Graphitic carbon nitride (gCN) has emerged as a promising material for sustainable energy storage applications, photocatalysis, and sensors. Despite extensive research, its precise crystallographic structure remains controversial, particularly regarding the distinction between heptazine-based and melon-like frameworks. In this study, we investigate the structural characteristics of gCN synthesized using different precursors, urea and melamine. Comprehensive characterization, including X-ray diffraction (XRD), confirms that all samples exhibit a melon-like framework with P21212 symmetry. This contradicts the widely cited but experimentally unsupported heptazine-based model. We further explore how precursor selection influences crystallinity, elemental composition, and electrochemical behavior. Additionally, density functional theory (DFT) studies are also incorporated to support the experimental findings. Notably, our study is among the first to report the electrochemical performance of gCN with a confirmed melon-like structure, highlighting the strong correlation between structural attributes and functional properties. These findings provide valuable insights into the structure-property relationships in gCN and open new avenues for its rational design and applications in energy storage and conversion technologies for metal-sulfur batteries.

The functional properties of BaTiO3 ceramics, produced by using the same pressing/sintering strategy from nanopowders with two distinct morphologies (cuboidal/equiaxed nanoparticles) and similar particle sizes, are comparatively investigated. The sintered ceramics exhibit similar nanoscale structures, with faceted crystalline grains and crystalline inclusions, clean grain boundaries and well-defined 90 degrees lamellar domains extending in some entire grains or finer nanodomains inside grain regions. The differences in the functional behavior originating from the different nanopowder morphology are described in terms of the nanoparticle assembly during the pressing step. The numerically simulated green body densification indicated a more efficient assembly resulting in higher density for the cubic particles (0.90 vs . 0.84 relative density) and a more homogeneous pore distribution in the spherical-derived ones. As a result of the higher density after sintering, the functional properties are enhanced in cuboid-originated ceramics. For comparison, the ceramic produced from cubic nanoparticles sintered at T-1 / T-2 = 1,250/800 degrees C shows higher permittivity (room temperature value of similar to 2100 - cubic vs. -1700 - rounded), enhanced ferroelectric characteristics (cubic: Ps = 8.57 mu C cm(-2) , Pr = 0.95 mu C cm(-2) , and Ec = 2.3 kV cm(-1) , with respect to Ps = 6.06 mu C cm(-2) , Pr = 0.4 mu C cm(-2) , and Ec = 1.4 kV cm(-1) , for spherical - derived ones, measured at E-max = 29.3 kV cm(-1) ) and a stronger dc-field dependence of their permittivity of similar to 12 % (cubic) vs. only similar to 2 % (spherical), for a dc-applied field in the range of -15 kV cm(-1) < E-dc < 15 kV cm(-1) . In contrast, the spherical particles-derived ceramics contain fewer defects and have a more homogeneous and finer porosity distribution in the ceramic volume and consequently, they are more stable and sustain larger field applications in comparison with the cubic-derived counterparts. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

We report the synthesis of perovskite oxyhydride BaTiO3-xHx cubes (100-300 nm) using the topochemical hydride reaction of the hydrothermally synthesized oxide. X-ray and neutron diffraction studies revealed that the anion (hydride/oxide) exchange is greatly improved, leading to a maximum hydride content of 0.7, which is higher than previously reported, while no reaction is seen for those with oleic acid on their surface. These results indicate that the well-defined {100} facets, as well as the absence of organic residues, are crucial for promoting hydrogenation. Kissinger analysis on BaTiO2.3H0.7 yielded an activation energy of 165 kJ/mol, much lower than that of BaTiO2.4H0.6 (313 kJ/mol). In contrast to oxides, oxyhydrides with well-defined facets have not been reported before; thus, this study opens new avenues for the rational synthesis of oxyhydride materials with controlled chemical composition and morphology.

This paper introduces a simple method for the measurement of the relative permittivity and the Pockels coefficient of electro-optic (EO) materials in a waveguide up to sub-THz frequencies. By miniaturizing the device and making use of plasmonics, the complexities of traditional methods are mitigated. This work elaborates the fabrication tolerance and simplicity of the method, and highlights its applicability to various materials, substrates and configurations. The method is showcased using drop-casted perovskite barium titanate (BaTiO3, BTO) nano-particle thin-films and it has previously been used to measure epitaxial thin film BTO. In this work we show the effective relative permittivity of drop casted BTO to be ε eff ∼ 30 at 200 MHz, dropping to ∼ 18 at 67 GHz and similarly, the effective Pockels coefficient was found to be r eff ∼ 16 at 350 MHz and ∼ 8 at 70 GHz. These values are a factor > 50 below the values found for thin film BTO. Yet, the fact that the method can be applied to such different samples and Pockels strengths gives testimony to its versatility and sensitivity.

BaTiO3 (BTO) nanoparticles produced by wet chemistry methods were embedded in several types of flexible materials in order to fabricate flexible electronic devices. Starting from the produced nanoparticle dielectric properties, flexible material dielectric properties were tested for high electromagnetic frequencies (30 GHz–2 THz) using time domain spectroscopy. Dielectric performances of the different materials obtained with variable nanoparticle concentrations up to 40 wt.%, embedded in, gelatin, epoxy, and styrene-butadiene were compared at several working temperatures between 0 °C and 120 °C. Beside the general trend of ε′ decrease with temperature and loses increase with the operating frequency, we were able to identify few matrix dependent optimal nanoparticle concentrations. The best composite performances were achieved by the BTO-SBS matrix, with filler concentration of 2 wt.%, where the losses have been of 1.5%, followed by BTO-gelatin matrix, with filler concentration of 40 wt.%, with higher losses percent of almost 10% for THz frequencies.

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr2O4 nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr2O4 nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10−4 at a frequency of 1 Hz. Nanoparticulate ZnCr2O4-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process.

We demonstrate here that the dielectric, electrical and optical properties of BaTiO3colloidal nanocrystals with a cuboidal shape can be modulated upon aliovalent doping with Ln3+rare earth ions (Ln = La3+, Ce3+, Nd3+, Sm3+, Gd3+, Dy3+, and Tm3+).

BaTiO3 nanocubes capped by polar tetrafluoroborate (BF4−) ligands are shown to have enhanced ferroelectric order and undergo sharper ferroelectric to paraelectric phase transitions relative to nanocubes capped with nonpolar oleic acid (OA) ligands.

Flexible composites containing BaTiO3 nanoparticles into Gelatin bio-polymer matrix were designed and investigated. Following the idea that the electric field concentration in corners/edges at the interfaces between dissimilar materials give rise to enhanced effective permittivity in composites, cuboid-like BaTiO3 nanoparticles have been employed as nanofillers into Gelatin matrix by using an inexpensive solution-based processing method. As predicted by finite element method simulations developed for cubic-like inclusions into a homogeneous polymer matrix, the experimental permittivity of xBT-(1-x)Gelatin composites increases when increasing the high-permittivity filler addition. For the composition x = 40 wt% (corresponding to 12 vol% BaTiO3 addition), permittivity reaches epsilon r -15.7 with respect to epsilon r -9.8 of pure Gelatine (measured at 105 Hz), while the average piezoelectric coefficient d33 as determined by piezoelectric force microscopy shows a remarkable increase up to 21 pm/V in composites with x = 40 wt%, in comparison to -7 pm/V in pure Gelatin. By using the experimentally determined material constants, the simulated piezoelectric voltage output vs. time has shown a similar increase (about a doubling of its amplitude) of the harvesting signal in the composite with x = 40 wt% BT, with respect to one of the polymer matrix, thus demonstrating the beneficial role of embedding BT nanoparticles into the biopolymer for increasing the mechanical harvesting response.

Highly uniform dielectric and semiconductor layers were incorporated from nanoparticle inks into flexible transparent field-effect transistors (FETs). The FETs showed superior performance characteristics, being promising for the development of silicon-free based electronics.

We report on the measurement of the electrical properties of individual pristine and doped BaTiO3 nanocubes by using in situ transmission electron microscopy with a two-electrode configuration. The dimensions of the nanocubes tested are between 10 and 20 nm, which rendered their in situ electrical characterization challenging. We characterized 4%Cr and 5%La (atomic percentage) doped BaTiO3 nanocubes and compared them with the properties of pristine BaTiO3 nanocubes synthesized by the same solvothermal method. We found that the resistance of all three types of nanocubes when displayed in log-scale shows a nearly linear dependence on the applied electric field (R2 ≥ 0.95) over a wide range of electric fields (50–900 kV/cm). Compared with pristine BaTiO3 nanocubes, the resistance of both 4%Cr and 5%La doped nanocubes showed reduced variation rates with respect to the electric field, with 5%La doping, demonstrating a better reduction in the variation rate. By developing techniques capable of evaluating the properties of individual BaTiO3 nanocubes, we expect that our work to open the door to the use of BaTiO3 nanomaterials in the design of future multilayer ceramic capacitors with improved volumetric efficiency and ferroelectrics-enabled nanodevices with advanced functionality.

The preparation and properties of BaTiO3 nanostructured ceramics with porosity level in the range of percolation limit (33% and 37% porosity) produced by partial sintering of cubic nanoparticles are presented. Hydrothermally synthesized cuboid-like particles were produced by using Field-Assisted Sintering Technique facility in which temperature and pressure were selected to ensure the consolidation of mechanically stable porous nanoceramics, while preserving as much as possible the starting grain shape. Nanosized grains in the range of (10–40) nm and multiscale porosity ranging from a few nm to hundreds of nm were observed in the sintered ceramics. The dielectric constant of porous nanoceramics assumes low values of ~280–320 and shows a flat thermal response typical to nanostructured ceramics, without a net ferroelectric-paraelectric peak, followed by a Curie-Weiss dependence in the paraelectric state, with negative Curie Weiss temperatures and lowered Curie constant, as result of porosity and ultrafine grain size. A strong conductivity relaxation around room temperature related to air-ceramic interface phenomena indicated a possible sensitivity of these ceramics for gas sensing. Preliminary qualitative tests with saturated acetone vapours have shown a good response of both resistive and reactive components of such porous BaTiO3 nanoceramics and possible gas sensing interface-related mechanisms were discussed.

Surface adsorbates and surrounding matrix species have been demonstrated to affect the properties of nanoscale ferroelectrics and nanoscale ferroelectric composites; potentially counteracting performance losses that can occur in small particle sizes. In this work, the effects of nonpolar oleic acid (OA) and polar tetrafluoroborate (BF4-) ligand capping on the surface of various sizes of BaTiO3 nanocubes have been investigated with combined neutron diffraction and neutron pair distribution function (PDF), density functional theory (DFT), and ab initio molecular dynamics (AIMD) methods. The low real space PDF region provides an unobstructed view of rhombohedral (split short and long) Ti-O distances in BaTiO3 nanocubes, mimicking the well-established order-disorder local structure found in bulk BaTiO3. Interestingly, the intermediate-range order in nanocubes is found to be orthorhombic, rather than tetragonal. It is concluded that polar ligands adsorbed at BaTiO3 surfaces stabilize the correlation length scale of local rhombohedral distortions in ferroelectric nanoparticles relative to nonpolar ligands.

Spinel chromite nanoparticles are prospective candidates for a variety of applications from catalysis to depollution. In this work, we used a sol–gel auto-combustion method to synthesize spinel-type MgCr2O4 nanoparticles by using fructose (FS), tartaric acid (TA), and hexamethylenetetramine (HMTA) as chelating/fuel agents. The optimal temperature treatment for the formation of impurity-free MgCr2O4 nanostructures was found to range from 500 to 750 °C. Fourier transform infrared (FTIR) spectroscopy was used to determine the lattice vibrations of the corresponding chemical bonds from octahedral and tetrahedral positions, and the optical band gap was calculated from UV–VIS spectrophotometry. The stabilization of the spinel phase was proved by X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) analysis. From field-emission scanning electron microscopy (FE-SEM), we found that the size of the constituent particles ranged from 10 to 40 nm. The catalytic activity of the as-prepared MgCr2O4 nanocrystals synthesized by using tartaric acid as a chelating/fuel agent was tested on the decomposition of hydrogen peroxide. In particular, we found that the nature of the chelating/fuel agent as well as the energy released during the auto-combustion played an important role on the structural, optical, and catalytic properties of MgCr2O4 nanoparticles obtained by this synthetic route.

Polymer–ceramic nanocomposite films comprising ceramic nanoparticles dispersed in a polymer matrix (0–3 composites) have garnered increasing interest due to their superior performance characteristics, and can be used in flexible modern electronics and energy storage systems.

Miniaturization and optimization of high capacitance multilayer ceramic capacitors and other composite optoelectronic devices is driving development of smaller and smaller oxide nanocrystals with high phase purity, uniform and tunable particle size/shape, and other meritorious characteristics. Ferroelectric barium titanate (BaTiO3) nanoparticles can be synthesized using a wide variety of solution-based methods, many of which include BaCO3 impurities in the final product. BaCO3 impurities have been purported to be a discrete phase or surface layer, but either form can be removed by washing the nanocrystals with a dilute acid. Systematic studies of the effect of the acid wash on the atomic-scale structure, morphology, and particle size distributions of the BaTiO3 nanoparticles have not previously been undertaken. Here, we present results from a series of six sets of solvothermally synthesized BaTiO3 nanocubes, where half of each batch was washed with dilute acetic acid. Using synchrotron X-ray diffraction and pair distribution functions, it is found that the crystallite size and atomic-scale structures (local and long-range) are unchanged by the washing step and it is concluded that the BaCO3 impurity phase observed via X-ray diffraction is a discrete phase and not a surface layer of adsorbed CO2 or CO32-. Transmission electron microscopy verified that the nanocubes' morphology and size distributions were unaffected by the washing step. This systematic study suggests that structural characterizations of BaTiO3 samples with different postsynthesis washing treatments can reasonably and credibly be compared.

We report the fabrication of BaTiO3-Ni magnetoelectric nanocomposites comprising of BaTiO3 nanotubes surrounded by Ni matrix. BaTiO3 nanotubes obtained from the hydrothermal transformation of TiO2 have both inner and outer surfaces, which facilitates greater magnetoelectric coupling with the surrounding Ni matrix. The magnetoelectric coupling was studied by measuring the piezoelectric behavior in the presence of an in plane direct magnetic field. A higher magnetoelectric voltage coefficient of 110 mV/cm.Oe was obtained, because of better coupling between Ni and BaTiO3 through the walls of the nanotubes. Such nanocomposite developed directly on Ti substrate may lead to efficient fabrication of magnetoelectric devices. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The recent demand of multifunctional materials and devices for advanced applications in energy conversion and data storage resulted into a revival of multiferroics, that is, materials characterized by the coexistence of ferromagnetism and ferroelectricity. Despite intense efforts made in the past decade, single-phase room temperature multiferroics are yet to be discovered/fabricated. Nanostructured ferroic materials could potentially exhibit multiferroism since a high fraction of their atoms/ions are superficial, thereby altering significantly the properties of the bulk phase. Alternately, a magnetic order can be induced into ferroelectric materials upon aliovalent doping with magnetic ions. Here, we report on the synthesis of aggregate-free single-phase transition-metal-doped BaTiO3 quasi-monodisperse cuboidal nanocrystals (NC) which exhibit multiferroic properties at room temperature and can be suitable for applications in data storage. The proposed synthetic route allows the inclusion of a high concentration of magnetic ions such as Mn+ (M = Cr, Mn, Fe, Co) up to a nominal concentration of 4% without the formation of any secondary phase. The size of the nanocrystals was controlled in a wide range from similar to 15 up to similar to 70 nm by varying the reaction time from 48 to 144 h. The presence of unpaired electrons and their magnetic ordering have been probed by electron paramagnetic resonance spectroscopy (EPR), and a vibrating sample magnetometer (VSM). Likewise, an acentric structure, associated with the existence of a dielectric polarization, was observed by lattice dynamics analysis and piezoresponse force microscopy (PFM). These results show that high-quality titanium-containing perovskite nanocrystals which display multiferroic properties at room temperature can be fabricated via soft solution-based synthetic routes, and the properties of these materials can be modulated by changing the size of the nanocrystals and the concentration of the dopant thereby opening the door to the design and study of single-phase multiferroic materials.

The coupling between magnetic and electric subsystems in composites of ferromagnetic and ferroelectric phases is a product property that is facilitated by mechanical strain that arises due to magnetostriction and the piezoelectric effect in the constituent phases. Such multiferroic composites are of immense interests for studies on the physics of electromagnetic coupling and for use in a variety of applications. Here, we focus on magneto-electric (ME) coupling in nanocomposites. Particular emphasis is on core-shell particles and coaxial fibers, thin film heterostructures, and planar structures with a variety of mechanical connectivity. A brief review of models that predict strong ME effects in nanostructures is followed by synthesis and characterization. Core-shell particulate composites can be prepared by hydrothermal processes and chemical or deoxyribonucleic acid-assisted assembly. Electrospinning techniques have been utilized to prepare defect free core-shell nanofibers. Core-shell particles and fibers can be assembled into superstructures with the aid of magnetic and electric fields and characterized for possible use in advanced technologies. Chemical-vapor deposition techniques have been shown to be effective for the preparation of heterostructures of ferrites and ferroelectrics. Exotic planar multiferroic structures with potential for enhancing ME coupling strengths are also considered. Scanning probe microscopy techniques are ideal for probing the nature of direct- and converse-ME coupling in individual nanostructures. Magnetoelectric characterization of assemblies of nanocomposites can be done by ME voltage coefficient, magnetic field induced polarization, and magneto-dielectric effects. We conclude with a brief discussion on possible avenues for strengthening the product properties in the nanocomposites.