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In this study, we investigated dense BaTi1−xNbxO3 ceramics prepared by the conventional solid-state reaction technique which shows energy storage properties and anomalous photovoltaic effect. Structural analysis of BaTi1−xNbxO3 compositions has been performed by fitting the XRD patterns with Rietveld method and all samples show coexisting tetragonal (P4 mm) and cubic (Pm-3 m) structures. Composition (x = 0.04) shows minimum band gap (2.4 eV), smaller than pure BaTiO3 ceramics which can be attributed to lattice distortion and oxygen vacancies. The improved breakdown strength and energy storage density is achieved for BaTi0.93Nb0.07O3 composition. This ferroelectric ceramic shows energy storage of 278.7 mJ/cm2 and high energy conversion efficiency (90.4%). The composition (x = 0.07) exhibit a very high photovoltage (26 V) under visible light wavelength. These findings provide a fresh approach to create high-performance functional ferroelectric materials for energy applications. [ABSTRACT FROM AUTHOR]

The layered multiferroic perovskite oxides are excellent functional materials for ferroelectric memory applications and also show application potential for cathode materials in lithium-oxygen battery due to high surface area, good stability, easy processing and low price. Synthesis of uniformly distributed layered perovskite oxides with low band gap, ionic-conducting and ferroelctric nature is still challenging. In this work, we have synthesized a new single-phase aurivillius phase Bi6FeNiTi3O18 ceramics by high-energy ball mill mechano-chemical reaction. The Rietveld refinement of XRD data reveals that the compound Bi6FeNiTi3O18 shows orthorhombic structure with space group P2/m and SEM images confirm the uniform layered morphology. Bi6FeNi Ti3O18 ceramic have shown very high Tc of 450 °C and typical relaxor behaviour. Impedance analysis reveals the effect of grains, grain boundaries and electrode on conductivity. Ferroelectric nature is confirmed by obtained P-E loop at room temperature. We also report much lower band gap (Eg = 1.87 eV) as compared to Bi6Fe2Ti3O18 (Eg = 3.2 eV) ceramics which is due to Ni 3d state formation below Fe 3d state. The present work provide new path to engineer the functional properties of perovskite oxides for memory and energy storage applications. [ABSTRACT FROM AUTHOR]

The lead-free dielectric capacitors with high-temperature stability, high energy storage density and high discharge efficiency are highly needed for pulse power and power electronic applications. In this regard, Ba0.7Sr0.3TiO3–PVDF (Polyvinylidene fluoride) ceramic-polymer composites have been synthesized using a cold sintering process. Ba0.7Sr0.3TiO3 (BST) nanopowder was synthesized using sol–gel combustion method. The BST nanopowder was used for synthesizing the Ba0.7Sr0.3TiO3–PVDF composite with 80 wt% BST and 20 wt% PVDF. X-ray diffraction analysis confirmed pure phase formation of BST and revealed presence of different phases of PVDF in certain conditions. Thermal stability and surface morphology of the composite has been studied using thermo-gravimetric analysis and SEM, respectively. Dielectric and ferroelectric properties have been studied. Polarization-Electric field hysteresis loop analysis of composite reveals that significantly higher dielectric breakdown strength (more than 400 kV/cm) have been achieved in comparison to pure ceramic which is the main criteria for a potential material for energy storage purpose. Discharge efficiency of BST/PVDF annealed composite upto 95% and high thermal stability up to 300 °C has been achieved in the present case. [ABSTRACT FROM AUTHOR]

Pure PVDF has higher breakdown strength but low dielectric and ferroelectric properties. Thus, we synthesized the LaFeO3 and GdFeO3 nanoparticles with the help of solid-state method. The H2O2-hydroxylated LaFeO3 (Hy-LFO) and GdFeO3 (Hy-GdFO) nanoparticles were used for the first time as filler in the PVDF to get nanocomposite films with improved dielectric and ferroelectric properties. The solution cast method has been used for the preparation of the nanocomposite films. The H2O2 hydroxylation improved the interfacial interaction between the filler and the PVDF matrix. X-ray diffraction and Fourier transform infrared spectroscopy spectra analyses confirmed the formation of polar phases (β, γ-phases) of PVDF in dominance with nonpolar phase (α-phase) after nanocomposite formation. Differential scanning calorimetry measurements reveal that the peak corresponding to the α-phase of PVDF is fully diminished in the nanocomposite films. The increment in polar phase fraction in developed nanocomposite films results from the interfacial interaction due to nanofiller. The ferroelectric hysteresis loop recorded for the PVDF/Hy-LFO and PVDF/Hy-GdFO nanocomposite films reveals relatively improved polarization as compared to pure PVDF. The developed nanocomposites can be suitable candidate for energy storage applications. [ABSTRACT FROM AUTHOR]

Tuning the band gap of ferroelectric materials to visible region without reducing the polarization can provide an ideal photovoltaic material for solar energy harvesting, significantly efficient than the conventional p–n junction-based cells. In the present work, we have tried to achieve this elusive goal by doping Mo at the Ti ionic site in proper ferroelectric PbTiO3 which is known to have very large polarization. A significant reduction of band gap is achieved from 3.14 eV (un-doped PbTiO3) to 2.41 eV for 10% Mo doping concentration. In this doping, Mo-4d states which are lower in energy than Ti-3d states introduce an intermediate state below conduction band edge leading to band gap reduction. Analysis of the XRD patterns reveals that the Mo-doped PbTiO3 retains tetragonal structure and tetragonality increases with increasing the doping concentration of Mo. It is also found that increase of Mo concentration in PbTiO3 tends to enhance the conductivity suitable for transport of charge carriers. This finding may help to discover and design optical perovskite oxides for light energy harvesting application. [ABSTRACT FROM AUTHOR]

Multicolour excitable scheelite type CaWO4:Eu3+ (CEW) and SrWO4:Eu3+ (SEW) nanophosphors were synthesized using high energy ball milling in nano-domain. The synthesized nanophosphors were characterized extensively using Rietveld analysis of X-ray diffraction data, Raman spectroscopy, electron microscopy, energy dispersive spectroscopy and selected area electron diffraction. Differences in optical characteristics of CEW and SEW are probed using time resolved photoluminescence spectroscopy. It was observed that aliovalent doping of Eu3+ in CaWO4 and SrWO4 at divalent Ca/Sr sites leads to formation of cation vacancies as confirmed using positron annihilation lifetime spectroscopy (PALS). PALS also revealed that defect density in SEW is more than CEW which degrades its optical performance by aiding in non-radiative relaxation. The close proximity in ionic radius of Eu3+ and Ca2+ ions leads to better structural homogeneity in case of CEW and less lattice distortion which is reflected in its high emission output and quantum yield. Stark splitting analyses revealed reduction in symmetry around europium ion in SEW as compared to CEW. This is reflected in high asymmetry ratio (EDT/MDT) in case of SEW which directly translates into its high luminescence lifetime. Lifetime spectroscopy also revealed that in both the samples europium ion is localized at two different environments; one closer to defect centre and one is far off. Our study indicates that both these nanophosphors have unique ability to get excited intensely by UV as well as visible light and emit very intense red light which can be explored in phosphor converted white LEDs. Judd-Ofelt analysis indicates better optical performance of CEW as compared to SEW phosphor. [ABSTRACT FROM AUTHOR]