Enhanced energy-storage performance and thermal stability in Bi0.5Na0.5TiO3-based ceramics through defect engineering and composition design

Dielectric ceramics have been widely used in advanced microelectronics systems due to their inherent rapid charging/discharging capabilities and superb power density. However, concurrently attaining high energy storage density (W_rec), superior efficiency (η), and excellent thermal stability are arduous tasks for actual applications in dielectric ceramics. Herein, the introduction of predictable defects A-site vacancies (V_A) and oxygen vacancies (V_O) into the morphotropic phase boundary (MPB) of (Bi_0.45La_0.05Na_0.5)_0.94Ba_0.06TiO₃ (BLNBT) ceramics leads to a pinning effect in the grain boundary to improve the breakdown strength and energy storage performance. According to this strategy, the novel Sr_0.8Bi_0.1□_0.1Ti_0.8Zr_0.2O_2.95 (SBTZ)-modified BLNBT ceramics are designed and manufactured, which include SBTZ with a high relaxation behavior gene and BLNBT with an inherently high maximum polarization gene. As a result, a large W_rec of 3.84 J/cm³ with an excellent η of 90.8%, and outstanding charge/discharge capabilities (C_D ～ 584.99 A/cm², P_D ～ 40.94 MW/cm³ and τ_0.9 ～ 95 ns) in the 0.75BLNBT-0.25SBTZ ceramic are achieved. Notably, the corresponding ceramic shows a slight degradation of W_rec with a variation of less than 8% (RT ～ 200 °C), while the η remains at over 90%. The predictable defect engineering strategy proposed in this work is an effective way to develop new Bi_0.5Na_0.5TiO₃-based systems with good energy storage performances.     

In-situ fabrication of barium titanate@polyvinyl pyrrolidone in polyvinylidene fluoride polymer nanocomposites for dielectric capacitor applications

We have demonstrated an in situ route to design barium titanate (BT)@polyvinyl pyrrolidone (PVP) nanoparticles (NPs) in PVP/polyvinylidene fluoride (PVDF) blends. Thus, the PVP simultaneously acted as a linker and a part of the polymer matrix. We have hydrothermally synthesized the tetragonal phase of BT NPs (~150 nm). The BT NPs content was varied from 0 to 15 vol%. The resulting polymer nanocomposites generated enormous interfaces because of homogeneously dispersed BT@PVP NPs. Furthermore, the PVP simultaneously tailored the interfacial properties surrounding the BT NPs and bulk of the polymer matrix. Therefore, we achieved an enhanced maximum polarization (P_max) and energy density (U_d) of 27.9 μC cm⁻² and 13.4 J cm⁻³ (2261 kV cm⁻¹), respectively, at 7.5 vol% BT NPs loadings. At the same time, PVP/PVDF blends showed P_max and U_d of only 3.9 μC cm⁻² and 4.6 J cm⁻³ (3369 kV cm⁻¹), respectively. This simple approach of in situ nanomaterials modification will lead to development of low-cost and time-efficient dielectric capacitors.     

Bi0·5K0·5TiO3-based lead-free relaxor ferroelectric with high energy storage performances via the grain size and bandgap engineering

Dielectric capacitors with high energy storage performance show a huge competitive advantage for use in vehicles and power electronics. Here, the (1-x) (0.75Bi_0·5K_0·5TiO₃?0.25BiFeO₃) – xSr_0.7Bi_0·2TiO₃ (BKT-BF-xSBT) materials were designed based on the dual optimization strategy of grain size and bandgap. The optimal performance was obtained in the BKT-BF-0.4SBT sample, achieving high energy storage density W_rec of 5.21 J/cm³ and high energy storage efficiency η of 90.87% at 360 kV/cm. The addition of SBT optimized the microstructure and relaxation behavior of BKT-BF ceramic, giving rise to the formation of polar nanoregions (PNRs), small grain size (G), compact grain boundaries, and wide bandgap (E_g) synchronously. Encouragingly, prominent stabilities against temperature, frequency, and cycle numbers, and favorable charge/discharge performance (power density P_D ≈ 64.5 MW/cm³, τ_0.9 ≈ 90 ns) are also accomplished in designed BKT-based ceramics. These findings indicate that the BKT-BF-xSBT ceramic system has excellent potential in the dielectric energy storage field and also provides a viable prospect for engineering design of high-efficiency lead-free dielectrics via bandgap and grain size.     

Effect of polyaniline (PANI) on Poly(vinylidene fluoride-co-hexaflouro propylene) (PVDF-co-HFP) polymer electrolyte membrane prepared by breath figure method

Poly(vinylidene fluoride-co-hexaflouro propylene) is a well-known material for polymer electrolyte membranes (PEMs) due to its low cost, high mechanical integrity and excellent chemical resistance; however, its pure form has limited characteristics that require further modification to achieve optimum results. Therefore, the different dosages of polyaniline (PANI) (10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt%) were incorporated into PVDF-HFP blend to fabricate PVDF-HFP/PANI polymer electrolyte membrane by using breath-figure method. The FTIR peaks of PVDF-HFP and PVDF-HFP/PANI membrane confirms the successful incorporation of PANI into PVDF-HFP blend, while TGA, DSC and XRD analysis shows the PANI effect on stability and ionic conductivity of PVDF-HFP membrane. The PVDF-HFP/PANI membrane with 30 wt% PANI found superior with the highest porosity of 83%, electrolyte uptake of 270% and ionic conductivity of 1.96 mS cm⁻¹; however, the other concentrations of PANI were also effective and enhanced the performance of PVDF-HFP membrane. This shows the improved performances of PVDF-HFP membrane were attributed to successful incorporation of PANI and the proposed membrane can be a suitable alternative PEM or a separator for energy devices.     

Robust flower-like ZnO assembled β-PVDF/BT hybrid nanocomposite: Excellent energy harvester

Need of renewable green energy sources due to low cost synthesis, mechanically strong, high energy storage capacity with improved dielectric performance have been receiving much attention. Present work render the ZnO particle and flower-like morphology assemble semicrystalline β phase PVDF/BT nanocomposite, successfully synthesized by spin coating method and characterized by XRD, SEM, EDS and FTIR techniques. Also the energy storage density of composite with modified structure is largely increased with value 0.056 Jcm⁻³ at 6 MV/m which is 66% higher than virgin β-PVDF and 82% piezoelectric energy harvesting efficiency. Maximum dielectric constant is 1774 at 1 Hz for PVDF-BaTiO₃-ZnO_f [P-BT-ZnO_f] nanocomposite film and maximum breakdown strength of 43 kVcm⁻¹. Electrochemical study reveals that P-BT-ZnO_f nanocomposite film manifest better potential material. In terms of mechanical performance, P-BT-ZnO_f nanocomposite shows maximum Young's modulus of 204 MPa, tensile strength of 28.7 MPa and 23.1% elongation to break. These results provide promising capability to enhance the performance of composites for energy storage application, transducers, sensors, capacitors etc.     

Absorption spectrum and crystal-field analysis of U4+ ions in CsCdBr3 single crystals

Single crystals of U⁴⁺:CsCdBr₃ were grown by the Bridgman–Stockbarger technique. It has been assumed, that U⁴⁺ ions are substituting two Cd²⁺ ions and possess the C_3v site symmetry. Thirty seven energy levels, located between 4000 and 25,000 cm⁻¹ and encompassing all but the ¹S₀ multiplet, were assigned from 7 K absorption spectra. The symmetry of the levels were determined on the basis of the observed small splitting of the Γ₃ doublets as well as by a comparison of low temperature absorption spectra of the U⁴⁺:CsCdBr₃ with that previously reported for U⁴⁺ in Cs₂UBr₆ and Cs₂ZrBr₆ single crystals. A crystal-field analysis was performed by fitting eight atomic (in the orthogonal formalism) and 6 crystal-field parameters to the experimental Stark levels with an r.m.s. deviation of 100 cm⁻¹. The obtained values of the Hamiltonian parameters are discussed and compared with those reported in previous analyses of U⁴⁺ ions. The relatively strong crystal field, resulting in N_v = 8530 cm⁻¹ proves that in the CsCdBr₃ crystals the U⁴⁺ ions are located at a high symmetry site.     

In-plane chemical pressure in (U1−yCey)O2 studied by Raman spectroscopy

We investigate the nature of bonding and charge states in (U_1−yCe_y)O₂ (y = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) by Raman spectroscopy. Raman spectrum of UO₂ exhibits two prominent bands below 1000 cm⁻¹, a F_2g mode at 446 cm⁻¹ and a F_1u LO mode at 578 cm⁻¹. As y is increased from 0 to 0.6, the F_1u exhibits a large blue shift of 90 cm⁻¹, and from y = 0.6 to 1.0, a red shift of 54 cm⁻¹. We show that our results can be interpreted as arising from anisotropic compression/relaxation of the lattice under Ce substitution and this can give an indication of its charge states. Alternate interpretations have been given in the literature on the effect of substituents and dopants to the Raman spectra of UO₂ and CeO₂. The present interpretation of chemical stress effects can be taken as another plausible explanation.     

New thioether–dithiolate complexes of Cp1Ir and some reactivity features

The reaction of [Cp1IrCl₂]₂ (Cp* = η⁵ − C₅Me₅) with the tridentate 3-thiapentane-1,5-dithiolate ligand, S(CH₂CH₂S⁻)₂ (tpdt), led to the formation of [Cp1Ir(η³ − tpdt)] (1) in 81% isolated yield. Subsequent reactions of 1 with [Cp1IrCl₂]₂ in 2:1 and 1:1 molar equiv ratios resulted in the formation of [Cp1Ir(μ − η²:η³ − tpdt)Cp1IrCl][PF₆] (2) and [Cp1Irμ − η²:η³ − tpdt)Cp1IrCl][Cp1IrCl₃] (3) in 86 and 79% yields, respectively, based on 1, whereas the reactions of 1 with [(COD)IrCl]₂ (COD = 1,5-cyclooctadiene) in 2:1 and 1:1 molar equiv ratios resulted in the formation of the homo-bimetallic derivatives Cp1Ir(μ − η¹:η³ − tpdt)(COD)IrCl (4) (92% yield) and [Cp1Ir(μ − η²:η³ − tpdt)(COD)Ir] [(COD)IrCl₂] (5) (82% yield). Reactions between 1 and [(COD)RhCl]₂, yielded the hetero-bimetallic derivatives Cp1Ir(μ − η¹:η³ − tpdt)(COD)RhCl (6) and [Cp1Ir(μ − η²:η³ − tpdt)(COD)Rh][(COD)RhCl₂] (7), in 92 and 93% yields, respectively. The reaction of 1 with methyl iodide gave mono-methylated derivative [Cp1Ir(η³-C₄H₈S₃Me)]I (8) (93% yield). All these compounds have been comprehensively characterized.     

Dielectric properties of tetragonal tungsten bronze films deposited by RF magnetron sputtering

Tetragonal tungsten bronze (TTB) films have been synthesised on Pt(111)/TiO₂/SiO₂/Si substrates from Ba₂LnFeNb₄O₁₅ ceramics (Ln = La, Nd, Eu) by RF magnetron sputtering. X-ray diffraction measurements evidenced the multi-oriented nature of films with some degrees of preferential orientation along (111). The dependence of the dielectric properties on temperature and frequency has been investigated. The dielectric properties of the films are similar to those of the bulk, i.e., ε ∼150 and σ ∼10⁻⁶ Ω⁻¹ cm⁻¹ at 1 MHz and room temperature. The films exhibit two dielectric anomalies which are attributed to Maxwell Wagner polarization mechanism and relaxor behaviour. Both anomalies are sensitive to post-annealing under oxygen atmosphere and their activation energies are similar E_a ∼0.30 eV. They are explained in terms of electrically heterogeneous contributions in the films.     

Fourier transform and high sensitivity cw-cavity ringdown absorption spectroscopies of ozone in the 6030–6130 cm−1 region. First observation and analysis of the 3ν1+3ν3 and 2ν2+5ν3 bands

The absorption spectrum of ¹⁶O₃ has been recorded between 6030 and 6130 cm⁻¹ by Fourier Transform Spectroscopy (GSMA, Reims) and cw-cavity ringdown spectroscopy (LSP, Grenoble). The two new bands 3ν₁+3ν₃ and 2ν₂+5ν₃ centered at 6063.923 and 6124.304 cm⁻¹, respectively are observed and analyzed. Rovibrational transitions with J and K_a values up to 40 and 10, respectively, could be assigned. The rovibrational fitting of the observed energy levels shows that some rotational levels of the (303) and (025) bright states are perturbed by interaction with the (232), (510) and (124) dark states. The observed energy levels could be reproduced with a rms deviation of 5×10⁻³ cm⁻¹ using a global analysis based on an effective Hamiltonian including the five interacting states. The energy values of the three dark vibrational states provided by the fit are found in good agreement with theoretical predictions.The parameters of the resulting effective Hamiltonian and of the transition moment operator retrieved from the measured absolute line intensities allowed calculating a complete line list of 2035 transitions, available as Supplementary Material. The integrated band strengths are estimated to be 1.22×10⁻²⁴ and 3.15×10⁻²⁴ cm⁻¹/(mol cm⁻²) at 296 K for the 3ν₁+3ν₃ and 2ν₂+5ν₃ bands, respectively. A realistic error for these band strengths is 15% (see text).     

M/Xn (MAl,Mg; XBr,I) batteries based on anion transport mechanism

A new type of electrochemical storage energy batteries of M/X_n (MAl, Mg; XBr, I, n = 3, 2) were found. They can operate with nonaqueous electrolyte or solid electrolyte showing high voltage and moderate rate performances. The discharging mechanism is related to the formation and growth of the electrolyte phase MX_n on the surface of M electrode. The MX_n phase is X⁻ conductor and X⁻ anions play the transport role in electrode and electrolyte in these systems. Our finding shows that anion-conducting electrochemical batteries can be also promising for energy storage compared to cation-conducting systems in current batteries.     

Investigation of the phonon band gap effect on Raman-active optical phonons in SrMoO4 crystal

The phonon dispersions of SrMoO₄ crystal are calculated using the lattice dynamical calculations approach. Spontaneous Raman spectra in the SrMoO₄ were measured in the temperature range from 10 K to 295 K, and the temperature dependence of the linewidth of the B_g (95 cm⁻¹) and A_g (888 cm⁻¹) Raman modes was analyzed using the lattice dynamical perturbative approach. We found that different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the phonon spectrum resulting in different anharmonic interactions. The calculated temperature dependence of the linewidth of A_g (888 cm⁻¹) mode was well accounted for the experimental one by including both down-conversion by the cubic term and the dephasing by quartic term. The dephasing processes are increased only at high temperatures and the effect of dephasing is related to the size of a large phonon band gap.     

Influence of composition and processing parameters on the properties of solution-processed aluminum phosphate oxide (AlPO) thin films

The effects of precursor solution concentration, composition, and spin-processing parameters on the thickness and electrical properties of ultra-smooth aluminum oxide phosphate (Al₂O_3−3x(PO₄)_2x or “AlPO”) thin films prepared using aqueous solutions are reported. Compositions were verified by electron probe micro-analysis and range from Al₂O_1.5(PO₄) to AlPO₄ (x = P:Al from 0.5 to 1.0). Film thicknesses were determined using X-ray reflectivity measurements and were found to depend systematically on solution concentration, P:Al ratio, and spin-speed. Metal-insulator-semiconductor devices were fabricated to determine electrical properties as a function of composition. As the P:Al ratio increased from 0.5 to 1.0, the dielectric constant decreased from 6.0 to 4.6, leakage currents increased from 0.45 to 65 nA cm⁻² at 1 MV cm⁻¹ and dielectric breakdown (defined as leakage currents >10 μA cm⁻²) decreased from 9.74 to 2.84 MV cm⁻¹. These results establish composition, concentration, and spin-speed for the production of AlPO films with targeted thicknesses and electrical properties.     

Investigation of anharmonicity in rotational phonon mode for BaWO4 crystal

Spontaneous Raman spectra in the BaWO₄ were measured in the temperature range from 4 K to 280 K, and the temperature dependence of the linewidth of the A_g (191 cm⁻¹) Raman mode was analyzed using the lattice dynamical perturbative approach and one-phonon density of states (PDOS). The linewidth slope for the 191 cm⁻¹ peak for an external mode is 7.2 times larger than that for the 926 cm⁻¹ peak for a breathing mode. The different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the one-phonon density of states (PDOS) resulting in different anharmonic interactions. The origin may be that the ratio of up-conversion TDOS to down-conversion TDOS for Eg mode (191 cm⁻¹) is more than that for A_g (926 cm⁻¹). The peak of the Eg mode (191 cm⁻¹) is attributed to the coupling mode both a rotation of the Barium and an out-of-phase rotation of the oxygen in x–y plane as a librational mode.     

Effect of post-deposition annealing temperature on RF-sputtered HfO2 thin film for advanced CMOS technology

Structural and electrical properties of HfO₂ gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering are investigated. The HfO₂ high-k thin films have been deposited on p-type <100> silicon wafer using RF-Magnetron sputtering technique. The Ellipsometric, FTIR and AFM characterizations have been done. The thickness of the as deposited film is measured to be 35.38 nm. Post deposition annealing in N₂ ambient is carried out at 350, 550, 750 °C. The chemical bonding and surface morphology of the film is verified using FTIR and AFM respectively. The structural characterization confirmed that the thin film was free of physical defects and root mean square surface roughness decreased as the annealing temperature increased. The smooth surface HfO₂ thin films were used for Al/HfO₂/p-Si MOS structures fabrication. The fabricated Al/HfO₂/p-Si structure had been used for extracting electrical properties such as dielectric constant, EOT, interface trap density and leakage current density through capacitance voltage and current voltage measurements. The interface state density extracted from the G–V measurement using Hill Coleman method. Sample annealed at 750 °C showed the lowest interface trap density (3.48 × 10¹¹ eV⁻¹ cm⁻²), effective oxide charge (1.33 × 10¹² cm⁻²) and low leakage current density (3.39 × 10⁻⁹ A cm⁻²) at 1.5 V.     

Vibrational spectroscopic study of syngenite formed during the treatment of liquid manure with sulphuric acid

Syngenite (K₂Ca(SO₄)₂·H₂O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. C_s site symmetry was determined for the two sulphate groups in syngenite (P2₁/m), so all bands are both infrared and Raman active. The split ν₁ (two Raman+two infrared bands) was observed at 981 and 1000 cm⁻¹. The split ν₂ (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm⁻¹. In the infrared spectrum, only one band was observed at 439 cm⁻¹. From the split ν₃ (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm⁻¹. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm⁻¹. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm⁻¹. From the split ν₄ (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm⁻¹. The 298 K Raman spectrum showed one band at 641 cm⁻¹, while at 77 K four bands were observed at 607, 621, 634 and 643 cm⁻¹. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm⁻¹, OH-bending mode at 1631 cm⁻¹, OH-stretching modes at 3248 (symmetric) and 3377 cm⁻¹ (antisymmetric) and a combination band at 3510 cm⁻¹ of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes.     

First principles study of dielectric and vibrational properties of pyrochlore hafnates

We present the first principles study of dielectric, and vibrational properties of pyrochlore hafnates, RE₂Hf₂O₇ (RE = La, Nd, Sm, Eu, Gd, Tb) in their cubic structure using density functional theory and density functional perturbation theory, incorporating ultrasoft pseudopotentials and plane waves. The full set of zone centre Raman and infra red frequencies, along with the contribution of all infra red active modes towards dielectric constant and mode effective charges is calculated and discussed. In all the studied hafnates dominant contribution to static dielectric constant is found to come from three infrared active phonons around 125 cm⁻¹, 170 cm⁻¹ and 305 cm⁻¹. In addition, calculated structural properties are in very good agreement with experimental results. Mixed ionic-covalent bonding is found from the analysis of dynamical charges, static charges and density of states.     

Crystallization behavior of poly(lactic acid) with a self-assembly aryl amide nucleating agent probed by real-time infrared spectroscopy and X-ray diffraction

The effect of a self-assembly nucleating agent, N,N′,N″-tricyclohexyl-1,3,5-benzenetricarboxylamide (BTCA), on the crystallization behavior of poly(lactic acid) (PLA) was probed by time-resolved Fourier transform infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). The vibrational changes associated with inter- and intra-chain interactions during crystallization were monitored. In the initial period of crystallization, the order of intensity changes is as follows: 1458 cm⁻¹ > 1210 cm⁻¹ » 921 cm⁻¹, 1458 cm⁻¹ ∼ 1210 cm⁻¹ > 921 cm⁻¹, and 1458 cm⁻¹ ∼ 1210 cm⁻¹ ∼ 921 cm⁻¹ for neat PLA, PLAs containing 0.1 wt% and 0.3 wt% BTCA, respectively. This indicates that BTCA can accelerate both the formation of skeletal conformational-ordered structure and, especially, the 10₃ helix one. The incorporation of BTCA changes the crystallization mechanism but has no impact on the crystal form of PLA.     

Tailoring the dielectric properties and energy storage density of 1−x(0.94NaNbO3−0.06SZ)−xBi2O3 through substitution strategy

Energy storage using dielectric capacitors is a growing area of research and development. However, designing a highly performing dielectric capacitor is still a challenge. Despite the excellent results achieved in lead-based dielectrics, lead-free substitutes are essential because of the environmental concerns associated with lead-based products. The lead-free 1?x (0.94NaNbO₃? 0.06SrZrO₃)+ x Bi₂O₃ ceramics abbreviated NNSZ + xB for x = 0.0, 0.05, 0.1, 0.15, and 0.20 was fabricated via solid-state reaction. A recoverable energy density of 2.93 J cm?³ was obtained for NNSZ+0.1B, associated with high thermal stability (25–130 °C), excellent cycling (N = 10⁵), and high efficiency (η) of 83.5%. Moreover, the introduction of Bi₂O₃ significantly improved the electrical insulation (?_r at 1 kHz = 1608 and tan δ = 0.0038) and breakdown strength (380 kVcm?¹) of NNSZ+0.1B by minimizing the formation of sodium, bismuth, and oxygen vacancies. The results obtained in this study provide a benchmark for further investigations on NaNbO₃-based ceramics. More importantly, this study suggests that NNSZ + xB ceramics can be used in pulsed power technology.