Smita A. Acharya

Structural and dielectric anomalies near the MPB region of Na0.5Bi0.5TiO3–SrTiO3 solid solution

In the present attempt, (1 − x)NBT(Na0.5Bi0.5TiO3)–xST(SrTiO3) (x = 0.24–0.28) solid solutions are studied near the MPB region to investigate short-range structural and dielectric anomalies. X-ray diffraction study confirms the presence of MPB by the co-existence of rhombohedral (202), (122) and pseudocubic (002), (112) peaks at x = 0.25–0.26. For x = 0.24, the absence of pseudocubic peaks indicate the complete diffusion of cubic ST phase into the rhombohedral phase of pure NBT. RAMAN spectra exhibit the appearance of new vibrational modes at A and B sites by the splitting of bands in the NBT–ST at the MPB (x = 0.25–0.26), which are not detected for x 0.26. This can be assigned to local ordering at the A-site cations (Bi/Na/Sr) and B-site TiO6 octahedral distortion, respectively. The high-temperature RAMAN spectra confirm the structural stability at up to 550 °C of all NBT–ST samples near the MPB. Dielectric transition temperature is shifted from 360 °C to 160 °C with ST and shows a single broad anomaly. The broadening of the dielectric peak with deviation from Curie–Weiss law proves the dielectric dispersion near the MPB region of NBT–ST. The MPB origin is the outcome of local imbalance due to chemical inhomogeneity at the A site and short-range disordering at the B site. This induces strain-charge disparity, which influences dielectric behavior.

Novel perovskite–spinel composite approach to enhance the magnetization of LaFeO3

In the present work, the perovkite–spinel interface effect on the bulk magnetic behavior of lanthanum ferrite (LaFeO3) based composite systems is under investigation in view of the enhancement of the magnetization of LaFeO3. By using LaFeO3 as the perovskite phase and NiFe2O4 as the spinel phase with the compositions x = 0, 20, 30, 40 and 100 wt%, a composite system is developed by mechanical mixing. The structures are confirmed using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Physical interaction at the interface of the LaFeO3 and NiFe2O4 phases is realized by XRD peak broadening and shifting. The M–T and M–H curves are closely monitored to investigate the perovskite–spinel interface effect on the bulk magnetic behavior of the composites. Significant enhancement in the magnetization of the perovskite–spinel composite phase with a 60% LaFeO3–40% NiFe2O4 composition over individual phases is detected. The composition effect up to 60 : 40 of LaFeO3–NiFe2O4 is considered to preserve the dominance of the LaFeO3 phase. The spin coupling mechanism across the interface is speculated for the enhancement of the magnetization in the composite. Mossbauer spectroscopic investigation confirms the co-existence of magnetization in the composites.

Effect of isovalent dopants on photodegradation ability of ZnS nanoparticles

Isovalent (Mn, Cd, Cu, Co)-doped-ZnS nanoparticles having size vary in between 2 to 5nm are synthesized by co-precipitation route. Their photocatalytic activity for decoloration of Cango Red and Malachite Green dyes is tested in visible radiation under natural conditions. Structural and morphological features of the samples are investigated by X-ray diffraction, Raman spectroscopy, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and UVVis spectrometer. Single phase zinc blende structure of as-synthesized undoped and doped-ZnS is confirmed by XRD and revealed by Rietveld fitting. SEM and TEM images show ultrafine nanoparticles having size in the range of 2 to 5nm. UV-Vis absorption spectra exhibit blue shift in absorption edge of undoped and doped ZnS as compared to bulk counterpart. The photocatalytic activity as a function of dopant concentration and irradiation time is systematically studied. The rate of de-coloration of dyes is detected by UVVis absorption spectroscopy and organic dye mineralization is confirmed by table of carbon (TOC) study. The photocatalytic activity of Mn-doped ZnS is highest amongst all dopants; however Co as a dopant is found to reduce photocatalytic activity than pure ZnS.

Microwave-Assisted Chemical Reduction Routes for Direct Synthesis of (fct) L1 0 Phase of Fe-Pt

Abstract Microwave-assisted chemical reduction route has been explored for the direct synthesis of fct L10-phase of Fe-Pt nanoparticles in the present work. Effects of microwave power and irradiation time on the growth process are systematically studied. Using this facile and high yield technique we could tune particle size from 7 to 17 nm. Prepared Fe-Pt NPs exhibited ordered face centered tetragonal (fct) L10 phase without any post-synthesis treatment. The particle size and magnetic properties of the prepared Fe-Pt were found to be very sensitive to the microwave irradiation power, while influence of exposure time was insignificant. The hysteresis measurements were performed at 300 K to study magnetic properties of the synthesized Fe-Pt as a function of crystallite size. Coercivity and saturation magnetization were observed to be decreasing with diminishing particle size. The microwave-assisted route is found to be a simple technique for direct synthesis of metal alloys and may prove to be a potential tool of high density data storage materials such as Fe-Pt.

Fabrication of 1D Microtubes of ZnS by Microwave Irradiation Method

1D tubes of ZnS were prepared by microwave irradiation process. The X-RD pattern indicated that as-prepared sample was hexagonal ZnS structure with cell constant a = 3.5277 A° and c = 5.79 A°. SEM observed the tubes-like structure having the length ranging from 10–20 μm with the average diameter of 5 μm and wall thickness of 1–2 μm. The EDAX pattern exhibited the atomic percentage ratio of Zn : S = 59 : 41, indicating that it was rich in zinc. Effect of microwave power and exposure time on the growth process was investigated. It was revealed that the microwave power plays a vital role in determining the diameter of the tubes. This simple technique using a multimode microwave source may prove to be a potential tool for growing similar 1D structure of other -oxide, -sulphide, -selenide based compounds.

Synthesis and Characterization of Nanosized Dy-Doped of Ceria Developed by Microwave Assisted Combustion Route

Nanosized Ce1-xDyxO2-x/2 (DDC, x = 0.05—0.25 mol%) were synthesized by combustion routes induced by microwaves (MS) and compared with the same composition prepared by conventional (CS) method. The conventional and microwave sintering routes were also used to consolidate the pellets. The samples were characterized by X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and AC impedance spectroscopy. The as-combusted powders prepared by microwaves were found to be pure oxides with low crystallinity, and exhibited excellent sintering behavior. Highly dense DDC pellets with fine and homogeneously grown grains (400 nm) were achieved by microwave, while conventionally densified pellets had average grain size of 1100 −1400 nm. The ionic conductivity measured for pellet sintered by MS at 1050°C for 1 h is, σ550°C = 7.42 × 10−2 S/cm, Ea = 0.86 eV, and for CS at 1300°C for 5 h, is σ550°C = 9.79 × 10−3 S/cm, Ea = 1.05 eV.

XPS study of surface state of novel perovskite system Dy0.5Sr0.5Co0.8Fe0.2O3-δ as cathode for solid oxide fuel cells

In the present attempt,novel perovskite oxide Dy0.5Sr0.5Co0.8Fe0.2O3–δ (DSCF) as cathode material has been synthesized by an Ethylene glycol-citrate combined sol-gel combustion route. Orthorhombic symmetry structure is confirmed by X-ray diffraction (XRD) and data is well fitted using Rietveld refinement by Full-Prof software suite. Chemical natureof surface of DSCF has been analyzed by using X-ray photoelectron spectroscopy (XPS). XPS result shows that Dy ions are in +3 oxidation state and Sr in +2 states. However Co2p and Fe2p spectra indicates partial change in oxidation state from Co3+/Fe3+ to Co4+/Fe4+. These attribute to develop active sites on the surface for oxygen ions. O1s XPS spectra shows two oxygen peaks relatedto lattice oxygen in perovskite and absorbed oxygen in oxygen vacancy are detected. O1s spectra demonstrate the existence of adsorbed oxygen species on the surface of DSCF oxide which is quite beneficial for intermediate temperature of Solid Oxide Fuel Cell.

Novel ceramic-polyamide nanocomposites approach to make flexible film of PZT ceramics: Structural and dielectric study

ABSTRACT In the present attempt, Lead zirconate titanate/polyamide Nylon-6 (PZT/N-6) nanocomposite films were successfully prepared using solution casting approach. The nanoscale PZT particles synthesized by sol-gel route were homogeneously dispersed in Nylon-6 matrix by ultrasonication. Formation of nanocomposite was confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The structural study verifies the semi-crystalline nature of Nylon-6 and rhombohedral phase of PZT with formation of compositions as physical mixture having no interface interaction. Structural stability of the nanocomposite was investigated by Thermal gravimetry analysis (TGA) and Differential thermal analysis (DTA) up to about 340°C. The surface microstructure of nanocomposites film having 50:50 compositions of PZT and Nylon-6 shows uniform dispersion of PZT nanoparticles in Nylon-6 matrix with negligible pores. However higher % of PZT in composition exhibits agglomeration with significant number of pores; it causes reduction in dielectric constant and hence rise in dielectric loss. Room temperature (298 K) dielectric constant of PZT/N-6 nanocomposite films are smaller than pure PZT and found highly influenced by dispersion of PZT in N-6 matrix. For higher content of PZT in N-6 leads to lower dielectric constant and higher dielectric loss, while 50:50 PZT/N-6 nanocomposition gives highest dielectric constant and comparative lower loss. 50:50 PZT/N-6 nanocomposites film can be used in devices where flexibility of PZT is expected.

Study of multi-functionality of lanthanum ferrite (LaFeO3)

In the present work, multifunctional behaviors of LaFeO3 (LFO) are investigated by studying its dielectric and photocatalytic properties, respectively. LFO is synthesized by microwave-assisted co-precipitation route. Orthorhombic structure is confirmed by X-ray diffraction (XRD) and data is well fitted using Rietveld refinement by Full-Prof suite. Frequency and Temperature dependence dielectric behavior are systematically studied. The dielectric constant of LFO was found to be 2500 – 3000 with dissipation factor less than 5%. Photodegradation of toxic dye (Methylene Blue) using as-prepared LFO is also investigated. UV-visible absorption spectra are used to study the photodegradation behaviour. Photodegradation of methylene blue (MB) taken from textile industries by LFO are reported. The colossal value of dielectric constant of LFO exhibits high potential to use as room temperature capacitive component for device miniaturization in microelectronics as well as photodegradation ability shows good photocatalyst.

Percolation Effect of PZT-BNT Composite System on Sinterability and Dielectrics Behaviour in View of Development of LTCC

Ceramic composite of (1−x)Pb(Zr0.52Ti0.48)O3-x Bi0.5Na0.5TiO3 (PZT-BNT, where x = 0, 25, 50, 75, 100 wt%) were developed in LTCC view point. The presence of biphase composition was confirmed by X-ray diffraction (XRD). The microstructural study of compositions by scanning electron microscopy (SEM) reveals mixing of two phases in powder form of composites. Good densification of compacted pellet of bulk ceramics was also confirmed by SEM. Sintering temperature was reduced from 1270°C for PZT-phase to 1000°C for PZT-BNT composite phases. Enhancement of sinterability of composite system was assigned to solid-state bimodal mixed-phase sintering approach. Dielectric permittivity as a function of temperature exhibits diffuse phase transition in composite system. Complex dielectric permittivity with respect to frequency shows a dispersive behaviour due to Maxwell-Wagner effect at low frequency and Debye relaxation at high frequency range. The percolation effect between two ceramics phases on enhancement of sinterability and dielectric behaviour of the composites is intriguing feature of the work.