Polyaniline—Graphene Electrodes Prepared by Electropolymerization for High-Performance Capacitive Electrodes: A Brief Review

Both polyaniline (PANI) and graphene are widely studied for their application as capacitive electrodes in energy storage devices. However, although PANI can be easy synthesized, is of low cost and has a higher specific capacitance than graphene, pristine PANI electrodes do not present long-term stability due to their large volume changes during release/doping of the electrolyte ions and surface area reduction with charge-discharge cycling. That is why a combination of PANI with carbonaceous materials, especially conductive and high-surface-area graphene as well as more widely used reduced graphene oxide (rGO), provides an effective approach to solve these problems. At the same time, the electropolymerization process is one of the possible methods for synthesis of PANI composites with G or rGO as freestanding electrodes. Therefore, no binders or additives such as carbon black or active carbon need to be used to obtain PANI/rGO electrodes by electrochemical polymerization (EP), in contrast to similar electrodes prepared by the chemical oxidative polymerization method. Thus, in this paper, we review recent advances in EP synthesis of PANI/rGO nanocomposites as high-performance capacitive electrode materials, combining the advantages of both electrical double-layer capacitance of rGO and pseudocapacitance of PANI, which hence exhibit long cycle life and high specific energy.publishe

Comment on “Hole-pinned defect-dipoles induced colossal permittivity in Bi doped SrTiO3 ceramics with Sr deficiency”

With this contribution, as a comment to the publication in Journal of Materials Science & Technology 44 (2020) 54, reporting giant dielectric response, structural characterization and numerical simulations in Sr1-1.5xBixTiO3 ceramics, we show that the reported results are rather contradicting and not well analysed, while the suggested mechanism for the giant permittivity response is not valid or doubtful and has to be reconsidered. Moreover, many details and data are missing making impossible not only to call the obtained results very suitable for practical application but even to reproduce them.publishe

Nonstoichiometry Role on the Properties of Quantum-Paraelectric Ceramics

Among the lead-free perovskite-structure materials, strontium titanate (SrTiO3—ST) and potassium tantalate (KTaO3—KT), pure or modified, are of particular importance. They are both quantum paraelectrics with high dielectric permittivity and low losses that can find application in tunable microwave devices due to a dependence of the permittivity on the electric field. Factors as Sr/Ti and K/Ta ratio in ST and KT ceramics, respectively, can alter the defect chemistry of these materials and affect the microstructure. Therefore, if properly understood, cation stoichiometry variation may be intentionally used to tailor the electrical response of electroceramics. The scientific and technological importance of the stoichiometry variation in ST and KT ceramics is reviewed and compared in this chapter. The differences in crystallographic phase assemblage, grain size, and dielectric properties are described in detail. Although sharing crystal chemical similarities, the effect of the stoichiometry is markedly different. Even if the variation of Sr/Ti and K/Ta ratios did not change the quantum-paraelectric nature of ST and KT, Sr excess impedes the grain growth and decreases the dielectric permittivity in ST ceramics, while K excess promotes the grain growth and increases the dielectric permittivity in KT ceramics

Low-Temperature Dielectric Response of Strontium Titanate Thin Films Manipulated by Zn Doping

The voltage dependence of the dielectric permittivity ε' and the low dielectric loss tanδ of incipient ferroelectrics have drawn vast attention to the use of these materials for the development of tuning elements in electronics and telecommunications. Here, we study the DC electric field dependence of low-temperature ε' in ~320 nm thick sol-gel-derived SrTi1-xZnxO3-δ thin films with x = 0.01 and 0.05, deposited on Pt/TiO2/SiO2/Si substrates. Incorporation of Zn onto Ti sites is found to decrease ε' compared to undoped SrTiO3 films, while increasing the relative tunability nr up to ~32.9% under a DC electric field of 125 kV/cm at low temperatures. The hysteresis-free variation in ε' with electric field and tanδ values below 0.6% observed for SrTi1-xZnxO3-δ film with x = 0.01 make this compound more attractive for tunable device applications.publishe

ARCHITECTURE AND CONSTRUCTION STUDENTS' PERCEPTION OF “TECHNICAL DRAWING” AND “DESCRIPTIVE GEOMETRY" DISCIPLINE CONTENT

The present paper highlights the results of pedagogical research conducted at the Architectural Department in the Kamianets-Podilskyi Professional College of Construction, Architecture and Design. The study considers the vocational pre-higher education students’ perceptions of various graphic works in drawing and descriptive geometry in the context of graphic work features, and understanding the significance of drawing works for the formation of a future specialist in the construction industry. Students were suggested to fill in the forms with a list of the curriculum topics and give grades according to three criteria: usefulness for the future profession, the complexity of the graphic work and the engagement in performing the task.Research results provide problem-solving solutions related to teaching methodology of such disciplines as "Technical Drawings", "Drawings and Basics of Descriptive Geometry" and "Descriptive geometry".Based on research findings, the recommendations concerning teaching and increasing interest in educational material can be made. It has been found that certain topics do not arouse much interest in students, so we recommend improving students' motivation in the classroom by employing engaging tasks, taking into account the peculiarities of perception and attention when studying these topics. The topics that are difficult to master according to students' responses require more hours for studying, and the topics that students consider least useful should be reviewed, reformatted, or even excluded from the program.

Oxygen vacancies as a link between the grain growth and grain boundary conductivity anomalies in titanium-rich strontium titanate

Titanium-rich (Sr/Ti = 0.995) strontium titanate (ST) ceramics, air-sintered in a temperature range of 1400–1625 °C, were reported to possess anomalies in the grain growth and analogous anomalies in the grain boundary (GB) conductivity activation energy. However, these two interface-related phenomena, occurring at GBs, could not be associated with each other using a simple “brick-layer” model. In this work we revise the topic and advocate that the deviation from the model comes from the oxygen vacancies localized at GBs of the rapidly-cooled ST ceramics. To verify this, we annealed the ceramics in oxygen and performed their systematic and comparative analysis using impedance spectroscopy. A levelling-off in the GB conductivity activation energy, which increases for ≤1.24 eV, and a four-fold decrease in the GB permittivity are observed after annealing. Thus, we confirm a key role of oxygen vacancies in relation between the grain growth and GB conductivity anomalies of as-sintered Ti-rich ST ceramics.publishe

Behind the High Electrical Performance of Flash Sintered Potassium Sodium Niobate Piezoelectric Ceramics

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Effect of Microstructural Refinement on Electrical Properties of BST-Based Ceramics Prepared by Spark Plasma Sintering and Spark Plasma Texturing

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High Frequency Characterization and Nonlinear Analysis of BST Thick Films Produced by Electrophoretic Deposition

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Electric field modification of magnetotransport in Ni thin films on (011) PMN-PT piezosubstrates

This study reports the magnetotransport and magnetic properties of 20 nm-thick polycrystalline Ni films deposited by magnetron sputtering on unpoled piezoelectric (011) [PbMg1/3Nb2/3O3](0.68)-[PbTiO3](0.32) (PMN-PT) substrates. The longitudinal magnetoresistance (MR) of the Ni films on (011) PMN-PT, measured at room temperature in the magnetic field range of -0.3T < mu H-0 < 0.3 T, is found to depend on the crystallographic direction and polarization state of piezosubstrate. Upon poling the PMN-PT substrate, which results in a transfer of strain to the Ni film, the MR value decreases by factor of 20 for the current along [100] of PMN-PT and slightly increases for the [01 (1) over bar] current direction. Simultaneously, a strong increase (decrease) in the field value, where the MR saturates, is observed for the [01 (1) over bar] ([100]) current direction. The anisotropic magnetoresistance is also strongly affected by the remanent strain induced by the electric field pulses applied to the PMN-PT in the non-linear regime revealing a large (132 mT) magnetic anisotropy field. Applying a critical electric field of 2.4 kV/cm, the anisotropy field value changes back to the original value, opening a path to voltage-tuned magnetic field sensor or storage devices. This strain mediated voltage control of the MR and its dependence on the crystallographic direction is correlated with the results of magnetization reversal measurements. (C) 2015 AIP Publishing LLC