Laser X-ray Conversion and Electron Thermal Conductivity

The influence of electron thermal conductivity on the laser x-ray conversion in the coupling of 3w. laser with Au plane target has been investigated by using a non-LTE radiation hydrodynamic code. The non-local electron thermal conductivity is introduced and compared with the other two kinds of the flux-limited Spitzer-Harm description. The results show that the non-local thermal conductivity causes the increase of the laser x-ray conversion efficiency and important changes of the plasma state and coupling feature.

X-ray Diffraction and Electrical Conductivity Studies on Ag-Cu-Se System

A number of X-ray patterns and electrical conductivities of five different samples of Ag-Cu-Se system have been measured. These samples of Ag-Cu-Se system: (Ag1.188, Cu0.812)Se, (Ag,Cu)Se; (Ag0.9, Cu1.1 )Se, (Ag0.8, Cu1.2)Se and (Ag0.6, Cu1.4)Se were prepared under controlled conditions. Analysis of the experimental data shows that Frenkel defects are predominated in (Ag1.188, Cu0.812)Se and Schottky defects prevailing in the other samples. The activation energy values △E calculated from the linear behaviour of electrical conductivity a with temperature (0-90℃) reveal that the impurity content increases in the direction of (Ag,Cu)Se→(Ag0.8,Cu1.2 )Se

The effect of nitrogen on the compressibility and conductivity of iron at high pressure

Although nitrogen in the Earth’s interior has attracted significant attention recently,it remains the most enigmatic of the light elements in the Earth’s core.In this work,synchrotron X-ray diffraction(XRD)and electrical conductivity experiments were conducted on iron nitrides(Fe_(2)N and Fe_(4)N)in diamond anvil cells(DACs)up to about 70 GPa at ambient temperature.These results show that iron nitrides are stable up to at least 70 GPa.From the equation of state(EOS)parameters,iron nitrides are more compressible than iron carbides.Moreover,using the van der Pauw method and Wiedemann-Franz law,the electrical and thermal conductivity of samples were determined to be much lower than that of iron carbides.The conductivities of Fe_(2)N and Fe_(4)N were similar at 20–70 GPa,suggesting no evident effects by varying the N stoichiometries in iron nitrides.Iron nitrides are less dense and conductive but more compressible than carbides at 0–70 GPa.This study indicates that less nitrogen than carbon can explain geophysical phenomena in the deep Earth,such as the density deficit.

Micro-Structure, Ac Conductivity and Spectroscopic Studies of Cupric Sulphate Doped PVA/PVP Polymer Composites

A series of polyvinyl alcohol/polyvinyl pyrrolidone polymer composite films doped with different amount of cupric sulphate (CuSO4) were prepared by means of solution casting technique. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-Visible absorbance spectroscopy (UV-Vis) and Ac conductivity measurement studies. XRD patterns of these films recorded at room temperature show the increase in amorphousity of the matrix with the increase in the concentration of CuSO4 in polymer composites. Microstructural parameters were computed using an in-house program employing XRD data. Recorded FT-IR spectra give information about the stretching and bending of the characteristic absorption bands in these films. The variation in the transmittance has been studied with the help of recorded UV-Vis spectra and hence the optical band gap present in the samples is also calculated. The measured Ac conductivity shows how the conductivity varies in these films with the presence of different amount of CuSO4 in these films.

Structural and Electrical Conductivity Studies in Nickel-Zinc Ferrite

The magnetic particles of nickel-zinc ferrite with chemical composition Ni1-xZnxFe2O4 were synthesized successfully by citrate precursor auto-combustion method using high purity nitrates and citric acid as chelating agent. The prepared powder of nickel-zinc ferrites was sintered at 1000℃ for 1 hr to obtain good crystalline phase and was used for further study. The X-ray diffraction technique was employed to confirm the single phase formation of nickel ferrite. The X-ray diffraction pattern shows the Bragg’s peak which belongs to cubic spinel structure. The values of lattice constant, X-ray density, bulk density, and porosity were calculated. The temperature dependence of the electrical conductivity plot shows the kink, which can be attributed to ferromagnetic-paramagnetic transition. The activation energy obtained from resistivity plots in paramagnetic region is found to be more than that in ferrimagnetic region. The conduction mechanism in nickel-zinc ferrite particles has been discussed on the basis of hopping of electrons.

Features of the Conductivity of the Ag8Ge1-xMnxTe6 Solid Solutions

Samples of Ag8Ge1-xMnxTe6 solid solutions with different manganese content (x = 0, 0.05, 0.1, 0.2) were prepared by fusing and further pressing their powders under the pressure of 0.6 GPa. In addition of Mn atoms to the Ag8GeTe6 compound leads to compression of their lattice. All p-type samples acquire a high resistance below the transition at temperatures of 180 - 220 K. The electrical conductivity of all compositions in the range of 220 - 300 K increases due to hopping mechanism, and at temperatures T > 320 K, a semiconductor characteristic is observed. By studying impedance spectra of samples, it was established that at 80 K solid solutions behave like a homogeneous dielectric material. At high temperatures and frequencies of an external electric field, a significant role of grain boundaries in conductivity was revealed. The dielectric anomaly occurring at low frequencies is also associated with an effect that manifests itself in the grain boundary.

DC Conductivity and Spectroscopic Characterization of Poly (o-toluidine) Doped with Binary Dopant ZrOCl₂/AgI

Aqueous binary dopant (ZrOCl2/AgI) is used in different ratio such as 1:1, 1:2 and 2:1 (w/w) for chemical doping to enhance the conductivity of synthesized Poly (o-toluidine) (POT). The doping of Poly (o-toluidine) is carried out using tetrahydrofuran as solvent. Doped samples are characterized using various techniques such as I-V characteristics, UV-Visible spectroscopy, X-ray diffractometry (XRD), FTIR and Photoluminescence (PL) studies. A significant enhancement in DC conductivity has been observed with the introduction of binary dopant. UV-Visible study shows that optical parameters change considerably after doping. Interestingly, both direct and indirect band gaps are observed in the doped samples. XRD patterns show the semi-crystalline nature of doped Poly (o-toluidine). FTIR study shows structural modifications in functional groups with doping in POT. A Photolyminescence spectrum exhibits the emission properties of the samples.

Measurement of conversion efficiency of soft X-ray from 0.35μm laser-irradiated aluminum planar targets

Conversion efficiency of soft X-ray from 0.35μm pulse laser-irradiated aluminium planar target at laser intensities 10^13- 10^15 W/cm^2 on the Xingguang-Ⅱ facility （laser energy 5 - 90 J, focal spot - Φ 200μm full width of half maximun （FWHM） 400 - 800 ps） was measured. A simple model was given to explain soft X-ray conversion efficiency. In this model, because of the heat conduction from the laser-heated spot, the conversion was very small at lower irradiance limit, while at higher limit it was bounded by the energy lost in blow off plasma. Consequently, at the laser intensity around 2×10^14 W/cm^2 , the X-ray conversion efficiency reaches a maximum.

Variations induced in human erythrocytes by ultra-low X-ray doses

In this work, the effect of different ultra-low doses of X-ray on human erythrocytes was investigated. Also, the effect of ascorbic acid added to erythrocyte suspension before X-rays was studied. The mean X-ray exposure level was about 10 μGy/h. Samples of erythrocytes suspension with and without ascorbic acid was exposed to X-ray doses in the range from 2.5 to 20 μGy. The obtained results showed pronounced radio-hemolysis of erythrocytes at doses starting from nearly 7.5 μGy. The effect was enhanced, for low doses, when ascorbic acid of relatively high concentration was added to erythrocyte samples. The changes may be attributed to a dose-dependent damage by oxidative stress at the level of the whole cell and to the production of reactive oxygen species, which can cause this damage. It may be concluded that X-rays, even at low levels of exposure, can induce oxidizing effect on erythrocytes. Accordingly, such results should be taken into account for workers operating on X-rays equipments.

A stable radiochromic semiconductive viologen-based metal-organic framework for dual-mode direct X-ray detection

Direct X-ray detectors,which directly convert X-rays into electrical signals through semiconductors,have higher space solution than scintillator-mediated indirect X-ray ones and are high desirable for early cancer detection and other applications,but the mainstream commercialα-Se detector is still largely limited by high production costs,large leakage current and low stability.This article reports an easily prepared,stable radiochromic semiconductive metal–organic framework(MOF),(MV)[Cd_(3)(tdc)_(4)]·2H_(2)O(RCS-1,H_(2)tdc=2,5-thiophenedicarboxylic acid;MV^(2+)=methyl viologen cation)with direct X-ray detecting ability.With a large bulk resistivity of 8.40×10^(9)Ωcm,this material ensures minimal dark current and low noise for X-ray detection.Additionally,it exhibits higher sensitivity to W KαX-rays(98.58μC Gy^(-1)cm^(-2))thanα-Se(~20μC Gy^(-1)cm^(-2)).Meanwhile,unlike most reported direct X-ray detecting semiconductors,compound RCS-1 shows remarkable color change upon X-ray irradiation owing to the presence of photochromism-active viologen cations.This feature offers an appealing visual detecting ability to direct X-ray detectors that provide only the electrical signals.

Synthesis of Nitrogen-Doped Graphene via Thermal Annealing Graphene with Urea

Chemical doping is an effective method to intrinsically modify the chemical and electronic property of graphene. We propose a novel approach to synthesize the nitrogen-doped graphene via thermal annealing graphene with urea, in which the nitrogen source can be controllably released from the urea by varying the annealed temperature and time. The doped N content and the configuration N as well as the thermal stabilities are also evaluated with X-ray photoelectron spectroscopy and Raman spectra. Electrical measurements indi- cate that the conductivity of doped graphene can be well regulated with the N content. The method is expected to produce large scale and controllable N-doped graphene sheets for a variety of potential applications.

Low thermal conductivity and anisotropic thermal expansion of ferroelastic(Gd_(1−x)Y_(x))TaO_(4) ceramics

In this paper,(Gd_(1−x)Y_(x))TaO_(4) ceramics have been fabricated by solid-phase synthesis reaction.Each sample was found to crystallize in a monoclinic phase by X-ray diffraction(XRD).The properties of(Gd_(1−x)Y_(x))TaO_(4) were optimized by adjusting the ratio of Gd/Y.(Gd_(1−x)Y_(x))TaO_(4) had a low high-temperature thermal conductivity(1.37–2.05 W·m^(−1)·K^(−1)),which was regulated by lattice imperfections.The phase transition temperature of the(Gd_(1−x)Y_(x))TaO_(4) ceramics was higher than 1500℃.Moreover,the linear thermal expansion coefficients(TECs)were 10.5×10^(−6) K^(−1)(1200℃),which was not inferior to yttria-stabilized zirconia(YSZ)(11×10^(−6) K^(−1),1200℃).(Gd_(1−x)Y_(x))TaO_(4) had anisotropic thermal expansion.Therefore,controlling preferred orientation could minimize the TEC mismatch when(Gd_(1−x)Y_(x))TaO_(4) coatings were deposited on different substrates as thermal barrier coatings(TBCs).Based on their excellent properties,it is believed that the(Gd_(1−x)Y_(x))TaO_(4) ceramics will become the next generation of high-temperature thermal protective coatings.

IN SITU SYNTHESIS,CHARACTERIZATION AND FREQUENCY DEPENDENT AC CONDUCTIVITY OF POLYANILINE/CoFe_(2)O_(4)NANOCOMPOSITES

The polyaniline(PANI)/CoFe_(2)O_(4)nanocomposites were prepared by an in situ polymerization of aniline in an aqueous solution.The composites were characterized by X-ray diffraction(XRD),Fourier transform infrared(FTIR)spectrum,thermogravimetric analysis(TGA)and scanning electron micrograph(SEM).The AC conductivity and dielectric properties of these composites were investigated in the frequency range 1 kHz
10 MHz at room temperature.The AC conductivity was found to be constant up to 1 MHz and thereafter it increases steeply and it was observed maximum for the PANI with 60 wt%of CoFe_(2)O_(4)nanocomposite.At lower frequencies the values of dielectric constant is maximum for pure CoFe_(2)O_(4)nanoparticles.

Structural, Magnetic and Transport Properties of Gd and Cu Co-Doped BiFeO3 Multiferroics

The novel polycrystalline Bi0.85Gd0.15CuxFe1-xO3 (x = 0, 0.025, 0.05, 0.075, 0.10) multiferroics are synthesized by the usual solid-state reaction route. The synthesis of the desired phase has been verified by the X-ray Diffraction (XRD) patterns. With major structural phases, few traces of secondary phases of Bi2Fe4O9 and Bi25FeO40 appear for all the compositions. A discontinuous series of structural changes with varying compositions are observed for the doped samples. The bulk density (ρB) increases with Cu content reaches the highest at x = 0.05 and then declines. The complex initial permeability and dielectric characterizations are performed by Wayne Kerr Impedance Analyzer. The x = 0.05 samples having maximum density exhibit the highest permeability (μi’) implying a close relation between μi’ and the density. The reduction of μi’ at higher Cu concentration is due to the low density of the samples associated with the increased intragranular pores. The dielectric constant (ε’) is measured against frequency in the range 1 kHz - 10 MHz. It is perceived that ε’ falls with the rise in frequency up to 100 kHz. This dielectric dispersion is observed at a lower frequency as a result of interfacial polarization outlined by Maxwell-Wagner. The maximum ε’ is obtained for x = 0.025 composition. In the low-frequency range, the AC conductivity σAC is practically independent of frequency and resembles the DC conductivity (σDC). In the vicinity of high frequency recognized as the hopping region, σAC rises since the conductive grains are more active at high frequencies. The co-doping with Gd and Cu in BiFeO3 ceramics enhances the magnetic and dielectric properties of the ceramics and hence can be utilized for fabricating multifunctional devices.

Solid polymeric electrolyte of poly(ethylene)oxide-50% epoxidized natural rubber-lithium triflate (PEO-ENR50-LiCF3SO3)

A solid polymer electrolyte (SPE) films consist-ing of polyethylene oxide (PEO), 50% epoxi-dized natural rubber (ENR50) and LiCF3SO3 with various compositions of PEO-ENR50 and vari-ous weight percentage of LiCF3SO3 were pre-pared by solution casting technique. The poly-mer electrolyte films were characterized using DSC, XRD and AC impedance spectroscopy. The SPE with the PEO-ENR50 composition of 70-30 shows the highest conductivity of 4.2 × 10-5 Scm-1 at the 15 wt.% of LiCF3SO3 compared with the other composition of PEO/ENR50. This composition was then chosen to investigate the effect of LiCF3SO3 on the thermal property, structure and conductivity of the electrolyte. The highest room temperature conductivity of 1.4 × 10-4 Scm-1 was achieved at 20 wt.% of LiCF3SO3. The conductivity result is supported by the DSC and XRD analysis which showed the semi- crystalline nature of PEO turning to amor-phous state due to the increase in LiCF3SO3 content.

Stability of phases in (Ba, Gd)MnO_3 solid solution system

The existing phases in BaxGd1-xMnO3 solid solution system （0≤x≤ 1） were studied by analyzing the detailed crystal structure of each composition from the results of the Rietveld method using powder X-ray diffraction data. For a small substitution of Ba for Gd （0≤x〈0. 1）, the orthorhombic phase with a perovskite type structure （Pnma space group） was stably formed and this fact was supported by the electron diffraction data. There existed an intermediate phase of Ba0.33Gd0.67MnO3, which was characterized as the tetragonal phase with perovskite structure. The composition range of this phase was narrow and almost line compound. Between the regions of these phases, there existed two-phase region. There was also a two-phase region between the intermediate tetragonal phase and BaMnO3. Measurement of electrical conductivities of these orthorhombic solid solutions and tetragonal phases showed semiconducting behaviors for both phases and the existence of the phase transition at high temperature for the orthorhombic phase, The transition temperature decreased as the Ba content increased.

Enhanced electrical conductivity in Zr-Doped(La_(0.7)Ba_(0.3))(Mn_(0.5)Fe_(0.5))O_(3)solid solutions

The perovskite(La_(0.7)Ba_(0.3))(Mn_(0.5)Fe_(0.5))_(1−x)Zr_(x)O_(3),where x=0.1,0.2 and 0.3,ceramics were synthesized by solid-state reaction method.The introductory structural studies were followed through by X-ray diffraction technique and the results have disclosed that all the samples were crystallized into an isolated phase.The Zr substitution in the resulting solid solutions increases the electrical conductivity and the maximum value of ac conductivity has been found to be~118.8 S.cm^(−1)for x=0.3 at 200°C(at 1 MHz).The frequency dependence of ac conductivity data follows Jonscher’s power law.The variation of the exponent n versus temperature follows the nonoverlapping small polaron tunneling(NSPT)model.The dielectric relaxation has been observed to be of non-Debye nature for all measuring temperatures(50-200°C).The impedance spectroscopy reveals that all the samples exhibit negative temperature coefficient of resistance(NTCR)behavior.The prepared samples(for x>1)are supposed to be suitable for cathode materials in SOFCs.

SYNTHESIS,PIEZOELECTRIC,DIELECTRIC AND CONDUCTIVITY STUDIES ON Dy_(2)O_(3)SUBSTITUTED(Bi_(0.94)Na_(0.94))_(0.5)Ba_(0.06)TiO_(3)CERAMICS

Polycrystalline(Bi_(0.94)Na_(0.94))_(0.5)Ba_(0.06)TiO_(3)ceramics(r=0,0.04,and 0.08,designated as BNBT6:BNBT6:4Dy and BNBT6.8Dy,respectively)were prepared by conventional high tem-perat ure sintering method.The X-ray difraction patterms show pure perovskite structure with no secondary phases.Lattice parameters and unit cell volumes have decreased due to Dy_(2)O_(3)substi-tution.SEM micrographs revealed denser samples(prel>97%)with wmiformly distributed grainsizes.The room temperature piezoelectric properties of Dy_(2)O_(3)substit ut ed sample at a=0.04 wererelatively higher.d_(33)=147 pC/N,k_(p)=28%and Q_(m)=-128.The samples exhibited infinitesimalchange in thickness(α15 nm)to an applied voltage of 100 V,which could be utilized in actuatorapplications.Relaxor behavior and broad dielectric maxima with diffuse phase transition wereobser ved.The value of RT dielectric constant has increased while dielectric loss was decreased dueto Dy_(2)O_(3),substitution.Conductivity in the materials obeys Jonscher's universal power law.The conductivity in the low frequency region is associated with short range translational hopping whileit is associated with the reorientational hopping in the high frequency region.The charge carrier concentration term remained constant over the entire temperature range of(30-500°C).

Sb_(2)Te_(3)/graphite nanocomposite: A comprehensive study of thermal conductivity

Thermoelectric performance largely depends on the reduction of lattice thermal conductivity(kL).The study of the thermal conductivity(k)of a Sb_(2)Te_(3)/graphite nanocomposite system demonstrates-40%reduction in kL with graphite incorporation.A plausible explanation of intrinsic low kL observed in Sb_(2)Te_(3) based system is presented by modeling experimental specific heat(Cp)data.Raman spectroscopy measurement combined to X-Ray diffraction data confirms the presence of graphite as separate phase in the composite sample.It is found that phonon scattering dominates heat transport mechanism in the nanostructured Sb_(2)Te_(3)/graphite composite.Large reduction in kL is accomplished by intensifying scattering rate of phonons via various sources.Graphite introduces effective scattering sources,i.e.,defects of different dimensionalities in synthesized nanocomposite sample.Furthermore,graphite mediates phonon-phonon coupling and enhances lattice anharmonicity,which causes an intrinsic scattering of phonons with all frequencies in the Sb_(2)Te_(3)/graphite nanocomposite sample.Dislocation density and phonon anharmonicity of the synthesized samples are estimated from in depth analysis of temperature dependent synchrotron powder diffraction and Raman spectroscopic data.kL value as low as 0.8 W m1 K1 at 300 K,achieved with graphite dispersion in Sb_(2)Te_(3) based composite system makes the present comprehensive study an interesting concept to be developed in thermoelectric materials.

The crystal structures and physical properties of the solid solution compound Ba_5Y_(8-x)Mn_4O_(21-1.5x)(x = 0,1)

New oxometallides with the formula Ba5Y8-xMn4021-1.5x （x = 0, 1） are prepared through an atmosphere-controlled solid-state reaction. Two single-phase samples with Ba/Y/Mn atomic ratios 5/8/4 （Y8） and 5/7/4 （Y7） are obtained. The crystal structures and the physical properties of the compounds are investigated by X-ray powder diffraction, magnetization, conductivity, and dielectricity measurements. The Ba5Y8-xMn4021-1.5x compound is demonstrated to be a Y-deficient solid solution. The solid solution compound Ba5Y8-xMn4021-1.5x crystallizes into tetragonal symmetry with the space group I4/m. Detailed structure analysis by Rietveld refinement of the X-ray powder diffraction data reveals that the Y vacancies occur preferentially at the Y（2） site. Thermal magnetization measurements indicate the presence of antiferromagnetic interaction between Mn ions in the compounds, and temperature-dependent resistivity measurements show that insulator-semiconductor transitions occur around 175 K and 170 K for the Y8 and Y7 samples, respectively. Strong frequency dependences of the dielectric constant are observed above -175 K for the two compounds.