Studies on thin film materials on acrylics for optical applications

Deposition of durable thin film coatings by vacuum evaporation on acrylic substrates for optical applications is a challenging job. Films crack upon deposition due to internal stresses and leads to performance degradation. In this investigation, we report the preparation and characterization of single and multi-layer films of TiO2, CeO2, Substance2 (E Merck, Germany), Al2O3, SiO2 and MgF2 by electron beam evaporation on both glass and PMMA substrates. Optical micrographs taken on single layer films deposited on PMMA substrates did not reveal any cracks. Cracks in films were observed on PMMA substrates when the substrate temperature exceeded 80degreesC. Antireflection coatings of 3 and 4 layers have been deposited and characterized. Antireflection coatings made on PMMA substrate using Substance2 (H2) and SiO2 combination showed very fine cracks when observed under microscope. Optical performance of the coatings has been explained with the help of optical micrographs.

Activities in the spinel solid solution, phase equilibria and thermodynamic properties of ternary phases in the system Cu Fe O

A review of the structural and thermodynamic information and phase equilibria in the Cu-Fe-O system suggested that a consistent, quantitative description of the system is hampered by lack of data on activities in the spinel solid solution CuFe2O4-Fe3O4. Therefore the activity of Fe3O4 in this solid solution is derived from measurements of the oxygen potentials established at 1000°C by mixtures containing Fe2O3 and spinel solid solutions of known composition. The oxygen pressures were measured manometrically for solid solutions rich in CuFe2O4, while for Fe3O4-rich compositions the oxygen potentials were obtained by an emf technique. The activities show significant negative deviations from Raoult’s law. The compositions of the spinel solid solutions in equilibrium with CuO + CuFeO2 and Cu + CuFeO2 were obtained from chemical analysis of the solid solution after magnetic separation. The oxygen potential of the three-phase mixture Cu + CuFeO2 + Fe3O4(spinel s.s.) was determined by a solid oxide galvanic cell. From these measurements a complete phase diagram and consistent thermodynamic data on the ternary condensed phases, CuFeO2 and CuFeO2O4, were obtained. An analysis of the free energy of mixing of the spinel solid solution furnished information on the distribution of cations and their valencies between the tetrahedral and octahedral sites of the spinel lattice, which is consistent with X-ray diffraction, magnetic and Seebeck coefficient measurements.

Gibbs’ energy of formation of YBa2Cu3O7-x (tetragonal)

The high temperature ceramic oxide superconductor YBa2Cu3O7-x (1–2–3 compound) is generally synthesized in an oxygen-rich environment. Hence any method for determining its thermodynamic stability should operate at a high oxygen partial pressure. A solid-state cell incorporating CaF2 as the electrolyte and functioning under pure oxygen at a pressure of 1·01 × 105 Pa has been employed for the determination of the Gibbs’ energy of formation of the 1–2–3 compound. The configuration of the galvanic cell can be represented by: Pt, O2, YBa2Cu3O7−x , Y2BaCuO5, CuO, BaF2/CaF2/BaF2, BaZrO3, ZrO2, O2, Pt. Using the values of the standard Gibbs’ energy of formation of the compounds BaZrO3 and Y2BaCuO5 from the literature, the Gibbs’ energy of formation of the 1–2–3 compound from the constituent binary oxides has been computed at different temperatures. The value ofx at each temperature is determined by the oxygen partial pressure. At 1023 K for O content of 6·5 the Gibbs’ energy of formation of the 1–2–3 compound is −261·7 kJ mol−1.

Gibbs energy of formation of CuCrO4 and phase relations in the system Cu-Cr-O below 735 K

A solid state galvanic cell incorporating yttria-stabilized zirconia electrolyte and ruthenium(IV) oxide electrodes has been used to measure the equilibrium chemical potential of oxygen corresponding to the decomposition of CuCrO4 in the range 590–760 K. For the reaction CuO(tenorite) + CuCr2O4(spinel) + 1.5O2(g)→2CuCrO4(orth), ΔGXXX = −183540 + 249.6T(±900) J mol−1. The decomposition temperature of CuCrO4 in pure oxygen at a pressure of 1.01 × 105 Pa is 735(±1) K. By combining the results obtained in this study with data on the Gibbs energy of formation of CuCr2O4 and CuCrO2 reported earlier, the standard Gibbs energy of formation of CuCrO4 and the phase relations in the system Cu-Cr-O at temperatures below 735 K have been deduced. Electron microscopic studies have indicated that the decomposition of CuCrO4 to CuCr2O4 is topotactic.

Gibbs’ free energies of formation of Cu2Ln2O5 (Ln = Tb, Dy, Er, Yb) compounds

The standard Gibbs' free energies of formation of compounds of type Cu2L%05 (Ln = Tb,Dy,Er,Yb) were measured using the solid state cell in the temperature range of 970 to 1323 K For formation of Cu2L?O5 compounds from their binary component oxides according to the reaction 2 CUO (s) + L%03 (s) -, Cu,,L%05 (s),the Gibbs' free energy changes can be represented by the following equations:AGO = 13 080 - 13.70 'I" (+80) J mol-' (Ln = Tb)AGq = 11 480 - 13.51 T (260) J mol-I (Ln = Dy)AGO = 10 750 - 13.99 T (260) J mol-I (Ln = Er)AGO = 9 920 - 13.90 T (260) J mol-' (Ln = Yb) Since formation of the compounds is endothermic, the compounds become thermodynamically unstable with respect to their component oxides below 955 K for Cu2Tb205, 850 K for Cu2Dy205, 768 K for Cu2Er205 and 714 K for Cu2Yb2OS When the oxygen partial pressure over Cu2L%05 is lowered, they decompose according to the scheme, 2 CU,L%O, (s) -r 2 L%03 (s) +2 cu20 (s) + 02(g)The equilibrium chemical potentials of oxygen corresponding to the dissociation reactions are computed from the emf data and auxiliary information on Cu20 and CuO. The computed decomposition temperatures at an oxygen partial pressure of 5.0 x ld Pa are compared with those obtained directly from combined thermogravimetric (TGA) and differential thermal analyses (DTA).The free energy, enthalpy and entropy of formation of Cu2Ln205 compounds show systematic variation with the ionic radius of the trivalent lanthanide ion. The trends obtained in this study are compared with information available in the literature. The staZbility of Cu2Ln205 compounds increases with the decrease in ionic radii of the ~ n ion~. +

System Cu-Rh-O: Phase diagram and thermodynamic properties of ternary oxides CuRhO2 and CuRh204

An isothermal section of the phase diagram for the system Cu-Rh-O at 1273 K has been established by equilibration of samples representing eighteen different compositions, and phase identification after quenching by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive analysis of X-rays (EDX). In addition to the binary oxides Cu2O, CuO, and Rh2O3, two ternary oxides CuRhO2 and CuRh2O4 were identified. Both the ternary oxides were in equilibrium with metallic Rh. There was no evidence of the oxide Cu2Rh2O5 reported in the literature. Solid alloys were found to be in equilibrium with Cu2O. Based on the phase relations, two solid-state cells were designed to measure the Gibbs energies of formation of the two ternary oxides. Yttria-stabilized zirconia was used as the solid electrolyte, and an equimolar mixture of Rh+Rh2O3 as the reference electrode. The reference electrode was selected to generate a small electromotive force (emf), and thus minimize polarization of the three-phase electrode. When the driving force for oxygen transport through the solid electrolyte is small, electrochemical flux of oxygen from the high oxygen potential electrode to the low potential electrode is negligible. The measurements were conducted in the temperature range from 900 to 1300 K. The thermodynamic data can be represented by the following equations: {fx741-1} where Δf(ox) G o is the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides. Based on the thermodynamic information, chemical potential diagrams for the system Cu-Rh-O were developed.

Phase relations in the system Cu-La-O and thermodynamic properties of CuLaO2 and CuLa2O4

Phase relations in the system Cu-La-O at 1200 K have been determined by equilibrating samples of different average composition at 1200 K, and phase analysis of quenched samples using optical microscopy, XRD, SEM and EDX. The equilibration experiments were conducted in evacuated ampoules, and under flowing inert gas and pure oxygen. There is only one stable binary oxide La2O3 along the binary La-O, and two oxides Cu2O and CuO along the binary Cu-O. The Cu-La alloys were found to be in equilibrium with La2O3. Two ternary oxides CuLaO2 and CuLa2O4+

Phase relations in the system Cu-Eu-O and thermodynamic properties of CuEu2O4 and CuEuO2

Phase relations in the system Cu-Eu-O have been determined by equilibrating samples of different average composition at 1200 K and by phase analysis after quenching using optical microscopy (OM), x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray (EDX). The equilibration experiments were conducted in evacuated ampoules and under flowing inert gas and pure oxygen. The Cu-Eu alloys were found to be in equilibrium with EuO. The higher oxides of europium, Eu3O4 and Eu2O3, coexist with metallic copper. Two ternary oxides CuEu2O4 and CuEuO2 were found to be stable. The ternary oxide CuEuO2, with copper in the monovalent state, can coexist with Cu, Cu2O, Eu2O3 and CuEu2O4 in different phase fields. The compound CuEu2O4 can be in equilibrium with Cu2O, CuO, CuEuO2, Eu2O3, and O2 gas under different conditions at 1200 K. Thermodynamic properties of the ternary oxides were determined using three solid-state cells based on yttria-stabilized zirconia as the electrolyte in the temperature range from 875 to 1250 K. The cells essentially measure the oxygen chemical potential in the three-phase fields: Cu+Eu2O3+CuEuO2, Cu2O+CuEuO2+CuEu2O4, and Eu2O3+CuEuO2+CuEu2O4. The thermodynamic properties of the ternary oxides can be represented by the equations: $\begin{gathered} {\raise0.5ex\hbox{$Couldn't find \end for begin{gathered} Thermogravimetric analysis (TGA) studies in Ar+O2 mixtures confirmed the results from emf measurements. An oxygen potential diagram for the system Cu-Eu-O at 1200 K was evaluated from the results of this study and information available in the literature on the binary phases.

Suppressed rf dissipation in 107Ag17+ ion irradiated Bi2Sr2CaCu2O8 single crystals by enhanced flux line tilt modulus

We have studied the isothermal, magnetic field (H‖c) dependent rf power P(H) dissipation (Hrf‖a) in the superconducting state of Bi2Sr2CaCu2O8 single crystals prior to and after irradiation with 250 MeV 107Ag17+ ions. In the pristine state, P(H) shows an initial decrease with increase in field, reaches a minimum at HM(T) and increases monotonically for H>HM(T). This behavior arises when the electromagnetic coupling between the pancake vortices in adjacent CuO layers becomes dominant on increasing the field and minimizes the distortions of the flux lines by confining the 2D vortices. In the post irradiated state, such an initial decrease and the minimum in P(H) is not observed but only a much reduced rf dissipation that monotonically increases with field from H = 0 onwards is seen. We attribute this difference to the strong enhancement of the tilt modulus C44 of the flux lines on irradiation when the pancake vortices in adjacent CuO bilayers are pinned along the track forming a well-stacked flux line in the field direction (‖c). We have also observed that the rf dissipation disappears at a certain temperature Tsf, at which the normal core of the flux line becomes commensurate with the columnar track diameter.

Anisotropic electrical transport property in La4BaCu5O13+δ and La4BaCu4NiO13+δ epitaxial thin films

Epitaxial films of La4BaCu5O13+δ and La4BaCu4NiO13+δ oxides are grown with a-b plane parallel to (100) of LaAlO3 and SrTiO3 by pulsed-laser deposition. The conductivity measurements performed along the c direction using LaNiO3 as the electrode show metallic behavior whereas they show semiconducting behavior in the a-b plane. Anisotropic transport property of these thin films is explained on the basis of nearly 180° connected Cu–O–Cu chains with an average Cu–O distance of 1.94 Å along the c direction and nearly 180° and 90° connected Cu–O–Cu chains in the a-b plane with short and long Cu–O distances ranging from 1.863 to 2.303 Å. YBa2Cu3O7−x has been grown along (00l) on La4BaCu5O13+δ and shows a Tc of 88 K.

Study of surface oxidation of rare-earth-metals by photoelectron-spectroscopy

Surface oxidation of La, Ce, Sm and Tb metals has been investigated by He(II) ultraviolet photoelectron spectroscopy (u.p.s.) and X-ray photoelectron spectroscopy (X.p.s.). Oxidation of La gives rise to La2O3 on the surface. While Ce2O3 appears to be the stable oxide on the surface, we find evidence for formation of CeO2 at high oxygen exposure. Valence band of Sm clearly shows the presence of both divalent and trivalent states due to interconfigurational fluctuation. Exposure of Sm to oxygen first depletes the divalent Sm at the surface. While Sm2O3 is the stable oxide on the surface of Sm, Tb2O3 is the stable oxide on the surface of Tb (and not any of the higher oxides).

Recent advances in auto exhaust catalysis

In last 30 years innovative research in the area of auto exhaust catalysis is being developed and CeO2 has been found to play a major role in this area due to its unique redox properties. In this review, auto exhaust emission and its impact on earth’s environment, global concern and recent advances in science and technology in automotive exhaust catalysis have been documented. A new preparative method of dispersing metal ions by solution combustion technique over CeO2 and TiO2 resulting mainly Ce1−xMxO2−δ, Ti1−xMxO2−δ and Ce1−x−yTixMyO2−δ (M = Pd, Rh and Pt) catalysts, structure of these materials, their catalytic properties towards auto exhaust catalysis, structure–property relation and mechanism of catalytic reactions are accounted here. In these materials, metal ions are incorporated into substrate matrix to a certain limit in the solid solution form and we have established a new direction in heterogeneous catalysis by turning to the concept of dispersed metal ions as catalytically active sites from the conventionally nurtured idea of metal particles as active centers for catalysis.

Exfoliation of copper hydroxysalt in water and the conversion of the exfoliated layers to cupric and cuprous oxide nanoparticles

P-aminobenzoate- intercalated copper hydroxysalt was prepared by coprecipitation at high pH (similar to 12). As the pH was reduced to similar to 7 on washing with water, the development of partial positive charge on the amine end of the intercalated anion caused repulsion between the layers leading to delamination and colloidal dispersion of monolayers of copper hydroxysalt in water. The dispersed copper hydroxysalt monolayers were used as precursors for the synthesis of copper(I)/(II) oxide nanoparticles at room temperature. While the hydroxysalt layers yielded spindle-shaped CuO particles when left to stand, they formed hollow spherical nanoparticles of Cu(2)O when treated with an alkaline solution of ascorbic acid.

Neutron scattering study of combustion-synthesized Ce1−xCuxO2−x

Powder neutron di®raction and Hi-Q neutron di®raction data have been recorded and analysed in order to obtain the local and long range order of Cu in Cu-doped CeO2 with three doping levels of Cu. Rietveld method and MCGR techniques of data analysis for the two types of data reveal that the Cu ion is in the 2+ oxidation state and has a vacancy in its ¯rst coordination shell. These deductions from the data analysis ¯t well with the mechanism of catalysis we propose.

Non-resonant rf absorption evidence for reentrant melting of vortex lattice in Bi2Sr2CaCu2O8 single crystals

We have studied the magnetic field dependent rf (20 MHz) losses in Bi2Sr2CaCu2O8 single crystals in the low field and high temperature regime. Above HCl the dissipation begins to decrease as the field is increased and exhibits a minimum at HM>HCl. For H>HM the loss increases monotonically. We attribute the decrease in loss above HCl to the stiffening of the vortex lines due to the attractive electromagnetic interaction between the 2D vortices (that comprise the vortex line at low fields) in adjacent CuO bilayers. The minimum at HM implies that the vortex lines are stiffest and hence represents a transition into vortex solid state from the narrow vortex liquid in the vicinity of HCl. The increase in loss for H>HM marks the melting of the vortex lattice and hence a second transition into vortex liquid regime. We discuss our results in the light of recent theory of reentrant melting of the vortex lattice by G. Blatter et al. (Phys. Rev. B 54, 72 (1996)).