BiFeO3 Coupled Polysulfide Trapping in C/S Composite Cathode Material for Li-S Batteries as Large Efficiency and High Rate Performance

We demonstrated the efficient coupling of BiFeO3 (BFO) ferroelectric material within the carbon–sulfur (C-S) composite cathode, where polysulfides are trapped in BFO mesh, reducing the polysulfide shuttle impact, and thus resulting in an improved cyclic performance and an increase in capacity in Li-S batteries. Here, the built-in internal field due to BFO enhances polysulfide trapping. The observation of a difference in the diffusion behavior of polysulfides in BFO-coupled composites suggests more efficient trapping in BFO-modified C-S electrodes compared to pristine C-S composite cathodes. The X-ray diffraction results of BFO–C-S composite cathodes show an orthorhombic structure, while Raman spectra substantiate efficient coupling of BFO in C-S composites, in agreement with SEM images, showing the interconnected network of submicron-size sulfur composites. Two plateaus were observed at 1.75 V and 2.1 V in the charge/discharge characteristics of BFO–C-S composite cathodes. The observed capacity of ~1600 mAh g−1 in a 1.5–2.5 V operating window for BFO30-C10-S60 composite cathodes, and the high cyclic stability substantiate the superior performance of the designed cathode materials due to the efficient reduction in the polysulfide shuttle effect in these composite cathodes.

Piezoelectricity in hafnia

Because of its compatibility with semiconductor-based technologies, hafnia (HfO2) is today’s most promising ferroelectric material for applications in electronics. Yet, knowledge on the ferroic and electromechanical response properties of this all-important compound is still lacking. Interestingly, HfO2 has recently been predicted to display a negative longitudinal piezoelectric effect, which sets it apart from classic ferroelectrics (e.g., perovskite oxides like PbTiO3) and is reminiscent of the behavior of some organic compounds. The present work corroborates this behavior, by first-principles calculations and an experimental investigation of HfO2 thin films using piezoresponse force microscopy. Further, the simulations show how the chemical coordination of the active oxygen atoms is responsible for the negative longitudinal piezoelectric effect. Building on these insights, it is predicted that, by controlling the environment of such active oxygens (e.g., by means of an epitaxial strain), it is possible to change the sign of the piezoelectric response of the material.

Ferroelectric Materials Based Coupled Nanogenerators

Innovations in nanogenerator technology foster pervading self-power devices for human use, environmental surveillance, energy transfiguration, intelligent energy storage systems, and wireless networks. Energy harvesting from ubiquitous ambient mechanical, thermal, and solar energies by nanogenerators is the hotspot of the modern electronics research era. Ferroelectric materials, which show spontaneous polarization, are reversible when exposed to the external electric field, and are responsive to external stimuli of strain, heat, and light are promising for modeling nanogenerators. This review demonstrates ferroelectric material-based nanogenerators, practicing the discrete and coupled pyroelectric, piezoelectric, triboelectric, and ferroelectric photovoltaic effects. Their working mechanisms and way of optimizing their performances, exercising the conjunction of effects in a standalone device, and multi-effects coupled nanogenerators are greatly versatile and reliable and encourage resolution in the energy crisis. Additionally, the expectancy of productive lines of future ensuing and propitious application domains are listed.

Enhancement of Charge Transfer in TiO2/BiOI Heterojunction Using BiFeO3 as Interface Modifier for Photoelectrochemical Conversion

The solution-processed TiO2/BiFeO3/BiOI ternary heterojunction with cascade energy level alignments was developed for photoelectrochemical conversion, in which, BiOI was deposited on BiFeO3 sensitized TiO2 mesoporous film by spin-coating method. BiFeO3 as ferroelectric material was served here as a mediator for improvement of charge separation and transfer. The photocurrent generation in TiO2/BiFeO3/BiOI sample are very stable, even measured after 50 light on/off cycles with 2000s. Moreover, compared with the TiO2/BiOI film, TiO2/BiFeO3/BiOI film showed about twice as high photocurrent density and photocatalytic activity. Kelvin probe force microscope showed that the surface potential of TiO2/BiFeO3/BiOI film was 0.456 V, which was obviously larger than 0.226 V in TiO2/BiOI sample. The increased surface potential should be originated from the polarization electric-field Eself by BiFeO3 interlayer, in which the direction of electric-field was supposed to be directed toward the BiOI. The presence of Eself consequently resulted in the better dissociation of photo-generated electrons and holes. Charge transport dynamics suggested that charge transfer rate increased from 6.813 s-1 of TiO2/BiOI heterojunction to 22.280 s-1 of TiO2/BiFeO3/BiOI heterojunction, and surface charge recombination rate reduced from 10.305 s-1 of the TiO2/BiOI to 7.707 s-1 of TiO2/BiFeO3/BiOI heterojunction, which results in the enhanced photoelectrochemical conversion in TiO2/BiFeO3/BiOI heterojunction.

ANNEALING TEMPERATURES’ EFFECTS ON MICROSTRUCTURE AND OPTICAL PROPERTIES OF Ba0.95Sr0.05TiO3 FILMS

ANNEALING TEMPERATURES’ EFFECTS ON MICROSTRUCTURE AND OPTICAL PROPERTIES OF Ba0.95Sr0.05TiO3 FILMS. Ferroelectric materials, one of which is Barium Strontium Titanate (BST), can be applied for photovoltaic. Ferroelectric films function as the P-type semiconductor in the P-N junction. BST (Ba0.95Sr0.05TiO3) films have been deposited on Pt/Si (111) and quartz substrates via the CSD method prepared by spin coater. The films were annealed at various temperatures of 800 °C, 900 °C, and 1000 °C to observe the annealing temperatures' effects on the microstructure and optical properties of the BST films. From the XRD results, the intensity of diffraction peaks gets higher along with the higher annealing temperature. It thus causes the level of crystallization and the crystal size of the Ba0.95Sr0.05TiO3 films to increase. The morphology results reveal that the grains size of the Ba0.95Sr0.05TiO3 films is getting larger with the higher annealing temperature. The optical properties examined in the Ba0.95Sr0.05TiO3 films include absorbance and bandgap energy values. Values of bandgap energy show a decrease with increasing sintering temperature. The smallest bandgap energy of the Ba0.95Sr0.05TiO3 film is achieved at 1000 °C of 3.20 eV. BST films were annealed at temperature 1000 °C attained from this study can be considered as candidate for a photovoltaic ferroelectric material.

Effect of electrical poling on the structural, dielectric and photoluminescence properties of small concentration of Ho+3 substituted NBT

The effect of electrical poling on the room temperature structural, dielectric and photoluminescence properties of small concentration (i.e. 0.5 mole%) of Ho+3 substituted sodium bismuth titanate ferroelectric material (Na0.5Bi0.495Ho0.005TiO3 abbreviated as NBT-0.5Ho) has been investigated. Its crystal structure was found to be the mixture of two phases of rhombohedral (R3c) and monoclinic (Cc) in which monoclinic (Cc) coexisted as major phase. Comparative study of X-ray diffraction (XRD) patterns of electrically poled and unpoled specimens of NBT-0.5Ho revealed that electric field irreversibly transformed crystal structural of dominant Cc (≈-94.05% phase fraction) phase to R3c (≈70.6% phase fraction) as major phase. Dielectric value and its dispersion with frequency were significantly decreased in poled specimen which is ascribed to electric field driven structural change. Two photoluminescence (PL) emissions at 655nm and 756nm were obtained in NBT-0.5Ho. PL intensity was considerably tuned in effect of electrical poling in term of quenching. Obtain quenching is correlated with induced structural ordering towards higher symmetry phase (R3c) in effect of electric poling which is confirmed from XRD analysis. Obtained additional functionality of photoluminescence in the NBT-0.5Ho ferroelectric material and its tuning in effect of electric field opens the possibility in the material for optoelectronic devices applications.

Analyzing Frequency Spectra of Dielectric Loss to Clarify Influence of L,α-alanine Doping on Phase Transition in Triglycine Sulfate

As reported in the literature, the doping of L,α-alanine (LA) led to increasing the phase transition temperature in triglycine sulfate (TGS) – a bio-ferroelectric material that has been widely applied in industry. The nature of this anomaly is commonly investigated by considerably complicated theoretical and experimental techniques. Unlike previous studies, the present work proposes a simple physical method of analyzing frequency spectra for dielectric loss to clarify the relationship between the movement of phase transition positions and the shift of relaxation frequencies observed in the spectra. The experimental results obtained for LA-doped TGS samples synthesized at different LA contents (0, 5, 10, 20, and 30 wt.%) were used for the analysis. It was indicated that the increase in phase transition temperature was accompanied by the decrease in relaxation frequencies due to the enhanced viscosity created by strong hydrogen bonds formed between amino acids of alanine and TGS structure.

Directed synthesis of a hybrid improper magnetoelectric multiferroic material

Preparing materials which simultaneously exhibit spontaneous magnetic and electrical polarisations is challenging as the electronic features which are typically used to stabilise each of these two polarisations in materials are contradictory. Here we show that by performing low-temperature cation-exchange reactions on a hybrid improper ferroelectric material, Li2SrTa2O7, which adopts a polar structure due to a cooperative tilting of its constituent TaO6 octahedra rather than an electronically driven atom displacement, a paramagnetic polar phase, MnSrTa2O7, can be prepared. On cooling below 43 K the Mn2+ centres in MnSrTa2O7 adopt a canted antiferromagnetic state, with a small spontaneous magnetic moment. On further cooling to 38 K there is a further transition in which the size of the ferromagnetic moment increases coincident with a decrease in magnitude of the polar distortion, consistent with a coupling between the two polarisations.

Necessary conditions for steep switching in a constant Resistor-Capacitor RCFET

We establish that the phenomenon of transient negative capacitance, conventionally linked to the delay in the response of a domain switching, of a ferroelectric material, and modelled by a non-linear capacitor, can in fact be considered to be more generally applicable to any phenomenon that can be represented by an RC-equivalent circuit. We demonstrate the conditions for sub-60 mV/dec switching in an RC-FET, even if the R and C were constant along both forward and backward sweeps. For semiconductor charge Qch, we show that the necessary condition for sub-60 mV/dec switching (dQch)/(dΨs) = (q/(kBT))Qch, where Ψs is the surface potential, is possible only if Qch > 0 (i.e. when the transistor is ON) during the backward sweep. This insight contributes further understanding on the causes of hysteresis in commonly used SPICE models of FE-FETs. Graphic abstract