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.     

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.     

Decays of excited baryons in the large- N<Subscript>c</Subscript> expansion of QCD

We present the analysis of the decay widths of excited baryons in the framework of the 1/N _c expansion of QCD. These studies are performed up to order 1/N _c and include both positive- and negative-parity excited baryons.     

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.     

Bacteriochlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> as a sensitizer for photodynamic therapy

A simple scheme of modification of the native pigment bacteriochlorophyll a, extracted from the biomass of phototropic bacteria, for the purpose of obtaining a water-soluble derivative — bacteriochlorin e ₆ — which is similar in molecular structure to the effective sensitizer chlorin e ₆ and, in addition, has an intense longwave absorption band in the near-infrared region of the spectrum where biological tissues weakly absorb light — has been developed. The ease of production of bacteriochlorin e ₆ in combination with its physicochemical and spectral properties allow it to be considered as a promising sensitizer for photodynamic therapy.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 745–748, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

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.     

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.     

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.     

Factors affecting the superconductivity in the process of depositing Nd1.85Ce0.15CuO4-δ by the pulsed electron deposition technique

On SrTiO₃ single crystal substrate, by using the pulsed electron deposition technique, the high-quality electron doped Nd_1.85Ce_0.15CuO_4−δ superconducting film was successfully fabricated. After careful study on the R-T curves of the obtained samples deposited with different substrate temperatures, thicknesses, annealing methods and pulse frequencies, the effects of them on the superconductivity of the films were found, and the reasons were also analyzed. Additionally, by using the same model of the pulsed laser deposition technique, the relation between the target-to-substrate distance and the deposition pressure was drawn out as a quantitative one. Supported by the Key Project of Zhejiang Provincial Natural Science Foundation (Grant No. Z605131), the ‘100 Talents Project’ of Chinese Academy of Sciences, the Creative Research Group of National Natural Science Foundation of China (Grant No. 60321001) and the National Natural Science Foundation of China (Grant No. 60571029)     

Nature of the axial-vector mesons from their N<Subscript>c</Subscript> behavior within the chiral unitary approach

By describing within the chiral unitary approach the s -wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone bosons, we find that the main component of the axial-vector mesons --b ₁(1235) , h ₁(1170) , h ₁(1380) , a ₁(1260) , f ₁(1285) and the two states associated to the K ₁(1270) -- does not follow the QCD dependence on the number of colors for ordinary q mesons.     

Density functional theory study on the structural and electronic properties of Ag-adsorbed (MgO)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters

Equilibrium geometries, charge distributions, stabilities and electronic properties of the Ag-adsorbed (MgO) _n (n = 1–8) clusters have been investigated by density functional theory (DFT) with generalized gradient approximation (GGA) for exchange-correlation functional. The results show that hollow site is energetically preferred for n⩾4, and the incoming Ag atoms tend to cluster on the existing Ag cluster. The Mulliken populations indicate that the interaction between the Ag atom and Magnesia clusters is mainly induced by a weak atomic polarization. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of Magnesia clusters is minor. Furthermore, the investigations on the first energy difference, fragmentation energies and electron affinities show that the Ag(MgO)₄ and Ag(MgO)₆ are the most stable among studied clusters. Supported by the Startup Fund of High-level Personal for Shihezi University (Grant No. RCZX200747)     

Magnetic phases in UNi<Subscript>2</Subscript>Si<Subscript>2</Subscript>

The tetragonal compound UNi₂Si₂ exhibits in zero magnetic field three different antiferromagnetic phases belowT _N =124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q _z ). Two additional order-order magnetic phase transitions are observed below T _N , namely atT ₁=108 K and T ₂=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel to the c-axis. UNi₂Si₂ single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity, susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5 T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties of UNi₂Si₂.     

Anomalous absorption in H<Subscript>2</Subscript>CN and CH<Subscript>2</Subscript>CN molecules

Structures of H₂CN and CH₂CN molecules are similar to that of H₂CO molecule. The H₂CO has shown anomalous absorption for its transition 1₁₁–1₁₀ at 4.8 GHz in a number of cool molecular clouds. Though the molecules H₂CN and CH₂CN have been identified in TMC-1 and Sgr B2 through some transitions in ortho as well as in para species, here we have investigated the condition under which transitions 1₁₁–1₁₀ and 2₁₂–2₁₁ of these molecules may show anomalous absorption. For the present investigation, we have calculated energy levels and radiative transition probabilities. However, we have used scaled values for collisional rate coefficients. We found that relative values of collisional rate coefficients can produce the required anom-alous absorption in 1₁₁–1₁₀ and 2₁₂–2₁₁ transitions in the molecules.      

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.      

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.     

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.     

Study of structural phase transitions in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6+δ</Subscript> by x-ray photoelectron spectroscopy

We have used x-ray photoelectron spectroscopy to investigate the charge state of oxygen found in the basal structural plane of YBa₂Cu₃O₆+γ.. We have observed a change in this state after thermal treatment, with a transition to the adjacent structural phase region. We have shown that changes in the charge state of oxygen can be used as an indicator of structural changes occurring in YBa₂Cu₃O₆+δ.. We have found that the rate of structural relaxation yttrium barium cuprate depends on the amount of structural water it contains. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 195–198, March–April, 2007.     

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.     

Synthesis of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> complex substrates and growth of GaN films

With the solid phase reaction between pulsed-laser-deposited (PLD) ZnO film and α-Al₂O₃ substrate, ZnAl₂O₄/α-Al₂O₃ complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl₂O₄ changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding scanning electron microscope (SEM) images indicate that the surface morphology of ZnAl₂O₄ transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRD spectra present that ZnAl₂O₄ prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl₂O₄/α-Al₂O₃ substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD). XRD spectra indicate that GaN film on this kind of complex substrate changes fromc-axis single crystal to poly-crystal as ZnAl₂O₄ layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results indicate that islands on thin ZnAl₂O₄ layer can promote nucleation at initial stage of GaN growth, which leads to the (0001)-oriented GaN film.     

Characterization of Y<Subscript>2</Subscript>BaCuO<Subscript>5</Subscript> nanoparticles synthesized by nano-emulsion method

Nanoscale yttrium–barium–copper oxide (Y₂BaCuO₅, Y211) particles were synthesized using the emulsion method and the solution method. The basic water-in-oil (w/o) emulsion system consisted of n-octane (continuous oil phase), cetyltrimethylammonium bromide (cationic surfactant), butanol (cosurfactant) and water. The composition of the emulsion system was varied and characterized by measuring the conductivity of the solutions and droplet size. The droplet size of emulsion was determined by using the dynamic light scattering method. The water content, cosurfactant content, and surfactant/n-octane ratio affected the droplet size which was in the range of 3–8 nm, and hence the w/o emulsion system was referred to as a nano-emulsion system. A model was used to verify the droplet size. The influence of salt (Y₂(NO₃)₃) content on the droplet size was investigated and the addition of salt reduced the droplet size. The effects of reaction time and temperature on the Y211 particle sizes were also investigated. The particles were characterized using the TEM, SEM, and XRD. Nanoparticles produced by the nano-emulsion method were calcined at 850°C to form the Y211 phase as compared to solid state processing temperature of 1050°C. Based on the TEM analysis, the average diameter of the Y211 particles produced using the nano-emulsion method was in the range of 30–100 nm. The effect of adding 15% Y211 nanoparticles to the superconductor YBCO-123 as flux pinning centers, was investigated, and the transition temperature was reduced by 3 K.