Third-order optical nonlinearity of (Ba0.7Sr0.3)TiO3 ferroelectric thin films fabricated by soft solution processing

(Ba_0.7Sr_0.3)TiO₃ (BST) ferroelectric thin films with perovskite crystal structure were fabricated by soft solution processing on a quartz substrate. The third-order nonlinear optical properties were investigated by using Z-scan technique. Positive nonlinear refractive index and nonlinear absorption coefficient were determined to be 4×10⁻⁷ esu and 1.2×10⁻⁶ m/w, respectively. The real part and imaginary part of third-order optical nonlinear susceptibility were calculated and the values were 6.43×10⁻⁸ and 5.14×10⁻⁸ esu, respectively. All of these results show ferroelectric BST thin film is promising for applications in nonlinear optical devices.     

Double edge optical absorption by v-SiO2 in the vacuum ultraviolet

The absorption edge of v-SiO₂ in the vacuum ultraviolet now appears, from experiments on pressure-densified v-SiO₂, to comprise two distinct linear parts, the Urbach edge and a lesser edge below it.     

Polymeric sheets in Mg4C60

We present preliminary results on the preparation and structure of Mg₄C₆₀, a new fulleride polymer. A series of Mg_xC₆₀ compositions (0<x<6) were prepared by solid state reaction. While most samples were multiphase, a single phase material was obtained at the nominal composition Mg₄C₆₀. The X-ray diffraction pattern of Mg₄C₆₀ was successfully indexed and fitted to a rhombohedral structure based on two-dimensional polymeric sheets of C₆₀ ions. This result extends the family of fulleride polymers to the salts of multiply charged cations and thus opens a new direction in this field.     

Optical and structural properties of nanosized ZnGa2O4:Cr phosphor

Nanosized ZnGa₂O₄:Cr³⁺ powder is synthesized through hydrothermal method. The average particle size is 20 nm and they are spherical in shape. The excitation band from the charge transfer between Cr³⁺-O²⁻ shows a blueshift behavior due to quantum confinement effect. X-ray diffraction pattern, Fourier transform-infrared spectrum, and electron paramagnetic resonance signal indicate that nanosized ZnGa₂O₄:Cr³⁺ phosphor shows many defect-related energy states and heavy lattice distortion in comparison with bulk ZnGa₂O₄:Cr³⁺ phosphor. Many defect states result in more nonradiative loss and shorter decay time.     

Color centers in neutron-irradiated Y3Al5O12, CAF2 and LiF single crystals

The thermal annealing behavior of the Y₃Al₅O₁₂, CaF₂ and LiF single crystals bombarded at Algiers with reactor neutrons has been monitored by optical absorption spectroscopy. The irradiation was performed at about 315 K. On heating samples after irradiation, the optical absorption bands decrease and disappear completely at 873 and 523 K in the case of Y₃Al₅O₁₂ and CaF₂, respectively. Activation energies of 1.2±0.02 and 0.9±0.2 eV are estimated for Y₃Al₅O₁₂ and CaF₂, respectively. On the other hand, the LiF crystal shows a complex annealing behavior. Here, the optical absorption spectrum presents different shapes after each annealing temperature. Four steps are distinguished and discussed on heating samples from 300 to 673 K. Above 673 K, the absorption drops by about 50%; it completely disappears at 773 K.     

The size and strain effects on the Raman spectra of Ce1−xNdxO2−δ (0≤x≤0.25) nanopowders

Ultrafine Ce_1−xNd_xO_2−δ (x=0-0.25) powders were synthesized by self-propagating room temperature synthesis. Raman spectra were measured at room temperature in the 300-700 cm⁻¹ spectral range. The shift and asymmetric broadening of the Raman F_2g mode at about 454 cm⁻¹ in pure and doped ceria samples could be explained with combined size and inhomogenous strain effects. Increased concentration of O²⁻ vacancies with doping is followed by an appearance of new Raman feature at about 545 cm⁻¹.     

Polymorphic transformation of the Γ-form of d-sorbitol upon milling: structural and nanostructural analyses

In this paper, we study the structural, nanostructural and thermodynamic evolutions of crystalline Γ-sorbitol upon mechanical milling. The investigations have been performed by powder X-ray diffraction and differential scanning calorimetry. The results clearly show that the evolution upon milling can be divided in two stages. The first one only reveals micro and nanostructural modifications of the crystallites appearing through a size reduction, deformations, and changes of shape. On the other hand, the second stage reveals a complete structural transformation of the Γ-form of sorbitol towards the metastable A-form of sorbitol. Special attention has been paid to the nanostructural features derived from the first stage, which trigger the ultimate structural transformation.     

Electrochemical synthesis and optical properties of ZnO thin film on In2O3:Sn (ITO)-coated glass

ZnO thin films were electrochemically deposited onto the ITO-coated glass substrate from an electrolyte consisted of 0.1 M Zn(NO₃)₂ aqueous solution at 65 ± 1 °C. A compact ZnO film with (0 0 2) preferred orientation was obtained at the applied potential of −1.3 V for 1200 s. It was also found that the morphology of the ZnO films grown at the potential of −1.3 V was characterized of single or coalescent hexagonal platelets. However, the ZnO crystals grown at the potential of −2.0 V was changed to be a bimodal size distribution. The band gap energy of the as deposited ZnO films, about 3.5 eV, was independent of both the applied potential and the deposition time, respectively. The minor amount of Zn(OH)₂ might be co-deposited with the formation of ZnO revealed by the FT-IR spectroscopy. Three strategies to improve the ZnO crystal quality based on the photoluminescence properties were proposed in the paper, which were (a) adopting the lower deposition potential, (b) increasing the deposition time at a certain potential, and (c) annealing after as-deposition, respectively.     

Static susceptibility and heat capacity studies on V3O7·H2O7 nanobelts

V₃O₇·H₂O nanobelts were prepared by a hydrothermal method at 190 °C using V₂O₅·nH₂O gel and H₂C₂O₄·2H₂O as starting agents. The obtained nanobelts have diameters ranging from 40 to 70 nm with lengths up to several micrometers. Measurements of the static magnetic susceptibility and the specific heat show a discontinuous phase transition at around T=145 K, which separates two regions of paramagnetic behavior.     

Dipolar and magnetic ordering in Nd-modified BiFeO3 nanoceramics

The polycrystalline samples of Bi_1−xNd_xFeO₃ (BNFO) with x=0, 0.05, 0.1, and 0.15 were prepared by a chemical route (metal ion complex precursor solution method). A systematic change in crystal structure from rhombohedral to tetragonal on increasing Nd substitution was observed. The reduction of low-frequency dispersion in permittivity and loss pattern due to Nd substitution in BiFeO₃ (BFO) was observed in its dielectric response curve. The loss tangent (tan δ) was found to be reduced on increased Nd concentration in BNFO. Dielectric anomaly near the reported Neel temperature of BFO and peaks in all the BNFO samples were observed in the permittivity vs. temperature graph. Significant opening in the room temperature M–H loop was observed on Nd substitution, which was more prominent for higher concentration of Nd.     

Thermal, mechanical, electrical, linear and nonlinear optical properties of a nonlinear optical l-ornithine monohydrochloride single crystal

Optically transparent semiorganic nonlinear optical bulk single crystal of l-ornithine monohydrochloride (LOMHCL) of dimension 11×3×2 mm³ has been grown from its aqueous solution by slow solvent evaporation technique. The grown crystal was characterized by powder X-ray diffraction to confirm the crystal structure. Investigation has been carried out to assign the vibrational frequencies of the grown crystals by Fourier transform infrared spectroscopy technique. Thermal behavior of the grown crystals was studied by thermogravimetric analysis. The second harmonic generation (SHG) efficiency of LOMHCL was determined by Kurtz and Perry powder technique. The optical absorption study confirms the suitability of the crystal for device applications. The mechanical properties of the grown crystals have been studied using Vickers microhardness tester. Dielectric and photoconductivity studies are also carried out for the grown samples.     

SiO2-PbF2-CdF2 glasses and glass ceramics

Lead-Cadmium fluorosilicate stable glasses were prepared and the vitreous domain region determined in the composition diagram. Characteristic temperatures were obtained from thermal analysis and the structural studies performed illustrate clearly the role played by lead atoms in the glasses crystallization behavior and the glass-forming ability of cadmium atoms. The occurrence of either a cubic lead fluoride or a lead-cadmium fluoride solid solution in crystallizing samples was found to be dependent on Er³⁺ doping. The optically active ions were found to concentrate in the crystalline phase and in fact play the role of nucleating agent as suggested from X-ray diffraction and EXAFS measurements.     

Neutron diffraction studies of Tb2Rh3Si5 compound

In this work neutron diffraction studies of Tb₂Rh₃Si₅ compound are reported. The compound crystallizes in the monoclinic crystal structure of Lu₂Co₃Si₅-type. At 1.5 K an antiferromagnetic ordering with a propagation vector k=(1/2;1/2;1/2) was observed. The Tb magnetic moments of 9.8(2) μ_B form a non-collinear magnetic structure. In the vicinity of Néel temperature of 8 K a change of the magnetic ordering is evidenced. The change seems to be connected with phase transition from commensurate to incommensurate sine-wave modulation of the Tb magnetic moments.     

Some properties of the phonon spectra of transition metal disilicides VSi2, NbSi2, and TaSi2

The phonon spectra of metallic disilicides VSi₂, NbSi₂, and TaSi₂ have been studied in detail by inelastic neutron scattering at 300 K and specific heat measurements between 10 K and 250 K. The specific heat calculated from the generalised phonon density of states extracted from neutron measurements is in good agreement with the measured lattice contribution to the specific heat. The properties of the phonon spectra are discussed in relation with other data reported for these isostructural and isoelectronic disilicides.     

Structural and optical properties of a-Si1−xCx:H films synthesized by dc magnetron sputtering technique

Hydrogenated amorphous SiC films (a-Si_1−xC_x:H) were prepared by dc magnetron sputtering technique on p-type Si(1 0 0) and corning 9075 substrates at low temperature, by using 32 sprigs of silicon carbide (6H-SiC). The deposited a-Si_1−xC_x:H film was realized under a mixture of argon and hydrogen gases. The a-Si_1−xC_x:H films have been investigated by scanning electronic microscopy equipped with an EDS system (SEM-EDS), X-ray diffraction (XRD), secondary ions mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR), UV-vis-IR spectrophotometry, and photoluminescence (PL). XRD results showed that the deposited film was amorphous with a structure as a-Si_0.80C_0.20:H corresponding to 20 at.% carbon. The photoluminescence response of the samples was observed in the visible range at room temperature with two peaks centred at 463 nm (2.68 eV) and 542 nm (2.29 eV). In addition, the dependence of photoluminescence behaviour on film thickness for a certain carbon composition in hydrogenated amorphous SiC films (a-Si_1−xC_x:H) has been investigated.     

Refractive index, oscillator parameters and temperature-tuned energy band gap of Tl4In3GaS8-layered single crystals

Transmission and reflection measurements in the wavelength region 450-1100 nm were carried out on Tl₄In₃GaS₈-layered single crystals. The analysis of the room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 2.32 and 2.52 eV, respectively. The rate of change of the indirect band gap with temperature dE_gi/dT=-6.0×10⁻⁴ eV/K was determined from transmission measurements in the temperature range of 10-300 K. The absolute zero value of the band gap energy was obtained as E_gi(0)=2.44 eV. The dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico single-effective-oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index were found to be 4.87 eV, 26.77 eV, 8.48×10¹³ m⁻² and 2.55, respectively.     

Characterization of thermal, optical and carrier transport properties of porous silicon using the photoacoustic technique

In this work, the porous silicon layer was prepared by the electrochemical anodization etching process on n-type and p-type silicon wafers. The formation of the porous layer has been identified by photoluminescence and SEM measurements. The optical absorption, energy gap, carrier transport and thermal properties of n-type and p-type porous silicon layers were investigated by analyzing the experimental data from photoacoustic measurements. The values of thermal diffusivity, energy gap and carrier transport properties have been found to be porosity-dependent. The energy band gap of n-type and p-type porous silicon layers was higher than the energy band gap obtained for silicon substrate (1.11 eV). In the range of porosity (50-76%) of the studies, our results found that the optical band-gap energy of p-type porous silicon (1.80-2.00 eV) was higher than that of the n-type porous silicon layer (1.70-1.86 eV). The thermal diffusivity value of the n-type porous layer was found to be higher than that of the p-type and both were observed to increase linearly with increasing layer porosity.     

Preparation of Mg55Ni35Si10 Amorphous Powders by Mechanical Alloying and Consolidation by Vacuum Hot Pressing

Amorphous Mg55Ni35Si10 powders are fabricated by using a mechanical alloying technique. The amorphous powders are found to exhibit a relatively high crystallization temperature of 380℃. The as-milled amorphous Mg55Ni35Si10 powders are consolidated successfully into bulk body by vacuum hot pressing technique. Limited nanocrystallization is noticed. The Vickers microhardness range of the Mg55Ni35Si10 bulk sample is 7834 to 8048 MPa. Its bending strength and compressive strength are 529 MPa and 1466 MPa, respectively.     

Synthesis of Fe3O4/CNTs magnetic nanocomposites at the liquid-liquid interface using oleate as surfactant and reactant

Carbon nanotubes (CNTs)-based magnetic nanocomposites have attracted significant research interest owing to their great potentialities in various technological fields. In this investigation, a kind of novel Fe₃O₄/CNTs magnetic nanocomposites were prepared by in situ chemical precipitation using oleate as reactant and surfactant at the liquid-liquid interface of cyclohexane/ethanol/water mixture solvent. The as-prepared samples were characterized via transmission electron microscopy (TEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and vibration sample magnetometry (VSM). Results indicated that the Fe₃O₄/CNTs magnetic nanocomposites dispersed well in organic medium were prepared organic medium, were prepared. The magnetic nanocomposites were proved to be superparamagnetic with coercive force of 3.69 Oe. A mechanism scheme was proposed to illustrate the formation process of the magnetic nanocomposites.