Narrow Results

Ceramics of the composition BaBiO₃ (BB) were sintered in oxygen to obtain a single phase with monoclinic $I$2/$m$ symmetry as suggested by high-resolution X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states — 3$+$ and 5$+$. Optical spectroscopy showed presence of a direct bandgap at $\sim$ 2.2eV and a possible indirect bandgap at $\sim$ 0.9eV. This combined with determination of the activation energy for conduction of 0.25eV, as obtained from ac impedance spectroscopy, suggested that a polaron-mediated conduction mechanism was prevalent in BB. The BB ceramics were crushed, mixed with BaTiO₃ (BT), and sintered to obtain BT–BB solid solutions. All the ceramics had tetragonal symmetry and exhibited a normal ferroelectric-like dielectric response. Using ac impedance and optical spectroscopy, it was shown that resistivity values of BT–BB were orders of magnitude higher than BT or BB alone, indicating a change in the fundamental defect equilibrium conditions. A shift in the site occupancy of Bi to the A-site is proposed to be the mechanism for the increased electrical resistivity.

$(1-y)$(BiFe${}_{1-x}$GdxO₃)–y(PbZrO₃) composites $(y=0.5)$, having four different Gd concentrations ($x=0.05$, 0.1, 0.15, and 0.2), were synthesized and their structural, dielectric, and ferroelectric properties have been studied using different characterization techniques. In addition, to investigate the effect of ion implantation on the microstructure and dielectric properties, these composites were exposed to 2MeV He${}^{+}$-ions. Modifications of the structure, surface morphology and electrical properties of the samples before and after ion exposure were demonstrated using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) technique, and LCR meter. The compositional analysis was carried out using energy dispersive X-ray spectrometry (EDS). XRD results demonstrated a decrease in the intensity profile of the dominant peak by a factor of 6 showing a degradation of the crystallinity. Willliamson–Hall (WH) plots reveal reduction in the grain size after irradiation along with an increase in strain and dislocation density. A decrease in the dielectric constant and loss has been recorded after ion beam exposure with reduction in ac conductivity value. The contribution of grain and grain boundary effect in conduction mechanism has been addressed using Nyquist plots. All the samples demonstrate a lossy ferroelectric loop which shows a clear modification upon irradiation. The role of structural defects modifying the physical properties of the composite materials is discussed in this work.

Grain boundary effect on BaTiO₃ has been widely investigated for several decades. However, all of them tailored the grain boundary by grain size of BaTiO₃. In this case, a direct way was introduced to modify the grain boundary by coating technique to investigate the role of grain boundary in ferroelectric materials. Nonferroelectric phase TiO₂ was employed to investigate grain boundary effects on the electrical properties of BaTiO₃ piezoelectric ceramics. TiO₂ coating can result in the reduction of piezoelectric and ferroelectric properties and the annealing process in oxygen can increase piezoelectric behavior of pure BaTiO₃ due to valence state of Ti ions while that remains for Ti-modified composition possibly due to the increased grain boundary effect by impedance analysis. Compared with ferroelectric grain, grain boundary plays a critical role to impact the electrical properties of perovskite-type ferroelectric materials.

Pb(${\text{In}}_{1∕2}$${\text{Nb}}_{1∕2}$)O₃-Pb(${\text{Mg}}_{1∕3}$${\text{Nb}}_{2∕3})$O₃-PbTiO₃ (PIN-PMN-PT) relaxor ferroelectric crystals in 5^″ diameter by 5^″ length were grown by the Bridgman (BR) method for the first time. Typical issues in the crystal growth concerning large volume of the melt, high density of the crystal and corrosion of the melt on the wall of Pt crucible are discussed.

This research summarizes the analytical and experimental results of heat-transfer processes influence on defects formation during sapphire crystal growth by horizontal directed crystallization method (HDC). The shape of solid-melt interface significantly influences the process of sapphire crystals growth by this method. We receive the Stefan problem solution for sapphire crystals growth. It allows investigating the crystal growth process and the related factors (thermal stresses on different stages of growth process), their influence on defects formation. We investigate the main reasons for the formation of defective structures of the solid phase of sapphire crystals and the influence of thermal unit construction, the crystal geometry on the quality of the resulting sapphire crystal. We study the structure formation process, impurity distribution, and the nature of the defects in the crystal during it growth.

A tunable high-Q surface acoustic wave (SAW) resonator in the form of several parallel-connected interdigital transducers loaded on a varying capacitance on lithium niobate substrates was developed and studied. The working frequency range was 90–2450MHz. A method of calculating such resonators, considering losses in the metal film as well as losses due to the propagation of SAWs and transformations into bulk waves is proposed. Such a design allows one to obtain a quality factor over 5000 in the frequency range 2400–2483MHz. The resonant frequency shifts by 600kHz when the capacitance changes by $\pm 25$% of the value of 21pF (or 32ppm/pF) and has an almost linear character.

Molecular dynamics (MD) is a technique of atomistic simulation which has facilitated scientific discovery of interactions among particles since its advent in the late 1950s. Its merit lies in incorporating statistical mechanics to allow for examination of varying atomic configurations at finite temperatures. Its contributions to materials science from modeling pure metal properties to designing nanowires is also remarkable. This review paper focuses on the progress of MD in understanding the behavior of iron — in pure metal form, in alloys, and in composite nanomaterials. It also discusses the interatomic potentials and the integration algorithms used for simulating iron in the literature. Furthermore, it reveals the current progress of MD in simulating iron by exhibiting some results in the literature. Finally, the review paper briefly mentions the development of the hardware and software tools for such large-scale computations.