Effect of size reduction on charge ordering in La0.5Ca0.5MnO3

In this paper we report size-induced collapse of charge ordering in nanoparticles of La0.5Ca0.5MnO3 (LCMO). This happens when the particle size approximately 100 nm or below. The investigation shows that a tuning of size can tune the nature of ground state in manganites. The particles were synthesized by sol-gel route (polyol based) and were characterized by X-ray-diffraction (XRD) and Transmission Electron Microscope (TEM). The collapse of charge ordering stabilizes the ferromagnetic phase with metallic character. The resulting phase appears to be electronically phase segregated. We base our conclusions on detailed magnetization and resistivity measurements as well as the evolution of the structure on size reduction. The observed data have been explained as arising due to a combined effect of both phases. Size reduction reduces the orthorhombic distortion and enhances the Double exchange that stabilizes the ferromagnetic phase and increases the band width. It is likely that this enhanced band-width leads to weakening of the charge-ordering and its eventual collapse.     

Exploring a reversible NOR from a 4 × 4 modified Fredkin gate and its optical mapping using a LiNbO3-based MZI

Journal of Computational Electronics - The extensive search for the implementation of reversible logic using emerging technologies has paved the way for the rise of optical computing. The...     

Electron Microscopic Study on the Suction Cast In Situ Ti-Fe-Sn Ultrafine Composites

The current investigation reports detailed study on the microstructural evolution in the suction cast hypereutectic Ti₇₁Fe_29?x Sn _x alloys during Sn addition with x = 0, 2, 2.5, 3, 3.85, 4.5, 6, and 10 at. pct and the solidification of these ternary alloys using SEM and TEM. These alloys have been prepared by melting high-purity elements using vacuum arc melting furnace under high-purity argon atmosphere. This was followed by suction casting these alloys in the water-cooled split Cu molds of diameters, ? = 1 and 3 mm, under argon atmosphere. The results indicate the formation of binary eutectic between bcc solid solution ??-Ti and B2 FeTi in all alloys. ??-Ti undergoes eutectoid transformation, ??-Ti ?? ??-Ti + FeTi, during subsequent solid-state cooling, leading to formation of hcp ??-Ti and FeTi. For alloys x < 2, the primary FeTi forms from the liquid before the formation of eutectic with minute scale Ti₃Sn phase. For alloys with 2 ?? x ?? 10, the liquid is found to undergo ternary quasi-peritectic reaction with primary Ti₃Sn, L+Ti₃Sn ?? ??-Ti+FeTi, leading to formation of another kind of FeTi. In all the other alloy compositions (3.85 ?? x ?? 10), Ti₃Sn and FeTi dendrites are observed in the suction cast alloys with profuse amount of Ti₃Sn being formed for alloys with x ?? 4.5. The current study conclusively proves that the liquid undergoes ternary quasi-peritectic reaction involving four phases, L + Ti₃Sn ?? ??-Ti + FeTi, which lies at the invariant point Ti_69.2±0.8Fe_27.4±0.7Sn_3.4±0.2 (denoted by P). Below P, there is one univariant reaction, i.e., L ?? ??-Ti + FeTi for all alloy compositions, whereas above P, liquid undergoes one of the univariant reactions, i.e., L + ??-Ti ?? Ti₃Sn (Sn = 2, 2.5, 3, and 4.5 at. pct) or L + FeTi ?? Ti₃Sn for alloys (Sn = 6, 10 at. pct). For alloy with Sn = 3.85 at. pct, the ternary quasi-peritectic reaction is co-operated by two monovariant eutectic reactions, i.e., L ?? ??-Ti + FeTi below P and L ?? FeTi + Ti₃Sn above P. Detailed microstructural information allows us to construct liquidus projection of the investigated alloys. The results are critically discussed in the light of available literature data.     

Characterization and transport properties of ceramic filler incorporated natural rubber composites

Crystalline glass–ceramic fillers were prepared from calcium carbonate, silica, alumina, and calcium fluoride by heating and subsequent quenching in cold water. The fillers were incorporated into natural rubber (1,4-cis-polyisoprene) and the filled rubber composites were crosslinked with sulfur in the presence of different rubber additives. The unfilled and filled rubber composites were characterized. The transport properties of benzene, toluene, and p-xylene (BTX) through the rubber composites were studied in terms of sorption, diffusion, permeation, and mass transfer coefficients. The effect of the ceramic fillers on the mechanical, thermal and transport properties were studied. The sorption data at different temperatures were used for calculating activation energy of diffusion, permeation, free energy, and enthalpy of sorption. The BTX remained in the liquid state within the composite matrix as evident from negative ΔS. The diffusion coefficient (D) and mass transfer coefficient (k_mtc) of BTX decreased with the increase in filler loading. Accordingly, for the transport of BTX the unfilled rubber showed a D (D × 10⁷ cm²/s) and mass transfer coefficient (k_mtc × 10⁴ cm/s) of 5.67/3.97/2.96 and 7.71/7.08/7.04, respectively which decreased to 5.06/2.95/2.57 and 7.53/6.95/6.90, respectively for the composite containing 50 wt.% ceramic filler.     

Microwave‐Enhanced Efficient Regioselective Synthesis of 1,3,4‐Trisubstituted 2‐Mercaptoimidazoles on a Soluble Support

A novel efficient synthetic method for regioselective synthesis of optically active 2‐mercaptoimidazoles with three points of structural diversity was investigated on a polyethylene glycol (PEG) support. The key synthetic steps involve (i) synthesis of thiourea derivatives of polymer‐supported amino acids with isothiocyanates and (ii) one‐pot regioselective condensation of PEG‐linked thiourea with α‐bromo ketones to furnish the 2‐mercaptoimidazole skeleton under microwave conditions. An excellent regioselectivity was observed during this one‐pot condensation reaction which was further supported by NOE studies. In addition to three sets of structural diversity, supplementary chirality at the α‐position of the 2‐mercaptoimidazole skeleton is the key feature of this synthesis. A representative set of 2‐mercaptoimidazoles was efficiently assembled on soluble support utilizing various L ‐amino acids, isothiocyanates and α‐bromoaryl ketones with good yields.     

Synthesis and characterization of highly soluble poly(ether imide)s containing indane moieties in the main chain

A new indane containing unsymmetrical diamine monomer ( 3 ) was synthesized. This diamine monomer leads to a number of novel semifluorinated poly (ether imide)s when reacted with different commercially available dianhydrides like benzene‐1,2,4,5‐tetracarboxylic dianhydride (PMDA), benzophenone‐3,3′, 4,4′‐tetracarboxylic dianhydride (BTDA), 4,4′‐(hexafluoro‐isopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA), and 4,4′‐(4,4′‐Isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) by thermal imidization route. All the poly(ether imide)s showed excellent solubility in several organic solvents such as N‐methylpyrrolidone (NMP), N,N‐dimethylformamide (DMF), N,N‐dimethylacetamide (DMAc), tetrahydrofuran (THF), chloroform (CHCl₃) and dichloromethane (DCM) at room temperature. These light yellow poly (ether imide)s showed very low water absorption (0.19–0.30%) and very good optical transparency. Wide angle X‐ray diffraction measurements revealed that these polymers were amorphous in nature. The polymers exhibited high thermal stability up to 526°C in nitrogen with 5% weight loss, and high glass transition temperature up to 265°C. The polymers exhibited high tensile strength up to 85 MPa, modulus up to 2.5 GPa and elongation at break up to 38%, depending on the exact polymer structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Integrated Blind Signal Separation and Neural Network Based Energy Detector Architecture

Wireless Personal Communications - Energy detector is the simplest spectrum sensing technique in cognitive radio in terms of computation complexity as it is developed assuming only channel noises...     

Benzotrifluoromethyl group‐substituted poly(para‐phenylenevinylene): Effect on solubility,optical, and electronic properties

A new organosoluble benzotrifluoromethyl group containing poly(p‐phenylenevinylene) (BTFM‐PPV) has been synthesized via Gilch polymerization. The polymer is soluble in common organic solvents such as tetrahydrofuran, chloroform, dichloromethane, toluene, and xylene. BTFM‐PPV exhibited fluorescence emission peak with a very high blue shift at 474 nm with an excitation wavelength at 420 nm compared with many other PPV derivatives reported earlier. Incorporation of fluorated bezotrifluoromethyl pendent group in the PPV backbone lowers the HOMO and LUMO energy levels of BTFM‐PPV (2.48 eV) which retarded the hole injection and increase the electron injection in the device. The current–voltage (I–V) characteristic of the polymer was measured by fabricating the polymer as ITO/BTFM‐PPV/Al diode. The device performance was markedly improved by incorporation of 4‐fluoro‐3trifluoromethylphenyl units into the polymer main chain. The turn on voltage of the device observed from the I–V measurements was 7 V. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010