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The structural and electroactive properties of the as-prepared random copolymer polyvinylidene-co-hexafluoropropylene thin film are explored as a function of thermal treatment at various temperature regions. The thermal treatment of the polymer thin film not only changes the structural conformations that is very natural but establishes a polar domain in the non-polar α-phase. Here, we discover an anomalous temperature-dependent crossover behavior from the non-polar α-phase to an appreciable enhancement in ferroelectric and piezoelectric responses. The maximum unipolar strain (S m a x = − 5.01 %) , an ultrahigh value of normalized piezoelectric coefficient (d 33 ∗ = − 556 pm / V) , high electromechanical coupling factor (K p = 0.78) factor including the high dielectric constant (ϵ ′ = 23 at 100 Hz) at a relatively low electric field of 900 kV/cm may, therefore, be an effect of the established polar domain for the sample annealed at 105 °C. The direct piezoelectric charge coefficient (d33), a key factor for the performance of a prepared polymer thin film system as an energy harvester, lies in the range of − 10 ± 2 pC / N. Also, the annealed sample exhibited a persistent polarization after several cumulative cycles of applied stress. [ABSTRACT FROM AUTHOR]

The influence of donor (L a 3 +) and acceptor (S c 3 +) dopant on structural and electrical properties of lead-free B i 0.5 N a 0.5 Ti O 3 (BNT) ceramics system was investigated. Both donor and acceptor substitutions induced a structural transformation of pure BNT ceramics from a rhombohedral to a pseudocubic structure. Splitting of the (111) p c peak in pure BNT was considered symmetry identification for a rhombohedral structure. A micrometer level grain size (1.70 μm–2.81 μm), dense microstructure with good ferroelectric and piezoelectric performance (d 33 = 56 − 45 pC / N) was obtained. The 3% La content BNT ceramic shows an improved dielectric property. The Curie temperature increases from 355 °C for pure BNT to 365 °C for donor-doped and 370 °C for acceptor-doped BNT. The donor doping created cationic vacancies; acceptor doping induces oxygen vacancies that stabilized the polarization level. Maximum remnant polarization (P r) value has been obtained for 3% La-doped (P r = 27 μ C / c m 2) and 5% Sc-doped (P r = 20 μ C / c m 2) BNT system. Bipolar strain increased with the increase in donor dopant concentration resulting in a large electrostrictive coefficient (Q11 ∼ 0.0122%–0.045%) has been obtained. Electric field-induced unipolar strain value was enhanced to its maximum value (Smax = 0.14%) for 3% La content with normalized strain d 33 ∗ = 209 pm / V and Smax = 0.13% for 5% Sc with normalized strain d 33 ∗ = 155 pm / V at an applied electric field of 70 kV/cm and 50 kV/cm, respectively. The enhanced strain was considered to be associated with low internal bias field and maximum polarization level. In terms of capacitive response, 5% Sc holds a maximum current (∼0.017 mA) during polarization switching. [ABSTRACT FROM AUTHOR]

The need of lead-free high performance ceramics with large electrostrictive effect, minimum hysteresis loss and energy storage ability at room temperature has become indispensable. At room temperature one of the key challenges in ceramic materials is to enhance the electrostrictive and energy storage properties simultaneously. In this regards, lead-free gadolinium modified barium zirconate titanate (Ba1-xGd2x/3)(Zr0.3Ti0.7)O3 (x=0.02, 0.04, 0.06, 0.08, 0.10) ceramic was experimentally investigated to gain the competent electromechanical parameters near room temperature. Dielectric measurements exhibit a diffuse type of phase transition of relaxor phenomena and slim hysteresis loop with low remnant polarization and low hysteresis loss were observed. A moderate electric field of 30 kV/cm, recoverable energy and storage efficiency increases with Gd content. Strain-electric field hysteresis curves such as S-E, S-E², and S-P² profiles indicate improved electrostrictive characteristic of the ceramics. Results show that a maximum strain S∼0.083% with large electrostrictive coefficient Q11∼0.054 m4/C² and M11∼0.142×10-16 m²/V² were obtained for x=0.02 based BGdZT composition near relaxor-paraelectric phase boundary. The behavior of electrostrictive effect and energy storage efficiency suggested new possibilities of high precision lead-free ceramic actuator in a moderate field. [ABSTRACT FROM AUTHOR]

This paper deals with the development of nanocrystalline Cu–Ni and Fe–Ni thin film thermocouples (TFTCs) by using ion-assisted anodic vacuum arc deposition technique. The crystallographic structure and surface morphology of individual layer films have been studied by x-ray diffraction and scanning electron microscopy, respectively. The resistivity, temperature coefficient of resistance, and thermoelectric power of as deposited and annealed films have been measured. The observed departure of these transport parameters from their respective bulk values can be understood in terms of intrinsic scattering due to enhanced crystallite boundaries. From the measured values of thermoelectric power and the corresponding temperature coefficient of resistance of annealed Cu, Ni, and Fe films, the calculated values of log derivative of the mean free path of conduction electrons at the Fermi surface with respect to energy (U) are found to be -0.51, 3.22, and -8.39, respectively. The thermoelectric response of annealed Cu–Ni and Fe–Ni TFTCs has been studied up to a maximum temperature difference of 300 °C. Reproducibility of TFTCs has been examined in terms of the standard deviation in thermoelectric response of 16 test samples for each pair. Cu–Ni and Fe–Ni TFTCs agree well with their wire thermocouple equivalents. The thermoelectric power values of Cu–Ni and Fe–Ni TFTCs at 300 °C are found to be 0.0178 and 0.0279 mV/°C, respectively. [ABSTRACT FROM AUTHOR]

A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O15 (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters γ and ΔTres. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy=0.02 eV and freezing temperature=362 °C. All these measurements confirmed its relaxorlike phase transition. [ABSTRACT FROM AUTHOR]