Journal of Advanced Dielectrics

This study is based on energy harvesting from vibration and deals with the comparison of different techniques. In the present scenario, energy harvesting has drawn the attention of researchers due to a rapid increase in the use of wireless and small-scale devices. So, there is a huge thirst among scientists to develop permanent portable power sources. In the surroundings, a lot of unutilized energy is wasted which can be collected and used for power generation. Research works have been extensively carried out to develop energy harvesting devices catering to the increasing needs of being efficient and economical. Effective energy harvesting mainly depends on the design of the transducer. Different types of design techniques, material properties, and availability of energy harvesters are reviewed in this paper. The paper aims to explore the advantages and limitations of different energy harvesting principles, advances, and findings of the recent past. This study also discusses some of the key ideas for the enhancement of power output. This paper provides a broad view of the energy harvesting system to the learners, which will facilitate them to design more efficient energy harvesting devices by using different principles.

PbTiO₃ nanorods with tetragonal phase were synthesized by hydrothermal method and heat treatment, and temperature-dependent electrical transport properties of individual PbTiO₃ nanorod were investigated. The results show that the conductivities of PbTiO₃ nanorods are gradually enhanced with temperature increasing from 77.4 to 295K, and exhibit the typical nonlinear I–V characteristics. The barrier height between Au electrode and nanorod is reduced from 0.137 to 0.088eV with increasing bias from 0.2 to 1V. The corresponding values of thermal activation energies are 0.172 and 0.06eV below the conduction band for 180–295 and 77.4–180K, respectively. This semiconductor-like behavior may result from the larger number of surface defects or localized states in the amorphorized PbTiO₃.

The modification of the structure lanthanum orthoferrites (LaFeO${}_3)$ to obtain ceramic materials with enhanced structural, optical, and electrical properties constitutes an active area of research. The preparation of La${}_{0.8}$Pb${}_{0.2}$(Fe, Ti)${}_{0.5}$O₃ (LPFTO) ceramic nanoparticles by following a cation substitution approach from LaFeO₃ using sol–gel and sintering methods is described. The electrical and dielectric properties of the obtained material are investigated. The contribution of grain and grain boundary in the conduction mechanism is demonstrated by complex impedance analysis. The LPFTO ceramic nanoparticles exhibit a giant dielectric constant of the order of 10⁸. The conductivity analysis suggests the occurrence of thermally activated semiconductor behavior. Moreover, the ferromagnetic–paramagnetic semiconductor transition temperature is observed at 385K. The ac conductivity behavior satisfies the nonoverlapping small-polaron tunneling (NSPT) model.

The multiferroic ceramics Bi${}_{0.8}$Ba${}_{0.2}$Fe${}_{1-x}$Sb_xO₃ with $x=0$, 0.01, and 0.02 were synthesized using the solid-phase reaction technique. The samples were sintered at two different temperatures, 850^∘C and 900^∘C. Scanning electron microscopy revealed the effect of antimony concentration on grain size and formation. The effect of Sb-doping on the crystal structure and ferroelectric properties of these ceramics was investigated using X-ray diffraction, Raman spectroscopy, and dielectric measurements. The dielectric constant was enhanced upon Fe${}^{3+}$ substitution by Sb${}^{3+}$ without affecting the dielectric loss of the ceramics. The tetragonal distortion of the rhombohedral symmetry of BiFeO₃ caused by Ba-doping at Bi${}^{3+}$ site was lifted by Sb-doping at Fe${}^{3+}$ site.

Polycrystalline samples of Bi${}_{1-x}$La_xFeO₃ [$x=0.5$, 0.6, 0.7 and 0.8] were synthesized through high temperature solid state reaction method. The structural studies of the compounds were done using X-ray diffraction technique. Dielectric constant and dielectric loss were studied for various frequencies (100Hz–10⁴Hz) at different temperatures. The temperature-dependent non-Debye type relaxation process was suggested in the materials from the analysis of frequency-dependent electrical data at different temperatures. Temperature dependence of dc and ac conductivity at various frequencies showed negative temperature coefficient of resistance (NTCR) behavior. The frequency dependence of ac conductivity at different temperatures obeyed Jonscher’s universal power law. The temperature dependence of dc and ac conductivity was fitted to Arrhenius equation. The activation energies at different temperature ranges were calculated to know the charge species involved in the conduction process.

In this work, we have successfully grown high quality epitaxial $\beta$-Ga₂O₃ thin films on $\beta$-Ga₂O₃ (100) and Al₂O₃(0001) substrates using pulsed laser deposition (PLD). By optimizing temperature and oxygen pressure, the best conditions were found to be 650–700^∘C and 0.5Pa. To further improve the quality of hetero-epitaxial $\beta$-Ga₂O₃, the sapphire substrates were pretreated for atomic terraced surface by chemical cleaning and high temperature annealing. From the optical transmittance measurements, the films grown at 600–750^∘C exhibit a clear absorption edge at deep ultraviolet region around 250–275nm wavelength. High resolution transmission electron microscope (HRTEM) images and X-ray diffraction (XRD) patterns demonstrate that $\beta$-Ga₂O₃(-201)//Al₂O₃(0001) epitaxial texture dominated the epitaxial oxide films on sapphire substrate, which opens up the possibilities of high power electric devices.

In this work, we report the dielectric and ferroelectric properties of CuO-doped ($1-x$)[0.5573Pb(Mg${}_{1∕3}$Nb${}_{2∕3}$)O₃-0.4427PbTiO₃]-$x$Ba(Zn${}_{1∕3}$Nb${}_{2∕3})$O₃ (PMNT-$x$BZN) relaxor ferrielectric ceramic samples with $x=0.1725$, 0.1925, 02125 and 0.2325, which were fabricated by a conventional solid-state reaction method. By introducing the CuO into PMNT-$x$BZN, the sintering temperature of this system is drastically lowered from 1280^∘C to 1120^∘C. The second pyrochlore phase, which is often generated during sintering at high temperature, is also inhibited. Meanwhile, broad dielectric peaks with strong dielectric relaxation characteristics are observed from $-150^{\circ }$C to 100^∘C. Slim and slanted $P$-$E$ hysteresis loops and purely electrostrictive strains with V-shape are obtained simultaneously in studied compositions from 30^∘C to 150^∘C. These results suggest that CuO could effectively lower the sintering temperature while maintaining the dielectric and ferroelectric properties of PMNT-$x$BZN relaxor ferroelectric ceramics.

This paper throws light on the preparation of transition metal-doped Mg${}_{0.5-x}T{M}_x$Zn${}_{0.5}$Al₂O₄ ($x=0$, 0.05 and $TM=\mathrm{\text{Co}}$, Ni, Cu) aluminates via solid-state reaction route. The X-ray diffraction characterization analysis confirmed that all the samples have crystallized into the psuedocubic phase having space group Fd3$m$ and were single phased. The incorporation of transition metals viz. Co${}^{2+}$, Ni${}^{2+}$, Cu${}^{2+}$ in the Mg${}_{0.5}$Zn${}_{0.5}$Al₂O₄ matrix does not result in the appearance of new peaks or any considerable shift in diffraction peaks within the limits of XRD experimentation. This infers homogeneous dispersion of dopants at the Mg-site which is attributed to nearly same ionic radii of the dopants to that of Mg-site in Mg${}_{0.5}$Zn${}_{0.5}$Al₂O₄. Lattice structure, bonding nature and hence the spinel formation were verified through Raman scattering technique. The compositional verification was carried out via energy dispersive analysis of X-rays (EDAX). The surface morphology and hence the microstructural studies were carried out using field emission scanning electron microscopy (FESEM). The synthesized Mg${}_{0.5-x}T{M}_x$Zn${}_{0.5}$Al₂O₄ ($x=0$, 0.05 and $TM=\mathrm{\text{Co}}$, Ni, Cu) aluminate samples were tested for polarization studies keeping their insulating nature into consideration and they displayed a sign of well-behaved P-E loop.