Search Results (61)

Barium titanate (BaTiO₃) has long been recognized as a promising photocatalyst for solar-driven water splitting due to its unique ferroelectric, piezoelectric, and electronic properties. This review provides a comprehensive analysis of atomistic simulation studies of BaTiO₃, highlighting the role of density functional theory (DFT), ab initio molecular dynamics (MD), and classical all-atom MD in exploring its photocatalytic behavior, in line with various experimental findings. DFT studies have offered valuable insights into the electronic structure, density of state, optical properties, bandgap engineering, and other features of BaTiO₃, while MD simulations have enabled dynamic understanding of water-splitting mechanisms at finite temperatures. Experimental studies demonstrate photocatalytic water decomposition and certain modifications, often accompanied by schematic diagrams illustrating the principles. This review discusses the impact of doping, surface modifications, and defect engineering on enhancing charge separation and reaction kinetics. Key findings from recent computational works are summarized, offering a deeper understanding of BaTiO₃’s photocatalytic activity. This study underscores the significance of advanced multiscale simulation techniques for optimizing BaTiO₃ for solar water splitting and provides perspectives on future research in developing high-performance photocatalytic materials. Full article

In recent decades, substantial progress has been made in embedding molecules, nanocrystals, and nanograins into nanofibers, resulting in a new class of hybrid functional materials with exceptional physical properties. Among these materials, functional nanofibers exhibiting ferroelectric, piezoelectric, pyroelectric, multiferroic, and nonlinear optical characteristics have attracted considerable attention and undergone substantial improvements. This review critically examines these developments, focusing on strategies for incorporating diverse compounds into nanofibers and their impact on enhancing their physical properties, particularly ferroelectric behavior and nonlinear optical conversion. These developments have transformative potential across electronics, photonics, biomaterials, and energy harvesting. By synthesizing recent advancements in the design and application of nanofiber-embedded materials, this review seeks to highlight their potential impact on scientific research, technological innovation, and the development of next-generation devices. Full article

Lithium niobate (LiNbO₃) has remarkable ferroelectric properties, and its unique crystal structure allows it to undergo significant spontaneous polarization. Lithium niobate plays an important role in the fields of electro-optic modulation, sensing and acoustics due to its excellent electro-optic and piezoelectric properties. Thin-film LiNbO₃ (TFLN) has attracted much attention due to its unique physical properties, stable properties and easy processing. This review introduces several main preparation methods for TFLN, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), magnetron sputtering and Smartcut technology. The development of TFLN devices, especially the recent research on sensors, memories, optical waveguides and EO modulators, is introduced. With the continuous advancement of manufacturing technology and integration technology, TFLN devices are expected to occupy a more important position in future photonic integrated circuits. Full article

Polymer composites of P(VDF-TrFE) and Tris(hydroxymethyl) nitromethane as filler material with different concentrations have been prepared. Tris(hydroxymethyl) nitromethane is an organic ferroelectric material with low preparation cost and easy processing, and it is also lightweight. Its properties enable it to be a potential candidate for use as filler material in polymers to improve their ferroelectric, dielectric, and piezoelectric properties. We investigated the effect of filler content on the ferroelectric and dielectric properties of the polymer. Our results show that Tris(hydroxymethyl) nitromethane retains its crystallinity after embedding it in the polymer matrix. It does not alter the crystalline ferroelectric β-phase of the polymer. All composites possess higher polarization compared to pure P(VDF-TrFE). Up to 11.4 µC/cm² remnant polarization and a dielectric constant of 14 at 1000 Hz have been obtained with the free-standing 10 wt% composite film. Full article

Though much progress has been achieved in the discovery of new molecular ferroelectrics in recent years, practical applications and related physics are still rarely explored due to the difficulty in high-quality film production and patterning issues. Single-crystalline films and patterns are in high demand for high device performance. Through a template-assisted space-confined strategy, herein, ordered single-crystalline nanowire patterns and optoelectronic devices of a semiconducting molecular ferroelectric (SMF), hexane-1,6-diammonium pentaiodobismuth (HDA-BiI₅), were successfully demonstrated. The coupling of semiconducting and ferroelectric polarization of the SMF devices enables a broadband self-powered photodetection from ultraviolet to visible light, as well as polarization-tunable photoresponsivity. These may open an avenue for high-performance SMF optoelectronic memory devices with low cost and flexibility. Full article

Recently, two new polymorphs have been added to the nematic class: the polar-twisted nematic (N_PT) in 2016 and the ferroelectric nematic (N_F) in 2020. Comprised of achiral molecules, both exhibit local polar ordering and adopt modulated structures, right- and left-handed helical organizations—form chirality—albeit on vastly different dimensional scales; modulations have a ~10 nanometer pitch in the N_PT and ~500 nm in the N_F. Here, we focus on the structure and symmetries of the N_PT phase and the ensuing physical properties. Based on an array of order parameters that fully describe the molecular ordering and the nano-modulations thereof, we present a consistent formulation of the dielectric, optical, surface anchoring, and elasticity properties of the N_PT materials. We show that these properties are distinctly different from those associated with an elastically modulated, locally uniaxial, nematic. Full article

The use of chiral organic ligands as linkers and metal ion nodes with specific coordination geometry is an effective strategy for creating homochiral structures with potential ferroelectric properties. Natural Cinchona alkaloids, e.g., quinine and cinchonine, as compounds with a polar quinuclidine fragment and aromatic quinoline ring, are suitable candidates for the construction of molecular ferroelectrics. In this work, the compounds [CnZnCl₃]·MeOH and [CnZnBr₃]·MeOH, which crystallize in the ferroelectric polar space group P2₁, were prepared by reacting the cinchoninium cation (Cn) with zinc(II) chloride or zinc(II) bromide. The structure of [CnZnBr₃]·MeOH was determined from single-crystal X-ray diffraction analysis and was isostructural with the previously reported chloride analog [CnZnCl₃]·MeOH. The compounds were characterized by infrared spectroscopy, and their thermal stability was determined by thermogravimetric analysis and temperature-modulated powder X-ray diffraction experiments. The intermolecular interactions of the different cinchoninium halogenometalate complexes were evaluated and compared. Full article

Ferroelectric and antiferroelectric smectic liquid crystalline (LC) phases are still at the center of investigations and interests for both their fundamental properties and variety of technological applications. This review aims to report the main contributions based on different nuclear magnetic resonance (NMR) techniques to the study of chiral liquid crystalline calamitic mesogens forming smectic phases, such as the SmA, the SmC* (ferroelectric), and the SmC*_A (antiferroelectric) phases. ²H NMR and ¹³C NMR techniques and their combination were of help in clarifying the local orientational properties (i.e., the molecular and fragments’ main orientational order parameters) at the transition between the SmA and the SmC* phases, and in the particular case of de Vries liquid crystals, NMR studies gave important clues regarding the actual models describing the molecular arrangement in these two phases formed by de Vries LCs. Moreover, this review describes how the combination of ²H NMR relaxation times’ analysis, ¹H NMR relaxometry, and ¹H NMR diffusometry was successfully applied to the study of chiral smectogens forming the SmC* and SmC*_A phases, with the determination of relevant parameters describing both rotational molecular and internal motions, collective dynamics, and translational self-diffusion motions. Several cases will be reported concerning NMR investigations of chiral ferroelectric and antiferroelectric phases, underlining the great potential of combined NMR approaches to the study of supramolecular, conformational, and dynamic properties of liquid crystals. Full article

We attained wurtzite Sc_xAl_1−xN (0.16 ≤ x ≤ 0.37) thin films by varying the Sc and Al fluxes at a fixed active nitrogen flux during plasma-assisted molecular beam epitaxy. Atomic fluxes of Sc and Al sources via measured Sc percentage in as-grown Sc_xAl_1−xN thin films were derived as the feedback for precise determination of the Sc_xAl_1−xN growth diagram. We identified an optimal III/N atomic flux ratio of 0.78 for smooth Sc_0.18Al_0.82N thin films. Further increasing the III/N ratio led to phase separation under N-rich conditions, validated by the observation of high-Sc-content hillocks with energy-dispersive X-ray spectroscopy mapping. At the fixed III/N ratio of 0.78, we found that phase separation with high-Al-content hillocks occurs for x > 0.37, which is substantially lower than the thermodynamically dictated threshold Sc content of ~0.55 in wurtzite Sc_xAl_1−xN. We postulate that these wurtzite-phase purity degradation scenarios are correlated with adatom diffusion and the competitive incorporation process of Sc and Al. Therefore, the Sc_xAl_1−xN growth window is severely restricted by the adatom kinetics. We obtained single crystalline Sc_0.37Al_0.63N thin films with X-ray diffraction (002)/(102) ω rocking curve full-width at half-maximums of 2156 arcsec and 209 arcsec and surface roughness of 1.70 nm. Piezoelectric force microscopy probing of the Sc_0.37Al_0.63N epilayer validates unambiguous polarization flipping by 180°. Full article

Strontium aluminate, with suitable lattice parameters and environmentally friendly water solubility, has been strongly sought for use as a sacrificial layer in the preparation of freestanding perovskite oxide thin films in recent years. However, due to this material’s inherent water solubility, the methods used for the preparation of epitaxial films have mainly been limited to high-vacuum techniques, which greatly limits these films’ development. In this study, we prepared freestanding single-crystal perovskite oxide thin films on strontium aluminate using a simple, easy-to-develop, and low-cost chemical full-solution deposition technique. We demonstrate that a reasonable choice of solvent molecules can effectively reduce the damage to the strontium aluminate layer, allowing successful epitaxy of perovskite oxide thin films, such as 2-methoxyethanol and acetic acid. Molecular dynamics simulations further demonstrated that this is because of their stronger adsorption capacity on the strontium aluminate surface, which enables them to form an effective protective layer to inhibit the hydration reaction of strontium aluminate. Moreover, the freestanding film can still maintain stable ferroelectricity after release from the substrate, which provides an idea for the development of single-crystal perovskite oxide films and creates an opportunity for their development in the field of flexible electronic devices. Full article

Since the discovery of the first ferroelectric liquid crystal (FLC) in the chiral smectic C (SmC*) phase, ferroelectricity in liquid crystals has attracted much attention due to not only the fundamental interest but also the applications. This review focuses on the evolution of the design concept for ferroelectric smectic liquid crystals. It progresses from considering macroscopic phase symmetry to designing intermolecular interactions. For the purpose of understanding the molecular organization in smectic phases, we propose a dynamic model of constituent molecules in the smectic A (SmA) and SmC* phases based on ¹³C NMR studies. Then, we follow the structure–property relationship in ferroelectric SmC* liquid crystals for FLC displays. We reconsider de Vries-like materials that can provide defect-free alignment. We pay attention to the electro-optical switching in the chiral de Vries smectic A phase. Finally, we show several liquid crystals exhibiting polar smectic A phases and discuss how the polar order occurs in the highest symmetric smectic A phase. Full article

This work is devoted to the study of nanosized polymer polyvinylidene fluoride (PVDF) thin ferroelectric films (two-dimensional ferroelectrics) and their composites with graphene layers, using molecular dynamics methods to (1) study and calculate the polarization switching time depending on the electric field and film thickness, (2) study and calculate the polarization switching time depending on changes of the PVDF in PVDF-TrFE film, and (3) study the polarization switching time in PVDF under the influence of graphene layers. All calculations at each MD run step were carried out using the semi-empirical quantum method PM3. A comparison and analysis of the results of these calculations and the kinetics of polarization switching within the framework of the Landau–Ginzburg–Devonshire theory for homogeneous switching in ferroelectric polymer films is carried out. The study of the composite heterostructures of the “graphene-PVDF” type, and calculations of their polarization switching times, are presented. It is shown that replacing PVDF with PVDF-TrFE significantly changes the polarization switching times in these thin polymer films, and that introducing various graphene layers into the PVDF layered structure leads to both an increase and a decrease in the polarization switching time. It is shown that everything here depends on the position and displacement of the coercive field depending on the damping parameters of the system. These phenomena are very important for various ferroelectric coatings. Full article

The ferroelectric phase transition of the perovskite barium titanate as well as its technical importance regarding the switching of respective polar properties is well known and has been thoroughly studied, both experimentally and on theoretical grounds. While details about the phase diagram as well as transition temperatures are experimentally well known, the theoretical approaches still face difficulties in contributing a detailed description of these phase transitions. Within this work, a new methodological approach is introduced to revisit the ferroelectric phase transition with first-principles methods. With the chosen ab initio molecular dynamics (AIMD) method in combination with the applied NpT ensemble, we are able to join the accuracy of density functional theory (DFT) with ambient conditions, realized using a thermostat and barostat in an MD simulation. The derived phase diagram confirms recent corrections in the theoretical models and reproduces the phase boundary pressure dependence of T_C. In conclusion of the statistical atomistic dynamics, the nature of the transition can be described in a more detailed way. In addition, this work paves the way towards locally patterned piezoelectrica by means of acoustic standing waves as well as piezoelectrically induced acoustic resonators. Full article

The huge dielectric constant of ferroelectric nematic liquid crystals (FNLCs) seems to bring about a difficulty of molecular alignment control in exchange for a potential device application. To obtain a satisfactory level of uniform molecular alignment, it is essential to understand how the molecules near the alignment surface are anchored. In this study, bulk molecular alignment with an anti-parallel rubbing manner, which has not yet been investigated extensively, is explained using a conventional torque balance model introducing a polar anchoring function, and it is shown that the disappearance of the bulk twist alignment with decreasing cell thickness can be explained self-consistently. To validate this estimation for a room-temperature FNLC substance, the Brewster angle reflection method was attempted to confirm the surface director’s deviation from the rubbing direction caused by the polar surface anchoring. Full article

We measured the anelastic, dielectric and structural properties of the metal-free molecular perovskite (ABX${}_3$) (MDABCO)(NH${}_4$)I${}_3$, which has already been demonstrated to become ferroelectric below $T_{\mathrm{C}}=$ 448 K. Both the dielectric permittivity measured in air on discs pressed from powder and the complex Young’s modulus measured on resonating bars in a vacuum show that the material starts to deteriorate with a loss of mass just above $T_{\mathrm{C}}$, introducing defects and markedly lowering $T_{\mathrm{C}}$. The elastic modulus softens by 50% when heating through the initial $T_{\mathrm{C}}$, contrary to usual ferroelectrics, which are stiffer in the paraelectric phase. This is indicative of improper ferroelectricity, in which the primary order parameter of the transition is not the electric polarization, but the orientational order of the MDABCO molecules. The degraded material presents thermally activated relaxation peaks in the elastic energy loss, whose intensities increase together with the decrease in $T_{\mathrm{C}}$. The peaks are much broader than pure Debye due to the general loss of crystallinity. This is also apparent from X-ray diffraction, but their relaxation times have parameters typical of point defects. It is argued that the major defects should be of the Schottky type, mainly due to the loss of (MDABCO)${}^{2+}$ and I${}^{-}$, leaving charge neutrality, and possibly (NH${}_4$)${}^{+}$ vacancies. The focus is on an anelastic relaxation process peaked around 200 K at ∼1 kHz, whose relaxation time follows the Arrhenius law with $\tau$${}_0$ ∼ ${10}^{-13}$ s and $E\simeq 0.4$ eV. This peak is attributed to I vacancies (V${}_{\mathrm{X}}$) hopping around MDABCO vacancies (V${}_{\mathrm{A}}$), and its intensity presents a peculiar dependence on the temperature and content of defects. The phenomenology is thoroughly discussed in terms of lattice disorder introduced by defects and partition of V${}_{\mathrm{X}}$ among sites that are far from and close to the cation vacancies. A method is proposed for calculating the relative concentrations of V${}_{\mathrm{X}}$, that are untrapped, paired with V${}_{\mathrm{A}}$ or forming V${}_{\mathrm{X}}$–V${}_{\mathrm{A}}$–V${}_{\mathrm{X}}$ complexes. Full article