Dielectric and optical properties of TlGa1 − x Er x S2 (x = 0, 0.001, 0.005, 0.01) single crystals

TlGa_{1 ? x} Er _x S₂ (x = 0, 0.001, 0.005, 0.01) solid solutions, based on the layered compound TlGaS₂, have been prepared by direct elemental synthesis. The effect of Er concentration on the dielectric and optical properties of the TlGa_{1 ? x} Er _x S₂ solid solutions has been studied. The results demonstrate that increasing the Er content of the TlGa_{1 ? x} Er _x S₂ solid solutions decreases the real part of their complex dielectric permittivity and increases their dielectric loss tangent. The conductivity (σ) of the TlGa_{1 ? x} Er _x S₂ solid solutions in the frequency range f = 1 to 35 MHz exhibits σ ～ f ^0.8 behavior, indicative of hopping charge transport through their band gap. We have evaluated the key parameters of this charge transport mechanism. We have studied temperature-dependent optical properties of the TlGa_{1 ? x} Er _x S₂ solid solutions. At temperatures in the range T = 77–200 K, the TlGa_0.999Er_0.001S₂ solid solution has an absorption band near its fundamental absorption edge, which is due to transitions to a direct exciton state.     

Synthesis and Crystal Structures of New RRuxGa1 – x (R = Er,Tm, Lu) Gallides and R2Ru1 – xIn1 + x (R = Dy,Ho, Er,Tm, Lu) Indides

Inorganic Materials - A number of new intermetallic compounds of variable composition, RRuxGa1 – x(R = Er, Tm, Lu) and R2Ru1 – xIn1 + x (R = Dy, Ho, Er, Tm, Lu), whose structures belong...     

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.     

Crystalline structure and dielectric properties of (Sr1−1.5x Bi x ) TiO3 ceramics

The crystalline structure, microstructure and dielectric properties of the (Sr_1–1.5x Bi _x )TiO₃ (0 x 0.267) ceramics were studied. Cubic solid solutions were determined for x 0.2 at room temperature. However, lattice distortion was detected by Raman spectra. A dense microstructure with the grain sizes of 2–4 m was obtained for (Sr_1–1.5x Bi _x )TiO₃ (0 x 0.2) ceramics. The Bi concentration was examined and found to be in agreement with the nominal composition and overall uniformly distributed in the sample. Different from the observations in the earlier literature for other doped quantum paraelectrics, where only an induced dielectric anomaly was reported, there are three Bi induced dielectric modes A, B, and C in the Bi doped SrTiO₃ samples. The occurrence of the impurity modes and the ferroelectric relaxor mode and their evolution are demonstrated as a function of Bi concentration.     

Optical and electrical properties of Y3+ ion substituted orthorhombic mullite Y(x)Al(6−x) Si2O13 nanoparticles

Y³⁺ substituted mullite Y_(x)Al_(6?x)Si₂O₁₃ nanoparticles where x varied from 0.005 to 0.05 have been synthesized via co-precipitation technique. X-ray diffraction results revealed that orthorhombic mullite was the major phase in the samples of x = 0.0–0.025, whereas corundum α-Al₂O₃ was predominant at high Y³⁺-ion content of x = 0.05. Transmission electron microscope images showed orthorhombic-like structure for the pure sample. Meanwhile, the doped samples exhibited similar morphologies of larger particle sizes associated with small amount of glassy liquid phase. FT-IR spectrum evinced the formation of corundum particularly at high Y³⁺ ion content (5 %). The photoluminescence emission spectra were strongly affected by the Y³⁺ ion content. Moreover, mullite sample doped with 0.5 % Y³⁺ ion achieved the minimum electrical resistivity of 0.28 × 10⁹ Ω cm and the minimum dielectric loss value of 0.37 in the radiowave frequency region (10 MHz) as well as the minimum dielectric loss value of 0.41 in the microwave frequency region (1 GHz).     

Structural,electrical and magnetic properties of polycrystalline La0.67(Ca1−x Sr x )0.33MnO3 manganites

Polycrystalline La_0.67(Ca_1?x Sr _x )_0.33MnO₃ with different substitution level of strontium element, were synthesized via solid state reaction. Structure of samples was characterized by X-ray diffraction (XRD). XRD patterns reveal that La_0.67Ca_0.33MnO₃ exhibits orthorhombic structure with space group Pnma. Phase transitions from orthorhombic to rhombohedral take place as Ca ions were gradually substituted by Sr ions. The XRD data were further analyzed by Rietveld refinement technique. The data show that Mn–O–Mn bond angle increases as x increases. Microstructures obtained from SEM show that substitution of Sr ions has demoted the grain growth and densification process during sintering. The substitution of Sr ions has greatly influenced the hopping integral of electron via double exchange interaction, thus affecting the electrical properties and magnetic properties as well. The resistivity decreases and the metal–insulator transition temperature (T _p ) shifts to higher temperature as x increases. The magnetoresistance (MR) effect gradually decreases and MR peak shifts to higher temperature as x increases. The magnetization measured at room temperature is found to be increasing as x increases.     

Structural,magnetic, and electrical properties of RFeO3 (R = Dy,Ho, Yb & Lu) compounds

Journal of Materials Science: Materials in Electronics - In this research, the nanosized rare-earth orthoferrites (RFeO3) with R?=?Dy, Ho, Yb &amp; Lu were synthesized by...     

Optical and electrical properties of Ba1−x Sr x TiO3 nanopowders at different Sr2+ ion content

Barium strontium titanate (BST) Ba_1?x Sr _x TiO₃ nanopowders have been successfully synthesized using oxalate precursor route. The effect of Sr²⁺ ion content from 0.3 to 0.7 on the crystal structure, crystallite size, microstructure, electrical and optical properties was systematically studied. The results revealed that well crystalline single BST phase was formed by annealing the oxalate precursor at 1,000 °C for 2 h. The crystallite size of the BST powders was decreased with increasing the Sr²⁺ ion molar ratios. The crystallite size was decreased from 56.0 to 33.1 nm when the Sr²⁺ ion content increased from 0.3 to 0.7. Additionally, the lattice parameter (a), unit cell volume and X-ray density of BST ware decreased whereas the porosity, % were increased with Sr²⁺ ion concentration. The BST phase appeared as cubic-like structure. The spectrophotometer measurement results demonstrated that the room temperature band gap energy varied with the Sr²⁺ ion composition x. The band gap energy was shifted to low energy and it was decreased from 3.6 to 3.2 eV with increasing the Sr²⁺ ion content from 0.3 to 0.7. Moreover, the DC resistivity was enhanced with increasing the Sr²⁺ ion ratio. The dielectric response obtained for the stressed samples corresponds to a true resonance rather than a dispersion process with a characteristic frequency around 1 GHz at room temperature. However, the peaks commonly observed at GHz frequency were changed with varying the Sr²⁺ ion composition. The high imaginary components of dielectric permittivity for x = 0.3 was found at higher frequency region around 1.6 GHz compared with the samples with x values of 0.5 and 0.7 in which the frequency regions were around 1.25 and 1.15 GHz, respectively.     

Structural,electrical, and magnetic properties of erbium (Er3+) substituted Cu–Cd nano-ferrites

In the present work, we reported the structural, electrical, and magnetic properties of erbium Er³⁺-substituted Cu–Cd nano-ferrites with generalized formula Cu_0.8Cd_0.2Er_xFe_2?xO₄ (where x?=?0.000, 0.0010, 0.0015, 0.002, 0.0025, 0.003), as synthesized by the Citrate-Gel Auto-Combustion. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies were carried out to investigate their microstructural and surface morphology. The XRD measurements confirm pure cubic spinel phase composition of these nanoparticles. The crystallite size ranges over 9.22–19.22 nm and it reduces with the increase in erbium Er³⁺ concentration from 0.000 to 0.003. The vibration properties were carried out by using FTIR spectrometer. The two probe measurements were used to determine DC resistivity, Curie temperature, and DC conductivity. The plot between DC electrical resistivity and temperature indicates the semiconductor behavior. At room temperature, the vibrating sample magnetometer (VSM) was used to investigate magnetic properties, and the observed values revealed the ferrimagnetic behavior with high saturation magnetization (34.24 emu/g) and high coercivity (1121.70 Oe).

     

Synthesis and luminescent properties of BaLn2(1−x)ZnO5:2xTb3+ (Ln = Y, Gd) nanophosphors

The synthesis of BaLn_2(1?x)ZnO₅:2xTb³⁺ (Ln = Y, Gd) nanophosphors using solution combustion method with an aim to study the effect of sintering temperature and Tb³⁺ ions concentration on the luminescent properties has been investigated. Under UV excitation, BaY_2(1?x)ZnO₅ and BaGd_2(1?x)ZnO₅ nanoparticles exhibit apparent characteristic green emission from ⁵D₄ state to ⁷F_6?3 states of Tb³⁺ ions with the strongest at 544 nm. Luminescence concentration quenching could be observed when the Tb³⁺ ions contents were more than 4 mol% in both nanophosphors. The luminescence decay curves suggest monoexponential behavior of both nanophosphors. X-ray diffraction results confirmed the single-phased orthorhombic structure of both powders belonging to space group Pbnm. TEM analysis indicates the spherical morphology of nanoparticles with average grain size in the range of 85–95 nm. BaY_2(1?x)Tb_2x ZnO₅ and BaGd_2(1?x)Tb_2x ZnO₅ nanophosphors may have potential applications in field emission displays based on their uniform shape, low-cost synthetic route, and diverse luminescent properties.     

Synthesis and electrical properties of (BaTiO3)1 ?x (K0.5Bi0.5TiO3) x solid solutions

(BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions exhibiting positive temperature coefficient of resistance behavior have been prepared using BaTiO₃ presynthesized through oxalate coprecipitation. The peak in their dielectric permittivity has been shown to shift to higher temperatures (above 120°C) with increasing x. We have examined the effect of K_0.5Bi_0.5TiO₃ content on the microstructure of the (BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions. The results demonstrate that, with increasing x, both the minimum and maximum resistivities of the materials in the temperature range of their positive temperature coefficient of resistance behavior increase. The materials prepared using barium titanate presynthesized by the oxalate route have higher Curie temperatures and temperatures where they exhibit positive temperature coefficient of resistance behavior and lower minimum resistivities than do the materials prepared by solid-state reactions.     

Structural and optical properties of Cd1−xZnxS (0 ≤ x ≤ 0.3) nanoparticles

Cd_1?xZn_xS nanoparticles for Zn = 0–30 % were successfully synthesized by a conventional chemical co-precipitation method at room temperature. X-ray diffraction spectra confirmed the pure zinc blend cubic structure of undoped CdS; but Zn-doping on Cd–S matrix induced the mixed phases of cubic and hexagonal structure. The reduced crystal size, d-value, cell parameters and higher micro-strain at lower Zn concentration were due to the distortion produced by Zn²⁺ in Cd–S lattice. The enhancing diffraction intensity at lower Zn concentrations was due to the substitution of Zn²⁺ ions instead of Cd²⁺ ions whereas the reduced intensity after 20 % was due to the presence of Zn²⁺ ions both as substitutionally and interstitially in Cd–S lattice. The nominal stoichiometry and chemical purity was confirmed by energy dispersive X-ray analysis. The initial blue shift of energy gap from undoped CdS (3.75 eV) to Zn = 10 % (3.82 eV) was due to the size effect and also the incorporation of Zn²⁺ in the Cd–S lattice. The observed red shift of energy gap at higher Zn concentrations could be attributed to the improved crystallinity. The band gap tailoring was useful to design a suitable window material in fabrication for solar cells and other opto-electronic devices. The characteristic IR peaks around 617–619 cm^?1 and the reduced intensity by Zn-doping confirmed the presence of Zn in Cd–S lattice.     

Thermodynamic properties of Ca1 − x Er x F2 + x and Ca1 − x Yb x F2 + x heterovalent solid solutions

The heat capacity of single crystals of the Ca_{1 ? x} Er _x F_{2 + x} (x = 0.05, 0.10) and Ca_0.95Yb_0.05F_2.05 fluorite solid solutions was determined by adiabatic calorimetry in the temperature range 55–300 K. The results were used to obtain temperature dependences of the Debye characteristic temperature, entropy, and enthalpy for the solid solutions.     

Electrochemical,optical, and magnetic properties of Ni x InSe (0 < x ≤ 1) intercalation compounds

We have studied the electrochemical, optical, and magnetic properties of nickel-intercalated InSe single crystals. The energy position of the excitonic maximum and the full width at half maximum of the excitonic band in the Ni _x InSe intercalation compounds have been shown to be nonmonotonic functions of nickel concentration. Nickel-intercalated InSe possesses ferromagnetic properties: the dependence of its magnetic moment on magnetic field has the form of a hysteresis loop, characteristic of hard-magnetic ferromagnets.     

Structural and Magnetic Studies of Ca2?x Sm x MnO Compounds (x=0–0.4)

The Ca_2?x Sm _x MnO₄ (x=0?C0.4) compounds were synthesized by a solid?Csolid method and characterized by XRD at room temperature. The XRD profiles were indexed with a tetragonal structure (I/4mmm space group) for x??0.3 and orthorhombic one (Pnma space group) for x=0.4. The magnetic measurements were studied as a function of temperature (T=2?C300?K) and applied field (?? ₀ H=0?C10?T). When the temperature decreases, each compound has shown first a ferromagnetic?Cparamagnetic (FM?CPM) transition and then an antiferromagnetic?Cferromagnetic (AFM?CFM) one. The transition temperatures are found to be Sm-doping dependent. For all compounds, a spin-glass phenomenon is evidenced by FC/ZFC magnetization curves.     

Synthesis and magnetic properties of Y0.5Ca0.5BaCo4 − x Zn x O7+δ (x = 0, 1.0) solid solutions

We have synthesized Y_0.5Ca_0.5BaCo_{4 ? x} Zn _x O₇ (x = 0, 1.0) solid solutions using solid-state reactions and a glycine-nitrate route and investigated their crystal structure, microstructure, and thermal behavior in an oxygen atmosphere. The effect of Zn on the magnetic behavior of the Y_0.5Ca_0.5BaCo₃ZnO₇ cobaltite has been examined.     

Magnetocrystalline Anisotropies of RFe_(10)V_2 (R=Y, Tb, Dy, Ho, and Er) and Their Hydrides

The magnetocrystalline anisotropies of RFe10V2 (R=Y, Tb, Dy, Ho and Er) and their hydrides were studied by X-ray diffraction, magnetization and a.c. susceptibility measurements. The uniaxial anisotropy of Fe-sublattice and R-sublattice with positive second order Stevens αJ in RFe10V2 compounds is weakened by hydrogenation, while that of R-sublattice with negative αJ (Er) enhanced. Such a change of anisotropy causes planar-easy magnetic structures in RFe10V2 (R=Tb and Dy) at room temperature and induces spin reorientation in HoFe10V2 after hydrogenation. The change of anisotropy of R-sublattice after hydrogenation may be owed to a decrease of the second order crystalline coefficient.