Growth of strontium oxalate crystals in agar–agar gel

Single crystals of strontium oxalate have been grown by using strontium chloride and oxalic acid in agar–agar gel media at ambient temperature. Different methods for growing crystals were adopted. The optimum conditions were employed in each method by varying concentration of gel and reactants, and gel setting time etc. Transparent prismatic bi-pyramidal platy-shaped and spherulite crystals were obtained in various methods. The grown crystals were characterized with the help of FT–IR studies and monoclinic system of crystals were supported with lattice parameters a = 9·67628 ?, b = 6·7175 ?, c = 8·6812 ?, b\boldsymbol{\beta} = 113·566^°^{\boldsymbol\circ}, and V = 521·84 ?³ calculated from X-ray diffractogram.     

High-<Emphasis Type="Italic">T</Emphasis><Subscript>C</Subscript> phase transition in K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> lead-free ceramic synthesised using solid-state reaction

Solid-state reaction synthesised K₂Ti₆O₁₃ lead-free ceramic was characterized using XRD, SEM, and X-band EPR, at room temperature. EPR-spectra showed the presence of ( \textFe_\textTi^￠ - V_\textO ^·· ) \left( {{\text{Fe}}_{\text{Ti}}^{\prime } - V_{\text{O}}^{ \bullet \bullet } } \right) defect associate dipoles, in orthorhombic phase, responsible for the broadening of the dielectric anomaly identified in the ε _r (T) plots at T _C  ~ 300 °C. This anomaly resembled a ferroelectric–paraelectric type phase transition following Curie–Weiss type trend. Besides, dielectric loss mechanism jointly represented electrical conduction, dipole orientation, and space charge polarization.     

Computation of X-ray powder diffractograms of cement components and its application to phase analysis and hydration performance of OPC cement

The importance of computed X-ray diffraction patterns of various polymorphs of alite (M₃, T₁, R{\bf \emph{M}_{3}, \emph{T}_{1}, \emph{R}}), belite (b\boldsymbol{\beta}, g\boldsymbol{\gamma}), aluminate (cubic, orthorhombic), aluminoferrite, gypsum and hemihydrate in the quantitative phase analysis of cement and its early stage hydration performance is highlighted in this work with three OPC samples. The analysis shows that the predominant silicate phases present in all the samples are M₃{\bf \emph{M}_{3}}-alite phase and b\boldsymbol{\beta}-belite phase, respectively. Both cubic and orthorhombic phases of C ₃ A, brownmillerite, gypsum and hemihydrates are present at different levels. Quantitative phase analysis of cement by Rietveld refinement method provides more accurate and comprehensive data of the phase composition compared to Bogue method. The comparative hydration performance of these samples was studied with w/c{\bf \emph{w/c}} ratio, 0·5 and the results are interpreted in the light of difference in phase compositions viz. b\boldsymbol{\beta}-C ₂ S/C ₃ S ratio, fraction of finer cement particles present in the samples and theoretical modeling of C ₃ S hydration.     

Phase relation of LaFe 11·6 Si 1·4 compounds annealed at different high-temperature and the magnetic property of LaFe 11·6– x Co x Si 1·4 compounds

LaFe _11·6 Si _1·4 compounds are annealed at different high temperatures from 1323 to 1623?K. The powder X-ray diffraction patterns show that large amount of NaZn₁₃-type phase begins to be observed in LaFe _11·6 Si _1·4 compound after being annealed at 1423?K for 5?h. In the temperature range from 1423 to 1523?K, the $\boldsymbol{\alpha} $ -Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed in the XRD pattern in the LaFe _11·6 Si _1·4 compound annealed at 1523?K (5?h). With annealing temperature increasing to 1573?K and 1673?K, La ₅ Si ₃ phase is detected, and there is a certain amount of LaFeSi phase when the annealing temperature is 1673?K. The amount of impurity phases in the LaFe _11·6 Si _1·4 compound annealed by the two-stage annealing consisting of high temperature ( $\boldsymbol{>}$ 1523?K) and 1523?K is larger than that of the single stage annealing at 1523?K under the same time. According to the results of different high-temperature annealing, LaFe $_{{\bf 11{\cdot}6}-\boldsymbol{x}}$ Co $_{\boldsymbol{x}}$ Si _1·4 ( $\boldsymbol{0{\cdot}1} \boldsymbol{\le} \boldsymbol{x} \boldsymbol{\le} \boldsymbol{0{\cdot}8}$ ) compounds are annealed at 1523?K (5?h). The main phase is NaZn13-type phase, and the impurity phase is a small amount of $\boldsymbol{\alpha} $ -Fe in LaFe $_{{\bf 11{\cdot}6}-\boldsymbol{x}}$ Co $_{\boldsymbol{x}}$ Si _1·4 compounds. With increase in Co content from $\boldsymbol{x} \boldsymbol{=} \boldsymbol{0{\cdot}1}$ to $\boldsymbol{0{\cdot}8}$ , the Curie temperature $\boldsymbol{T}_{\!\boldsymbol{\rm C}}$ , goes up from 207 to 285?K. The introduction of Co element weakens the itinerant electron metamagnetic transition, and also results in the change of magnetic transition type from first to second order at about $\boldsymbol{x = 0{\cdot}5}$ . The magnetic entropy change decreases from 19·94 to 4·57?J /kg K with increasing Co concentration at a low magnetic field of 0?C2?T. But the magnetic hysteresis loss around $\boldsymbol{T}_{\!\boldsymbol{\rm C}}$ reduces remarkably from 26·2?J /kg for $\boldsymbol{x = 0{\cdot}1}$ to 0?J /kg for $\boldsymbol{x} \boldsymbol{=} \bf 0{\cdot}8$ .     

Kinetics of flow stress in ultra-pure tantalum single crystals in stress/temperature regime III

The temperature dependence of the critical resolved shear stress (CRSS), τ, of ultra-pure tantalum single crystals (RRR ≥ 14000) observed below 250 K for a range of shear-strain rates [(g)\dot] = 2×10 ^{- 5} - 6×10 ^{- 3}  \texts ^{- 1} \dot{\gamma } = 2\times 10^{ - 5} - 6\times 10^{ - 3} \,{\text{s}}^{ - 1} was analyzed within the framework of a kink-pair nucleation model of flow stress. The CRSS/strain-rate data follow the model formulation t ^{1/ 2} = C + D  ln[(g)\dot] \tau^{ 1/ 2} = C + D\,{ \ln }\dot{\gamma } , where C and D are positive constants, for each deformation temperature T in the range 78–250 K. Evaluation of the various slip-parameters of flow stress points to (211)[[`1]11] [\bar{1}11] slip system responsible for the yielding of ultra-pure tantalum single crystals in the so-called stress/temperature regime III (T < 250 K). The value of the pre-exponential factor [(g)\dot]_\texto \dot{\gamma }_{\text{o}} in the Arrhenius-type equation for the shear-strain rate [(g)\dot] \dot{\gamma } is found to be of the order of 10⁵ s⁻¹, which is substantially lower than that ( [(g)\dot]_\texto ~ 10⁷  \texts ^{- 1} ) \left( {\dot{\gamma }_{\text{o}} \sim 10^{7} \,{\text{s}}^{ - 1} } \right) determined in the stress/temperature regime II (250–400 K) and contradicts the assumption invariably made in most of the theoretical models of flow stress that [(g)\dot]_\texto \dot{\gamma }_{\text{o}} is a constant over a wide temperature range.     

Two-Band Eliashberg Theory in Doped MgB $_{2}$_{2}: Experimental Tc and Superconductive Gaps

The variation of the critical temperature and of the superconductive gaps as functions of doping (Al, C) in the diboride MgB has been studied in the framework of the two-band Eliashberg theory and traditional phonon coupling mechanism. We have solved the two-band Eliashberg equations using first-principle calculations or simple assumptions for the variation of the relevant physical quantities. We have found that the experimental curves can be exactly explained only if the Coulomb pseudopotential changes with x by tuning the Fermi level toward the σ band edge. We also found that a small amount of impurities changes the structural properties of the material, so we cannot treat the Mg and MgB systems as a contamination with Al or C of MgB, but as new materials. Finally, we compare the predictions of our theory with the available experimental data.     

Metal-coated magnetic nanoparticles for surface enhanced Raman scattering studies

We report the optimization and usage of surfactantless, water dispersible Ag and Au-coated g\boldsymbol\gamma–Fe₂_{\boldsymbol 2}O₃_{\boldsymbol 3} nanoparticles for applications in surface-enhanced Raman scattering (SERS). These nanoparticles, with plasmonic as well as super paramagnetic properties exhibit Raman enhancement factors of the order of 10⁶ (10⁵) for Ag (Au) coating, which are on par with the conventional Ag and Au nanoparticles. Raman markers like 2-naphthalenethiol, rhodamine-B and rhodamine-6G have been adsorbed to these nanoparticles and tested for nonresonant SERS at low concentrations. Further, to confirm the robustness of Ag-coated nanoparticles, we have performed temperature-dependent SERS in the temperature range of 77–473 K. The adsorbed molecules exhibit stable SERS spectra except at temperatures $\boldsymbol >$\boldsymbol >323 K, where the thermal desorption of test molecule (naphthalenethiol) were evident. The magnetic properties of these nanoparticles combined with SERS provide a wide range of applications.     

Effect of defect dipoles on the dielectric and electrical properties of Mn:K2Ti6O13 lead-free ceramics: EPR spectroscopy-cum-dielectric-spectroscopy

In this paper, we report the synthesis of Mn:K₂Ti₆O₁₃ lead-free ceramics in a monoclinic phase with microtubular surface morphology via high temperature solid-state reactions. EPR-spectroscopy, achieved at room temperature and at X-band frequencies, recognised Mn²⁺, Mn³⁺, and Mn⁴⁺ partial substitutions at Ti⁴⁺ lattice sites with dominating Mn²⁺ substitution, and identified ( \textFe_\textTi^￠ {\text{Fe}}_{\text{Ti}}^{\prime } – V_\textO ^·· V_{\text{O}}^{ \cdot \cdot } ) and ( \textMn_\textTi^￠￠ {\text{Mn}}_{\text{Ti}}^{\prime \prime } – V_\textO ^·· V_{\text{O}}^{ \cdot \cdot } ) defect associate dipoles exhibited in the low-field EPR signals which smeared with excessive doping due to augmented exchange interactions. These dipoles rendered diffusive nature to the ferroelectric-paraelectric type phase transitions recognized in the ε _r (T) plots. Space charges, dipole orientation, and electrical conduction cooperatively contributed to dielectric losses. The study also provides a select composition with x = 0.05 mol% doping, performing low loss with high dielectric permittivity useful for high-temperature applications. Conductivity data proposed a shift from electronic (hopping) conduction mechanism in the low-temperate region to ionic (intratunnel) conduction at high-temperatures. Whereas slight doping augmented a.c. conductivity due to increased spin-phonon interaction and commanding electron hopping conduction, heavy doping reduced it, attributed to shrinkage of tunnel space and trapping of conduction electrons.     

Effect of particle size on microstructure and strength of porous spinel ceramics prepared by pore-forming <Emphasis Type="Italic">in situ</Emphasis> technique

The porous spinel ceramics were prepared from magnesite and bauxite by the pore-forming in situ technique. The characterization of porous spinel ceramics was determined by X-ray diffractometer (XRD), scanning electron microscopy(SEM), mercury porosimetry measurement etc and the effects of particle size on microstructure and strength were investigated. It was found that particle size affects strongly on the microstructure and strength. With decreasing particle size, the pore size distribution occurs from multi-peak mode to bi-peak mode, and lastly to mono-peak mode; the porosity decreases but strength increases. The most apposite mode is the specimens from the grinded powder with a particle size of 6·53 μm, which has a high apparent porosity (40%), a high compressive strength (75·6 MPa), a small average pore size (2·53 μm) and a homogeneous pore size distribution.     

Non-linear viscoelasticity of vapor grown carbon nanofiber/polystyrene composites

The strain (γ) dependences of viscoelasticity and electrical resistance (R) of vapor grown carbon nanofiber (VGCF)/polystyrene (PS) composites have been studied using simultaneous measurement technique. The composites containing at least 4 vol.% VGCF present two regions of strain softening at γ < 10% and γ > 30%, respectively. Using strain amplification factor introduced by hydrodynamic effects as vertical and horizontal shifting factors, the curves of dynamic storage modulus (G′) and loss modulus (G″) as a function of γ for the composites can be superposed, respectively, on those for the pure matrix at γ ≥ 30%. Significant deflection from the master curves can be observed at γ < 30%. R tested as a function of γ provides direct evidences for breakdown of filler–filler interactions even by a small strain perturbation. It is suggested that breakdown of filler–filler interactions plays a vital role in strain softening at small strains, whereas the matrix provides the main contribution to strain softening at large strains. Dynamic moduli G_{\textf,(0.1% ,j)}^￠ G_{{{\text{f,}}(0.1\% ,\varphi )}}^{\prime } and G_{\textf,(0.1% ,j)}^￠￠ G_{{{\text{f,}}(0.1\% ,\varphi )}}^{\prime \prime } of the filler phase at volume fraction φ at 0.1% strain are used to account for the viscoelastic contribution of the initial filler structure. Ratios of dynamic moduli of the filler phase to the composite at 0.1% strain, G_\textf,0.1% ^￠ /G_\textc,0.1% ^￠ G_{{{\text{f,}}0.1\% }}^{\prime } /G_{{{\text{c,}}0.1\% }}^{\prime } and G_\textf,0.1% ^￠￠ /G_\textc,0.1% ^￠￠ G_{{{\text{f,}}0.1\% }}^{\prime \prime } /G_{{{\text{c,}}0.1\% }}^{\prime \prime } , exhibit percolation-like transition as a function of φ, which is in consistence with the electric percolation transition.     

Correlation between diffraction and viscosity data for Bi–Ga molten alloys

Structure of Bi_100-x_{\boldsymbol{100-x}}Ga_x_{\boldsymbol{x}} molten alloys containing 38·5, 50, 70 and 91·5 at. % Ga has been studied by means of X-ray diffraction method and compared with viscosity measurements data. Significant changes in the structure factor profile were observed in vicinity of the concentration 70 at. % Ga. The dynamic viscosity coefficient was calculated by use of a statistical atomic distribution model and a Born–Green kinetic theory. The concentration dependence of viscosity is in agreement with change of structure parameters obtained from diffraction data.     

Thermodynamic Functions of Fermi Gas with Quadruple BCS-Type Binding Potential with dx2 - y2 d_{x^2 - y^2 } -Wave-Pairing Symmetry

A gas of spin 1/2 fermions with an interaction V+W = -||^-1 _k,k g _k,k(k)(k) b _k b _-k - 2 _k(k)n _k+ n _k-, where n _k± = a _k±, b _k = a _k+ a _k- and a _k, satisfy Fermi anticommutation relations, is investigated in the -pairing case. W+V₄ is nonzero only within a thin layer of one-fermion energies around the chemical potential , and (k) denotes the characteristic function of the corresponding range of momenta. Two cases are studied: 1⁰ = 0, 2⁰ = 0.10025 eV. In the first case the system exhibits a first order transition, in the second, the transition is second order. Temperature dependence of the system's thermodynamic functions is examined and compared with that of the s-pairing case.     

Barrier characteristics of Pt/Ru Schottky contacts on <Emphasis Type="Italic">n</Emphasis>-type GaN based on <Emphasis Type="Italic">I–V–T</Emphasis> and <Emphasis Type="Italic">C–V–T</Emphasis> measurements

We have investigated the current–voltage (I–V) and capacitance–voltage (C–V) characteristics of Ru/Pt/n-GaN Schottky diodes in the temperature range 100–420 K. The calculated values of barrier height and ideality factor for the Ru/Pt/n-GaN Schottky diode are 0·73 eV and 1·4 at 420 K, 0·18 eV and 4·2 at 100 K, respectively. The zero-bias barrier height (Φ_b0) calculated from I–V characteristics is found to be increased and the ideality factor (n) decreased with increasing temperature. Such a behaviour of Φ_b0 and n is attributed to Schottky barrier (SB) inhomogeneities by assuming a Gaussian distribution (GD) of barrier heights (BHs) at the metal/semiconductor interface. The current–voltage–temperature (I–V–T) characteristics of the Ru/Pt/n-GaN Schottky diode have shown a double Gaussian distribution having mean barrier heights ( [`(F)]<sub>\textb0</sub> {\bar{{\Phi}}_{\text{b}0}} ) of 1·001 eV and 0·4701 eV and standard deviations (σ <sub>0</sub>) of 0·1491 V and 0·0708 V, respectively. The modified ln (J<sub>0</sub> /T<sup>2</sup> )-( q<sup>2</sup>s <sub>0</sub><sup>2</sup>/2k<sup>2</sup>T<sup>2</sup> ){ln} ({{J}_{0} /{T}^{2}} )-( {{q}^{2}{\sigma} _{0}^{2}/{2}{k}^{2}{T}^{2}} ) vs 10<sup>3</sup>/T plot gives [`(F)]_\textb0 \bar{{\Phi}}_{\text{b}0} and Richardson constant values as 0·99 eV and 0·47 eV, and 27·83 and 10·29 A/cm²K², respectively without using the temperature coefficient of the barrier height. The difference between the apparent barrier heights (BHs) evaluated from the I–V and C–V methods has been attributed to the existence of Schottky barrier height inhomogeneities.     

Thermal conductivity of geomaterial foams based on silica fume

Porous materials have been prepared from a solution containing sodium silicate and sodium hydroxide with the addition of silica fume. Kaolin and diatomite were also tested as additives to the initial formulation. This method yields consolidated geomaterial foams without requiring thermal treatment above 50 ^°C50\,{}^{\circ}\hbox{C}. The influence of chemical composition on the thermal conductivity was studied. The choice of raw materials was found to play an important role. The accuracy of thermal conductivity measurements was evaluated by comparing the steady state heat flow method with the laser flash technique for five different reference materials giving values within 6%. Using the steady state heat flow method, a value of 0.12 ±0.01 W m^-1 K^-10.12 \pm 0.01\,{\rm W}\,{\rm m}^{-1}\,{\rm K}^{-1} was then obtained for consolidated foams, made with kaolin as the precursor, containing approximately 70% of porosity.     

Evolution of the microstructure and mechanical properties of eutectic Fe<Subscript>30</Subscript>Ni<Subscript>20</Subscript>Mn<Subscript>35</Subscript>Al<Subscript>15</Subscript>

The microstructure of the eutectic alloy Fe₃₀Ni₂₀Mn₃₅Al₁₅ (in at.%) was modified by cooling at different rates from 1623 K, i.e., above the eutectic temperature. The lamellar spacing decreased with increasing cooling rate, and in water-quenched specimens lamellae widths of ~100 nm were obtained. The orientation relationship between the fcc and B2 lamellae was found to be sensitive to the cooling rate. In a drop-cast alloy the Kurdjumov–Sachs orientation relationship dominated, whereas the orientation relationship in an arc-melted alloy with a faster cooling rate was \textfcc( [`1]12 )//\textB2( 0 1 1 );  \textfcc[ 1[`1]1 ]//\textB2 [ 1[`1]1 ]  \textand \textfcc( 0[`1]1 )//\textB2( 00 1 );\text fcc[ 0 1 1 ]//\textB2[ [`1][`1]0 ] {\text{fcc}}\left( {\bar{1}12} \right)//{\text{B2}}\left( {0 1 1} \right);\;{\text{fcc}}\left[ {1\bar{1}1} \right]//{\text{B2 }}\left[ {1\bar{1}1} \right] \,{\text{and}}\,{\text{fcc}}\left( {0\bar{1}1} \right)//{\text{B2}}\left( {00 1} \right);{\text{ fcc}}\left[ {0 1 1} \right]//{\text{B2}}\left[ {\bar{1}\bar{1}0} \right] . The hardness increased with microstructural refinement, obeying a Hall–Petch-type relationship. The strength of the alloy decreased significantly above 600 K due to softening of the B2 phase.     

Effect of drawing on the dielectric properties and polarization of pressed solution cast β-PVDF films

Poly(vinylidene fluoride), PVDF, samples containing exclusively the polar β phase were obtained by crystallization from N,N-dimethylformamide (DMF) solution at 60 °C and subsequent pressing. Some of these samples were uniaxially drawn at 120 °C at draw ratio of 4, resulting in oriented films. Oriented and unoriented samples were characterized as to relative fraction of β phase, degree of crystallinity and orientation by infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The dependence on frequency of the real ( e_\textr^￠ \varepsilon_{\text{r}}^{\prime} ) and imaginary ( e_\textr^￠￠ \varepsilon_{\text{r}}^{\prime\prime} ) components of the relative permittivity of the samples was determined between 10⁴ and 1.7 × 10⁷ Hz. The coercive field and stable and metastable remanent ferroelectric polarization were determined from the hysteresis loop obtained by the ramp voltage technique, described in detail in this work. The results allowed verification of the effect of drawing on structure and of the resulting structure on the dielectric properties, remanent polarization, and coercive field of β-PVDF. A possible effect of the crystal–amorphous interphase region on the metastable remanent polarization is suggested. The results obtained with the oriented and unoriented samples were compared with those obtained for films commercialized by Piezotech S.A.     

Influence of pH and bath composition on properties of Ni–Fe alloy films synthesized by electrodeposition

Fe?CNi films were electrodeposited on ITO glass substrates from the electrolytes with different molar ratio of Ni $^{\boldsymbol{2+}}$ /Fe $^{\boldsymbol{2+}}$ and different pH values (2 $\boldsymbol{\cdot}$ 1, 2 $\boldsymbol{\cdot}$ 9, 3 $\boldsymbol{\cdot}$ 7 and 4 $\boldsymbol{\cdot}$ 3) at 25 $\boldsymbol{^\circ}$ C. The properties of Fe?CNi alloy films depend on both Ni $^{\boldsymbol{2+}}$ and Fe $^{\boldsymbol{2+}}$ concentrations in electrolyte and pH values. The content of Ni increases from 38% to 84% as the mole ratio of NiSO $_{\boldsymbol{4}}$ /FeSO $_{\boldsymbol{4}}$ increasing from 0 $\boldsymbol{\cdot}$ 50/0 $\boldsymbol{\cdot}$ 50 to 0 $\boldsymbol{\cdot}$ 90/0 $\boldsymbol{\cdot}$ 10 in electrolyte and slightly decreases from 65% to 42% as the pH values increase from 2 $\boldsymbol{\cdot}$ 1 to 4 $\boldsymbol{\cdot}$ 3. The X-ray diffraction analysis reveals that the structures of the films strongly depend on the Ni content in the binary films. The magnetic performance of the films shows that the saturation magnetization ( $\boldsymbol{M}_{\boldsymbol{\rm s}})$ decreases from 1775 $\boldsymbol{\cdot}$ 01 emu/cm $^{\boldsymbol{3}}$ to 1501 $\boldsymbol{\cdot}$ 46 emu/cm $^{\boldsymbol{3}}$ with the pH value increasing from 2 $\boldsymbol{\cdot}$ 1 to 4 $\boldsymbol{\cdot}$ 3 and the saturation magnetization ( $\boldsymbol{M}_{\boldsymbol{\rm s}})$ and coercivity ( $\boldsymbol{H}_{\boldsymbol{\rm c}})$ move up from 1150 $\boldsymbol{\cdot}$ 44 emu/cm $^{\boldsymbol{3}}$ and 58 $\boldsymbol{\cdot}$ 86 Oe to 2498 $\boldsymbol{\cdot}$ 88 emu/cm $^{\boldsymbol{3}}$ and 93 $\boldsymbol{\cdot}$ 12 Oe with the increase of Ni $^{\boldsymbol{2+}}$ concentration in the electrolyte, respectively.     

Spherical and rod-like Gd 2 O 3 :Eu 3?+? nanophosphors—Structural and luminescent properties

A comparative study of spherical and rod-like nanocrystalline Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ (Gd $_{\boldsymbol{1\cdot92}}$ Eu $_{\boldsymbol{0\cdot08}}$ O $_{\boldsymbol 3}$ ) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ . Upon calcinations at 800 $^{\boldsymbol\circ}$ C for 3?h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH) $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ phase and it converts to pure cubic phase of Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ on calcination at 600 $^{\boldsymbol \circ}$ C for 3?h. TEM micrographs of hydrothermally prepared cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ phase shows nanorods with a diameter of 15?nm and length varying from 50 to 150?nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50?C250?nm. Dominant red emission (612?nm) was observed in cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ which has been assigned to $^{\boldsymbol 5}{\bf \textit{D}}_{\boldsymbol 0}$ $\boldsymbol \to$ $^{\boldsymbol 7}{\bf \textit{F}}_{\boldsymbol 2}$ transition. However, in hexagonal Gd(OH) $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ , emission peaks at 614 and 621?nm were observed. The strong red emission of cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap ( $\boldsymbol{E}_{\boldsymbol{\rm g}}$ ) was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.     

Techniques for exploring the suboptimal set

The ε-suboptimal set X_e\mathcal{X}_{\epsilon} for an optimization problem is the set of feasible points with objective value within ε of optimal. In this paper we describe some basic techniques for quantitatively characterizing X_e\mathcal{X}_{\epsilon} , for a given value of ε, when the original problem is convex, by solving a modest number of related convex optimization problems. We give methods for computing the bounding box of X_e\mathcal{X}_{\epsilon} , estimating its diameter, and forming ellipsoidal approximations.     

Shear-thickening behaviour of concentrated polymer dispersions under steady and oscillatory shear

The rheological behaviour of a 58 vol.% dispersion of styrene/acrylate particles in ethylene glycol was investigated using a plate-on-plate rheometer. Experimental results showed that the concentrated polymer dispersion exhibited a strong shear-thickening transition under both steady shear and dynamic oscillatory conditions. The low-frequency dynamic oscillatory behaviour could be reasonably interpreted in terms of the steady shear behaviour. Accordingly, the critical dynamic shear rate [(g)\dot]_{\textc_d} , \dot{\gamma }_{{{\text{c\_d}}}} , agreed well with the critical shear rate obtained in steady flow [(g)\dot]_{\textc_s} , \dot{\gamma }_{{{\text{c\_s}}}} , where [(g)\dot]_{\textc_d} \dot{\gamma }_{{{\text{c\_d}}}} was calculated as the maximum shear rate by the critical dynamic shear strain γ _c and the frequency ω, i.e. [(g)\dot]_{\textc_d} = wg_\textc . \dot{\gamma }_{{{\text{c\_d}}}} = \omega \gamma_{\text{c}} . However, during high-frequency dynamic oscillation, it was observed that the shear thickening occurred only when an apparent critical shear strain was reached, which could not be fully explained by the wall-slipping effect. Based on freeze fracture microscopic observations, the effect of the micro-sized flocculation of particles on the rheology of concentrated dispersions was also discussed.