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The electrical properties of polymer composites based on polycarbonate (PC) and panipol CXM (CX), filled with reduced graphene oxide (rGO), were investigated. The composite preparation conditions allowed good dispersion of rGO in the polymer matrix. We show here that when used as a nanofiller in polymers, rGO offers an appreciable improvement of the electrical current in 3 orders of magnitude (from 10-10 A to 10-7 A at 10 V), as observed in current-voltage (I-V) data for both PC and CX polymers with rGO. The suggested mechanism for the observed switching effects is the migration of oxygen groups aided by both the electrical field and Joule heating. Moreover, some reset- and set- like changes similar to resistive switching were observed in the I-V data of PC and CX-based films upon the addition of rGO. Clockwise (resembling a memristive system type II) and counter-clockwise (resembling a memristive system type I) directions were detected in the I-V data of the analyzed films. According to the obtained results, rGO can be a good filler for PC and CX polymer-based films for application in electronic and photonic areas, due to the significant improvement of the electrical conductivity of these polymers. [ABSTRACT FROM AUTHOR]

Structure, microstructure and low-temperature dielectric properties of undoped SrTiO3 (STO) thin films prepared by sol–gel and deposited on Si/SiO2/TiO2/Pt substrates are studied. The effect of annealing temperature and of buffer layers on properties of STO films is analysed. Dielectric permittivity ε′, relative tunability nr and polarization P are lowest for STO films prepared without buffer layers and annealed at 750 °C and are highest for films prepared with buffer layers and annealed at 900 °C. The increase of c/a ratio for films with buffer layer and of the grain size for films annealed at higher temperature is used to explain the improved dielectric response. The dielectric permittivity of STO films prepared by low-cost sol–gel technique with optimized deposition conditions is found to be comparable to that of STO films fabricated by more sophisticated and expensive methods such as pulsed laser deposition. [ABSTRACT FROM AUTHOR]

Abstract: The structure–property relations of Mg-doped SrTiO3 (ST) sol–gel thin films deposited on Pt/TiO2/SiO2/Si substrates have been investigated in order to determine the effect that Mg dopants have on the dielectric properties of SrTiO3. It has been predicted that Mg-doped SrTiO3 should exhibit a dielectric anomaly similar to that observed recently in Bi doped SrTiO3 but, to date, no polar state has been reported. It has been suggested that this may relate to the low solubility of Mg on the A-site in bulk ceramics (<0.05at.%). However, for Sr1−x Mg x TiO3 (SMT) (x ⩽0.30) films annealed at 750°C, all Mg ions were accommodated in the perovskite lattice and for SMT films annealed at 900°C, the solubility limit of Mg was x =0.10, above which a Mg-rich ilmenite second phase was observed. Irrespective of the higher solid solubility limit of Mg in the ST lattice for sol–gel ST films compared to equivalent ceramics, no ferroelectric or relaxor phase transition was observed, refuting previous predictions for this dopant. [Copyright &y& Elsevier]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]

Abstract: In order to inspect bulk properties of the SrTiO3 ceramics grains, dielectric permittivity and temperature shift of a zero-phonon R-emission line of the Cr3+ impurity-ion probes were studied in sol–gel SrTiO3:Cr (3×10−2%) ceramics of the average grain size ∼24μm. We found that non-dispersive permittivity (100Hz to 1MHz) increases on cooling less steeply than in single crystals reaching ∼5000 at 30K. At lower temperatures the dispersion appears and the permittivity saturates at ∼8K (ɛ′≈7000, 400Hz). However, the temperature shift of the R-line in ceramics remains practically identical to that for SrTiO3 single crystals, in which R-line shifts with temperature is Δν ∼1/ɛ′∼ . This indicates that the bulk of the grains in ceramics exhibits properties inherent to SrTiO3 quantum paraelectric, which agrees with the “generalized brick-wall” approach developed recently to describe polarization response of granular high permittivity materials. [Copyright &y& Elsevier]

The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼1.54 Å is estimated, which is ∼7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1-1.5xBixTiO3. [ABSTRACT FROM AUTHOR]

Harvesting ambient mechanical energy at the nanometric scale holds great promise for powering small electronics and achieving self-powered electronic devices. The current review is focused on kinetic energy harvesters, particularly on flexible piezoelectric nanogenerators (p-NGs) based on barium titanate (BaTiO 3 ) nanomaterials. p-NGs based on nanotubes, nanowires, nanofibres, nanoplatelets, nanocubes or nanoparticles of BaTiO 3 fabricated in vertical or lateral orientation, as well as mixed composite structures, are overviewed here. The achievable power output level is shown to depend on the fabrication method, processing parameters and potential application conditions. Therefore, the most widely studied aspects, such as influence of geometry/orientation, BaTiO 3 content, poling process and other factors in the output performance of p-NGs, are discussed. The current standing of BaTiO 3 -based p-NGs as possible candidates for various applications is summarized, and the issues that need to be addressed for realization of practical piezoelectric energy harvesting devices are discussed.

The current development of clean and high efficiency energy sources such as solar or wind energy sources has to be supported by the design and fabrication of energy storage systems. Electrochemical capacitors (or supercapacitors (SCs)) are promising devices for energy storage thanks to their highly efficient power management and possible small size. However, in comparison to commercial batteries, SCs do not have very high energy densities that significantly limit their applications. The value of energy density directly depends on the capacitance of full SCs and their cell voltage. Thus, an increase of SCs electrode specific capacitance together with the use of the wide potential window electrolyte can result in high performance SCs. Conductive polymer polyaniline (PANI) as well as carbonaceous materials graphene (G) or reduced graphene oxide (RGO) have been widely studied for usage in electrodes of SCs. Although pristine PANI electrodes have shown low cycling stability and graphene sheets can have low specific capacitance due to agglomeration during their preparation without a spacer, their synergetic effect can lead to high electrochemical properties of G/PANI composites. This review points out the best results for G/PANI composite in comparison to that of pristine PANI or graphene (or RGO). Various factors, such as the ratio between graphene and PANI, oxidants, time, and the temperature of chemical oxidative polymerization, which have been determined to influence the morphology, capacitance, cycling stability, etc. of the composite electrode materials measured in three-electrode system are discussed. Consequently, we provide an in-depth summary on diverse promising approaches of significant breakthroughs in recent years and provide strategies to choose suitable electrodes based on PANI and graphene.

The voltage dependence of the dielectric permittivity ε ' and the low dielectric loss tan δ 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 SrTi 1-x Zn x O 3-δ thin films with x = 0.01 and 0.05, deposited on Pt/TiO 2 /SiO 2 /Si substrates. Incorporation of Zn onto Ti sites is found to decrease ε ' compared to undoped SrTiO 3 films, while increasing the relative tunability n r 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 tan δ values below 0.6% observed for SrTi 1-x Zn x O 3-δ film with x = 0.01 make this compound more attractive for tunable device applications.

Strontium titanate-based materials with ferroelectric or relaxor-like properties have drawn vast attention as polar dielectrics for electronics and telecommunications. Here, we study the lattice dynamics in sol-gel-derived Sr 1-1.5x Bi x TiO 3 thin films with x = 0.0053 and 0.167, deposited on Al 2 O 3 substrates, using a variable-temperature far-infrared spectroscopy in a transmittance mode. Bi doping, known to induce a low-frequency dielectric relaxation in SrTiO 3 (ST) ceramics and films, due to off-centre dopant ion displacements generating electric dipoles, is shown to affect the polar phonon behaviour of thin films. We show that in weakly Bi-doped films, the low-frequency polar TO1 mode softens on cooling but less than in undoped ST. In heavily Bi-doped ST films, this mode displays no significant frequency variation with temperature from 300 to 10 K. The polar phonon behaviour of polycrystalline Bi-doped ST thin films is comparable with that of Bi-doped ST ceramics, which exhibit dielectric relaxations and harden soft-mode behaviour instead of the ferroelectric phase transition.

Thanks to the advanced technologies for energy generation such as solar cells and thermo- or piezo-generators the amount of electricity transformed from light, heat or mechanical pressure sources can be significantly enhanced. However, there is still a demand for effective storage devices to conserve electrical energy which addresses the wide range of large stationary applications from electric vehicles to small portable devices. Among the large variety of energy-storage systems available today, electrochemical energy sources and, in particular, supercapacitors (SC), are rather promising in terms of cost, scaling, power management, life cycle and safety. Therefore, this review surveys recent achievements in the development of SC based on composites of such carbon-derived materials as graphene (G) and reduced graphene oxide (rGO) with carbon nanotubes (CNT). Various factors influencing the specific capacitance are discussed, while specific energy and power as well as cycling stability of SC with G/rGO-CNT composite electrode materials are overviewed.

If piezoelectric micro-devices based on K 0.5 Na 0.5 NbO 3 (KNN) thin films are to achieve commercialization, it is critical to optimize the films' performance using low-cost scalable processing conditions. Here, sol-gel derived KNN thin films are deposited using 0.2 and 0.4 M precursor solutions with 5% solely potassium excess and 20% alkali (both potassium and sodium) excess on platinized sapphire substrates with reduced thermal expansion mismatch in relation to KNN. Being then rapid thermal annealed at 750 °C for 5 min, the films revealed an identical thickness of ~340 nm but different properties. An average grain size of ~100 nm and nearly stoichiometric KNN films are obtained when using 5% potassium excess solution, while 20% alkali excess solutions give the grain size of 500-600 nm and (Na + K)/Nb ratio of 1.07-1.08 in the prepared films. Moreover, the 5% potassium excess solution films have a perovskite structure without clear preferential orientation, whereas a (100) texture appears for 20% alkali excess solutions, being particularly strong for the 0.4 M solution concentration. As a result of the grain size and (100) texturing competition, the highest room-temperature dielectric permittivity and lowest dissipation factor measured in the parallel-plate-capacitor geometry were obtained for KNN films using 0.2 M precursor solutions with 20% alkali excess. These films were also shown to possess more quadratic-like and less coercive local piezoelectric loops, compared to those from 5% potassium excess solution. Furthermore, KNN films with large (100)-textured grains prepared from 0.4 M precursor solution with 20% alkali excess were found to possess superior local piezoresponse attributed to multiscale domain microstructures.