Dielectric Materials for High Power Energy Storage

PhDEnergy storage is currently gaining considerable attention due to the current energy crisis and severe air pollution. The development of new and clean forms of energy and related storing devices is in high demanded. Dielectric capacitors, exhibiting high power density, long life and cycling life, are potential candidates for portable devices, transport vehicles and stationary energy resources applications. However, the energy density of dielectric capacitors is relatively low compared to that of traditional batteries, which inhibits their future development. In the current work, three types of dielectrics, namely antiferroelectric samarium-doped BiFeO3 (Bi1-xSmxFeO3), linear dielectric (potential antiferroelectric) BiNbO4 and incipient ferroelectric TiO2, have been investigated to develop their potential as energy storage capacitors. For the samarium-doped BiFeO3 (Bi1-xSmxFeO3) system, the effect of samarium content in the A-site (x=0.15, 0.16, 0.165 and 0.18) on the structural phase transitions and electrical properties across the Morphotropic Phase Boundary (MPB) were studied. A complex coexistence of rhombohedral R3c, orthorhombic Pbam and orthorhombic Pnma was found in the selected compositions. The R3c phase is the structure of pure BiFeO3, the Pbam phase has a PbZrO3-like antiferroelectric structure and the Pnma phase has a SmFeO3-like paraelectric structure. The presence of the PbZrO3-like antiferroelectric structure was confirmed by the observation of the 14{110}, 14{001}, 12{011} and 12{111} superlattice reflections in the transmission electron microscopy diffraction patterns. The weight fractions of the three phases varied with different calcination conditions and Sm substitution level. By increasing the calcination temperature, the weight fractions of the Pbam increased, while that of the R3c decreased. The fraction of the Pnma phase is mainly derived by the Sm concentration and is barely affected by the calcination temperature. The increase of Sm concentration, determined an increase of the weight fraction of the Pnma phase and a decrease of the Pbam and the R3c phases. Temperature dependent dielectric measurements and high temperature XRD of Bi0.85Sm0.15FeO3 revealed several phase transitions. The drastic weight fraction change between the Pbam and the Pnma phase around 200 °C is assumed as the Curie transition of the antiferroelectric Pbam phase. The transition at 575 °C is related to the diminishing of the R3c phase and is suggested as the Curie transition of the ferroelectric R3c phase. The Curie point of the antiferroelectric Pbam phase and the ferroelectric R3c phase in the Bi1-xSmxFeO3 ceramics shifted towards lower temperature with an increase of the Sm concentration. Current peaks were obtained in current-electric field loops in Bi0.85Sm0.15FeO3, which are correlated to domain switching in the R3c phase. The ferroelectric behavior was suppressed in Bi1-xSmxFeO3 (x=0.16, 0.165, 0.18), which is due to the gradually diminished contribution from the R3c phase. The system Bi0.82Sm0.18FeO3 showed the highest energy density of 0.64 J cm-3 (error bar ±0.02). For the BiNbO4 system, single phase α-BiNbO4 (space group Pnna) and β-BiNbO4 (space group P-1) powder and ceramics were produced. The longstanding issue related to the sequence of the temperature-induced phase transitions has been clarified. It is demonstrated that the β phase powder could be converted back to the phase when annealed in the temperature range 800 °C -1000 °C with certain incubation time. The β to phase transition is a slow kinetic process because sufficient temperature and time are required for the transition. In bulk ceramics with β phase, this transformation is impeded by inner stress, while it is favored by graphite-induced reducing atmosphere. A high temperature phase has been revealed and the structure has been resolved. The structure of the phase is monoclinic with a space group of P21/c. The lattice parameters are: a = 7.7951(1) Å, b = 5.64993(9) Å, c = 7.9048(1) Å, = 104.691(2) Z=4. The volume is 336.76 (2) Å3. The calculated density is 7.217 g cm-3. The phase relationships among , and phases have been clarified. It was found that the phase (for both powder and ceramic) transforms into the phase at 1040 °C on heating, and that the phase always transforms into the phase at 1000 °C on cooling. Meanwhile, a reversible first-order to phase transition is observed at ca. 1000 °C for both powder and ceramic if no incubation is processed on heating. The electric properties of both α- and - BiNbO4 have been investigated. The breakdown field of both ceramics were too low to observe any possible field-induced transition. As a result, linear P-E loops were obtained in each phase. The energy densities of α- and - BiNbO4 ceramics are 0.03 and 0.04 J cm-3 (error bar ±0.001), respectively. For the TiO2 system, ceramics were produced by conventional sintering and spark plasma sintering (SPS). Compared to conventional sintering, SPS technique produced dense ceramics without using sintering aids and avoided abnormal grain growth. Relaxation behavior related to the oxygen hopping among vacant sites is observed in the temperature range of 200 to 600 °C. TiO2 exhibits ultra-low loss at terahertz frequencies due to the reduced contribution of oxygen vacancies relaxation. TiO2 has a high breakdown field, but still has low polarization. The highest energy density obtained inTiO2 ceramics is 0.3 J cm-3 (error bar ±0.01).China Scholarship Counci

A specific and rapid method for detecting Bacillus and Acinetobacter species in Daqu

Daqu is a spontaneous, solid-state cereal fermentation product used for saccharification and as a starter culture for Chinese Baijiu production. Bacillus and Acinetobacter, two dominant microbial genera in Daqu, produce enzymes and organic acids that influence the Daqu quality. However, there are no rapid analytical methods for detecting Bacillus and Acinetobacter. We designed primers specific to the genera Bacillus and Acinetobacter to perform genetic comparisons using the 16 S rRNA. After amplification of polymerase chain reaction using specific primers, high-throughput sequencing was performed to detect strains of Bacillus and Acinetobacter. The results showed that the effective amplification rates for Bacillus and Acinetobacter in Daqu were 86.92% and 79.75%, respectively. Thus, we have devised and assessed a method to accurately identify the species associated with Bacillus and Acinetobacter in Daqu, which can also hold significance for bacterial typing and identification

SrFe12O19 based ceramics with ultra-low dielectric loss in the millimetre-wave band

The following article appeared in Applied Physics Letters, 112,143501 and may be found at https://doi.org/10.1063/1.5022271. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.Non-reciprocal devices such as isolators and circulators, based mainly on ferromagnetic materials, require extremely low dielectric loss in order for strict power-link budgets to be met for millimetre (mm)-wave and terahertz (THz) systems. The dielectric loss of commercial SrFe12O19 hexaferrite was significantly reduced to below 0.002 in the 75 - 170 GHz band by thermal annealing. While the overall concentration of Fe2+ and oxygen vacancy defects is relatively low in the solid, their concentration at the surface is significantly higher, allowing for a surface sensitive technique such as XPS to monitor the Fe3+/Fe2+ redox reaction. Oxidation of Fe2+ and a decrease in oxygen vacancies is found at the surface on annealing, which is reflected in the bulk sample by a small change in unit cell volume. The significant decrease in dielectric loss property can be attributed to the decreased concentration of charged defects such as Fe2+ and oxygen vacancies through annealing process, which demonstrated that thermal annealing could be effective in improving the dielectric performance of ferromagnetic materials for various applications

An Adaptive and Secure Holographic Image Watermarking Scheme

A novel adaptive secure holographic image watermarking method in the sharp frequency localized contourlet transform (SFLCT) domain is presented. Based upon the sine logistic modulation map and the logistic map, we develop an encrypted binary computer-generated hologram technique to fabricate a hologram of a watermark first. Owing to the enormous key space of the encrypted hologram, the security of the image watermarking system is increased. Then the hologram watermark is embedded into the SFLCT coefficients with Schur decomposition. To obtain better imperceptibility and robustness, the entropy and the edge entropy are utilized to select the suitable watermark embedding positions adaptively. Compared with other watermarking schemes, the suggested method provides a better performance with respect to both imperceptibility and robustness. Experiments show that our watermarking scheme for images is not only is secure and invisible, but also has a stronger robustness against different kinds of attack

Multi-Image Encryption Method via Computational Integral Imaging Algorithm

Under the framework of computational integral imaging, a multi-image encryption scheme based on the DNA-chaos algorithm is proposed. In this scheme, multiple images are merged to one image by a computational integral imaging algorithm, which significantly improves the efficiency of image encryption. Meanwhile, the computational integral imaging algorithm can merge images at different depth distances, thereby the different depth distances of multiple images can also be used as keys to increase the security of the encryption method. In addition, the high randomness of the chaos algorithm is combined to address the outline effect caused by the DNA encryption algorithm. We have experimentally verified the proposed multi-image encryption scheme. The entropy value of the encrypted image is 7.6227, whereas the entropy value of the merge image with two input images is 3.2886, which greatly reduces the relevance of the image. The simulation results also confirm that the proposed encryption scheme has high key security and can protect against various attacks

3D Copyright Protection Based on Binarized Computational Ghost Imaging Encryption and Cellular Automata Transform

In this paper, a watermark embedding scheme based on ghost image encryption and cellular automata transformation is proposed. In this scheme, the watermark forms speckle through different light intensities into a key, and the cellular automata transformation algorithm is embedded into the 3D image. Compared with the traditional watermarking encryption method, this scheme combines ghost imaging and the cellular automata transformation algorithm, which double guarantees and increases the confidentiality of the watermark. The binary computing ghost imaging discussed in this paper saves the storage space of password text and makes the transmission of password text more convenient and faster. Experiments on this method also verify that the watermark-embedded image has higher imperceptibility and higher robustness against attacks, and that the extracted watermark has good integrity

An Adaptive and Secure Holographic Image Watermarking Scheme

A novel adaptive secure holographic image watermarking method in the sharp frequency localized contourlet transform (SFLCT) domain is presented. Based upon the sine logistic modulation map and the logistic map, we develop an encrypted binary computer-generated hologram technique to fabricate a hologram of a watermark first. Owing to the enormous key space of the encrypted hologram, the security of the image watermarking system is increased. Then the hologram watermark is embedded into the SFLCT coefficients with Schur decomposition. To obtain better imperceptibility and robustness, the entropy and the edge entropy are utilized to select the suitable watermark embedding positions adaptively. Compared with other watermarking schemes, the suggested method provides a better performance with respect to both imperceptibility and robustness. Experiments show that our watermarking scheme for images is not only is secure and invisible, but also has a stronger robustness against different kinds of attack

3D Copyright Protection Based on Binarized Computational Ghost Imaging Encryption and Cellular Automata Transform

In this paper, a watermark embedding scheme based on ghost image encryption and cellular automata transformation is proposed. In this scheme, the watermark forms speckle through different light intensities into a key, and the cellular automata transformation algorithm is embedded into the 3D image. Compared with the traditional watermarking encryption method, this scheme combines ghost imaging and the cellular automata transformation algorithm, which double guarantees and increases the confidentiality of the watermark. The binary computing ghost imaging discussed in this paper saves the storage space of password text and makes the transmission of password text more convenient and faster. Experiments on this method also verify that the watermark-embedded image has higher imperceptibility and higher robustness against attacks, and that the extracted watermark has good integrity