Electrocaloric effect in La-doped BNT-6BT relaxor ferroelectric ceramics

Relaxor [(Bi1/2Na1/2)0.94Ba0.06](1-1.5x)LaxTiO3 (x = 0, 0.03, 0.06, 0.09) ceramics (La-doped BNT-6BT) with composition close to the morphotropic phase boundary (MPB) were successfully prepared by using the conventional solid state reaction method. All samples present almost a pure perovskite phase with the coexistence of tetragonal and rhombohedral. With the increase of La doping content, the degree of the dielectric relaxor dispersion around the dielectric peak which is close to the room temperature increases, and also the transition temperature of ferroelectric-to-relaxor (TF-R) shifts 120 K towards a lower temperature at x = 0.09. The maximum value of the temperature change (ΔT) of the electrocaloric (EC) effect decreases sharply from 1.1 K at x = 0–0.064 K at x = 0.09. A large positive EC effect (maximum ΔT ~ 0.44 K) in a broad temperature range (~ 90 K) close to room temperature is achieved at x = 0.03, indicating that it is a promising lead-free material for application in solid state cooling system. Moreover, it is found that the Maxwell relationship can be well used to assess the EC effects of the La-doped BNT-6BT ceramics when the operating temperature is higher than that of the TF-R, indicating that these relaxor ceramics would perform as an ergodic

Enhanced energy storage performance of (1-x)(BCT-BMT)-xBFO lead-free relaxor ferroelectric ceramics in a broad temperature range

Relaxor ferroelectrics with high energy storage performances are very attractive for modern applications in electronic devices and systems. Here, it is demonstrated that large energy densities (0.52e0.58 J/cm3) simultaneously with high efficiencies (76è2%) and thermal stabilities (the minimum variation of efficiency < 4% from 323 K to 423 K at x ¼ 0.04) have been achieved in the (1-x)(BCT-BMT)-xBFO lead-free relaxor ferroelectric ceramics prepared using a conventional solid-state reaction method. Large dielectric breakdown strengths and great relaxor dispersion around the dielectric peaks are responsible for the excellent energy storage performances. The energy storage performances of as-prepared ceramics at high BFO doping amount (x ¼ 0.06 and 0.07) were deteriorated seriously due to low dielectric breakdown strengths. However, they could be greatly improved when aged, since the operable electric field was significantly enhanced from 10 kV/cm of as-prepared samples to 100 kV/cm of aged samples due to the reduced concentration of oxygen vacancies during the aging process. The excellent energy storage performances may make them attractive materials for applications in modern energy storage systems in a broad temperature range

Modeling research on wheat protein content measurement using near-infrared reflectance spectroscopy and optimized radial basis function neural network

In this study, near-infrared reflectance spectroscopy and radial basis function (RBF) neural network algorithm were used to measure the protein content of wheat owing to their nondestructiveness and quick speed as well as better performance compared to the traditional measuring method (semimicro-Kjeldahl) in actual practice. To simplify the complex structure of the RBF network caused by the excessive wave points of samples obtained by near-infrared reflectance spectroscopy, we proposed the particle swarm optimization (PSO) algorithm to optimize the cluster center in the hidden layers of the RBF neural network. In addition, a series of improvements for the PSO algorithm was also made to deal with its drawbacks in premature convergence and mechanical inertia weight setting. The experimental analysis demonstrated that the improved PSO algorithm greatly reduced the complexity of the network structure and improved the training speed of the RBF network. Meanwhile, the research result also proved the high performance of the model with its root-mean-square error of prediction (RMSEP) and prediction correlation coefficient (R) at 0.26576 and 0.975, respectively, thereby fulfilling the modern agricultural testing requirements featuring nondestructiveness, real-timing, and abundance in the number of samples

A Green Supply-Chain Decision Model for Energy-Saving Products That Accounts for Government Subsidies

Government subsidies are a common policy adopted to promote energy conservation and emission reduction. The decision-making that occurs within the green supply chain for energy-saving products under government subsidies is an area of great academic interest and game theory is becoming a popular tool in such research. In this paper, we examined centralized and decentralized decision-making models for the green supply chain and a coordinated decision-making model for revenue-sharing contracts based on game theory. We studied the effects of government subsidies on retail prices, energy conservation levels, market demand, supply chain profits, and social welfare for energy-saving products. We then compared the effectiveness of the three models using a numerical example. Our results revealed the range of contract parameters for which manufacturer and retailer profits increase. Our results show that government subsidies can significantly improve social welfare and promote the improvement of energy-saving products. Centralized decision-making generates higher profits than decentralized decisions and government subsidies were positively correlated with the level of energy conservation, product prices, and market demand. Revenue sharing contract coordination decisions can coordinate the supply chain and achieve the same effect as centralized decisions

Na2CaV4O12: A low-temperature-firing dielectric with lightweight, low relative permittivity, and dielectric anomaly around 515 C

A low temperature fired Na2CaV4O12 ceramic was synthesized via a solid-state reaction route at a temperature range of 350–550 °C. The Thermal analysis confirmed the densification and melting temperature of Na2CaV4O12 to be 530 °C and 580 °C, respectively. Dielectric properties together with the electrical conductivity were characterized at a broad frequency and temperature range. A super-low relative permittivity of εr = 7.72 and loss tangent of tanδ = 0.06 were obtained at 1 MHz at room temperature. A dielectric anomaly peak took place around 515 °C, which was associated with the phase transition from P4/nbm to P 4‾ b2. Ac impedance spectrum coupled with complex modulus plots unveiled the electrical conduction mechanism, which was dominated by the short-range movement of the charge carriers at low temperatures (T ≤ 220 °C) however long-range migration of charge carriers emerged at higher temperatures

Phase transformation and ionic conductivity mechanism of a low-temperature sintering semiconductor Na2CaV4O12

Alkaline earth metal vanadates have drawn attention because of their potential applications in electrochemical devices. Here, Na2CaV4O12 was prepared at extremely low temperatures (350-550 oC) and showed a semiconductor behavior with a bandgap of 2.92 eV. A phase transition from P4/nbm to P ̅ b2 occurred at 510 oC was identified by an in-situ XRD upon heating, where the 16 n site for oxygen atoms in the P4/nbm phase evolves into two distinguishable 8i sites in the P ̅ b2 phase. Ionic conduction in Na2CaV4O12 at elevated temperatures was reported for the first time in the present work. A strong correlation between ionic conductivity and phase structure of Na2CaV4O12 is observed. The charged carriers are mainly sodium ions for the low-temperature P4/nbm phase, while mixed conduction contributed by sodium ions and oxide ions happened in the transformed phase. Bond valence-based energy landscape calculations disclosed a two-dimensional interstitial diffusion mechanism for Na+ ions in the Na2Ca-layers, as well as a two-dimensional diffusion mechanism for oxide ions in the V4O12-layers. The novel semiconductor ceramic would have potential applications in all-solid sodium ions batteries or solid oxide fuel cells as electrolytes

The Microstructure and Mechanical Properties of 5083, 6005A and 7N01 Aluminum Alloy Gas Metal Arc-Welded Joints for High-Speed Train: A Comparative Study

This study aimed to conduct a comparative study on the microstructure and mechanical performance of 5083, 6005A and 7N01 Al joints used in China Railway High-speed (CRH) trains. We connected 10 mm-thick plates by three-layer and three-pass gas metal arc welding (GMAW). The results indicated that 6005A and 7N01 Al joints were more sensitive to grain boundary liquation in the partially melted zone (PMZ) than 5083 Al joins. Besides, recrystallization was obtained in heat-affected zones (HAZ). The 5083 Al joints experienced the most severe recrystallization and the grain size changed from 6.32 (BM) to 32.44 (HAZ) &mu;m duo to intracrystalline strain induced by cold-rolled processes. The 7N01 Al alloys experienced the lowest extent of recrystallization and the grain size increased from 5.32 (BM) to 22.31 (HAZ) &mu;m. Furthermore, significant precipitate evolution in the HAZ was observed. Original thin &beta;&rdquo; precipitates dissolved in HAZ of 6005A Al joints and transformed to the softer &beta; phase. However, less precipitation transition was examined in 5083 and 7N01 Al joints. The precipitates&rsquo; evolution produced a softening region in HAZ of 6005A joints where the hardness was only 55 HV. The microhardness profile of the other two Al joints was less affected. The tensile strength of 5083, 6005A, and 7N01 Al alloy joints reached 323, 206 and 361 MPa, respectively. The 5083 Al and 6005A Al joints failed at HAZ near the fusion line while 7N01 Al joints failed at the fusion zone owing to the high strength of the base metal. The liquation, coarse grains by recrystallization, and precipitate evolution all decreased local strength, resulting in the fracture at HAZ