Quantification of relaxor behavior in (1 − x)Na0.5Bi0.5TiO3 – xCaTiO3 lead-free ceramics system

This work examines the relaxor behavior of lead-free ceramic (1 − x)Na_0.5Bi_0.5TiO₃–xCaTiO₃ systems. A stable rhombohedral (R3c) phase is detected at room temperature for all compositions by XRD and Raman spectroscopy. Relaxor behavior was observed in the temperature range 300 K - 400 K for all materials. Ceramics exhibit normal ferroelectric properties at room temperature, and then they develop relaxor characteristics with increasing temperature showing the same dispersive properties. This work quantifies the relaxor phenomenon at low temperature. For instance, the maximum temperature of relaxor and the order of dispersion were determined at the strongest dispersion. Finally, the substitution by low CT concentration unaltered the relaxor behavior at low temperature.     

High electric field-induced strain with ultra-low hysteresis and giant electrostrictive coefficient in barium strontium titanate lead-free ferroelectrics

Ferroelectrics with high electrostrictive properties are of great interest in fundamental researches and industrial applications. In this work, the phase structural evolution, dielectric properties as well as electrostrictive properties in barium strontium titanate [(Ba_1-xSr_x)TiO₃, BST] lead-free ferroelectrics with x from 0.05 to 0.4 were investigated in details. High electric field-induced strain (∼0.2%) at 60 kV/cm are obtained in x = 0.05 and 0.1 compositions. More importantly, almost purely positive strains with ultra-low hysteresis (<8%) determined from bipolar strain-electric field curves are observed in compositions with x from 0.05 to 0.3, suggesting the dominating role of electrostrictive effect. Temperature-insensitive and composition-insensitive longitudinal electrostrictive coefficient Q₃₃ for BST ceramics with giant values from 0.0409 m⁴/C² to 0.0479 m⁴/C² is identified. These features suggest that BST ceramics not only possess high electric field-induced strain with ultra-low hysteresis and giant Q₃₃, but also are good candidates for potential application in high-precision actuator devices.     

A bird's eye view of Ghana's renewable energy sector environment: A Multi-Criteria Decision-Making approach

This study examines Ghana's renewable energy (RE) sector environment using PESTLE analysis (Political, Economic, Social, Technological, Legal, and Environmental). The Analytical Hierarchical Process (AHP) was employed to rank the various identified factors using inputs from 20 experts in Ghana's RE sector. The consulted experts ranked economic factors as the most critical challenge in the sector. According to them, the cost of capital in Ghana is too high, especially for long-term investments such as RE. The country's abundant RE resources and its geographical location were ranked highest in terms of the opportunities in the RE sector.     

Effect of zeolite crystallization parameters on C2C4 olefin production over iron-impregnated silicalite-2

Silicalite-2 can be synthesized with n-butylamine as an organic template in the system n-butylamine-Na₂O-SiO₂-H₂O and is impregnated withf Fe as carbon monoxide hydrogenation catalyst having high C₂C₄ olefins selectivity. The composition of the synthesis mixture was varied in a wide range. The influence of the parameters on crystallization and catalysis was examined by X-ray powder diffraction and synthesis gas reaction. The synthesis and catalytic properties of silicalite-2 with 1, 6-diaminohexane and TEAOH as organic templates have also been reported. The results presented indicate that silicalite-2 prepared with n-butylamine and at pH 12.5 by a two-step method possesses good catalytic characteristics in the direct conversion of synthesis gas to light olefins.     

Depth profiling of lithium by use of the nuclear reaction 7Li(p, α)4He

The nuclear reaction ⁷Li(p, α)⁴He induced by a primary beam of 1.5 MeV protons was used for measuring depth profiles of Li in Al. From the experiments with a detection angle of 90° a detection sensitivity of about 400 ppm was obtainable for a proton incidence at 30° from the surface. The best depth resolution was about 0.1 μm at 85° incidence. The sampling depth was over 17 μm at 50° incidence. These results are in good agreement with theoretical predictions. After the measurement of the reaction cross section, the applicability of the method to analyzing Li behaviour in solids was experimentally demonstrated on an AlLi (3.53 at.%) alloy.     

Synthesis,ferroelectric and piezoelectric properties of some (Na0.5Bi0.5)TiO3 system compositions

Some (Na_0.5Bi_0.5)TiO₃ (NBT) system compositions, including NBT, (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (NBBT) and 0.4 wt.% CoO added NBBT (NBBTC), were prepared by a citrate method. The ferroelectric and piezoelectric properties of the resulting ceramics were investigated. The results confirm that the citrate method is a feasible and advantageous route to produce NBT system ceramics. NBBT ceramic made by the citrate method exhibits a high piezoelectric constant (d₃₃) of 180 pC/N. An essential relation between the piezoelectric properties and the ferroelectric nature of the ceramics was detected. It was found that lowering the coercive field (E_c) and enhancing the remanent polarization (P_r) of NBT system ceramics simultaneously lead to desired piezoelectric properties.     

Enhanced Fill Factor and Power Conversion Efficiency of Single Oxide Ferroelectric Photovoltaic Devices with Designed Nanostructures

The ferroelectric photovoltaic effect has promising potential for the next generation of solar cells. However, due to disadvantages such as wide bandgap and low fill factor (FF), the power conversion efficiency (PCE) values reported in ferroelectric photovoltaic devices remain considerably below expectations. Herein, enhanced photovoltaic effect in the films with the nanostructure of ferroelectric nanocrystalline particles embedded in the amorphous or poor crystalline matrix is investigated. The nanostructures are realized by controlled crystallization and doping in Zn_0.92-xCu_x(Fe_0.04Li_0.04)O (ZCFLO) films. Benefiting from the improved carrier dynamic regulation in ferroelectric/boundary nanostructures and narrowed bandgap, the designed ZCFLO photoferroelectrics films exhibit high efficiency photovoltaic effect under AM 1.5G light, manifesting above-bandgap photovoltage, markedly improved FF (83.4%), switchable photoresponse (50.3 mA W⁻¹), and high PCE (14.4%). Meanwhile, the simple method presented in this work is fully compatible with large-scale manufacturing processes and may find applications in cost-efficiency optoelectronic devices.     

Graphene nanoplatelets for electrically conductive 3YTZP composites densified by pressureless sintering

3 mol% yttria tetragonal zirconia polycrystalline (3YTZP) ceramic composites with 2.5, 5 and 10 vol% graphene nanoplatelets (GNP) were pressureless sintered in argon atmosphere between 1350 and 1450 °C. The effects of the GNP content and the sintering temperature on the densification, microstructure and electrical properties of the composites were investigated. An isotropic distribution of GNP surrounding ceramic regions was exhibited regardless the GNP content and sintering temperature used. Electrical conductivity values comparable to the ones of fully dense composites prepared by more complex techniques were obtained, even though full densification was not achieved. While the composite with 5 vol% GNP exhibited electrical anisotropy with a semiconductor-type behaviour, the composite with 10 vol% GNP showed an electrically isotropic metallic-type behaviour.     

Effect of （Ba＋Sr）/Ti ratio on dielectric and tunable properties of Ba0.6Sr0.4TiO3 thin film prepared by sol-gel method

Ba0.6Sr0.4TiO3 （BST） thin films were fabricated on Pt coated Si （100） substrates by sol-gel techniques with molar ratio of （Ba＋Sr） to Ti changing from 0.76 to 1.33. The effect of （Ba＋Sr）/Ti ratio deviating from the stoichiometry on microstructure, grain growth, dielectric and tunable properties of BST thin films were investigated. TiO2 and （Ba,Sr）RTiO4 were found as a second phase at the ratios of 0.76 and 1.33, respectively. The variation of the ratio reveals more significant effect on the grain size in B-site rich samples than that in A-site rich samples. The dissipation factor decreases rapidly from 0.1 to 0.01 at 1 MHz with decreasing （Ba＋Sr）/Ti ratio. The tunability increases with decreasing ratio from 1.33 to 1.05, and then decreases with decreasing ratio from 1.05 to 0.76. The film with （Ba＋Sr）/Ti ratio of 1.05 has a maximum tunability of 32% and a dissipation factor of 0.03 at 1 MHz.