Site occupancy of Fe in ternary Ni<Subscript>75−</Subscript><Emphasis Type="Italic">x</Emphasis>Fe<Subscript>x+y</Subscript>Al<Subscript>25−</Subscript><Emphasis Type="Italic">y</Emphasis>alloys

The results of a detailed structural and magnetic study clearly indicate that regardless of the thermal history of the samples, Fe has a strong preference for the Ni sites in Ni-poor (nonstoichiometric) Ni₇₅Al₂₅ alloys. Fe substitution has a profound effect on the nature of magnetism in Ni₂₅Al₂₅ Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India.     

Preparation of TiO<Subscript>2</Subscript>-coated LiCo<Subscript>1/3</Subscript>Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by electrostatic self-assembly method and its properties

A precursor of TiO₂–LiCo_1/3Ni_1/3Mn_1/3O₂ was prepared by electrostatic self-assembly method. The final product was obtained by heating the precursor at 400–450 °C for 4–6 h in air. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical tests were used to examine the structural, morphology, elementary valence, and electrochemical characteristics. XRD indicated that the TiO₂-coated material can be indexed by α-NaFeO₂ layered structure, which belongs to hexagonal-type space group R3m. XPS results confirmed the existence of TiO₂ compound on the surface of the coated sample. The SEM image showed that the material had spherically porous morphology with the uniform size about 6 μm. The initial charge–discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ material was 168.8/160.0 mAh/g. After 60 cycles, the discharge capacity of the TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ sample was 147.0 mAh/g, and the coulombic efficiency was 94.0%. Compared with the uncoated sample, the electrochemical performance of TiO₂-coated LiCo_1/3Ni_1/3Mn_1/3O₂ was improved.     

Phase transition in Pd<Subscript>40</Subscript>Ni<Subscript>10</Subscript>Cu<Subscript>30</Subscript>P<Subscript>20</Subscript> bulk metallic glass under HP &; HT

The phase transitions in Pd₄₀Ni₁₀Cu₃₀P₂₀ bulk metallic glass (BMG) have been studied under high pressure and high temperature (HP & HT) by X-ray diffaction measurements with synchrotron radiation source. We found that the BMG underwent a phase transitions of amorphous-crystalline-amorphous at 10 GPa upon heating. The parallel experiments were carried out at 7 GPa, while we did not observe the amorphous-crystalline-amorphous transitions by increasing temperature. Quenching the melted BMG at 7 GPa, it was found that the phase crystallized from the melt differed from the primary phase crystallized from the starting amorphous solid upon heating suggesting there existed a distinct mechanism in two cases.     

Structural relaxation of Zr<Subscript>41</Subscript>Ti<Subscript>14</Subscript>Cu<Subscript>12.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>22.5</Subscript> bulk metallic glass under high pressure

Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) is annealed at 573 K under 3 GPa and its structural relaxation is investigated by X-ray diffraction, ultrasonic study, compression as well as sliding wear measurements. It is found that after the ZrTiCuNiBe BMG sample was annealed under high pressure, the mechanical properties were improved. Moreover, theBMG with relaxed structure exhibits markedly different acoustic properties. These results are attributed to the fact that relaxation under high-pressure results in a microstructural transformation in the BMG.     

A simulation study of rapid solidification and crystal configuration of Cu<Subscript>70</Subscript>Ni<Subscript>30</Subscript> alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

Investigation on structural characteristics of PVDF–AgCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite solid polymer electrolyte system

There has been an increasing interest towards the incorporation of nanosize ceramic fillers in polymer electrolytes. Solid polymer electrolytes based on polyvinylidene fluoride (PVDF), silver triflate (AgCF₃SO₃), and x wt% of aluminum oxide (Al₂O₃) nanopowders (where x = 1, 3, 5, and 10, respectively) have been prepared using solution casting technique. The structural characteristics of these thin film specimens were studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) patterns at room temperature. The appearance of new absorption bands and gradual shifts observed in some characteristic peaks confirmed the complex formation between polyvinylidene fluoride and silver triflate. Furthermore, the addition of nanosized filler Al₂O₃ has also indicated the interaction of the filler with the polymer salt complex. The XRD patterns obtained for all these samples in the 2θ range 10° to 70° showed the amorphous nature of these samples. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

Hyperfine structure in EPR spectra of the catalytic system TiCl<Subscript>4</Subscript> + Al(i-C<Subscript>4</Subscript>H<Subscript>9</Subscript>)<Subscript>3</Subscript>

In an EPR study of the catalytic system TiCl₄ + Al(i-C₄H₉)₃ in toluene and isopentane in TiCl₄/oligopiperylene + Al(i-C₄H₉)₃ in toluene, we have observed a dependence of the linewidth of the hyperfine structure on the mobility of the complex in solution. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 174–177, March–April, 2007.     

Structural investigation on PEO-based polymer electrolytes dispersed with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF₃SO₃) dispersed with various concentrations of aluminum oxide (Al₂O₃) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte. The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T _g) whereas the degree of crystallization (X _c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of all these samples has revealed the presence of absorption bands around 1,000 cm⁻¹; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity thereby revealing that the significant contribution to electrical conduction was due to ions only. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006     

Up-conversion emissions of Er<Superscript>3+</Superscript>-Yb<Superscript>3+</Superscript> codoped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by the arc discharge synthesis method

The Er³⁺-Yb³⁺ codoped Al₂O₃ nanoparticles with an average particle size of about 50 nm have been synthesized by an arc discharge synthesis method. The green and red up-conversion emissions centered at about 526, 547 and 677 nm, corresponding respectively to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978-nm semiconductor laser diode excitation. The Annealing has evident effect on the up-conversion emissions of the samples: The red up-conversion emission is noticeable before annealing; however, the green up-conversion emission becomes predominant after annealing. The mixture of (Er,Yb)₃Al₅O₁₂ and α-(Al,Er,Yb)₂O₃ phases is more favorable for green up-conversion emissions due to an enhancement of the ESA (I) of ⁴I_11/2+a photon→⁴F_7/2 and ET (III) of ²F_5/2(Yb³⁺)+⁴I_11/2(Er³⁺)→²F_7/2(Yb³⁺)+⁴F_7/2(Er³⁺) processes. The two-photon absorption up-conversion process is involved in the green and red up-conversion emissions. The results have proved that arc discharge synthesis is a new promising preparation technology for optical materials. Supported by National Natural Science Foundation of China (Grant No. 10804015), the Scientific Research Foundation for Doctor of Liaoning Province (Grant No. 20071095), and the Educational Committee Foundation of Liaoning Province (Grant No. 2008123)     

Effect of excess Y<Subscript>2</Subscript>O<Subscript>3</Subscript> addition on the physical properties of melt processed YBCO bulks

The YBCO superconductors with Y₂O₃ addition were prepared by a modified melt textured process and the effects of excess Y₂O₃ addition on the physical properties of melt textured YBCO have been investigated. It is found that the melt temperature of YBCO samples decreases drastically with the increasing Y₂O₃, and the maximum levitation forces are drastically different for samples with different Y₂O₃ addition. It is also found that the optimal Y₂O₃ addition to YBCO is about 10wt%. Considering the microstructure and the starting composition, the results are well discussed and interpreted.     

Optical transmission of ceramic shielding blocks made from Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

We have studied the transmission of bulk Al₂O₃ ceramic used as heat shields for the working chamber of a turbine. We have established that radiation scattered from such an object has a pronounced speckle structure, while the scattering indicatrix is the same as the indicatrix for an ideal scatterer. We show that existing highpower semiconductor laser sources make it possible to penetrate sufficiently deeply into such materials, and the small transmission coefficient is not the limiting factor for development of optical methods for inspecting the quality of ceramic shielding blocks. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 237–240, March–April, 2007.     

One-step synthesis of colloidal Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> and γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles at room temperature

A facile room-temperature synthesis has been developed to prepare colloidal Mn₃O₄ and γ-Fe₂O₃ nanoparticles (5 to 25 nm) by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant. The morphology of the as-prepared samples was observed by transmission electron microscopy. High-resolution transmission electron microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The magnetic properties of the samples were investigated with a superconducting quantum interference device magnetometer. The possible formation process has been proposed.     

Theoretical study of ZnO adsorption and bonding on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (0001) surface

ZnO adsorption on sapphire (0001) surface is theoretically calculated by using a plane wave ultrasoft pseudo-potential method based onab initio molecular dynamics. The results reveal that the surface relaxation in the first layer Al-O is reduced, even eliminated after the surface adsorption of ZnO, and the chemical bonding energy is 434.3(±38.6) kJ · mol⁻¹. The chemical bond of ZnO (0.185 ± 0.01 nm) has a 30° angle away from the adjacent, Al-O bond, and the stable chemical adsorption position of the Zn is deflected from the surface O-hexagonal symmetry with an angle of about 30°. The analysis of the atomic populations, density of state and bonding electronic density before and after the adsorption indicates that the chemical bond formed by the O²⁻ of the ZnO and the surface Al³⁺ has a strong ionic bonding characteristic, while the chemical bond formed by the Zn²⁺ and the surface O²⁻ has an obvious covalent characteristic, which comes mainly from the hybridization of the Zn 4s and the O 2p and partially from that of the Zn 3d and the O 2p.     

Inelastic neutron scattering and lattice dynamics of NaNbO<Subscript>3</Subscript> and Sr<Subscript>0.70</Subscript>Ca<Subscript>0.30</Subscript>TiO<Subscript>3</Subscript>

NaNbO₃ and (Sr,Ca)TiO₃ exhibit an unusual complex sequence of temperature- and pressure-driven structural phase transitions. We have carried out lattice dynamical studies to understand the phonon modes responsible for these phase transitions. Inelastic neutron scattering measurements using powder samples were carried out at the Dhruva reactor, which provide the phonon density of states. Lattice dynamical models have been developed for SrTiO₃ and CaTiO₃ which have been fruitfully employed to study the phonon spectra and vibrational properties of the solid solution (Sr,Ca)TiO₃.      

Tunable optical parametric oscillator based on a KTP crystal,pumped by a pulsed Ti<Superscript>3+</Superscript>:Al<Subscript>2</Subscript>O<Subscript>3</Subscript> laser

We present the characteristics of an optical parametric oscillator based on a KTP crystal, pumped with noncritical phase matching by a pulsed Ti³⁺:Al₂O₃ laser, tunable in the range 677–970 nm. Tunable generation of signal and idler waves is obtained in the ranges 1030–1390 nm and 2690–3050 nm respectively. The efficiency of conversion of the pump to the signal wave is ≈23%, which for pulses of duration ≈8 nsec ensures an energy in the range 1.0–11.5 mJ. The width of the emission spectrum for the signal wave is within the range 0.8–1.8 nm and is predominantly determined by the linewidth of the Ti³⁺:Al₂O₃ pump laser. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 351–356, May–June, 2007.     

Large influence of the synthesis conditions on the physico-chemical properties of nanostructured Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>

Magnetite synthesized via three different synthesis routes (coprecipitation process in aqueous media, electrochemical synthesis in presence of complexing agents and solid state reaction at high temperature) has been characterized by X-Ray diffraction, scanning electron microscopy, thermal analysis (TGA), FT-IR and Mössbauer spectroscopies. Although each procedure gave homogeneous magnetite powders, many differences could be seen in the physico-chemical properties of the samples mostly depending on the synthesis conditions. For instance, at least two factors seem to have a huge impact onto the Fe₃O₄ behaviour: the presence of hydration water molecules and the particle size of the powders since a superparamagnetic behaviour was observed with the thinnest particles, at room temperature, on the Mössbauer spectra via the appearance of line broadening and a pronounced central doublet.     

Surface morphology of PrBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript> single crystals after the long-lasting high-temperature reduction

The results of the detailed scanning electron microscopy study of PrBa₂Cu₃O_7-δ single crystals after the long-lasting high-temperature post-growth treatment are reported. The presence of the unstable decomposition products on the crystal surface indicates that the onset of superconductivity must be related to the structural transformations in the bulk (approximately 20% of the total volume of the examined crystals). The time-dependent character of the superconductivity in the Pr-123 crystals could be attributed to the migration of defects in the Pr−Ba sublattice from the bulk toward the surface.     

Influence of the sample orientation in Sn<Subscript>2</Subscript>P<Subscript>2</Subscript>S<Subscript>6</Subscript> crystals on the hydrostatic piezoelectric coefficients

The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d _h ⁽ⁱ⁾ of Sn₂P₂S₆ crystals has been studied. The hydrostatic piezoelectric coefficients d _h ⁽¹⁾ and d′ _h ⁽³⁾ , were measured, d _h ⁽¹⁾ =(244±3) pC/N and d′ _h ⁽³⁾ =(92±1) pC/N. The hydrostatic piezoelectric coefficient d _h ⁽³⁾ for orthogonal axis system was calculated to be d _h ⁽³⁾ =(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d _h ⁽¹⁾ equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d _h ) _mean corresponding to randomly oriented Sn₂P₂S₆ grains in a poled composite has been calculated to be (d _h ) _mean =136 pC/N.     

VUV luminescence of Er<Superscript>3+</Superscript> ions in LiYF<Subscript>4</Subscript> and BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals

Vacuum ultraviolet luminescence of Er³⁺ ions in LiYF4 and BaY₂F₈ crystals has been investigated. It is revealed that under excitation by 193 nm radiation from an ArF excimer laser the interconfigurational 5d–4f radiative transitions in Er³⁺ ions are observed. It is shown that from the LiYF₄:Er crystal only the spin-forbidden luminescence (λ = 165 nm) is detected, whereas both the spin-forbidden (λ = 169 nm) and spin-allowed (λ = 160.5 nm) components are observed from the BaY₂F₈:Er crystal.