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The microstructure, dielectric properties, relaxor behavior, and energy storage efficiency of un-substituted and niobium (Nb) substituted (Ba _0.85 Ca _0.15 )(Zr _0.1 Ti _0.9 ) _1-x Nb _x O _3 (for x = 0, 0.02 and 0.05) samples prepared by the solid-state reaction method has been studied in detail. All the samples exhibited perovskite structure with no trace of impurity. Composition-dependent phase transition was also observed on the addition of Niobium. At room temperature, the co-existence of rhombohedral and tetragonal phases is observed in the unsubstituted samples. As the composition changes from x = 0.02 to x = 0.05, a structural change from tetragonal to cubic is observed. A remarkable reduction in grain size, from 90 μ m (for x = 0) to 1.21 μ m for (x = 0.05), is observed with the addition of Niobium. This result suggests that Niobium acts as a grain growth inhibiter in barium calcium zirconium titanate (BCZT) ceramics. The effect of Niobium on transition temperature is studied from the temperature-dependent dielectric permittivity graph. It was clear that the transition temperature shifted to a lower temperature region, and for x = 0.05, at a very low temperature (−23 °C/250 K) the tetragonal to cubic transition was observed. At x = 0.05, the temperature-dependent dielectric permittivity showed a broadened curve, indicating a diffuse phase transition. The diffuse phase transition in Nb substituted samples is explained by Uchino and Nomura modified Curie Weiss law. Moreover, the observations on temperature-dependent dielectric permittivity measurements at various frequencies suggest that the substitution of Nb ^5+ induces relaxor behavior. The energy storage efficiency of unsubstituted and Nb substituted samples was calculated from the polarization versus electric field graph. A high storage efficiency of 84% was obtained for the Nb substituted sample (x = 0.05) at 12 kV cm ^−1 . Enhanced relaxor behavior and increased storage efficiency were observed in (Ba _0.85 Ca _0.15 )(Zr _0.1 Ti _0.9 ) _1-x Nb _x O _3 at x = 0.05. Thus we suggest that these are promising materials for energy storage applications.

Oxide thermoelectric ceramics attract extensive research interest due to their excellent thermal stability, non‐toxicity, cost‐effectiveness, and earth‐abundant constituent elements. In the present work, the authors study the effect of lanthanum (La) and samarium (Sm) co‐doping on the structural, microstructural, and thermoelectric properties of CaMnO3 ceramics. The X‐ray diffraction (XRD) studies show an increase in unit cell volume with an increase in Sm concentration. A shift in Raman modes is observed, confirming distortions in MnO6 octahedra with the substitution of rare‐earth elements. The co‐doping strategy leads to a two‐order increment in electrical conductivity and reduction in thermopower as expected due to the increase in Mn3+ and charge carrier concentration. The highest electrical conductivity value attained is ≈200 S cm−1 at around 570 K for La0.025Sm0.1Ca0.875MnO3. The maximum value of thermoelectric power factor achieved is 194 μW m–1 K–2, which is two orders higher than that of the undoped CaMnO3. [ABSTRACT FROM AUTHOR]

The effect of substrate temperature on the crystallographic texture and surface morphology of Ba0.5Sr0.5TiO3 deposited by rf magnetron sputtering on (111) oriented Pt (150 nm)/Ti (10 nm)/SiO2 (300 nm)/Si (100) substrates is reported. The onset of crystallinity is observed above 500 °C, beyond which all films are oriented along the (111) plane up to a temperature of 800 °C. Over this temperature range, the misfit strain and root mean square roughness (rmsroughness) peak at 600 °C, decreasing beyond this peak value. The tunability of the dielectric constant at 100 kHz is highest (60% for a field strength of 300 kV/cm) at the lowest values of rmsroughness and misfit strain and decreases as these values increase. It is also shown that the morphology of the Pt underlayers is strongly affected by the processing conditions. This in turn influences the tunable behavior of the BST films as much as the substrate temperature during growth and the consequent microstructural variations. [ABSTRACT FROM AUTHOR]

The various effects of the misfit strain and surface roughness on the tunable dielectric behavior of the various [Ba.sub.0.5][Sr.sub.0.5]Ti[O.sub.3] thin films are determined. The tenability of the dielectric constant and the root mean square values of the system are shown to exhibit an inverse relationship between them.

Dielectric constant ε′ and dielectric loss ε″ were measured in the frequency range of 500 Hz–3 MHz from room temperature (RT) to 350 °C for CoWO4 and CoWO4/PbWO4 nanocomposites sintered at 600 °C. Dielectric constant was found to be higher for nanocomposite samples as compared to CoWO4 sample and was maximum for Pb/Co ratio optimal value of 0.028. Relaxor like anomaly and colossal dielectric constants were observed above RT due to Maxwell–Wagner effect without structural and phase transition of the materials. Relaxor like properties for these materials were confirmed by Vogel–Fulcher and modified Curie–Weiss laws. However the samples sintered at 1000 °C do not show relaxor like behaviour and exhibit low dielectric constant ε′ at RT as compared to those sintered at 600 °C. P–E curve depicts the weak ferroelectric nature of the samples. [ABSTRACT FROM AUTHOR]

A tunable interdigitated capacitor is developed using Ba0.5Sr0.5TiO3 ferroelectic thin film and low-k fused silica substrate for applications in the microwave frequency range. The capacitance and quality factor of tunable IDC structure on BST5 film as a function of frequency up to 5 GHz are extracted using the conformal mapping method and partial capacitance technique. In this paper, the tunable capacitance properties of Au/Ba0.5Sr0.5TiO3 thin-film interdigital capacitors on low-k substrates are presented. [ABSTRACT FROM AUTHOR]

Large picosecond nonlinearities in Ba0.5Sr0.5TiO3 thin films, grown at different temperatures in situ on (100) MgO substrates using rf magnetron sputtering technique, were studied using the Z-scan technique. The nonlinear absorption mechanism, studied near 800 nm using ∼2 and 25 ps pulses, switched from reverse saturable absorption type in the films deposited at temperature<600 °C to three-photon absorption (3PA) in the films deposited at temperature>600 °C. The magnitude of the 3PA coefficient was estimated to be ∼10-21 cm3/W2. Two-photon absorption (2PA) was the dominant mechanism recorded with ∼6 ns pulses. The observed behavior is correlated with morphological and crystallographic texture of the films. The linear refractive index and optical band gap of the films have also been calculated and these show a strong dependence on the substrate temperature. [ABSTRACT FROM AUTHOR]

The untiring endeavour towards green energy is a trending research among the research community. Thermoelectric materials are of vital importance here owing to their emission-free operation. As a righteous candidate, calcium manganate materials are being explored to increase its figure of merit. In this study, the structural, microstructural, electrical transport, and high-temperature thermoelectric measurements of La x Dy x Ca 1-2 x MnO 3 { x = 0.025 (L25D25), 0.05 (L50D50), 0.075 (L75D75), and 0.1 (L100D100)} were systematically performed. The structural confirmation of the synthesised sample was validated using X-ray diffraction, which also revealed the orthorhombic (space group: Pnma ) crystallisation of co-doped samples with no traces of secondary peaks. A significant increase in the unit cell volume was observed with rare earth substitutions. The morphological studies revealed that the prepared samples were highly dense and the grain size was reduced with rare earth concentration. The substitution of La and Dy enhanced the conductivity values of pristine CMO by two orders of magnitude due to the high concentration of charge carriers and the presence of Mn 3+ ions due to rare earth doping. The conductivity increased with rare earth concentrations but diminished for x = 0.1 due to the localization of charges. The Seebeck coefficient values were negative for all the prepared samples, indicating electrons as the predominant carriers over the entire operating range. A minimum κ of 1.8 W m -1 K -1 was achieved for La 0.1 Dy 0.1 Ca 0.8 MnO 3 and the maximum value zT obtained was 0.122 at 1070 K for La 0.075 Dy 0.075 Ca 0.85 MnO 3 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

This work investigates and reports the effect of ZnO addition on the ferroelectric properties of (K 0.5 Na 0.5 )(Nb 0.7 Ta 0.3 )O 3 (KNNT) ceramics prepared by a solid state reaction method. Though literature is abundant on the study of the effect of ZnO on the sinterability, microstructure and electrical properties of KNN based materials, the effect of ZnO on their ferroelectric properties has seldom been studied in detail, especially in KNNT. In the current study, 2, 4 and 6 wt% of ZnO was added to KNNT ceramics. The XRD results revealed ZnO addition has no effect on the crystal symmetry of KNNT. However, a ZnO secondary phase was found in KNNT ceramics with 4 and 6 wt% ZnO doping. An increase in grain size was observed with increases in the concentration of ZnO, indicating a direct dependence of grain size on the concentration of ZnO in the KNNT matrix. From ferroelectric studies it was observed that a lower electric field was sufficient to get maximum polarization for ZnO doped KNNT samples compared to that of pure KNNT ceramics. A high remnant polarization ( P r = 14.0 μC cm -2 ) and lower coercive field ( E c = 5.6 kV cm -1 ) was obtained for 2 wt% ZnO doped KNNT. These samples showed the least fatigue (0.8%) after 10 9 cycles in comparison to pure (5%), 4 wt% ZnO doped (24.9%) and 6 wt% ZnO doped (30%) KNNT ceramics. The diminution in P s , P r , and E c was only 26.0%, 26.2% and 18.5%, respectively, with an increase in measurement temperature, which indicates improved thermal stability in 2 wt% ZnO doped KNNT. From the present study the optimum concentration of ZnO in KNNT is identify to be 2.0 wt% and their improved properties in comparison to the pure KNNT ceramics are discussed in detail., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Harvesting energy from surrounding vibrations and developing self-powered portable devices for wireless and mobile electronics have recently become popular. Here the authors demonstrate the synthesis of piezoelectric energy harvesters based on nanotube arrays by a wet chemical route, which requires no sophisticated instruments. The energy harvester gives an output voltage of 400 mV. Harvesting energy from a sinusoidal magnetic field is another interesting phenomenon for which the authors fabricated a magnetoelectric energy harvester based on piezoelectric-magnetostrictive coaxial nanotube arrays. Piezoelectric K 0.5 Na 0.5 NbO 3 (KNN) is fabricated as the shell and magnetostrictive CoFe 2 O 4 (CFO) as the core of the composite coaxial nanotubes. The delivered voltages are as high as 300 mV at 500 Hz and at a weak ac magnetic field of 100 Oe. Further tailoring of the thickness of the piezoelectric and magnetic layers can enhance the output voltage by several orders. Easy, single-step wet chemical synthesis enhances the industrial upscaling potential of these nanotubes as energy harvesters. In view of the excellent properties reported here, the lead-free piezoelectric component (KNN) in this nanocomposite should be explored for eco-friendly piezoelectric as well as magnetoelectric power generators in nanoelectromechanical systems (NEMS).