1 – x)O3 (PZT) is utilized in most applications because it has a large remanent polarization, high piezo- and pyroelectric coefficients and optimized electromechanical coupling factors, depending on precise composition. This paper will review some of the principles and applications of PZT films and highlight using transmission electron microscopy some of the basic problems and solutions involved in producing device-quality material on Si-substrates.     

Lattice models of hydrogen-bonded solvents. II

We consider a lattice model of a binary mixture in which each molecule of one component can form zero, one, or two bonds to molecules of the same species on neighboring vertices of the square lattice. We allow the energy of molecules with two bonds to depend on the valence angle, thus generalizing the first paper in this series. If straight polymeric configurations are favored over all others, then a phase transition occurs for low enough temperature. On the other hand, if bent configurations are favored, there is no phase transition. Analogous results are obtained for the hexagonal lattice, where we distinguish energetically betweencis andtrans isomerism of four bonded molecules.Supported by the Danish Science Foundation under grant 511-3635.     

Supramolecular non-symmetric dimers derived from cholesterol: synthesis and phase transitional properties

Three series of novel dimeric supramolecules, possessing both inter- as well as intramolecular H-bonding, have been prepared and investigated for their thermal properties. They were obtained in excellent yields by condensing cholesteryl ω-(3-hydroxy-4-formylphen-oxy)alkanoates with 4-(n-alkoxy)benzohydrazides, 3,4-bis(n-decyl-oxy)benzohydrazide and 3,4,5-tris(n-decyloxy)benzohydrazide. The influence of increase in the number of terminal n-alkoxy tails from one to three and the length and parity of the flexible spacer on phase transitional behaviour have been thoroughly investigated with the aid of microscopic, calorimetric and X-ray diffraction (XRD) techniques. The results of these complementary studies clearly illustrate the dependence of thermal behaviour of the dimers on these structural factors. The rigid intermolecular association via H-bonds through complementary benzohydrazide component enforce their self-assembly into frustrated and polar smectic phases; H-bond force coupled with the bulkiness of steroid moiety affects the electrical switching property of this fluid polar structure.     

Influence of the remanent polarisation on the liquid crystal alignment in composite films of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and a cyanobiphenyl-based liquid crystal

Polymer-dispersed liquid crystals (PDLCs) of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and nematic 4-cyano-4?-n-hexylbiphenyl (6CB) or 4-cyano-4?-n-pentylbiphenyl (5CB) were prepared to study the effect of the remanent polarisation of the polymer on the liquid crystal alignment. We measured the macroscopic alignment of the liquid crystal molecules in the thickness direction by means of Infrared Transition-Moment Orientational Analysis. Electrical poling at 100 V/µm caused an increased order parameter up to 0.15. After subsequent annealing above the nematic-to-isotropic phase-transition temperature, the order parameter was reduced to 0.02. Nevertheless, the order parameter was still higher than for non-poled film indicating a slight orientation in thickness direction. Both values are lower than those expected from model calculations. In agreement with dielectric measurements, we attribute this result to the shielding effect of mobile charge carriers within the liquid crystal inclusions.     

Lactic acid derivatives with terphenyl molecular core

New lactic acid derivatives, based on terphenyl molecular core laterally substituted by chlorine atom, have been synthesised and their liquid crystalline properties studied. We varied the molecular structure by prolonging the non-chiral chain and analysed the mesogenic properties with respect to its length. We found that all new compounds reveal the SmA*–SmC* phase sequence in an extremely broad temperature interval. The experimental techniques, namely the polarising optical microscopy, differential scanning calorimetry, x-ray diffraction and helical pitch measurements, have been applied to establish the physical properties. Studied compounds exhibit very high values of the spontaneous polarisation and the tilt angle grows continuously on cooling up to 42°. The pitch values drop down when prolonging the molecular non-chiral chain.     

Synthesis and characterizations of BNT–BT–KNN ceramics for energy storage applications

Dielectric, ferroelectric and piezoelectric properties of the (0.94–x) Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–xK_0.5Na_0.5NbO₃/BNT–BT–KNN ceramics with x = 0.02 and 0.05 (2KNN and 5KNN) were studied in detail. Dielectric study and temperature-dependent polarization hysteresis loops indicated a ferroelectric-to-antiferroelectric transition at depolarization temperature (T_d). The low T_d in both the ceramic samples suggested the dominant antiferroelectric ordering at room temperature (RT), which was also confirmed by RT polarization and strain hysteresis loops studies. Antiferroelectric-to-paraelectric phase transition temperature (T_m) was nearly same for both systems. The 5KNN ceramic samples showed the relaxor behaviour. The values of the dielectric constant, T_d, and maximum strain percentage increased, whereas the coercive field and remnant polarization decreased with the increase of the KNN percentage in the BNT–BT–KNN system. High-energy storage density ～0.5 J/cm³ at RT hinted about the suitability of the 5KNN system for energy storage applications.     

Dielectric and electro-optical studies of a nickel-ferrite-nanoparticle- doped ferroelectric liquid crystal mixture

Effect of magnetic nanoparticles (nickel ferrite) doping on the dielectric and electro-optical properties of a ferroelectric liquid crystal mixture has been studied. In a doped ferroelectric liquid crystal mixture, dispersion of a small amount (0.25 wt.%) of nickel ferrite nanoparticles decreases the polarization and improves the response time compared to an undoped mixture. The significant changes in the polarization and response time are explained on the basis of dipole–dipole interaction and anchoring phenomena. Dielectric permittivity also increases with increasing the temperature of the SmC* phase and shows a reduction in dielectric loss in a doped sample. A Goldstone mode is clearly observed at ～200 and ～500 Hz in an undoped and a doped sample, respectively.