Structural,thermal and transport studies on Ag1 − x Cuxl (0.05 ⩽ x ⩽ 0.25) solid electrolyte

Preparation and characterization studies on polycrystalline samples of Ag_{1 – x}Cu_xl wherex=0.05, 0.1, 0.15, 0.2 and 0.25, respectively, have been reported. Samples were analysed using powder X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques in order to identify the compositions and phase transition temperatures. A.c. electrical conductivity studies were carried out on pelleted specimens of various compositions in the frequency range 65.5 kHz to 1 Hz and over the temperature range 293–412 K. DSC results obtained in the temperature range 373–473 K have shown that the ß- to -phase transition temperature is enhanced from 426 K to 438 K whenx is increased from 0.05 to 0.25. XRD results have indicated that there is a shift ind-spacing when the Cul content is increased, suggesting changes in the crystal structure. Typical XRD patterns recorded for the composition Ag_0.95Cu_0.05l at three different temperatures (room temperature, 373 and 473 K, respectively) have confirmed that both face-centred cubic and hexagonal phases would be present at room temperature and at 373 K as well, whereas at 473 K the structure would be purely body-centred cubic in nature. A.c. impedance analysis of the above samples appears to suggest that their electrical conductivity, predominantly due to the migration of Ag⁺ ions, lies in the order of 10^–4S cm^–1 at room temperature.     

On the thermal decomposition of the zinc(II) hydroxide chlorides Zn5(OH)8Cl2·H2O and Β-Zn(OH)Cl

The thermal decomposition of Zn₅(OH)₈Cl₂·H₂O and -Zn(OH)Cl materials under several experimental conditions has been studied by thermal analysis, X-ray powder diffraction and X-ray high-temperature powder diffraction techniques. Several reaction schemes are proposed to account for thermal decomposition reactions undergone by both zinc hydroxide chlorides.     

Optical absorption,electrical conductivity and spectral response measurements on the system CdGa2S4(1−x)Se4x

The compounds CdGa₂S₄ and CdGa₂Se₄ belong to the defect chalcopyrite (space group 1 ¯4) family. A series of compounds CdGa₂S_4(1–xSe_4x has been prepared and their single crystals grown by the chemical transport reaction method. Optical absorption, spectral response, electrical conductivity and thermoelectric power measurements have been made. The optical absorption spectra revealed that the fundamental absorption edge varies with composition, from 2.2 to 3.25 eV. The plots (w)² versus w revealed that these compounds are direct band gap materials, but plots of (w)^1/2 versus w did not give convincing support to the presence of indirect transitions. The values of energy gaps were also deduced from spectral response (max) measurements and found to be in agreement with those deduced from optical absorption measurements. D.c. resistivity versus temperature studies revealed that, in spite of their large band gaps, these compounds exhibit intrinsic semiconduction above 250° C. The energy gap values matched with those obtained from other measurements. All samples were n-type and had a constant thermoelectric power 300 V° C^–1 in the temperature range 250 to 350° C. However, the thermal dependence of electrical conductivity and thermoelectric power indicated strong irreversibility with the thermal heating and cooling cycle. Such behaviour has been attributed to the diffusion of contact materials such Ga and In.     

Adsorption of lead(II) on O₂-plasma-oxidized multiwalled carbon nanotubes: thermodynamics, kinetics, and desorption

O(2)-plasma-oxidized multiwalled carbon nanotubes (po-MWCNTs) have been used as an adsorbent for adsorption of lead(II) in water. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy measurements show that the bulk properties of MWCNTs were not changed after O(2)-plasma oxidation. The adsorption capacity of MWCNTs for lead(II) was greatly enhanced after plasma oxidation mainly because of the introduction of oxygen-containing functional groups onto the surface of MWCNTs. The removal of lead(II) by po-MWCNTs occurs rather quickly, and the adsorption kinetics can be well described by the pseudo-second-order model. The adsorption isotherm of lead(II) onto MWCNTs fits the Langmuir isotherm model. The adsorption of lead(II) onto MWCNTs is strongly dependent upon the pH values. X-ray photoelectron spectroscopy analysis shows that the adsorption mechanism is mainly due to the chemical interaction between lead(II) and the surface functional groups of po-MWCNTs. The thermodynamic parameters (ΔH°, ΔS°, and ΔG°) calculated from the adsorption isotherms suggest that the adsorption of lead(II) onto MWCNTs is endothermic and spontaneous. The regeneration performance shows that lead(II) can be easily regenerated from po-MWCNTs by altering the pH values of the solution.     

Exploration of the structural,spectroscopic and thermal properties of double sulfate monohydrate NaSm(SO4)2·H2O and its thermal decomposition product NaSm(SO4)2

Samarium-sodium double sulfate crystalline hydrate NaSm(SO₄)₂·H₂O was obtained by the crystallization from an aqueous solution containing equimolar amounts of ions. The anhydrous salt of NaSm(SO₄)₂ was formed by a thermally induced release of the equivalent of water from NaSm(SO₄)₂·H₂O. The kinetic parameters of thermal decomposition were determined (E_a = 102 kJ/mol, A = 9·10⁶). The crystal structures of both compounds were refined from the X-ray powder diffraction data. Sulfate hydrate NaSm(SO₄)₂·H₂O crystallizes in the trigonal symmetry, space group P3₁21 (a = 6.91820(3) and c = 12.8100(1) Å, V = 530.963(7) ų). The anhydrous salt crystallizes in the triclinic symmetry, space group P-1 (a = 6.8816(2), b = 6.2968(2) and c = 7.0607(2) Å, α = 96.035(1), β = 99.191(1) and γ = 90.986(1)°, V = 300.17(1) ų). The vibrational properties of compounds are mainly determined by the sulfate group deformations. The luminescence spectra of both sulfates are similar and are governed by the transitions of samarium ions ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2). The anhydrous sulfate is stable up to 1100 K and undergoes an almost isotropic expansion when heated. After 1100 K, the compound decomposes into Sm₂(SO₄)₃ and Na₂SO₄.     

Hydrothermal synthesis,characterization and thermal stability studies of α-Fe2O3 hollow microspheres

A simple, cost-effective hydrothermal technique was used in this study to successfully fabricate hollow α-Fe₂O₃ microspheres, using only fructose and anhydrous ferric chloride without any organic solvent or additive. The synthesized α-Fe₂O₃ hollow microspheres were characterized by X-ray diffraction spectroscopy (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). Based on the results, the shell was composed of aggregated α-Fe₂O₃ nanoparticles, while the fructose-derived carbon core was decomposed during calcination, leaving a hollow interior. XRD analysis confirmed the presence of the α-phase and the absence of γ-phase Fe₂O_3. A mean diameter of 595 nm was estimated for the microspheres by the Gaussian fit of the histogram constructed from the diameters measured over the SEM images. EDX spectrum of the sample showed signals attributed to Fe and O, and a homogenous distribution of these elements was confirmed by elemental mapping studies. ATR-FTIR analysis confirmed the bending and stretching vibration modes of the Fe-O bond. TGA-DTA data depicted that thermal stability of α-Fe₂O₃ hollow microsphere was achieved at 480 °C and no weight loss was observed up to 1000 °C. High-temperature calcination results showed that the material can maintain its hollow morphology up to 700 °C. This material has potential applications in drug delivery, gas sensing, and lithium storage.     

Room temperature synthesis of rod-like FeC(2)O(4)·2H(2)O and its transition to maghemite, magnetite and hematite nanorods through controlled thermal decomposition

FeC(2)O(4)·2H(2)O nanorods with diameter of about 50?nm and length of up to several micrometers were synthesized at room temperature in a surfactant-assisted system, which was obtained by dissolving bis(2-ethylhexyl)sodium sulfosuccinate (AOT) in a mixed solution composed of water and ethylene glycol (EG). The influence of reaction conditions on the morphology of FeC(2)O(4)·2H(2)O is discussed in detail. Through direct thermal decomposition of FeC(2)O(4)·2H(2)O under different calcination conditions, maghemite (γ-Fe(2)O(3)), magnetite (Fe(3)O(4)) and hematite (α-Fe(2)O(3)) can be selectively obtained, preserving the rod-like morphology. Transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) characterizations showed that the as-obtained iron oxide nanorods were composed of fine particles with different crystal orientations. The magnetic properties of the as-obtained iron oxide nanorods were systematically investigated.     

Synthesis of “stabilized Mn1−xMgxO” system (0.001 ⩽ x ⩽ 0.15) and its structural,thermal, optical and magnetic studies

A novel method of preparation, involving careful formation of a stoichiometric solid solution of stabilized Mn_1-x Mg _x O system for eight different concentrations ofx (0.001 x 0.15) is described. A variety of physicochemical techniques such as X-ray diffraction, DTA-TGA, reflectance spectra, magnetic susceptibility and XPS data are used to determine structure-property correlations in the solid solutions, which are (i) X-ray diffraction studies reveal the linear decrease of cubic lattice parameter with increasing x, (ii) DTA-TG-DTG studies which confirm the formation of solid solution and the stability of these solid solutions in air which increases from 515 to 565 K withx, (iii) the diffused reflectance spectra shows nearly perfect octahedral symmetry around Mn²⁺ ions, (iv) magnetic susceptibility data indicates the usual dilution effects of diamagnetic ions in antiferromagnetic host lattice, (v) XPS studies reveal the presence of mixed phase of Mn₂O₃-MgO on the surface which protects the bulk MnO from its further oxidation to higher oxides of manganese. This shows the important role of Mg²⁺ in the chemical passivation of manganous oxide.     

Thermal and electrical studies on mixed crystals of CuxZn1−x(HCOO)2·2H2O

The electrical properties of CuxZn1–x(HCOO)2·2H2O have been studied over a temperature range of 78–400 K. Results of the electrical conductivity, d.c., a.c., thermoelectric power, , relative permittivity, r, and dielectric loss factor, r, were reported. Anomalies in the physical properties have been observed at 220 K and at the vicinity of the decomposition temperature, and the mechanism of decomposition of solids has been studied. A random nucleation process (A3) was found to be the predominant decomposition mechanism for the system investigated. The effects of chemical composition and crystal structure on the physical properties are discussed.     

Growth, Optical, Mechanical, Dielectric and Theoretical Studies on Potassium Pentaborate Tetrahydrate (KB_5O_8·4H_2O) Single Crystal by Modified Sankaranarayanan-Ramasamy Method

A nonlinear optical single crystal of potassium pentaborate tetrahydrate (KB5O8·4H2O) has been grown from aqueous solution by using unidirectional crystal growth method of Sankaranarayanan-Ramasamy (SR) with a due modification in the growth assembly. Potassium pentaborate crystal of 60 mm length and 10 mm diameter has been grown along (100) plane with a growth rate of 3 mm per day within a period of 20 days. The grown crystal was subjected to single crystal X-ray diffraction analysis to confirm that the cry...     

Chemical vapour transport of transition-metal oxides (II) epitaxial growth of RuO2, IrO2 and (Ru1−x,Irx)O2 on TiO2

Epitaxial Growth of RuO₂ and IrO₂ has been performed by Chemical Vapour Transport on prepared TiO₂ substrates. Two types of samples are found. The first shows epitaxial layers of the ruthenium and iridium oxides with orientations close to that of the substrate, and with low level interdiffusion of the components. The second shows no epitaxial growth, but the incorporation of Ru and Ir into the substrate surface giving a brown colouration. The transmission spectra of these samples in the visible range show an absorption increasing with photon energy. For the Ru doped surfaces, two absorption bands may be distinguished.     

Synthesis and spectral studies on some 3d metal complexes of a mesogenic ligand,N-(4′′′-n-butylphenyl)-4-(4′-hexyloxybenzoate)salicylaldimine

A mesogenic (nematic) Schiff's base, N-(4′′′-n-butylphenyl)-4-(4′-hexyloxy benzoate)salicylaldimine, Hbphbsal, (abbreviated as HL¹), was synthesized and its structure studied by elemental analyses, mass, NMR and IR spectra. A series of mesogenic/non-mesogenic 3d metal complexes of the general formula, [M(L¹)₂]_n where M^II = Mn, Co, Ni, Cu and Zn has been prepared and structures were studied by various spectroscopic techniques. Spectral studies imply coordination of the ligand (HL¹) as uni-negative bi/tri-dentate species to the metal ions, rendering overall geometry to distorted square planar (in case of Cu^II complex) and octahedral geometry. The ESR spectra confirmed the presence of mixed copper–nitrogen and oxygen bonds in the chelate based on the g_?? value. The Cu^II, Co^II and Ni^II complexes were found to be mesogenic (nematic) and their transition, melting and clearing points deviated from the ligand upon complexation.     

X-ray diffraction,Mössbauer spectrometry and thermal studies of the mechanically alloyed (Fe1−xMnx)2P powders

(Fe_1?xMn_x)₂P phosphide powders in the composition range 0.15?≤?x ≤ 0.75 have been mechanically alloyed and their structural, magnetic and thermal changes with composition have been investigated by means of X-ray diffraction, ⁵⁷Fe Mössbauer spectrometry, magnetization measurements and differential scanning calorimetry. The milling process induces changes in the crystal phase diagram of the (Fe_1?xMn_x)₂P system. The XRD results reveal the coexistence of a bcc Fe(Mn)-type, hexagonal (Fe₂P and Mn₂P-type), orthorhombic (MnP-type) and tetragonal Fe₃P-type structures for all compositions. The room temperature Mössbauer spectra confirm the formation of the Fe(Mn)-type, non-stoichiometric Fe₂P-type, FeP-type and Fe₃P-type structures. Saturation magnetization exhibits a comparable behavior to that of the average hyperfine magnetic field. The DSC scans show the existence of several endothermic and exothermic peaks in the temperature range (100–700)?°C related to different phase transitions. The endothermic peak at about 582–589?°C can be related to the ferromagnetic/paramagnetic transition temperature (Curie temperature, T_C) of the Fe(Mn)-type structure.     

Effect of Pb (Yb1/2Nb1/2)O3 on phase transition and thermal and electrical properties of PZ–PYbN solid solution on PZ-rich side

The (1 − x)PbZrO₃–xPb(Yb_1/2Nb_1/2)O₃ (PZ–PYbN) ceramics, with the compositions, x = 0.00–0.50, were prepared by the wolframite precursor method. The crystal structure and electrical and thermal properties of PbZrO₃ ceramic were investigated as a function of the composition, x, using X-ray diffraction, dielectric spectroscopy, hysteresis measurement and differential scanning calorimetry techniques. The results indicated that the solid solution, PZ–PYbN, changed from orthorhombic to rhombohedral symmetry when the amount of PYbN increased. The pyrochlore phase identified as Yb/Nb mixed compound was observed at the composition, x ≥ 0.2. For the compositions, x = 0.00–0.10, ceramics showed a sharp phase transition from AFE to PE. Furthermore, the intermediate FE phase was absent from the PZ–PYbN system.     

AC and DC Conductivity Studies on Lead-Free Ceramics: Sr1–xCaxBi4Ti4O15(x = 0, 0.2, 0.4, 0.6, 0.8)

Sr_1–xCa_xBi₄Ti₄O₁₅ [x = 0, 0.2, 0.4, 0.6, 0.8] ceramics are synthesized by solid-state reactive technique. Structural analyses are done by x-ray diffraction data. Morphological studies were carried out by scanning electron microscope, and the data showed plate-like structures. To understand the conductivity mechanism, frequency and temperature dependency of AC and DC conductivity studies are carried out. The conductivity measurements are done using an impedance analyzer (Wayn–Kerr) in the temperature range 100–600°C. The frequency-dependent AC conductivity at different temperatures indicates that the conduction process follows the universal power law, and the hopping frequency shifts toward higher frequency side with increase in temperature, below which the conductivity is frequency independent. The variation of DC conductivity confirms that the ceramics exhibit negative temperature coefficient of resistance behavior at high temperature. DC conductivity values do not show any linearity with doping concentration; for a particular composition SCBT06, the DC conductivity was low.     

Electrical conduction in γ-irradiated and unirradiated Fe3O4, CdFe2O4 and Co x ZN1−x Fe2O4 (0 ⩽x ⩽ 1) ferrites

The electrical conductivity of -irradiated and unirradiated finely divided ferrites of composition Fe₃O₄, CdFe₂O₄ and Co _x Fn_1–x Fe₂O₄(0 x 1) was studied in a nitrogen atmosphere as a function of temperature. Fe₃O₄, ZnFe₂O₄ and CdFe₂O₄ showed n-type conduction, whereas CoFe₂O₄ showed p-type conduction. For Co _x Zn_1-x Fe₂O₄ it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe₃O₄, and Co _x Zn_1–x Fe₂O₄(0 x 1) was explained by a hopping mechanism, whereas the conduction in ZnFe₂O₄ and in CdFe₂O₄ is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of -irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.     

Synthesis,sintering and thermal expansion of Ca1-x Sr x Zr4P6O24 — an ultra-low thermal expansion ceramic system

Ca_1-x Sr _x Zr₄P₆O₂₄ (O × 1.0) system which belongs to a new large family of low thermal expansion materials known as NZP or CTP, was synthesized by the solid state and the sol-gel methods. The conventional sol-gel method was modified by introducing a seeding step which resulted in significant improvement in the sintering characteristics and the microstructure of the sintered material. Sintering data were compared with those obtained by the powder mixing technique. Thermal expansion of the sintered samples was measured by classical dilatometry and by high-temperature X-ray diffractometry. It was found that CaZr₄P₆O₂₄ (x= 0) and SrZr₄P₆O₂₄ (x= 1) phases had opposite anisotropies in their respective axial thermal expansions. This behaviour led to the development of a crystalline solution composition of nearly zero expansion characteristic. Microstructures of the sintered specimens were examined by scanning electron microscopy.     

STM studies of island formation and surface ordering of Si on GaAs (001), (2×4) and c(4×4): Implications for δ-doping

Scanning tunnelling microscopy (STM) and reflection high energy electron diffraction (RHEED) have been used to study the deposition of Si below 400C onto GaAs (001) surfaces grown in situ by molecular beam epitaxy (MBE). The emphasis is on the island formation and growth, as well as surface ordering, for submonolayer quantities of Si (up to 0.2 ML) deposited on two different As-rich reconstructions of GaAs (0 0 1) (2 × 4) and c(4 × 4). For deposition on the c(4 × 4) surface, an asymmetric (3 × 1) RHEED pattern is formed, a consequence of anisotropic needle-like islands, which grow adjacent to each other along the [1 1 0] direction and produce a three-fold periodic superstructure. Individual islands grow by a site exchange process in which the additional As layer of the c(4 × 4) structure acts as a surfactant and enables the Si atoms to occupy Ga sites in the GaAs lattice. In contrast, Si deposition on the (2 × 4) surface does not lead to any new surface periodicities as monitored by RHEED. The Si atoms form poorly ordered clusters distributed randomly across the surface. The site exchange process cannot occur in this case as the (2 × 4) surface is terminated with only one layer of arsenic. Instead, the Si atoms occupy sites on top of the outer arsenic layer.     

Optical,thermal and radiation shielding properties of B2O3–NaF–PbO–BaO–La2O3 glasses

Journal of Materials Science: Materials in Electronics - The techniques of melt-quenching have been used to generate 53B2O3—2NaF—27PbO – $$(20-x)$$...     

PbGe4O9–MGe4O9 (M = Ba, Sr) and BaGe4O9–SrGe4O9 Solid Solutions

PbGe₄O₉–MGe₄O₉ (M = Ba, Sr) and BaGe₄O₉–SrGe₄O₉ samples prepared via melt solidification and by solid-state reactions were characterized by x-ray diffraction and x-ray microanalysis, and their dielectric, piezoelectric, and pyroelectric properties were studied. The results demonstrate that the presence of BaO or SrO in (1 – x)PbO · xMO · 4GeO₂ starting mixtures stabilizes -PbGe₄O₉. In -PbGe₄O₉ crystals, only 3% of the Pb atoms can be substituted with Ba or Sr. In BaGe₄O₉ and SrGe₄O₉ crystals, the fraction of Ba or Sr atoms substituted with Pb attains 40%. BaGe₄O₉ and SrGe₄O₉ form a continuous series of solid solutions. The ferroelectric phase transition near 140 K and the pyroelectric effect in the samples are due to the presence of -PbGe₄O₉. M_{1 – y} Pb _y Ge₄O₉ and Ba_{1 – x} Sr _x Ge₄O₉ solid solutions, isostructural with -PbGe₄O₉, possess neither ferroelectric nor pyroelectric properties.