Dhananjay K. Sharma

IMPEDANCE AND MODULUS SPECTROSCOPY CHARACTERIZATION OF SODIUM-BISMUTH TITANATE-BASED LEAD-FREE FERROELECTRIC MATERIALS

In this paper, we present impedance spectroscopy of Sodium Bismuth Titanate-based materials belonging to (1-x)Na1/2Bi1/2TiO3-xBaTiO3(x = 0.04) (NBT–BT) system. NBT–BT ceramics are prepared by high temperature solid-state reaction method. X-ray diffraction technique showed single-phase polycrystalline sample with an ABO3 perovskite structure. Dielectric behavior and the impedance relaxation were investigated in a wide range of temperature (room temperature (RT) –500°C) and frequency (1 kHz–1 MHz). A broad dielectric constant peak was observed over a wide temperature range around the phase transition temperature. The complex impedance plot exhibited one impedance semicircle identified over the frequency range of 1 kHz–1 MHz, which is explained by the grain effect of the bulk. The centers of the impedance semicircles lie below the real axis, which indicates that the impedance response is a Cole–Cole type relaxation.

Biosynthesized composites of Au-Ag nanoparticles using Trapa peel extract induced ROS-mediated p53 independent apoptosis in cancer cells

Abstract The current study highlights rapid, sustainable, and cost-effective biosynthesis of silver (Ag), gold (Au) nanoparticles (NPs), and bimetallic Au-AgNPs composites using bio-waste extract of Trapa natans. Growth of the NPs was monitored spectrophotometrically and peak was observed at ∼525 nm, ∼450 nm, and ∼495 nm corresponding to Plasmon absorbance of AuNPs, AgNPs, and Au-AgNPs, respectively. Transmission electron microscopy (TEM) revealed the size of AgNPs (∼15 nm), AuNPs (∼25 nm), and Au-AgNPs (∼26–90 nm). Synthesized NPs follow the Gaussian bell curve and its crystalline nature was identified by X-ray diffraction (XRD). Furthermore, Au-AgNPs induced cytotoxicity in various cancer cells (HCT116, MDA-MB-231, and HeLa) effectively at 200 μg/mL. Au-AgNPs-exposed cancer cells exhibited apoptotic features such as nuclear condensation, mitochondrial membrane potential loss, and cleavage of casp-3 and poly (ADP-ribose) polymerase-1 (PARP). Au-AgNPs exposure enhanced reactive oxygen species (ROS) and upon inhibition of ROS, apoptosis was reduced effectively. NPs treatment killed HCT116 WT and p53 knockout cells without any significant difference. Mechanistically, Au-AgNPs derived with Trapa peel extract significantly enhance ROS which trigger p53-independent apoptosis in various cancer cells effectively. Our study explores the use of bio-waste for the green synthesis of NPs, which can be attractive candidates for cancer therapy.

Modification of Nanoclay Systems: An Approach to Explore Various Applications

Nanoclay has a great potential in various fields. Small amount of nanoclay can change the whole physical and chemical properties of polymers, paints, inks and lubricants by dispersing nanoclay layers into the polymer matrices. The flexibility of interlayer gallery of nanoclay helps in the release of drugs to the targeted place. The controlled release of drugs takes place on account of the drug incorporated within the nanoclay galleries. This makes these nanomaterials as potential materials with its application in pharmaceutical field. Organoclays, a type of nanoclay are also being utilized for waste water treatment in junction with other sorbents viz. activated carbon and alum. Organoclays have been found to be the finest material for water treatment especially when the water contains enough amounts of oil and grease or humic acid. The use of nanoclays as reinforcing agent or additives in polymers for various properties is exploited for various applications. This chapter provides an overview of nanoclays or types of nanoclays with significance on the utilization of nanoclays as the filler in polymer matrices for the synthesis/fabrication of polymer nanocomposites, drug delivery agents, viscosity modifier for coatings, inks and lubricants and nanoclays for industrial effluent as well as potable water treatment.

Effect of Na on the structural and electrical properties of lead-free sodium potassium niobate ceramics

Abstract K1-xNaxNbO3 (where x = 0.48, 0.53, 0.56 and 0.60) (KNN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single orthorhombic phase was formed for KNN. Dielectric anomalies around 200°C and 370°C were identified as ferroelectric-ferroelectric and ferroelectric-paraelectric transition temperatures for KNN compound. The electrical behavior of KNN ceramics was studied by the help of impedance spectroscopy technique in the different temperature range. The impedance response in KNN ceramics could be resolved into a single contribution, associated with the bulk/grain. The conductivity studies confirm that the activation energies are strongly frequency dependent. A decreasing trend of Z′ with rise in temperature suggests the presence of negative temperature coefficient of resistance (NTCR) in the material in the low frequency region but tends to merge in the high frequency region at almost all temperatures.

Effect of potassium content on the dielectric and electrical properties of sodium potassium niobate ceramics

(KxNa1-x) NbO3 ceramics or KNN is considered as one of the most promising candidates for lead-free piezoelectric applications, because of its high Curie temperature and good electrical properties. However, it is well known that dense and well-sintered KNN ceramics are very difficult to obtain by conventional sintering process because of the high volatility of alkali elements at high temperatures. The major strategy to overcome this problem is simply adding excess alkali metals in the starting composition. KNN ceramics with potassium excess were prepared by high temperature solid state reaction technique. Effect of K excess on the phase structure and electrical properties of KNN ceramics were investigated. The results showed that the single phase orthorhombic perovskite structure was obtained in ceramics. Ferroelectric-paraelectric phase transition temperature was about 370 °C for all the samples. The dielectric permittivity was maximized, the dielectric loss was a minimum and the relative density was found to reach 95% of theoretical density for K content= 53% in KNN system. Impedance study shows the non-Debye type temperature of relaxation phenomenon in the system. Above the ferroelectric paraelectric phase transition temperature, the electrical conduction is governed by the thermal excitation of carriers from oxygen vacancies exhibiting NTCR behavior.

Dielectric relaxation and conductivity in lead-free sodium bismuth titanate ceramics

Perovskite structured Na0.5Bi0.5TiO3 (NBT) ceramics were synthesized by the solid-state sintering method. The presence of constituent phases and crystalline structure of the system was confirmed by X-ray diffraction technique exhibiting perovskite structure with rhombohedral symmetry. The dielectric behavior showed a broad peak at ∼400°C characterized as Curie temperature. The real part of impedance (Z′) as a function of frequency has higher values at lower frequencies and decreases up to 20 kHz and attains a constant value beyond that frequency. The broadening of peaks in frequency explicit plots of imaginary part of impedance (Z″) suggests that there is a spread of relaxation times, which involves more than two equilibrium portions. The purpose of giving dielectric data obtained from the impedance studies is to give the usefulness of the impedance formalism to evaluate the dielectric behavior in the present sample. The Nyquist plot and conductivity studies showed the NTCR character of NBT ceramic samples.