Carbon tax and low-carbon credit: Which policy is more beneficial to the capital-constrained manufacturer's remanufacturing activities?

Remanufacturing has attracted much attention for its enormous potential in resource recycling and low-carbon emission reduction. To investigate the effects of different government intervention policies on remanufacturing and carbon emissions, two profit maximization models of the capital-constrained manufacturer under carbon tax and low-carbon credit policies are constructed respectively. Then, through theoretical and numerical analyses, some significant findings are drawn: (1) Both carbon tax and low-carbon credit policies can encourage capital-constrained manufacturers to produce more remanufactured products, but which intervention policy is more advantageous also depends on the carbon emission cost of new products or financing cost of the remanufactured products. (2) Although carbon tax policy can effectively control carbon emissions, it is always at the expense of both capital-constrained manufacturers and consumers; while low-carbon credit policy can help capital-constrained manufacturers achieve the goal of win-win economic and environmental benefits when the remanufacturing carbon savings advantages are more apparent. (3) From the perspective of consumer benefits, carbon tax is more advantageous when the consumer willingness to pay for remanufactured products is higher; otherwise, low-carbon credit policy should be implemented. (4) The higher the environmental damage coefficient is, the more it can highlight the advantages of the two intervention policies in social welfare enhancement, especially the carbon tax policy; and when the environmental damage coefficient is given, the stronger the consumers' willingness to pay for remanufactured products is, the more it is conducive to reducing the negative effects caused by the carbon tax or low-carbon credit policy in social welfare enhancement, or increasing the corresponding positive effects. Based on above findings, some managerial insights and policy implications are provided to capital-constrained manufacturers and policy-makers.

Colossal Room-Temperature Ferroelectric Polarizations in SrTiO3/SrRuO3 Superlattices Induced by Oxygen Vacancies.

Artificial superlattices have demonstrated many unique phenomena not found in bulk materials. For this investigation, SrTiO3/SrRuO3 paraelectric/metallic superlattices with various stacking periods were synthesized via pulsed laser deposition. A robust room-temperature ferroelectric polarization (∼46 µC/cm2) was found in the superlattices with 2 unit cell (u.c.) thick SrRuO3 layers, despite the fact that neither SrTiO3 nor SrRuO3 is inherently ferroelectric. Results obtained from atomically resolved elemental mapping and X-ray photoelectron spectroscopy verified that oxygen vacancies accumulated at the SrTiO3/SrRuO3 interfaces, causing lattice distortions and increased tetragonality (c/a). The observed ferroelectric responses can be mainly attributed to the broken spatial inversion symmetry induced by the ordered distribution of oxygen vacancies at the SrTiO3/SrRuO3 interfaces, coupled with the triggering of external electric field. The resulting polarization mechanism induced by oxygen vacancies suggests viable ways for improving the electrical properties of ferroelectric materials, with the goal of expanding the functionality of a range of electronic devices.

Improved energy storage performance of PbZrO3 antiferroelectric thin films crystallized by microwave radiation.

Energy storage dielectric capacitors based on a physical charge-displacement mechanism have attracted much attention due to their high power density and fast charge-discharge characteristics. How to improve the energy storage capacity of dielectric materials has become an important emerging research topic. Here, antiferroelectric PbZrO3 films were prepared by chemical solution deposition on Pt/Ti/SiO2/Si substrates and crystallized by microwave radiation. The effects of microwave radiation on the antiferroelectric properties and energy storage performance were investigated. In contrast to ordinary heating, microwave radiation can crystallize the amorphous PbZrO3 films into the perovskite phase at 750 °C in only 180 seconds. The PbZrO3 films have a highly (100)-preferred orientation and dense microstructure, which is beneficial to enhance the stability of antiferroelectric phase and the electric breakdown strength. The PbZrO3 films show a recoverable energy storage density of 14.8 J cm-3 at 740 kV cm-1, which is approximately 40% higher than that of the PbZrO3 films crystallized by ordinary heating. The results reveal that microwave radiation is an effective method to improve energy storage performance of antiferroelectric films.

Emergent Ferroelectricity in Otherwise Nonferroelectric Oxides by Oxygen Vacancy Design at Heterointerfaces.

Introducing point defects in complex metal oxides is a very effective route to engineer crystal symmetry and therefore control physical properties. However, the inversion symmetry breaking, which is vital for many tantalizing properties, such as ferroelectricity and chiral spin structure, is usually hard to be induced in the bulk crystal by point defects. By designing the oxygen vacancy formation energy profile and migration path across the oxide heterostructure, our first-principles density functional theory (DFT) calculations demonstrate that the point defects can effectively break the inversion symmetry and hence create novel ferroelectricity in superlattices consisting of otherwise nonferroelectric materials SrTiO3 and SrRuO3. This induced ferroelectricity can be significantly enhanced by reducing the SrTiO3 thickness. Inspired by theory calculation, SrTiO3/SrRuO3 superlattices were experimentally fabricated and are found to exhibit surprising strong ferroelectric properties. Our finding paves a simple and effective pathway to engineer the inversion symmetry and thus properties by point defect control in oxide heterostructures.

Ultrahigh-Energy Storage Properties of (PbCa)ZrO3 Antiferroelectric Thin Films via Constructing a Pyrochlore Nanocrystalline Structure.

In recent years, antiferroelectric materials have been attracting considerable attention as energy storage capacitors due to their potential applications in pulsed power systems. In this work, antiferroelectric Pb0.88Ca0.12ZrO3 (PCZ) thin films were prepared via chemical solution deposition and annealed using rapid thermal annealing. The microstructures of PCZ thin films were controlled via annealing temperature, and the effects of microstructures on electric properties and energy storage performance were systematically studied. Our results indicate that PCZ thin films annealed at 550 °C crystallized into a nanocrystalline structure of the pyrochlore phase, while also displaying the highest recoverable energy density and efficiency (91.3 J/cm3 and 85.3%). We attribute the ultrahigh energy storage properties mainly to dramatic improvements in the electric breakdown strength caused by the dense nanocrystalline structure. The findings reported herein help to elucidate the relationship between energy storage performance and thin-film microstructure, thereby providing an effective way for improving the energy storage performance of antiferroelectric thin films.

Resistive Switching Behavior in Ferroelectric Heterostructures.

Resistive random-access memory (RRAM) is a promising candidate for next-generation nonvolatile random-access memory protocols. The information storage in RRAM is realized by the resistive switching (RS) effect. The RS behavior of ferroelectric heterostructures is mainly controlled by polarization-dominated and defect-dominated mechanisms. Under certain conditions, these two mechanisms can have synergistic effects on RS behavior. Therefore, RS performance can be effectively improved by optimizing ferroelectricity, conductivity, and interfacial structures. Many methods have been studied to improve the RS performance of ferroelectric heterostructures. Typical approaches include doping elements into the ferroelectric layer, controlling the oxygen vacancy concentration and optimizing the thickness of the ferroelectric layer, and constructing an insertion layer at the interface. Here, the mechanism of RS behavior in ferroelectric heterostructures is briefly introduced, and the methods used to improve RS performance in recent years are summarized. Finally, existing problems in this field are identified, and future development trends are highlighted.

Domain Evolution and Piezoelectric Response across Thermotropic Phase Boundary in (K,Na)NbO3-Based Epitaxial Thin Films.

Recent research progress in (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics has attracted increasing attention for their applications to microsystems or microelectromechanical systems (MEMS) in the form of thin films. This work demonstrates that high-quality KNN-based epitaxial films can be synthesized by a conventional sol-gel method, whose phase structure and domain characteristics have been investigated with emphasis on the temperature effect. A monoclinic MC structure is observed at room temperature in KNN-based epitaxial films, which is close to but different from the orthorhombic phase in bulk counterparts. Piezoresponse force microscopy (PFM) at elevated temperatures reveals continuous changes of ferroelectric domains in KNN films during heating and cooling cycles between room temperature and 190 °C. A distinct change in domain morphology is observed upon heating to 110 °C, accompanied by a clear variation of dielectric permittivity suggesting a thermotropic phase transition, which is revealed to belong to a MC-MA phase transition on the basis of structural and PFM analysis on local ferroelectric and piezoelectric behaviors. Enhanced piezoelectric response at the thermotropic phase boundary is observed, which is attributed to active domains and/or nanodomains formed across the boundary. Domain engineering by utilizing the phase transition should be important and effective in KNN-based films not only for property enhancement but also for its textured ceramics.

Enhancement of Polarization in Ferroelectric Films via the Incorporation of Gold Nanoparticles.

Ferroelectric thin films have been extremely studied for many applications such as nonvolatile memories, super capacitors, and solar cells. For these devices, improving the polarization properties of ferroelectric thin films is of great significance to their performance. Here, Au-lead zirconate titanate (PZT) nanocomposite thin films were prepared by a simple one-step chemical solution deposition (CSD) method on silicon substrates, and the effects of Au concentration on the ferroelectric properties were investigated. The experimental results show that the remanent polarization of the Au-PZT films with 1.2 mol % Au is about 80 µC/cm2, which is 50% higher than that of the pure PZT thin films. On the basis of the analysis of chemical valences, the enhanced polarization properties can be ascribed to the interaction between Au nanoparticles (Au NPs) and PZT at the Au-PZT interfaces. Our results demonstrate that the incorporation of an appropriate amount of Au NPs is an effective way to enhance the polarization properties of ferroelectric films. The Au-PZT nanocomposite thin films with excellent polarization properties on silicon substrates are expected to be widely used in integrated ferroelectric devices.

Resistive Switching and Modulation of Pb(Zr0.4Ti0.6)O3/Nb:SrTiO3 Heterostructures.

In this work, epitaxial Pb(Zr0.4Ti0.6)O3 (PZT) thin films with different thicknesses were deposited on Nb-doped SrTiO3 (NSTO) single-crystal substrates by chemical solution deposition (CSD), and their ferroelectric resistive switching behaviors were investigated. The results showed that the maximum ON/OFF ratio up to 850 could be obtained in the PZT/NSTO heterostructure with the 150 nm thick PZT film. On the basis of the Schottky-Simmons model and the modified semiconductor theory, we also evaluated the interfacial built-in field and the depletion layer at the PZT/NSTO interface, which can be modulated strongly by the ferroelectric polarization, but are independent of the thickness of the PZT thin films. It is clear that the ferroelectric resistive switching is related to the ferroelectric polarization and modulated by the thickness of ferroelectric films. Therefore, there is an optimal thickness of the PZT film for the maximum ON/OFF ratio due to the ferroelectricity and conductivity mutually restricting. It can be expected that by adjusting the ferroelectricity and conductivity of the ferroelectric thin film and its thickness, the maximum switching ratio can be further improved.