Phonon anomalies and structural transition in spin ice Dy2Ti2O7: a simultaneous pressure-dependent and temperature-dependent Raman study

We revisit the assignment of Raman phonons of rare-earth titanates by performing Raman measurements on single crystals of O18 isotope-rich spin ice Dy2Ti2O718 and nonmagnetic Lu2Ti2O718 pyrochlores and compare the results with their O16 counterparts. We show that the low-wavenumber Raman modes below 250 cm-1 are not due to oxygen vibrations. A mode near 200 cm-1, commonly assigned as F2g phonon, which shows highly anomalous temperature dependence, is now assigned to a disorder-induced Raman active mode involving Ti4+ vibrations. Moreover, we address here the origin of the new Raman mode, observed below TC similar to 110 K in Dy2Ti2O7, through a simultaneous pressure-dependent and temperature-dependent Raman study. Our study confirms the new mode to be a phonon mode. We find that dTC/dP = + 5.9 K/GPa. Temperature dependence of other phonons has also been studied at various pressures up to similar to 8 GPa. We find that pressure suppresses the anomalous temperature dependence. The role of the inherent vacant sites present in the pyrochlore structure in the anomalous temperature dependence is also discussed. Copyright (c) 2012 John Wiley & Sons, Ltd.

Synthesis, Spectral Characterization, Crystal Structure and Thermal Behavior of Tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate

Tert-butyl 2,2-bis(2,4-dinitrophenyl)ethanoate was prepared from the ethanolic solution of 1-chloro-2,4-dinitrobenzene, tert-butyl 3-oxobutanoate and triethylamine. Acetyl group in tert-butyl 3-oxobutanoate has cleaved off during the formation of the title molecule. UV-VIS, IR, 1H NMR, 13C NMR, Proton-Proton COSY data and single crystal XRD results support the proposed structure. Flammability test, impact sensitivity test and TG/DTA studies at different heating rates on the synthesized molecule imply that it is an insensitive high energy density material.

Preparation and characterization chemistry of nano-crystalline Ni-Cu-Zn ferrite

In submitted research; nanocrystalline powders having elements Ni0.5Cu0.25Zn0.25Fe2 xInxO4 with varied amounts of indium ( x = 0.0, 0.1, 0.2, 0.3 and 0.4) were grown-up by modified citrate to nitrate alchemy. The realism of single phase cubic spinel creation of the synthesized ferrite samples was studied by the DTA-TGA, XRD, SEM, EDX, FT-IR, VSM and dielectric measurements. SEM was applied to inspect the morphological variations and EDX was used to determine the compositional mass ratios. The studies on the dielectric constant (epsilon'), dielectric loss (epsilon `'), loss tangent (tan delta), ac conductivity (sigma(ac)), resistive and reactive parts of the impedance analysis (Z' and Z `') at room temperature were also carried out. The saturation magnetizations (Ms) were determined using the vibrating sample magnetometer (VSM). Ms. decreased with the increase In3+ doping content, as Fe3+ of 5(mu B) ions are replaced by In3+ of 5 mu(B) ions. (C) 2012 Elsevier B. V. All rights reserved.

New metal-organic precursors for MOCVD applications: Synthesis, characterization, crystal structure and thermal properties of mixed-ligand Mg(II) complexes

In an effort to develop new MOCVD precursors, mixed-ligand metal-organic complexes, bis (acetylacetonato-k(2)O,O') (2,2'-bipyridine-k(2)N,N') magnesium(II), and his (acetylacetonato-k(2)O,O') (1,10-phenanthroline-k(2)N,N') magnesium(II) were synthesized. Spectroscopic characterization and crystal structures confirmed them to be monomeric and stable complexes. Crystal structure analysis suggests in each of the magnesium(II) complexes, the metal center has a distorted octahedral coordination geometry. Thermo-gravimetric analysis (TGA/DTA) suggests that these complexes are volatile and thermally stable. The thermal characteristics of newly designed complexes make them attractive precursors for MOCVD applications. (c) 2012 Elsevier B.V. All rights reserved.

An empirical evaluation of a framework for design for variety and novelty

The objective of this paper is to empirically evaluate a framework for designing – GEMS of SAPPhIRE as req-sol – to check if it supports design for variety and novelty. A set of observational studies is designed where three teams of two designers each, solve three different design problems in the following order: without any support, using the framework, and using a combination of the framework and a catalogue. Results from the studies reveal that both variety and novelty of the concept space increases with the use of the framework or the framework and the catalogue. However, the number of concepts and the time taken by the designers decreases with the use of the framework and, the framework and the catalogue. Based on the results and the interview sessions with the designers, an interactive framework for designing to be supported on a computer is proposed as future work.

Computational representations for multi state design tasks and enumeration of mechanical device behaviour

The role of a computer emerged from modeling and analyzing concepts (ideas) to generate concepts. Research into methods for supporting conceptual design using automated synthesis had attracted much attention in the past decades. To find out how designers synthesize solution concepts for multi-state mechanical devices, ten experimental studies were conducted. Observations from these empirical studies would be used as the basis to develop knowledge involved in the multi-state design synthesis process. In this paper, we propose a computational representation for expressing the multi-state design task and for enumerating multi-state behaviors of kinematic pairs and mechanisms. This computational representation would be used to formulate computational methods for the synthesis process to develop a system for supporting design synthesis of multiple state mechanical devices by generating a comprehensive variety of solution alternatives.

Analysing modifica-tions in the synthesis of multiple state mechanical devices using configuration space and topology graphs

Automated synthesis of mechanical designs is an important step towards the development of an intelligent CAD system. Research into methods for supporting conceptual design using automated synthesis has attracted much attention in the past decades. In our research, ten experimental studies are conducted to find out how designers synthesize solution concepts for multi-state mechanical devices. The designers are asked to think aloud, while carrying out the synthesis. These design synthesis processes are video recorded. It has been found that modification of kinematic pairs and mechanisms is the major activity carried out by all the designers. This paper presents an analysis of these synthesis processes using configuration space and topology graph to identify and classify the types of modifications that take place. Understanding of these modification processes and the context in which they happened is crucial to develop a system for supporting design synthesis of multiple state mechanical devices that is capable of creating a comprehensive variety of solution alternatives.

Heat mediated synthesis of silver nanoparticles using citrus limon (lemon) extract

In the present study, silver nanoparticles were rapidly synthesized by treating silver ions with Citrus limon (lemon) extract at higher temperature. The effect of process parameters like reductant concentration, mixing ratio of the reactants, concentration of silver nitrate and heating time period were studied. The formation of silver nanoparticles was confirmed by surface plasmon resonance as determined by UV-visible spectra in the range of 400-500 nm. X-ray diffraction analysis revealed the distinctive facets (111, 200, 220, 222 and 311 planes) of silver nanoparticles. Nanoparticles below 50 nm with spherical and spheroidal shape were observed from microscopic studies. The study offers a rapid method to synthesize silver nanoparticles within ten minutes of interaction with the bio-reductant.

Zn-nicotinate complex - a precursor for ZnO nanoparticles

A zinc-nicotinate complex has been prepared by direct reaction of zinc acetate and nicotinic acid in the presence of template tetramethylethylenediamine and is characterized by elemental analysis, FTIR, and TGA/DTA. The Zn complex was a precursor for the synthesis of ZnO nanoparticles. A correlation of the thermal and spectral properties of the precursor complex with its structure has been discussed. Thermolysis under air was studied by thermogravimetry, and the resulting ZnO product was characterized by XRD and TEM, showing compact particles with a diameter of about 1750nm.

Cytotoxicity of aluminium oxide nanoparticles towards fresh water algal isolate at low exposure concentrations

The growing commercial applications had brought aluminium oxide nanoparticles under,toxicologists' purview. In the present study, the cytotoxicity of two different sized aluminium oxide nanoparticles (ANP(1), mean hydrodynamic diameter 82.6 +/- 22 nm and ANP(2), mean hydrodynamic diameter 246.9 +/- 39 nm) towards freshwater algal isolate Chlorella ellipsoids at low exposure levels (<= 1 mu g/mL) using sterile lake water as the test medium was assessed. The dissolution of alumina nanoparticles and consequent contribution towards toxicity remained largely unexplored owing to its presumed insoluble nature. Herein, the leached Al3+ ion mediated toxicity has been studied along with direct particulate toxicity to bring out the dynamics of toxicity through colloidal stability, biochemical, spectroscopic and microscopic analyses. The mean hydrodynamic diameter increased with time both for ANP(1) 82.6 +/- 22 nm (0 h) to 246.3 +/- 59 nm (24h), to 1204 +/- 140 nm (72 h)] and ANP(2) 246.9 +/- 39 nm (Oh) to 368.28 +/- 48 nm (24 h), to 1225.96 +/- 186 nm (72 h)] signifying decreased relative abundance of submicron sized particles (<1000 nm). The detailed cytotoxicity assays showed a significant reduction in the viability dependent on dose and exposure. A significant increase in ROS and LDH levels were noted for both ANPs at 1 mu g/mL concentration. The zeta potential and FT-IR analyses suggested surface chemical interaction between nanoparticles and algal cells. The substantial morphological changes and cell wall damage were confirmed through microscopic analyses (SEM, TEM, and CLSM). At 72 h, significant Al3+ ion release in the test medium 0.092 mu g/mL for ANP(1), and 0.19 mu g/mL for ANP(2)] was noted, and the resulting suspension containing leached ions caused significant cytotoxicity, revealing a substantial ionic contribution. This study indicates that both the nano-size and ionic dissolution play a significant role in the cytotoxicity of ANPs towards freshwater algae, and the exposure period largely determines the prevalent mode of nano-toxicity.

Structure-property correlation in BaO-TiO2-B2O3 glasses: glass stability, optical, hydrophobic, and dielectric properties

Glasses in the x(BaO-TiO2)-B2O3 (x = 0.25, 0.5, 0.75, and 1 mol.) system were fabricated via the conventional melt-quenching technique. Thermal stability and glass-forming ability as determined by differential thermal analysis (DTA) were found to increase with increasing BaO-TiO2 (BT) content. However, there was no noticeable change in the glass transition temperature (T-g). This was attributed to the active participation of TiO2 in the network formation especially at higher BT contents via the conversion of the TiO6 structural units into TiO4 units, which increased the connectivity and resulted in an increase in crystallization temperature. Dielectric and optical properties at room temperature were studied for all the glasses under investigation. Interestingly, these glasses were found to be hydrophobic. The results obtained were correlated with different structural units and their connectivity in the glasses.

Process Development for Functionalization of Cotton with Silver Nanoparticles Synthesized by Bio-based Approaches

Cotton is a widely used raw material for textiles but drawbacks regarding their poor mechanical properties often limit their applications as functional materials. The present investigation involved process development for one step coating of cotton with silver nanoparticles (SNP) synthesized using Azadirachta indica and Citrus limon extract to develop functional textiles. Addition of starch to functional textiles led to efficient binding of nanoparticles to fabric and led to drastic decrease in release of silver from fabricated textiles after ten washing cycles enhancing their environment friendliness. Differential scanning calorimetry, scanning electron microscopy, FT-IR analysis and mechanical studies demonstrated efficient binding of nanoparticles to fabric through bio-based processes. The functionalized textiles developed by the bio-based methods showed significant antibacterial activity against E. coli and S. aureus (with 99% microbial reduction). Present work offers a simple procedure for coating SNP using bio-based approaches with promising applications in specialized functions.

Ionothermal synthesis of TiO2 nanoparticles: Photocatalytic hydrogen generation

Rutile phase TiO2 nanoparticles have been successfully prepared at 120 degrees C for one day via the ionothermal method using imidazolium based functionalized ionic liquid. The obtained products have been characterized by various techniques. XRD pattern shows rutile phase with crystallite size similar to 15 nm. FTIR shows a band at similar to 410 cm(-1) assigned to Ti-O-Ti stretching vibrations and few other bands due to the presence of ionic liquid. UV-vis studies show maximum absorbance at similar to 215 nm due to the imidazolium moiety and a band at 316 nm due to TiO2 nanoparticles. TEM images show that the size of particle is similar to 30 nm. TG-DTA shows weight loss corresponding to the formation of stable TiO2 nanoparticles. The rutile TiO2 nanoparticle is a promising material for hydrogen generation through photocatalysis. (C) 2013 Elsevier B.V. All rights reserved.

Synthesis, structural and optical properties of nanocrystalline Ba2NaNb5O15

Fine powders comprising nanocrystallites of barium sodium niobate, Ba2NaNb5O15 (BNN) were obtained via a citrate assisted sol-gel route at a much lower temperature than that of the conventional solid-state reaction route. The phase evolution of BNN as a function of temperature was investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). DTA data followed by XRD studies confirmed the BNN formation temperature to be around 923 K. The as-synthesized powders heat-treated at 923 K/10 h attained an orthorhombic structure akin to that of the parent BNN phase. Transmission electron microscopy revealed that the nanocrystallites are associated with dislocations. The optical band gap was calculated using the Kubelka-Munk function. These nanocrystallites exhibited strong visible photoluminescence (PL) at room temperature. The PL mechanism was explained by invoking the dielectric confinement effect, defect states and generation of self-trapped excitons.

Low temperature combustion synthesis and magnetostructural properties of Co-Mn nanoferrites

In the present work, Co1-xMnxFe2O4 nanoparticles were synthesized by the low-temperature auto-combustion method. The thermal decomposition process was investigated by means of differential and thermal gravimetric analysis (TG-DTA) that showed the precursor yield the final product above 450 degrees C. The phase purity and crystal lattice symmetry were estimated from X-ray diffraction (XRD). Microstructural features observed by scanning electron microscopy (SEM) demonstrates that the fine clustered particles were formed with an increase in average grain size with Mn2+ content. Fourier transform infrared spectroscopy (FTIR) study confirms the formation of spinel ferrite. Room temperature magnetization measurements showed that the magnetization M-s increases from 29 to 60 emu/g and H-c increases from 13 to 28 Oe with increase in Mn2+ content, which implies that these materials may be applicable for magnetic data storage and recording media. (C) 2013 Elsevier B.V. All rights reserved.