Ankur Khare

Dielectric, ferroelectric and magnetic properties of hexagonal Ba6Y2Ti4O17 (BYTO) perovskite derived from semi wet route

Ba6Y2Ti4O17 (BYTO) ceramic was prepared by semi wet combustion route using metal nitrates and solid TiO2. The synthesized material was characterized by thermo-gravimetric analysis (TG/DTA), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). A systematic investigation of dielectric, ferroelectric and magnetic properties of BYTO ceramic was carried out. The material exhibited very high dielectric constant (e = 1.5 × 103) at 100 Hz and 303 K. The SEM, TEM images and Le-Bail analysis of XRD data shows hexagonal perovskite nature of the BYTO. The observed ferroelectric property showed the decrease of remnant polarization and coercive electric field with increase in temperature due to thermal fluctuation of material. The ferromagnetic to paramagnetic nature of the material increase with temperature due to disordering of magnetic domains. Impedance spectroscopic studies clearly show contribution of grain and grain boundary towards conductivity and dielectric permittivity of the material.

Morphometric and rheological study of lunar domes of Marius Hills volcanic complex region using Chandrayaan-1 and recent datasets

Marius Hills volcanic complex is one of the most important regions on the lunar surface having an abundant number of volcanic features like domes and cones. Systematic mapping of 106 domes/cones in the Marius Hills region was carried out in this study using high-resolution orthoimage and digital elevation models of Chandrayaan-1 and Kaguya missions. Various morphometric parameters like diameter, height, volume, flank slope, circularity index and form factor are derived for all the mapped domes. The rheological parameters, such as viscosity and eruption rate are estimated for isolated domes and cones superimposed over low domes. The morphometric and rheological properties of these domes are comparable to those located in the area near to Hortensius crater and other mare regions. Surface ages derived for a selected region in NW portion of the Marius Hills volcanic complex using crater size-frequency distribution technique yields ages of 2.98 and 1.91 Ga. It suggests that the domes in this region formed at about 2.98 Ga ago, and then, the younger mare basalts likely embayed this region about 1.98 Ga ago. Stratigraphic sequence of rilles, wrinkle ridge and domes shows that wrinkle ridges are the oldest, while the rilles are younger than the domes.

Dielectric studies of CCTO-based nanocomposite ceramic synthesized by a solid state route

Abstract In the present work, the nanocomposite 0.9CaCu3Ti4O12–0.1BaTiO3 (CC-BT) is synthesized by a solid-state reaction method by sintering at 950°C for 12 h. X-ray diffraction analysis confirms the presence of both BaTiO3 and CaCu3–Ti4O12 phases in the composite ceramic. Transmission electron microscopy analysis of the composite demonstrates the formation of nanoparticles with an average particle size of 40 ± 5 nm. The surface morphology of the composite sintered at 950°C for 12 h obtained by scanning electron microscopy analysis indicates the evolution of large and small grains with a bimodol distribution. The average and root mean square roughness were found to be 1.41 nm and 2.24 nm respectively by atomic force microscopy studies. The dielectric constant of CC-BT ceramic was determined to be 6231 at 100 Hz and 500 K. The presence of the semiconducting grains and the insulating grain boundaries in the composite supports the internal barrier layer capacitance mechanism operative in CC-BT nanocomposite.

Dielectric, ferroelectric and magnetic study of iron doped hexagonal Ba4YMn3O11.5−δ (BYMO) and its dependence on temperature as well as frequency

The effects of iron doping in Ba4YMn3O11.5−δ (BYMO) on dielectric, ferroelectric and magnetic properties were studied. The Ba4YMn3−xFexO11.5−δ (x = 0.05, 0.1, 0.2) are termed as BYMFO-05, BYMFO-1 and BYMFO-2, respectively. These samples were synthesized by a chemical route in which aqueous solutions of all the metal nitrates/acetates were used as starting materials. The synthesized materials were characterized by powder XRD, scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The Rietveld refinement confirms a hexagonal perovskite having the space group Rm. The particle size observed by TEM was found to be 7 nm. The remnant magnetization and remnant polarization increased with a decrease of temperature in all samples. The impedance spectroscopy reveals that the material has semiconducting grains and insulating grain boundaries which was also supported by an internal barrier layer capacitor model. The temperature and frequency dependent dielectric constant and the corresponding low dielectric loss indicate the material could be used for memory devices. A Debye type dielectric relaxation was observed only in the case of BYMFO-05, whereas temperature independent permittivity was observed in the cases of BYMFO-1 and BYMFO-2. The absence of a saturation in the magnetization as well as the ferroelectricity shows the lossy capacitor nature of the material.

Dielectric studies of 0·5 BaTiO3–0·5 Bi2/3Cu3Ti4O12 nanocomposite

A nanoceramic composite with a composition of 0·5 barium titanate (BaTiO3; BTO) and 0·5 Bi2/3Cu3Ti4O12 (BCTO) was synthesised using the solid-state method. Microstructural details were studied by X-ray diffraction (XRD) and scanning electron microscopy. XRD analysis confirmed the existence of both the BTO and BCTO phases. The average crystallite sizes obtained by the XRD analysis were found to be around 45 ± 16 nm. The sample sintered at 950°C for 12 h exhibited a very high dielectric constant (e r = 43 459) at 100 Hz and at room temperature. The presence of semiconducting grains with insulating grain boundaries significantly contributes to such a high dielectric constant value, supporting the internal barrier layer capacitance mechanism operative in BTO–BCTO composites. The dielectric loss (tan δ ) peaks observed for the BTO–BCTO composite with variation of frequency at few selected temperatures give an indication of the relaxation behaviour present in the composite.

Dielectric Studies of 0.5BaTiO 3 -0.5Bi 2/3 Cu 3 Ti 4 O 12 Nano-Composite

A nanoceramic composite with a composition of 0·5 barium titanate (BaTiO3; BTO) and 0·5 Bi2/3Cu3Ti4O12 (BCTO) was synthesised using the solid-state method. Microstructural details were studied by X-ray diffraction (XRD) and scanning electron microscopy. XRD analysis confirmed the existence of both the BTO and BCTO phases. The average crystallite sizes obtained by the XRD analysis were found to be around 45 ± 16 nm. The sample sintered at 950°C for 12 h exhibited a very high dielectric constant (e r = 43 459) at 100 Hz and at room temperature. The presence of semiconducting grains with insulating grain boundaries significantly contributes to such a high dielectric constant value, supporting the internal barrier layer capacitance mechanism operative in BTO–BCTO composites. The dielectric loss (tan δ ) peaks observed for the BTO–BCTO composite with variation of frequency at few selected temperatures give an indication of the relaxation behaviour present in the composite.