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In this communication, we report the preparation and properties of nano-CoFe2O4 by gel combustion in presence of KCl and subsequent heat treatments. The products were characterized by X-ray diffraction, Infrared spectroscopy, and Mössbauer Spectroscopy. Spinel type structure with all Fe in 3+ oxidation states was confirmed from the XRD and Mossbauer spectroscopy. The average crystallite sizes of the studied samples were about 6 and 50 nm. Low temperature magnetic and dielectric properties of the samples were studied by superconducting quantum interference device magnetometry and ac-impedance spectroscopy. The field and temperature dependent magnetization studies indicated superparamagnetic nature for 6 nm sample and ferromagnetic nature for 50 nm sample. The temperature-dependent dielectric properties measured over a wide range of frequencies indicated an increasing trend of dielectric permittivity with the decrease in crystallite size. Variable range polaron hopping conduction was observed in both samples. [ABSTRACT FROM AUTHOR]

In this paper we report a new high-pressure rhombohedral phase of Ce2Zr2O8 observed in high-pressure angle-dispersive x-ray diffraction and Raman spectroscopy studies up to nearly 12 GPa. The ambient-pressure cubic phase of Ce2Zr2O8 transforms to a rhombohedral structure beyond 5 GPa with a feeble distortion in the lattice. The pressure evolution of the unit-cell volume showed a change in compressibility above 5 GPa. The unit-cell parameters of the high-pressure rhombohedral phase at 12.1 GPa are ah = 14.6791(3) Å, ch = 17.9421(5) Å, and V = 3348.1(1) Å3. The structure relations between the parent cubic (P213) and rhombohedral (P32) phases were obtained via group-subgroup relations. All the Raman modes of the cubic phase showed linear evolution with pressure, with the hardest one at 197 cm-1. Some Raman modes of the high-pressure phase have a non-linear evolution with pressure, and softening of one low-frequency mode with pressure is found. The compressibility, equation of state, and pressure coefficients of Raman modes of Ce2Zr2O8 are also reported. [ABSTRACT FROM AUTHOR]

High pressure x-ray diffraction studies on inverse-perovskite BaLiF3 show that this compound is structurally stable up to ∼50 GPa. The bulk modulus of BaLiF3 is determined to be 75.9 GPa which is in close agreement with that determined from a semi-empirical formulation. Our ab initio calculations show that among the three alkaline earth fluoro perovskites (ALiF3, A = Ba, Ca, and Sr) which crystallize in the inverse-perovskite structure, BaLiF3 is the least brittle at ambient conditions and also that the degree of brittleness decreases at high pressures. The behavior of the elastic constants at high pressure accompanied by a reduction in the bandgap indicates a decrease in the directional nature of the bonding. [ABSTRACT FROM AUTHOR]

We studied the effects of high pressure on the crystalline structure of scheelite-type CdMoO4 and EuMoO4. We found that the compressibility of the materials is highly nonisotropic, with the c-axis being the most compressible one. We also observed clear evidence of a structural phase transition at 12 GPa (CdMoO4) and 8.8 GPa (EuMoO4). The high-pressure phase has a monoclinic structure similar to M-fergusonite. The transition is reversible, and no volume change is detected between the low- and high-pressure phases. The results contradict early x-ray diffraction studies carried out in CdMoO4 and are compared with those obtained previously in isomorphic molybdates. Finally, the equation of state for both compounds is also determined. [ABSTRACT FROM AUTHOR]

Controlled boron doping of diamond film using nontoxic reagents is a challenge in itself. During the present study, attempts have been made to dope diamond films in situ with boron from a solution of boric acid (H3BO3) in methanol (CH3OH) using a specially designed bubbler that ensured continuous and controlled flow of vapors of boron precursors during deposition. The samples are thoroughly characterized using a host of techniques comprising of x-ray photoelectron spectroscopy, Raman, x-ray diffraction, and current-voltage measurements (I-V). Cross-sectional micro-Raman spectroscopy has been used to obtain depth profile of boron in diamond films. Boron concentration ([B]) in the films is found to vary linearly on a semilog scale with molarity (M) of H3BO3 in CH3OH. Lattice constant of our samples is smaller than the reported American society for testing and materials (ASTM) values due to oxygen incorporation and it increases with [B] in the diamond samples. Heavily boron doped samples exhibit Fano deformation of the Raman line shape and negative and/zero activation barrier in temperature dependent I-V measurements that indicate the formation of metallic phase in the samples. The present study illustrates the feasibility of safe and controlled boron doping of diamond films using a solution of H3BO3 in CH3OH over a significant range of [B] from semiconductor to metallic regime but with a little adverse effect due to unintentional but unavoidable incorporation of oxygen. [ABSTRACT FROM AUTHOR]

We report results of a comprehensive study of the phase transition at TN (∼643 K) as a function of particle size in multiferroic BiFeO3 system. We employed electrical, thermal, and temperature dependent x-ray diffraction studies in order to characterize the transition in a host of samples. We also carried out detailed magnetic measurements over a temperature regime of 2–300 K under a magnetic field of 100–10 000 Oe both on bulk and nanocrystalline systems. While in the bulk system a sharp endothermic peak at TN together with a broad feature, ranging over nearly ∼100 K (ΔT), could be observed in calorimetry, the nanoscale systems exhibit only the broad feature. The characteristic dielectric anomaly, expected at TN, is found to occur both at TO and TN across ΔT in the bulk sample. The Maxwell-Wagner component due to interfaces between heterogenous regions with different conductivities is also present. The magnetic properties, measured at lower temperature, corroborate our observations in calorimetry. The metastability increases in the nanoscale BiFeO3 with divergence between zero-field cooled and field cooled magnetizations below ∼100 K and faster magnetic relaxation. Interestingly, in nanoscale BiFeO3 one also observes finite coercivity at lower temperature, which points out that suitable design of particle size and shape may induce ferromagnetism. The inhomogeneous distribution of Bi/Fe ions and/or oxygen nonstoichiometry seems to be giving rise to broad features in thermal, magnetic as well as electrical responses. [ABSTRACT FROM AUTHOR]

The influence of the native SiO2 in the phase formation sequence of Ti/Si system has been studied. Furnace annealing of Ti/Si couples has been investigated by secondary-ion-mass spectrometry, Rutherford backscattering, and glancing incidence x-ray diffraction. The influence of dilute concentration of oxygen at the interface in altering reaction kinetics was studied. These studies reveal that the highly metallic Ti5Si3 phase forms during the intermediate stages of heat treatment. This phase is found to catalyze the direct formation of the low-resistive C54 TiSi2 phase, completely bypassing its polymorphic C49 counterpart. X-ray-diffraction line profile analysis of Bragg peaks indicates that the formation of the C54 phase is accompanied by a reduction in the microstrain. Subsequent annealing results in the complete transformation to TiSi2 with an increase in the average grain size. [ABSTRACT FROM AUTHOR]

The radiation-resistant response of BaTiO3 in the tetragonal and rhombohedral phases on exposure to 100 MeV Ag7+ ion irradiation was investigated by in situ X-ray diffraction (XRD) at room temperature (300 K) and low temperature (25 K), respectively. This study revealed that the BaTiO3 in rhombohedral phase retained crystallinity up to an ion fluence of 1×1014 ions/cm2, whereas tetragonal phase amorphized at much lower fluence viz. 1×1013 ions/cm2. The in situ XRD along with Raman spectroscopy studies revealed that BaTiO3 in rhombohedral phase is more radiation resistant than that of tetragonal phase. The density functional theory ( DFT) calculations confirmed higher bond strength of rhombohedral phase as compared to tetragonal phase, which supported the experimental result of higher radiation stability of rhombohedral phase. The theoretical predictions on high-temperature phase will be of relevance to the nuclear waste applications. [ABSTRACT FROM AUTHOR]

Sodium borosilicate (NBS) and barium sodium borosilicate (BBS) glasses, used for immobilization of high-level nuclear waste with compositions (SiO2)0.477(B2O3)0.239(Na2O)0.170 (TiO2)0.023(CaO)0.068(Al2O3)0.023 and (SiO2)0.482(B2O3)0.244 (Na2O)0.220(BaO)0.054 were subjected leaching experiments under hydrothermal conditions in an autoclave at 200°C for different time durations. Morphological and structural transformations associated with leaching, have been monitored with techniques like XRD, SEM, solid-state nuclear magnetic resonance. XRD and SEM along with NMR studies have confirmed that, upon leaching, formation of an aluminosilicate phase, Zeolite-P (Na6Al6Si10O32.12H2O), occurs with NBS glass. BBS glass upon subjecting to the same conditions leads to formation of multiple amorphous phases having Q4 (silica rich phase) and Q³ structural units of Silicon along with structurally modified residual glass. Upon leaching BO3 structural units preferentially get released from BBS glass. Comparison of results with international simple glass confirmed that, for the latter, mass loss rates are one order of magnitude lower. [ABSTRACT FROM AUTHOR]

High-quality GaN layers were grown on sapphire (0001) substrates using laser molecular beam epitaxy (LMBE) by laser ablating a solid GaN target at different laser repetition rates (10–40 Hz) under a constant supply of r.f. nitrogen plasma. The effect of laser repetition rate on the structural and optical properties of GaN layers was systematically studied using high-resolution X-ray diffraction (HRXRD), field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy and photoluminescence (PL) spectroscopy. High-resolution X-ray rocking curve measurements revealed highly c-axis oriented GaN layers on sapphire grown at 30 Hz with a calculated screw dislocation density of ~1.42 × 107 cm−2, whereas the GaN layers grown at 10 or 40 Hz consisted the screw dislocation density in the range of 108–109 cm−2. Surface morphological analysis revealed a change in grain size as well as surface roughness as a function of laser repetition rate and is explained on the basis of growth kinetics. Vibrational Raman spectroscopy revealed that the GaN layer grown at 10 Hz shows an in-plane compressive stress of ~1 GPa, while the film grown at 30 Hz exhibits a minimum stress of ~0.3 GPa. The PL measurements show a highly luminescent band-to-band emission of GaN at 3.44 eV for the 10 Hz grown highly strained GaN layer and at 3.41 eV for the less strained film grown at 30 Hz along with a broad defect band emission centered around 2.28 eV. It is found that the GaN layers grown at 30 Hz have excellent structural and optical properties. We expect that the less strained thin and highly oriented GaN film grown by LMBE can further be utilized for developing prodigious low-temperature-grown nitride-based multilayer structures and devices. [ABSTRACT FROM AUTHOR]

Undoped MSb2O6 (where M = Zn, Cd, Ba) and single and double doped MSb2O6:RE (where RE = Tb3+ and Eu3+) nanophosphors were synthesized through a simple sonochemical process and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), diffuse reflectance (DRS) and photoluminescence (PL) spectrophotometry. The TEM micrographs show that the resulting nanoparticles have mostly a spherical shape. Energy transfer was observed from the host to the dopant ions and characteristic green emissions from Tb3+ ions and red emissions from Eu3+ ions were observed. The chromaticity diagrams of the ZnSb2O6:Tb3+(1.2%):Eu3+(0.8%), CdSb2O6:Eu3+(0.5%):Tb3+(1.5%) and BaSb2O6:Eu3+(1%):Tb3+(1%) nanophosphors yielded CIE and CCT (correlated color temperature) values in the white light region. The photocatalytic activities of the undoped and double doped antimonates were evaluated for the degradation of rhodamine B (RhB) under UV light. Undoped MSb2O6 (where M = Zn, Cd, Ba) as well as ZnSb2O6:Tb3+(1.2%):Eu3+(0.8%), CdSb2O6:Eu3+(0.5%):Tb3+(1.5%) and BaSb2O6:Eu3+(1%):Tb3+(1%) samples exhibited good photodegradation capacity for RhB. Thus double doped ZnSb2O6:Tb3+(1.2%):Eu3+(0.8%), CdSb2O6:Eu3+(0.5%):Tb3+(1.5%) and BaSb2O6:Eu3+(1%):Tb3+(1%) can be termed a bifunctional material exhibiting both photocatalytic properties and white light emission. [ABSTRACT FROM AUTHOR]

In this article, we report the structural phase transitions in Bi4 V2 O11 as observed from temperature-dependent Raman scattering and X-ray diffraction measurements. Four different types of highly disordered coordination polyhedra around the vanadium atoms with large dispersion of V-O bond lengths are observed in Bi4 V2 O11 at ambient temperature. The observed V-O bond lengths could be grouped into two categories, viz. shorter <1.7 Å and longer >1.7 Å. The Raman modes of Bi4 V2 O11 could be assigned to vibration of these bonds and V-O-V linkages. We could correlate the difference in degree of anharmonicity of the phonon modes with temperature to differences in V-O bond strength. The local structure of vanadium-oxygen network in Bi4 V1.8 Cu0.2 O10.7 was also obtained by similar studies. The effect of highly disordered anion sublattice in the doped compound is reflected in the broadening of the Raman modes. [ABSTRACT FROM AUTHOR]

Orthorhombic InVO4 was prepared by solid-state reaction method and characterized by powder X-ray diffraction and scanning electron microscopy. The frequency-dependent dielectric and conductivity properties were studied from 300 to 973 K by impedance spectroscopy. A significantly enhanced conductivity was observed at higher temperature whereas almost no conduction was observed below 723 K. Appreciable grain boundary conductivity was observed at higher temperature. The activation energies for grain and grain boundary conductivities are 0.87 and 1.28 eV, respectively. The relative permittivity of ~35 was observed in a wider range of frequencies and temperatures. The frequency dispersion dielectric studies indicated thermally activated hopping conduction process. The high temperature structural studies revealed no significant change in structural parameters except a gradual increasing trend in the unit cell parameters and amplitude of isotropic thermal parameters with increasing temperature. [ABSTRACT FROM AUTHOR]

Nanocrystalline La1− x Ca x CrO3 ( x = 0.25, 0.40, 0.50) powders were synthesized by gel-combustion process using aspartic acid as a fuel. Phase identification of the samples was carried out by powder X-ray diffraction. Pore distribution and microstructure of sintered pellets were investigated by small angle neutron scattering ( SANS) and scanning electron microscopy ( SEM). SANS and relative density measurement results indicate better sinterability for products with lower Ca2+ concentration. Four-probe direct current electrical conductivity of LaCrO3 with different Ca2+ concentrations was measured in the temperature range 350°C-1000°C in air as well as in hydrogen atmosphere. Linear behavior of Arrhenius plots of electrical conductivities in both air and hydrogen atmosphere indicates charge carrier transport is due to thermally activated hopping conduction of small hole-polarons. It was observed that the electrical conductivity decreased with increasing substitution of Ca2+ concentration instead of increasing small polaron concentration as expected. This trend in electrical conductivity is attributed to the neutralization of some small polarons due to formation of oxygen vacancies with increase in Ca2+ concentration. [ABSTRACT FROM AUTHOR]

La2NiMnO6 (LNMO) was prepared by a combustion method followed by heating at high temperature. Subsequently, the preformed LNMO was annealed in air, oxygen, or N2 atmosphere and characterized by powder x-ray diffraction (XRD), neutron diffraction, superconducting quantum interference device magnetometry, and dielectric analysis. Structural studies by XRD and neutron diffraction revealed the coexistence of partially cation disordered monoclinic (31 %) and rhombohedral (69%) phases in the sample annealed in air. However, the sample annealed in oxygen shows about 50:50% of monoclinic and rhombohedral phases. Relaxor-like behavior with relative permittivity of the order of 104 was observed in the sample annealed in air, while relative permittivity decreases to about 200 in samples annealed in oxygen atmosphere. The magnetic properties indicate a well-defined ferromagnetic phase in the oxygen-annealed sample compared to a feeble ferromagnetic signature in the air-annealed one. The dielectric and ferromagnetism of LNMO samples have been related to formation and annihilation of oxygen vacancies. [ABSTRACT FROM AUTHOR]

Ceria powders were prepared by gel combustion process using cerium nitrate and hitherto unexplored amino acids such as aspartic acid, arginine and valine as fuels. The powders have been characterized by X-ray and laser diffraction. Cold pressed compacts of these powders have been sintered at 1250°C for 2 h. Internal pore microstructure of the sintered compacts has been investigated by small angle neutron scattering (SANS) over a scattering wave vector q range of 0.003-0.17 nm-1. The SANS profiles indicate surface fractal morphology of the pore space with fractal dimensionality lying between 2.70 and 2.76. [ABSTRACT FROM AUTHOR]

Here we report the results of combined powder X-ray and neutron diffraction studies of Bi4-xNdxTi3O12 (0:0 ≤ x ≤ 2:0) compositions. The parent Bi4Ti3O12 has an orthorhombic lattice (space group: B2cb) with unit cell parameters a = 5:4432(5) Å, b = 5:4099(5) Å and c = 32:821(2) Å, and V = 966:5(1) Å3. This orthorhombic lattice is retained in all the studied compositions. The unit cell parameters gradually decrease with Nd3+ ion concentration with a discontinuity at x = 0:75. Orthorhombicity of the lattice decreases with increase in Nd3+ content in the lattice. The orthorhombic unit cell parameters for a representative Bi2Nd2Ti3O12 composition are: a = 5:3834(9), b = 5:3846(9) and c = 32:784(1) Å. The observed orthorhombic distortion at x = 2:0 is very small and thus the crystal structure apparently has a pseudo-tetragonal lattice. In addition, Nd3+ preferentially substitutes in the perovskite slab of the Aurivillius structure. The fraction of Nd3+ in the fluorite slab increases with increase in Nd3+ contents. [ABSTRACT FROM AUTHOR]

We report the results of the DC magnetization, neutron powder diffraction and neutron depolarization studies on the spin-chain compounds Ca3Co2-xFexO6 (x = 0, 0.1, 0.2 and 0.4). Rietveld refinement of neutron powder diffraction patterns at room temperature confirms the single-phase formation for all the compounds in rhombohedral structure with space group R3c. Rietveld refinement also confirms that Fe was doped at the trigonal prism site, 6a (0, 0, 1/4) of Co. The high temperature magnetic susceptibility obeys the Curie{Weiss law; the value of the paramagnetic Curie temperature (θp) decreases as the concentration of iron increases and it becomes negative for x = 0:4. No extra Bragg peak as well as no observable enhancement in the intensity of the fundamental (nuclear) Bragg peaks has been observed in the neutron diffraction patterns down to 30 K. No depolarization of neutron beam has been observed down to 3 K confirming the absence of ferro- or ferrimagnetic-like correlation. [ABSTRACT FROM AUTHOR]

Surface modification of polycrystalline α-alumina is carried out using ion implantation. Samples were implanted at 60 keV N+ ions with different ion doses ranging from 1 × 1015 to 1 × 1017 ions/cm2. Corrosion resistance is studied in a Ringer solution. The increase in corrosion resistance is due to the compound formation studied using Fourier transform infrared spectroscopy and glancing-angle X-ray diffraction techniques. Nanohardness is more at a lower ion dose and decreases at a higher ion dose. Microstrutural investigation shows that the decrease in corrosion resistance and nanohardness at a higher ion dose is due to the damage accumulation at the surface. [ABSTRACT FROM AUTHOR]

Nanocrystalline GdFeO3 powder was synthesized by a combustion technique, using glycine as the fuel and the corresponding metal nitrates as oxidants. Five different molar ratios of fuel-to-oxidant were chosen to study the effect of fuel content on the phase formation and the powder properties. The powders after calcination were characterized by x-ray diffraction (XRD) and crystallite sizes calculated by x-ray line broadening. The crystallite sizes for the phase pure products after calcination at 600 °C were in the range 40-65 nm. The transmission electron microscopy observations clearly highlight the pronounced crystallinity for the propellant chemistry samples. The nature of the agglomerates was investigated by light scattering studies. The lattice thermal expansion behavior was also studied by high-temperature XRD. [ABSTRACT FROM AUTHOR]

High-temperature dilatometric studies on (Pb1-xCax)TiO3 (x = 0.35, 0.35, 0.40, 0.45) ferroelectric ceramics reveal negative thermal expansion for x ≤ 0.40. The negative thermal expansion coefficient for x = 0.30, as obtained by dilatometry and powder x-ray diffraction, were found to be -8.541 x 10-6 K-1 and -11 x 10-6 K-1, respectively, which are comparable to those of other well-known negative thermal expansion materials like ZrW2O8, NaZr2(PO4)3. Results of temperature-dependent x-ray diffraction studies are also presented to show that the large negative thermal expansion behavior for x = 0.30 persists in a very wide range of temperatures, 70-570 K. Ca2+ substitution reduces the value of the negative thermal expansion coefficient of pure PbTiO3 crystal, but it enables the preparation of strong sintered ceramic bodies. The negative thermal expansion behavior is shown to disappear above the ferroelectric Curie point and is restricted to only the tetragonal compositions of (Pb1-xCax)TiO3. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Cet-xYxO2-x/2 (0.0 ≤ x ≤ 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO1.5 in CeO2 lattice, under the conditions of slow cooling from 1400°C, is represented as Ce0.55Y0.45·O1.775 (i.e., 45 mol% of YO1.5). The subsequent compositions were biphase. There was no solubility of CeO2 into the lattice of YO1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the αi (293-1123 K) values, within the homogeneity range, decreased on increased Y3+ content. A similar trend was observed for average lattice thermal expansion coefficient, αn (293-1473 K), as investigated using high-temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce1-xYxO2-x/2 (0.0 ≤ x ≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu1-xYxO2-x/2 (0.0 ≤ x ≤ 1.0), because CeO2 is widely used as a surrogate material for PuO2. [ABSTRACT FROM AUTHOR]

Nanoparticles of Zn0.95-xCo0.05InxO (x=0.0 to 0.07) were synthesized by the pyrolitic reaction of sol-gels obtained from respective metal precursors. X-ray diffraction and high-resolution transmission electron microscopy studies confirm the formation of impurity-free wurtzite type ZnO structure for all the compositions. While pristine ZnO is diamagnetic, Zn0.95Co0.05O nanoparticles show weak paramagnetic behavior at room temperature. When 'In.' is codoped with Co with x=0.0 to 0.07 in Zn0.95-xCo0.05InxO, a systematic increase in magnetic moment is observed up to x=0.07. First-principles modeling supports that the ferromagnetic phase become more favorable at higher indium doping concentrations. [ABSTRACT FROM AUTHOR]

Pressure dependent synchrotron x-ray diffraction studies on Pb0.70Ca0.30TiO3 (PCT30) ferroelectric ceramic reveal a crossover in the nature of phase transition from first order nature observed at ambient pressures to second order at high pressures. It is shown that Ca2+ doping affects the transition temperature but does not change the transition pressure of PbTiO3 significantly. The values of bulk modulus and its pressure derivative are also given in this letter. [ABSTRACT FROM AUTHOR]

In this article, structural and magnetic properties of a number of A2MMnO6 (A = La, Eu and Y; M = Mg, Co, Ni) type perovskites prepared under different oxygen partial pressure are compared. The results indicated that both structure and magnetic properties of such materials are sensitive to preparation conditions, which in general is governed by the nature of transition metal ions as well as rare-earth ions. It was also pointed out that even though the deviation in structure is only marginal, they affect appreciably to their magnetic properties. SYNPOSIS Sensitivities of structure and magnetic properties A2MMnO6 types of perovskites to the preparation conditions have been reviewed briefly. Although the deviation in structure is marginal, they affect appreciably to their magnetic properties. The observed magnetic properties of several A2MMnO6 types materials prepared under different conditions are summarized in this article. [ABSTRACT FROM AUTHOR]

Focuses on the structural analysis of excess-anion C-type rare earth oxide. Experimental observation of the analysis; Crystal structures of C-type earth oxide; Methodology used to study analysis.

In this manuscript, gel-combustion synthesis of Al 5 BO 9 :xTb3+ (x = 0.0%, 0.05%, 0.1%, 0.2% and 1.5%) phosphor along with the detailed structural characterizations using a host of techniques such as XRD, SEM, EDS, IR, EXAFS and PL etc. has been reported. XRD analysis confirmed the phase pure formation and also the nanocrystalline nature of the materials. Detailed EXAFS analysis explained the oxidation state and the coordination behaviour of Tb3+ ion in the Al 5 BO 9 matrix. PL study showed that the material can be a potential green light emitting phosphor. Thermoluminescence (TL) study revealed the presence of a wide shoulder peak and a broad dosimetry peak situating at 551 K. Net TL response from 10B and 11B enriched Al 5 BO 9 :0.1%Tb3+ thin pellets showed prolonged linearity within the thermal neutron fluence range of 3.2 × 1010 to 1.6 × 1011 n/cm2. Also, the maximum fading of the TL signal is only 9% during the storage period of 112 days. These indicates that the developed material can be a potential candidate for dosimetry applications involving high intensity slow neutron beams. The TL glow curve was deconvoluted which revealed the presence of five individual peaks whose kinetic parameters viz. activation energy (E), order of kinetics (b) and frequency factor (s) were evaluated using both glow curve deconvolution and Chen's peak shape method and the results were found to be in good agreement. [ABSTRACT FROM AUTHOR]

A new elpasolite-type (NH4,K)3VO2F4 compound was prepared and characterized by x-ray diffraction, differential scanning calorimeter (DSC), impedance analysis, and electrical polarization measurements. It crystallizes in an orthorhombic lattice with unit-cell parameters: a = 8.9584(4), b = 18.6910(14), c = 6.2174(4) Å, V = 1041.04(11) Å3, Z = 6. NH4+, and K+ ions are distributed statistically over crystallographically four equivalent sites. There are two distinguishable vanadium atoms forming cis- and trans-VO2F4 octahedra present in the unit cell. High-temperature studies by DSC and in situ x-ray diffraction revealed a first-order structural transformation from orthorhombic to cubic lattice around 343 K. Impedance measurements show two different kinds of conductivity behaviors for the two phases. In orthorhombic phase a significant conductivity resulting from involvement of protonic species is observed. In the orthorhombic phase, a clear ferroelectric hysteresis loop is observed. [ABSTRACT FROM AUTHOR]

The vanadium (V)-doped titania (Ti0.95V0.05O2) was impregnated in the host matrix of the pre-synthesized siliceous mesoporous material MCM-41 in a single pot synthesis step, by the wet impregnation route. The samples were characterized by x-ray diffraction, transmission electron microscopy (TEM), N2 adsorption, diffuse reflectance ultraviolet-visible spectroscopy (DRUVS). As compared to Ti0.95V0.05O2, the DRUV spectra of the impregnated catalysts showed a blue shift; still the absorption lies in the visible region. Presence of nano-sized (~2-12 nm) V-doped titania particles in V-TiO2/MCM-41 was revealed by TEM and the particle size was found to increase with the loading of the V-doped titania in the host matrix. All impregnated samples were found to be more active than either the bulk V-doped titania or titania for photocatalytic oxidation of ethylene in air at ambient conditions under both UV and visible irradiation. [ABSTRACT FROM AUTHOR]

Ca0.5Th0.5VO4 was prepared by a solid-state reaction of component oxides and characterized by powder x-ray diffraction (XRD) at ambient and higher temperatures and impedance spectroscopy. Crystal structure was refined by Rietveld refinements from powder XRD data. At room temperature, Ca0.5Th0.5VO4 has a zircon-type tetragonal (I41/amd) lattice with unit cell parameters: a = 7.2650(1) and c = 6.4460(1) Å. Despite the large charge difference, Ca2+ and Th4+ are statistically distributed over a single site. The crystal structure of Ca0.5Th0.5VO4 is built from the (Ca/Th)O8 (bisdisphenoid) and VO4 tetrahedra. The in situ high-temperature XRD studies on Ca0.5Th0.5VO4 revealed anisotropic thermal expansion behavior with coefficients of thermal expansion ac = 10.96 x 10-6/°C and aa = 5.32 x 10-6/°C. The impedance measurements carried out in the temperature range from ambient to 800 °C indicate semiconducting behavior with appreciable ionic conductivity above 400 °C. The activation energy obtained from the temperature-dependent AC conductivity data is ~1.37 eV. In wider range of frequencies and temperatures, the relative permittivity of approximately 50 to 60 is observed for Ca0.5Th0.5VO4. [ABSTRACT FROM AUTHOR]

Three solid solutions of pyrochlores in the series Nd2-yearsGdyZr2O7 (y = 0.8, 1.0, 1.2) were synthesized by the gel combustion method using citric acid as fuel. This results in a soft agglomerate powder as verified by dynamic light scattering. The single-phase nature of the products has been confirmed by x-ray diffraction. The increase in full width at half-maxima in the Raman spectra with an increase in Gd3+ content indicates that disorder increases with Gd3+ content. The morphology and particle size of the products were investigated by transmission electron microscopy. Scanning electron microscopy study reveals that the sintered pellets have a density higher than 92% of theoretical densities. The total ionic conductivity measurements in the temperature range 375-800 °C show that with the increase of disorder (Gd3+ content) in the system the activation energy of conduction increases from 0.98 to 1.06 eV and the preexponential factor, which is proportional to the number of mobile species, also follow the same trend of increase. The total conductivity measured in reducing atmosphere shows no change in electrical conductivity, which verifies a negligible contribution of electronic contribution in this system. [ABSTRACT FROM AUTHOR]

We report the synthesis of Th1-xMnχO2 (χ = 0, 0.001, 0.002, 0.004, and 0.01 wt%) nanoparticles by the urea combustion method using thorium nitrate gel followed by heat treatment at a higher temperature (T). The obtained Th1-xMnχO2 nanocrystals were characterized by x-ray diffraction (XRD), direct-current magnetization (M) measurements and electron paramagnetic resonance (EPR). XRD analysis revealed that Th1-xMnχO2 crystallizes in the cubic structure (Fm3m). M measurements showed ferromagnetic ordering at room temperature for Th0.99Mn0.01O2 samples annealed at 775 K. An intense and broad ferromagnetic resonance (FMR) having linewidth of ~1200 G, was observed at relatively lower fields in the EPR spectra of Th0.99Mn0.01O2 samples annealed at 775 K, indicating the presence of a ferromagnetic phase at room temperature. EPR measurements were used to estimate the number of spins involved in the ferromagnetic ordering. Out of the total Mn present in Th0.99Mn0.01O2 samples, about 25% of the Mn2+ ions were found to be responsible for the ferromagnetic ordering. In addition to the FMR signal, a weak hyperfine sextet was observed at g = 2.0048 (55Mn, I = 5/2), which corresponds to the -1/2 ? +1/2 transition of Mn2+ ions, suggesting its presence at thorium sites (uncoupled spins). X-ray photoelectron spectra indicated that the manganese ions exist mainly as Mn2+, Mn3+, and Mn4+. The room-temperature ferromagnetism may be attributed to the coupling between these Mn2+ ions at thorium sites in ThO2 rather than due to the formation of any metastable secondary phases. [ABSTRACT FROM AUTHOR]

CeScO3 was synthesized by a two step synthesis route involving a combustion method followed by vacuum healing at 1100 °C in the presence of Zr sponge which acts as an oxygen getler. The compound was characterized by various techniques such as X-ray diffraction (XRD), high temperature XRD, thermogravimetry, diffuse retlectance (DR)-UV visible spectrophotometry, and Raman spectroscopy. Fluorite-type (F-type) solid solution with composition Ce0.5-Sc0.5O1.75 was observed as an intermediate dedng the synthesis of CeScO3. Only by mere redox reaction was a reversible transformation between tluedte.type structure and perovskites structure observed. ceSco3 was found as semiconducting oxide with band gap of 3.2 eV arising mainly belween Op states in the valence band and Sc d and ce d states in the conduction band with small contributions coming from Ce f and Sc p states. First-principles potential plane-wave-based calculations were performed for the band gap and its origin in CeSco3. Photoluminescence measurement showed that CeScO3 is a potential host material giving broad blue emission. This was further confirmed by demonstrating CeSco3 doped with 2 mol % Tb3+ compound as an efficient green light emitter. [ABSTRACT FROM AUTHOR]

We report results of a comprehensive study of the phase transition at TN (∼643 K) as a function of particle size in multiferroic BiFeO3 system. We employed electrical, thermal, and temperature dependent x-ray diffraction studies in order to characterize the transition in a host of samples. We also carried out detailed magnetic measurements over a temperature regime of 2–300 K under a magnetic field of 100–10 000 Oe both on bulk and nanocrystalline systems. While in the bulk system a sharp endothermic peak at TN together with a broad feature, ranging over nearly ∼100 K (ΔT), could be observed in calorimetry, the nanoscale systems exhibit only the broad feature. The characteristic dielectric anomaly, expected at TN, is found to occur both at TO and TN across ΔT in the bulk sample. The Maxwell-Wagner component due to interfaces between heterogenous regions with different conductivities is also present. The magnetic properties, measured at lower temperature, corroborate our observations in calorimetry. The metastability increases in the nanoscale BiFeO3 with divergence between zero-field cooled and field cooled magnetizations below ∼100 K and faster magnetic relaxation. Interestingly, in nanoscale BiFeO3 one also observes finite coercivity at lower temperature, which points out that suitable design of particle size and shape may induce ferromagnetism. The inhomogeneous distribution of Bi/Fe ions and/or oxygen nonstoichiometry seems to be giving rise to broad features in thermal, magnetic as well as electrical responses. [ABSTRACT FROM AUTHOR]

Sugarcane bagasse was exposed to gamma radiation at different doses i.e. 100, 500, 1000 and 2000 kGy at a dose rate of 2.5 kGy/h and characterized for physical, chemical, morphological and structural properties. Results showed that on exposure of sugarcane bagasse, hemicellulose content reduced from 31% to 12.4% at 2000 kGy dose. The cellulose content of bagasse did not get affected much upto 1000 kGy exposure; however at 2000 kGy dose it decreased considerably. XRD study shows an initial increase in crystallinity index of bagasse at a dose level of 100 kGy while on further increase in radiation dose from 100 kGy to 2000 kGy the crystallinity index of bagasse decreases. Pores in the SEM photograph were observed on the surface of irradiated bagasse. UV–Vis spectra of bagasse showed a red shift indicating internal changes caused by radiation exposure. Study shows that the irradiation of bagasse results in disrupton of the lignocellulosic structure of Bagasse which opens up for easy accessibility of acids and hydrolytic enzymes for cellulosic hydrolysis resulting into fermentable sugars. [ABSTRACT FROM AUTHOR]

Structural and vibrational properties of orthorhombic BaTe2O6, a mixed valence tellurium compound, have been investigated by in situ synchrotron X-ray diffraction (XRD) studies up to 16 GPa and Raman spectroscopy up to 37 GPa using a diamond-anvil cell. The structure of orthorhombic BaTe2O6 has layers of [Te2O6]2-, formed by TeO6 octahedra and TeO5 square pyramids and Ba2+ ions stacked alternately along the 〈010〉 direction. A reversible pressure-induced structural transformation from the ambient orthorhombic (Cmcm) to a monoclinic (P21/m) structure is observed in both XRD and Raman spectroscopic investigations around 10 GPa. Ab initio calculations using density functional theory (DFT) corroborate this phase transition as well as the transition pressure. Both XRD and DFT calculations reveal that the high-pressure monoclinic structure is closely related to the ambient pressure orthorhombic structure, and the transformation is accompanied by a slight rearrangement of the structural units. Pressure evolution of unit cell parameters of the ambient pressure phase reveals an anisotropic compressibility with maximum compression along the b-axis as compared to other crystallographic directions. The bulk modulus and its derivative are found to be B0 = 88(2) GPa and B0 = 4.1(7) from high-pressure experiments, while those calculated by DFT are B0 = 123 GPa and B0' = 4.74. Pressure evolution of Raman spectra indicates significant changes across the orthorhombic to monoclinic phase transformation at 9.1 GPa and no evidence of further structural changes up to 37 GPa. Raman mode frequencies, pressure coefficients, and Grüneisen parameters in the low- and high-pressure phases of BaTe2O6 have been obtained for both monoclinic and orthorhombic phases. Finally, the mechanism for the instability of the orthorhombic phase under pressure is proposed. [ABSTRACT FROM AUTHOR]

Orthorhombic InVO4 was prepared by solid-state reaction method and characterized by powder X-ray diffraction and scanning electron microscopy. The frequency-dependent dielectric and conductivity properties were studied from 300 to 973 K by impedance spectroscopy. A significantly enhanced conductivity was observed at higher temperature whereas almost no conduction was observed below 723 K. Appreciable grain boundary conductivity was observed at higher temperature. The activation energies for grain and grain boundary conductivities are 0.87 and 1.28 eV, respectively. The relative permittivity of ~35 was observed in a wider range of frequencies and temperatures. The frequency dispersion dielectric studies indicated thermally activated hopping conduction process. The high temperature structural studies revealed no significant change in structural parameters except a gradual increasing trend in the unit cell parameters and amplitude of isotropic thermal parameters with increasing temperature. [ABSTRACT FROM AUTHOR]

Room-temperature angle-dispersive x-ray diffraction measurements on zircon-type TbVO4 and CeVO4 were performed in a diamond-anvil cell up to 50 GPa using neon as a pressure-transmitting medium. In TbVO4, we found at 6.4 GPa evidence of a nonreversible pressure-induced structural phase transition from zircon to a scheelite-type structure. A second transition to an M-fergusonite-type structure was found at 33.9 GPa, which is reversible. Zircon-type CeVO4 exhibits two pressure-induced transitions: first, an irreversible transition to a monazite-type structure at 5.6 GPa and, second, at 14.7 GPa, a reversible transition to an orthorhombic structure. No additional phase transitions or evidences of chemical decomposition are found in the experiments. The equations of state and axial compressibility for the different phases are also determined. Finally, the sequence of structural transitions and the compressibilities are discussed in comparison with other orhtovanadates and the influence of nonhydrostaticity commented. [ABSTRACT FROM AUTHOR]

A series of Mn-substituted BaMgF4 samples have been synthesized by a hydrothermal route. X-ray diffraction study reveals that the products are monophasic in nature. Scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) studies were carried out to investigate the morphology and stoichiometry for these compounds. X-ray photoelectron spectroscoy (XPS) and electron spin resonance (ESR) studies were done to confirm the oxidation state of dopant ion. Room temperature ferromagnetism was observed on Mn substitution at the Mg site in BaMgF4 samples. The saturation magnetization increases initially, shows a peaking effect, and then decreases with further increase in Mn concentration in BaMg1-xMnxF4 (0.0 ⩽ x ⩽ 0.15). However, ferroelectricity was found to decrease with an increase in Mn concentration in the series of investigated BaMg1-xMnxF4 (0.0 ⩽ x ⩽ 0.15) samples. First-principle calculations, using the projector augmented wave potentials on Mn-substituted BaMgF4, confirmed the decrease in magnetic moment with an increase in Mn content beyond certain concentration. These samples exhibit very weak magnetocapacitive coupling, which can be attributed to the very small magnetic signal observed in these samples. [ABSTRACT FROM AUTHOR]