X-ray,electrical conductivity and infrared studies of the system Zn1−x CO x Mn1−x Fe x CrO4

The system Zn_1–x Co _x Mn_1–x Fe _x CrO₄ is tetragonal in the range 0.0x0.4 and cubic in the range 0.5x1. Electrical resistivity temperature behaviour obeys Wilson's law for all the compounds and thermoelectric coefficient values vary between 135 to 226V K^–1. All compounds exhibit P-type semiconductivity and possess low mobility values (10^–9 cm² V^–1 sec^–1). The infrared spectra show the presence of two strong absorption bands around 500 and 600 cm^–1. The probable ionic configuration for the system is suggested to be Zn _1–x ²⁺ Fe _x ^–y3+ -Co _x ²⁺ [Mn _1–x ³⁺ Fe _y ³⁺ CO _x ^–y2+ Cr³⁺]O₄.     

Structural and magnetic property studies on low temperature chemically synthesised one-dimensional Zn1−xNixO nanorods

One-dimensional Zn_1?xNi_xO nanorods have been established through a facile surfactant/template free low temperature hydrothermal route, which involves the direct growth of the nanorod-like structures from an aqueous alkaline phase. The monophasic wurtzite structure of the Ni-doped ZnO nanocrystallites were initially studied using the X-ray diffractograms and their rod-like morphological appearance and homogeneity were analyzed through the aid of electron microscopes. Moreover, the substitution of Ni ions was found to contain the oxygen related vacancies and defect states in the nanostructures, through suppressing the E₂(high) and E₁(LO) modes in the Raman spectra. A similar trend was also observed in the subband gap emission, over the visible region of the emission spectra. The magnetic property studies on the Zn_1?xNi_xO semiconducting nanorods revealed the presence of paramagnetic characteristics at room temperature and antiferromagnetic interactions at 20 K.     

X-ray,electrical conductivity and magnetic hysteresis studies of the chalcogenide system Zn1−xCuxCr2Se4

X-ray diffraction studies performed here indicated solid-solution formation between ZnCr₂Se₄ and CuCr₂Se₄, and all the compounds could be indexed on the basis of cubic spinel lattice. The compositions between 0 x 0.8 showed semi-conducting behaviour, while CuCr₂Se₄ (x=1.0) exhibited metallic conductivity. Seebeck measurements showd P-type behaviour for 0 x 1. Magnetic hysteresis indicated a ferromagnetic nature for all the compounds except ZnCr₂Se₄ (x=0). The shapes of/ _i plotted againstT exhibited single domain behaviour, and Curie temperatures showed an increase with increasing copper concentration.     

Structural and optical studies of Zn1−xCdxS quantum dots synthesized by in situ technique in PVA matrix

Zn_1−xCd_xS (x = 0.1, 0.2, 0.3, 0.4, 0.5 … 0.9) quantum dots were synthesized successfully using novel in situ technique in polyvinyl alcohol (PVA) matrix. The PVA acted as a capping agent as well as a reducing agent. The structural and optical properties of the samples were studied by X-ray diffraction (XRD), TEM analysis, UV–Visible absorption and photoluminescence spectroscopy (PL). X-ray diffraction patterns revealed cubic zinc blende phase of the samples with lattice parameter in the range 5.47–5.75 Å. Optical band gap values were calculated from the absorption spectra and observed a decreasing band gap with increasing Cd:Zn ratio. The Raman spectra were recorded using conventional Micro Raman technique. Photoluminescence spectra showed asymmetric broad emission with multiple maxima. The concentration dependent quenching of PL intensity with increasing Cd:Zn ratio was observed along with a red shift. The nonlinear optical (NLO) and limiting properties were studied using Z-scan technique.     

Structural, optical, magnetic and electrical properties of Zn1−x Co x O thin films

Despite a considerable effort aiming at elucidating the nature of ferromagnetism in ZnO-based magnetic semiconductor, its origin still remains debatable. Although the observation of above room temperature ferromagnetism has been reported frequently in the literature by magnetometry measurement, so far there has been no report on correlated ferromagnetism in magnetic, optical and electrical measurements. In this paper, we investigate systematically the structural, optical, magnetic and electrical properties of Zn_1−x Co _x O:Al thin films prepared by sputtering with x ranging from 0 to 0.33. We show that correlated ferromagnetism is present only in samples with x > 0.25. In contrast, samples with x < 0.2 exhibit weak ferromagnetism only in magnetometry measurement which is absent in optical and electrical measurements. We demonstrate, by systematic electrical transport studies that carrier localization indeed occurs below 20–50 K for samples with x < 0.2; however, this does not lead to the formation of ferromagnetic phase in these samples with an electron concentration in the range of 6 × 10¹⁹ cm⁻³ ∼1 × 10²⁰ cm⁻³. Detailed structural and optical transmission spectroscopy analyses revealed that the anomalous Hall effect observed in samples with x > 0.25 is due to the formation of secondary phases and Co clusters.     

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.     

Investigation of structural,luminescence, and anti-bacterial properties of novel Zn1−xEuxAl2−yO4Sry phosphor

Journal of Materials Science: Materials in Electronics - In this research work, we synthesized novel zinc aluminate (Zn1?xEuxAl2?yO4Sry) sky bluish phosphors at 500&nbsp;°C via...     

Synthesis of nanosized (Zn1−xCox)Al2O4 spinels: New pink ceramic pigments

The Zn_1?xCo_xAl₂O₄ system has been reported to show a blue color with particles sizes that range from 36 nm to 30 μm. However, we have observed a pink color in this system with nanoparticles of an average size of 10 nm.Such differences in the optical properties of this nanosystem are related to the distribution of the cobalt cations in octahedral sites rather than in tetrahedral sites as in standard cobaltite spinels.The solid solution Zn_1?xCo_xAl₂O₄ (x = 0.2, 0.4, 0.6, 0.8 and 1) was synthesized by a co-precipitation reaction from the metallic salts and subsequent calcinations.The color properties and the high thermal stability (1400 °C) of these nanostructures suggest that they have the potential to be applied as satisfactory ceramic pigments.     

Structural, transport, magnetic, and dielectric properties of La1−x Te x MnO3 (x = 0.10 and 0.15)

In this study, we have investigated the structure, temperature-dependent resistivity, magnetization, and dielectric properties of La_1?x Te _x MnO_3±δ (x = 0.10 and 0.15). X-ray diffraction analysis confirms the rhombohedral crystal symmetry with space group R $ \overline{3} $ c. For both the samples, the temperature dependence of magnetization plots show paramagnetic-to-ferromagnetic phase transition. The Curie temperature (T _c) and magnitude of magnetization increase with the Te concentration. Field-dependent magnetization produces the asymmetric hysteresis loop that has been attributed to the magneto crystalline anisotropy induced by lattice distortion and the rare earth spin coupling at room temperature. Temperature-dependent resistivity plots exhibit metal–insulator transition (MIT) and charge-ordering state. These plots have been fitted using variable range hopping model, and the density of states [N(E_F)] has been estimated. Magnetoresistance is measured as a function of temperature in the field of 1T, 5T, and 8T. The dielectric constant shows an anomaly near MIT. The dielectric constant exhibits a peaking behavior with the applied frequency and the temperature dependence of dielectric constant attains colossal values at high temperatures.     

Structural and optical properties of Cd x Zn(1 − x)Te thin films

Seven Cd _x Zn_{(1 ? x} Te solid solutions with x = 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 were synthesized by fusing stoichiometric amounts of CdTe and ZnTe constituents in silica tubes. Each composition was used in the preparation of a group of thin films of different thicknesses. Structural investigation of the obtained films indicates they have a polycrystalline structure with predominant diffraction lines corresponding to (111) (220) and (311) reflecting planes, which can be attributed to the characteristics of growth with the (111) plane. The optical constants (the refractive index n, the absorption index k, and the absorption coefficient α) of Cd _x Zn_{(1 \s -x)} Te thin films were determined in the spectral range 500–2000 nm. At certain wavelengths it was found that the refractive index, n, increases with increasing molar fraction, x. It was also found that plots of α² (hv) and α^1/2 (hv) yield straight lines, corresponding to direct and indirect allowed transitions respectively obeying the following two equations: $$\begin{gathered} E_g^d = 1.583 + 0.277x + 0.197x^2 \hfill \\ E_g^{ind} = 1.281 + 0.111x + 0.302x^2 \hfill \\ \end{gathered}$$      

X-ray,transport, magnetic and catalytic studies of the system Cd1–x Cu x FeCrO4

The compounds of the system Cd_1–x Cu_xFeCrO₄, where 0.0 x 1.0, synthesized by the co-precipitation technique have been studied with a view to investigating the cation distribution and the transport and magnetic properties, and to correlating the physical properties of oxidic spinels with their catalytic behaviour in the decomposition of benzyl alcohol. All the compounds of the system were crystallized with the cubic-spinel structure. The activatio-energy values of electronic conduction varied between 0.69 and 0.16 eV. Thermoelectric power measurements indicated a p-type semiconducting nature for all the compounds. Magnetic hysteresis studies indicated that the compounds with x 0.4 were ferrimagnetic. The Curie temperatures increased with increases in the Cu²⁺ -ion concentration. A good correlation could be established between the physical properties and the catalytic behaviour of the system.     

Structural,spectral, dielectric,and magnetic properties of indium substituted Cu0.5Zn0.5Fe2−xO4 magnetic oxides

Journal of Materials Science: Materials in Electronics - The influence of indium on the properties of Cu0.5Zn0.5Fe2O4 nano ferrites synthesized by sol–gel auto-combustion technique was...     

The preparation,characterization and electrical properties of copper manganite spinels,CuxMn3−xO4, 0 ⩽x ⩽ 1

Single-phase copper manganite spinels Cu _x Mn_3–x O₄ with 0x1 were prepared by a careful thermal processing of copper-manganese co-precipitated hydroxide precursors. Powder X-ray diffraction (XRD) analysis of these spinels revealed the presence of a tetragonally distorted single spinel phase, with tetragonal distortionc/a > 1 which decreases with copper content. Thermogravimetric analysis (TGA) curves, run in an oxygen atmosphere for all the compositions studied, are characterized by a stability step up to 250 to 300° C, followed by a domain of oxidation between 300 and 900° C and finally a domain of reduction that restores the initial stoichiometry of the samples. The oxidation is observed to occur in two successive steps. The phenomenon appearing at the low temperature is due to the oxidation of Cu⁺ ions, while that at higher temperature corresponds to the oxidation of Mn²⁺ ions in tetrahedral sites. Further, electrical resistivity measurements confirm the presence of Cu⁺ ions on the tetrahedral sublattice of spinel. Correlation of the results obtained by XRD, TGA and electrical resistivity measurements permits one to infer the cation distribution, given by Cu _x ⁺ Mn _1–x ²⁺ [Mn _2–x ³⁺ Mn _x ⁴⁺ ] O ₄ ^2– .     

Effect of Zn Doping on Structural and Magnetic Properties of Ba4Ni2−x Zn x Fe36O60 Hexaferrites

Polycrystalline Ba₄Ni_2?x Zn _x Fe₃₆O₆₀ (0.0 ≤x ≤ 1.4) hexagonal ferrite samples have been prepared by conventional solid-state reaction method. Structural and magnetic properties of the prepared samples were then analyzed by the X-ray diffraction technique and with superconducting quantum interface device (SQUID) magnetometer, respectively. Variations of lattice parameters, density, and porosity with Zn content were measured. Magnetic properties such as complex permeability, relative quality factor, loss factor, and saturation magnetization have been investigated as a function of Zn content. The study revealed that Zn content has a significant effect on structural and magnetic properties of the Ba₄Ni₂Fe₃₆ O ₆₀ hexaferrites.     

Low temperature synthesis of Co3O4 and (Co1−xMnx)3O4 spinels nanoparticles

The (Co_1?xMn_x)₃O₄ solid solution have been synthesized in water at 60 °C by soda addition to a cationic solution. XRD patterns show that spinel oxide has been obtained except for pure cobalt composition which exhibits also the presence of hydroxide and oxy-hydroxide. Therefore, to reach this composition, a different synthesis route has been developed: the cationic solution is added to the soda and for the first time Co₃O₄ nanoparticles have been synthesized by a direct precipitation in aqueous solution at low temperature. For each composition, the particles are well crystallized and exhibit a size close to 50 nm. Each particle is composed by several crystallographic domains of about 10 nm. The cubic to tetragonal transition reported in the literature for x = 0.46 is observed in between x = 0.33 and x = 0.50. Raman spectra show that substitution of Co by Mn, in the cubic phase, introduces a random high disorder. In the tetragonal phase, occupation of the octahedral site remains a random occupation, while the tetrahedral site seems to be preferentially occupied by Co ions. All these results show that the precipitation is a simple, fast and safe process to synthesize pure phase of (Co_1?xMn_x)₃O₄ spinel solid solution in aqueous media at low temperature.     

Structural studies of compounds in the series GaSxSe1−x (0⩽x⩽1) grown by iodine vapour transport

A discontinuity in the length of thec-axis of compounds in the series GaS _x Se_1–x ) is observed at the compositionx=0.25. This is thought to be caused by a transition from the structure of GaS to the structure of GaSe. Although lattice parameter measurements indicate that the transition is abrupt, structure factor calculations and observations of the form of the (0 0 0 1) surface growth features indicate that the transition is not sharp, but takes place over the composition range 0.2x0.3. Growth features change in form asx varies, from hexagonal spirals characteristic of GaS to triangular spirals typical of GaSe.