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Presents information on a study which examined the grain-size effect on the phase transition induced by pressure in PbS. In situ high-pressure electrical resistance measurement; Synchrotron radiation x-ray powder diffraction measurement.

Presents information on a study which investigated the grain-size effect on the semiconductor-to-metal transition in ZnS by in situ hihg-pressure electrical resistance and optical measurements. Use of the transition in semiconductor compounds; Effect of crystallite size on structural stability in nanocrystals.

Highlights: [•] First high-pressure study of the thiospinel Cu?Fe?Cr2S4. [•] First determination of the bulk modulus and its pressure derivative. [•] Phase transition, reducing symmetry to lower than cubic, at 14.5GPa. [•] Jahn–Teller activity of Cu(2+) and high-spin to low-spin transition of Fe(2+). [ABSTRACT FROM AUTHOR]

This paper describes a few episodes from the early days of X-ray spectroscopy. It relies on contemporary publications, especially those by Barkla, Moseley, Siegbahn, and Compton. The paper addresses the subject from the vantage point of physics and should be of interest to the X-ray spectroscopist, who wants to obtain a glimpse of the history of his chosen field. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: High-pressure X-ray diffraction in ScB2, TiB2, YB4 and HoB4 powders and single crystals has been studied using synchrotron radiation as well as conventional X-rays. The experimental results are supported by calculations using density functional theory. ScB2, YB4 and HoB4 are hard materials (bulk modulus 180–200GPa), while TiB2 may be classified as superhard (bulk modulus about 260GPa). We report here first experimental and theoretical determinations of the bulk modulus for HoB4 (195(5) and 198.2GPa, respectively), and first experimental values of the bulk modulus for ScB2 (196(2)GPa) and YB4 (185(4)GPa). No pressure-induced phase transformations are observed in any of the above borides up to about 20GPa. A continuous temperature-driven orthorhombic distortion is observed for HoB4 below 285K. Values of the thermal expansion coefficient are reported for ScB2 and HoB4 at 293, 200 and 100K. The thermoelastic behavior is explained in terms of bonding characteristics. [Copyright &y& Elsevier]

The bulk modulus and thermal expansion of Zn3P2 has been investigated at pressures up to 21 GPa and temperatures down to 100 K. The experimental zero-pressure bulk modulus is 80.7±1.8 GPa, in accordance with the bulk modulus scaling and lattice properties of the related compound Cd3P2. A tetragonal to orthorhombic phase transformation occurs above 11 GPa with a relative volume change of-7.1%. Values for the thermal expansion coefficient are reported at 293, 200 and 100 K. [ABSTRACT FROM AUTHOR]

It is argued that mainly the selenium sublattice determines the overall compressibility of the cubic spinel selenides, AB2Se4, and that the bulk modulus for these compounds is about 100 GPa. The hypothesis is supported by experiments using high-pressure X-ray diffraction and synchrotron radiation, and by first-principles calculations using density functional theory. [ABSTRACT FROM AUTHOR]

The high-pressure structural behavior of Sr2CrReO6 has been studied experimentally using synchrotron radiation and the diamond anvil cell and theoretically using density functional theory. The experimental zero-pressure bulk modulus is B0=170±4 GPa and the pressure derivative is B0'=4.7±1.0. These results compare well with the calculated values 172.6 GPa and 5.7. A pseudo-cubic unit cell can describe the crystal structure at low pressure, but the tetragonal structure becomes evident at high pressure. [ABSTRACT FROM AUTHOR]

Abstract: Raman scattering and synchrotron X-ray diffraction have been used to investigate the high-pressure behavior of l-alanine. This study has confirmed a structural phase transition observed by Raman scattering at 2.3GPa and identified it as a change from orthorhombic to tetragonal structure. Another phase transformation from tetragonal to monoclinic structure has been observed at about 9GPa. From the equation of state, the zero-pressure bulk modulus and its pressure derivative have been determined as (31.5±1.4)GPa and 4.4±0.4, respectively. [Copyright &y& Elsevier]

Abstract: The temperature evolution of the lattice parameters measured from 295 to 125K exhibits a small instability below T c≈278K, indicating ferroelastic properties of Na2TiGeO5. The behavior is related to the specific crystal structure built of polyhedral layers with shared TiO5 pyramids and GeO4 tetrahedra, alternating with layers of Na+ cations. Antiparallel alignment of the short apical titanyl bond in adjacent rows of the polyhedral layer gives rise to spontaneous strain, when a distortion of the TiO5 groups occurs. Single-crystal structures determined at room temperature and 120K suggest that {110} domains, developing below T c, entail a tetragonal-to-orthorhombic symmetry change. The mechanism is attributed to a shortening of the O–O distance between the polyhedral layers, and to minor shifts of the positions of the Ti atoms and the correlated oxygen atoms along the c-axis. The structure distortion, however, is too small to allow any unambiguous determination of the symmetry-breaking effects. The bulk modulus and its pressure derivative have been determined as B 0=89(2)GPa and . A pressure-induced phase transformation takes place at P c≈12.5GPa, presumably to an orthorhombic structure. The pressure effect on the transition temperature is given by ΔT c/ΔP≈1.76K/GPa. [Copyright &y& Elsevier]

L-ALANINE has been studied by X-ray diffraction at ambient temperature and pressure up to 10.3 GPa. The material is found to transform to a tetragonal structure between 2 and 3 GPa and to a monoclinic structure between 8 and 10 GPa. The experimental bulk modulus is 25(5) GPa for the orthorhombic phase. The results are compared with previous measurements of L-ALANINE. [ABSTRACT FROM AUTHOR]

Abstract: A short review is given on X-ray diffraction at high pressure and high or low temperature using synchrotron radiation. Some selected applications are given for oxide, selenium and nitride spinels. Finally, a few remarks are presented on the bright prospect of photon based research using synchrotron radiation sources. [Copyright &y& Elsevier]

Abstract: The high-pressure structural behaviour of CeO2 and PrO2 has been investigated by synchrotron X-ray diffraction at pressures up to 20 and 35GPa, respectively. The experiments are accompanied by first principles calculations using the self-interaction corrected local spin density (SIC-LSD) approximation. The experimental values for the zero-pressure bulk modulus of CeO2 and PrO2 are 220(9) and 187(8)GPa, respectively. Our calculations reproduce the lattice constants with good accuracy, but find identical bulk modulii for CeO2 (176.9GPa) and PrO2 (176.8GPa). [Copyright &y& Elsevier]

Abstract: NaBi(MoO4)2 has been characterized by single-crystal and powder X-ray diffraction in the temperature and pressure ranges 13–297K and 0–25GPa, respectively. The domain structure developing below proves that NaBi(MoO4)2 undergoes a ferroelastic phase transition associated with tetragonal to monoclinic symmetry change. The character of the unit cell evolution as a function of temperature indicates a continuous transition with the spontaneous strain as an order parameter. The structural distortion, due to small displacements of Bi3+ and Na+ ions, develops slowly. Therefore the overall changes, as measured in single-crystal diffraction at 110 and 13K, appear to be subtle. High-pressure powder X-ray diffraction shows that the elastic behaviour is anisotropic, the linear compressibility along the a- and c-axes of the tetragonal unit cell being and , respectively. The cell contraction, stronger along the c-axis, causes the distances between the MoO4 layers to be shortened. Consequently, the cation migration in the channels formed by MoO4 tetrahedra becomes hindered, and any symmetry lowering phase transition is not observed up to 25GPa. The zero-pressure bulk modulus is , and its pressure derivative . [Copyright &y& Elsevier]

In view of the large scatter in the literature, we have re-evaluated the high-pressure behaviour and the bulk modulus of thorium dioxide, experimentally using high-pressure X-ray diffraction (XRD) in conjunction with synchrotron radiation. To compare with the experimental measurements, theoretical calculations were performed using the full-potential linear muffin-tin orbital method (FP-LMTO) together with the local density approximation (LDA) as well as the generalised gradient approximation (GGA). The experimental value for the bulk modulus is found to be 195.3 ± 2.0 GPa, which compares well with the calculated value of 198 GPa obtained by using the generalised gradient approximation to the exchange correlation potential. [Copyright &y& Elsevier]

Reactions of ZnO and TiO2 (anatase and rutile) in different mole ratios induced by high-energy ball milling were studied by X-ray diffraction. It was found that three main reactions could involve during high-energy ball milling: (1) (4 - X)ZnO + (2 + Y) TiO2 (anatase or rutile) → Zn4-XTi2+YO8; (2) ZnO + TiO2 (rutile) → ZnTiO3, and (3) TiO2 (anatase) → TiO2 (II) → TiO2 (rutile). Cubic Zn4-XTi2+YO8 nanocrystals with an average crystal size of about 15 nm can be prepared by high-energy ball milling, which could be an attractive process to fabricate material in industrial scale. No decomposition of ZnTiO3 into Zn2TiO4 and rutile was detected during milling. Anatase shows higher reaction activity than rutile and favours the formation of Zn4-XTi2+YO8 while rutile favours the formation of ZnTiO3. During the anatase-to-rutile transformation a transient metastable phase, TiO2 (II) which is a high-pressure phase of TiO2, is detected. [ABSTRACT FROM AUTHOR]

Crystallization kinetics of a Zr[sub 46.8]Ti[sub 8.2]CU[sub 7.5]Ni[sub 10]Be[sub 27.5] bulk glass in the supercooled liquid region have been investigated by performing in situ high-temperature and high-pressure x-ray diffraction measurements using synchrotron radiation. A pressure-time-temperature-transformation diagram, describing the onset of crystallization as a function of time during isothermal annealing under pressure, is presented. Different pressure dependences of crystallization kinetics in the temperature range for the glass have been observed and further be explained by a model of competing processes of the thermodynamic potential barrier of nucleation and the diffusion activation energy under pressure. [ABSTRACT FROM AUTHOR]

Comments on the reversible phase transition between amorphous and crystalline in Zr[sub 41.2]Ti[sub 13.8]Cu[sub 12.5]Ni[sub 10]Be[sub 22.5] under high pressure at room temperature. Characterization of metallic glasses; Analysis of diffraction patterns in the transition; Demonstrations on pressure-induced crystallization of the glasses.

The structural stability of a binary CdCa quasicrystal with a primitive icosahedral structure has been investigated by in situ high-pressure x-ray powder diffraction at an ambient temperature using synchrotron radiation. It is demonstrated that the icosahedral quasicrystalline structure of the sample is intrinsically stable up to 47 GPa. The bulk modulus at zero pressure and its pressure derivative of the icosahedral CdCa quasicrystal is 68.1±2.0 GPa and 4.3±0.2, respectively. The compression behavior of different Bragg peaks is isotropic, indicating no pressure-induced anisotropic elasticity in the stable binary icosahedral CdCa quasicrystals. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Poly(2-ethyl-2-oxazoline) [PEOX] is blended with polyvinylpyrrolidone [PVP] having a relatively high dielectric constant to improve the optical and electrical properties of the material. PEOX-PVP polymer blends with 0, 20, 40, 60, and 80 wt% PVP are characterized by their structural, optical, electrical and dielectric properties. SEM images and XRD spectra show that PEOX and PVP have a good miscibility and compatibility. XRD also confirms the amorphous structure of the samples. FTIR spectra indicate the presence of hydrogen bonding between PEOX and PVP. The optical energy band gap, E g opt , and the width of the band tail of localized states in the forbidden band gap, Δ E , as determined by UV–Vis spectroscopy, are changing with PVP content. Electrical and dielectric properties are measured at frequencies from 10 Hz to 8 MHz using LCR meter. The dielectric constant, the dielectric loss, and the loss tangent (tanδ) decrease, whereas the AC conductivity increases with increasing frequency. PEOX:PVP (80:20 wt%) is an optimum blend with superior properties as compared with pure PEOX. This flexible and high-dielectric-constant polymer blend may have potential application in energy storage. [ABSTRACT FROM AUTHOR]

Abstract: The high-pressure structural stability of CeN is investigated by experiment and theory. Experiments are carried out by energy-dispersive X-ray diffraction and synchrotron radiation, using a diamond anvil cell, to a maximum pressure of 77GPa. The experimental results are in remarkably good agreement with ab initio calculations using the full-potential linear muffin-tin orbital method within the generalized gradient approximation (GGA). The experimental zero pressure bulk modulus is B 0 =156(3)GPa, the pressure derivative being constrained to B 0′=4.00. The corresponding calculated data are B 0 =158.1GPa and B 0′=3.3. We report here the first experimental observation of the transformation of CeN from the ambient B1 type crystal structure to the B2 type. The onset of the transition is in the range 65–70GPa, and the relative volume change at the transition is ΔV/V =−10.9(3)%. These data compare well with the calculated transition pressure P tr =68GPa and ΔV/V =−10.8%. Experimentally, the transition is found to be rather sluggish. [Copyright &y& Elsevier]

Fe1.087Te exhibits three phases in the pressure range from ambient to 16.6?GPa and becomes amorphous at higher pressures. All three phases have tetragonal symmetry. The low pressure T-phase is stable in the pressure range 0?P<4.1?GPa and is found to be relatively soft having zero pressure bulk modulus B 0=36(1)?GPa. The intermediate cT-phase is less compressible with B 0=88(5)?GPa and stable in the pressure range 4.1?P<10?GPa while a more compressible phase was observed between 10 and 16.6?GPa. [ABSTRACT FROM PUBLISHER]

Single crystals of HoB4 have been grown and used for synchrotron X-ray diffraction studies at pressures up to 23 GPa and temperatures down to 100 K. The experimental bulk modulus 195±6 GPa is in good agreement with 188.4 and 198.2 GPa values calculated in the LSDA and LSDA+U approximations, indicating that mainly the boron sublattice determines the bulk modulus. The experimental c/a ratio decreases slightly with pressure, but the effect is small. An orthorhombic distortion begins at Tc≈ 295 K, i.e. at a temperature much higher than the Neel temperature TN1=7.1 K. The behavior is interpreted in terms of built-in strains and crystal mosaicity. [ABSTRACT FROM AUTHOR]

The VF3-type compounds MF3 with M = Fe and Ga have been studied by high-pressure energy-dispersive X-ray diffraction. The compression mechanism was found to be highly anisotropic for both compounds, with the c-axis showing little pressure dependence. The volume reduction is mainly achieved through coupled rotations of the MF6 octahedra around the c-axis, which reduces the length of the a-axis. The compression mechanism of both compounds is reasonably well described in terms of deformation of an 8/3/c2 sphere-packing model up to the pressures where the fluorine atoms become hexagonally close-packed. It is proposed that both compounds enter a phase with the fluorine atom arranged in a 'super-dense' sphere packing at higher pressures. The zero pressure bulk modulus of FeF3 and GaF3 was determined as 12(2) and 37(3) GPa, respectively, and a scaling relation between the zero pressure bulk modulus and unit cell volumes was found for TiF3, CrF3, FeF3 and GaF3. [ABSTRACT FROM AUTHOR]

Abstract: Gamma ray energy-absorption buildup factors were computed using the five-parameter geometric progression (G-P) fitting formula for seven thermoluminescent dosimetric (TLD) materials in the energy range 0.015–15MeV, and for penetration depths up to 40mfp (mean free path). The generated energy-absorption buildup factor data have been studied as a function of penetration depth and incident photon energy. Buildup factors determined in the present work should be useful in radiation dosimetry, diagnostics and therapy. The tissue equivalence of TLD materials is also discussed. [Copyright &y& Elsevier]

Abstract: The effective atomic number, Z eff, the effective electron density, N e,eff, and the energy dependence, ED, have been calculated at photon energies from 1keV to 1GeV for CaO–SrO–B2O3, PbO–B2O3, Bi2O3–B2O3, and PbO–Bi2O3–B2O3 glasses with potential applications as gamma ray shielding materials. For medium-Z glasses, Z eff is about constant and equal to the mean atomic number in a wide energy range, typically 0.3< E <4MeV, where Compton scattering is the main photon interaction process. In contrast, for high-Z glasses there is no energy region where Compton scattering is truly dominating. Heavy-metal oxide glasses containing PbO and/or Bi2O3 are promising gamma ray shielding materials due to their high effective atomic number and strong absorption of gamma rays. They compare well with concrete and other standard shielding materials and have the additional advantage of being transparent to visible light. The single-valued effective atomic number calculated by XMuDat is approximately valid at low energies where photoelectric absorption is dominating. [Copyright &y& Elsevier]

The effective atomic numbers Zeff of some fatty acids and amino acids have been calculated by two numerical methods, a direct method and an interpolation method, in the energy range of 1 keV–20 MeV. The notion of Zeff is given a new meaning by using a modern database of photon interaction cross sections (WinXCom). The results of the two methods are compared and discussed. It is shown that for all biomolecules the direct method gives larger values of Zeff than the interpolation method, in particular at low energies (1–100 keV) At medium energies (0.1–5 MeV), Zeff for both methods is about constant and equal to the mean atomic number of the material. Wherever possible, the calculated values of Zeff are compared with experimental data. [ABSTRACT FROM AUTHOR]

Effective atomic numbers for photon energy absorption, ZPEA,eff, and for photon interaction, ZPI,eff, have been calculated by a direct method in the photon-energy region from 1 keV to 20 MeV for biological molecules, such as fatty acids (lauric, myristic, palmitic, stearic, oleic, linoleic, linolenic, arachidonic, and arachidic acids), nucleotide bases (adenine, guanine, cytosine, uracil, and thymine), and carbohydrates (glucose, sucrose, raffinose, and starch). The ZPEA,eff and ZPI,eff values have been found to change with energy and composition of the biological molecules. The energy dependence of the mass attenuation coefficient, ZPEA,eff, and the mass energy-absorption coefficient, ZPI,eff, is shown graphically and in tabular form. Significant differences of 17%-38% between ZPI,eff and ZPEA,eff occur in the energy region 5–100 keV. The reasons for these differences, and for using ZPEA,eff rather than ZPI,eff in calculations of the absorbed dose, are discussed. [ABSTRACT FROM AUTHOR]

ReO[sub 3] has been studied at pressures up to 52 GPa by X-ray powder diffraction. The previously observed cubic Im3 high-pressure phase was shown to transform to a monoclinic MnF[sub 3]-related phase at about 3GPa. All patterns recorded above 12 GPa could be indexed on rhombohedral cells. The compressibility was observed to decrease abruptly at 38 GPa. It is therefore proposed thai the oxygen ions are hexagonaliy close packed above this pressure, giving rise to two rhombohedral phases labelled land I and II. The zero-pressure bulk moduli B[sub 0] of the observed phases were determined and the rhombohedral phase II was found to have an extremely large value of 617 (10) GPa. It was found that ReO[sub 3] transforms back to the Pm3m phase found at ambient pressure. [ABSTRACT FROM AUTHOR]

Abstract: BaFe2As2 has been studied by high-pressure energy dispersive X-ray diffraction. The compression mechanism was found to be highly anisotropic, and a tetragonal to orthorhombic phase transition was observed at about 17 GPa. The length of the - and -axes of the tetragonal phase is reduced by 2 and 11%, respectively, at the transition pressure. Furthermore, an increase in compressibility was observed at about 1 GPa. The zero-pressure bulk modulus was determined to be B 0=71(4) GPa using experimental data points in the pressure range from 1 to 16.5 GPa. The experimental results are supported by electronic structure calculations within the extended Hückel approximation. [Copyright &y& Elsevier]

The glass transition behavior and crystallization kinetics of Zr[sub 48]Nb[sub 8]Cu[sub 14]Ni[sub 12]Be[sub 18] bulk metallic glass have been investigated by differential scanning calorimetry and x-ray powder diffraction (XRD). The activation energies of both glass transition and crystallization events have been obtained using the Kissinger method. Results indicate that this glass crystallizes by a three-stage reaction: (1) phase separation and primary crystallization of glass, (2) formation of intermetallic compounds, and (3) decomposition of intermetallic compounds and crystallization of residual amorphous phase. The pressure effect on crystallization is studied by in situ high-pressure and high-temperature XRD using synchrotron radiation. Two crystallization temperatures, observed by in-situ XRD, behave differently with varying pressure. The onset crystallization temperature increases with pressure with a slope of 9.5 K/GPa in the range of 0 to 4.4 GPa, while the another crystallization temperature keeps almost unchanged in the applied pressure range. The results are attributed to the competing processes between the thermodynamic potential barrier and the diffusion activation energy under pressure. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The high-pressure structural behaviour of a series of binary thorium compounds Th X ( X = C, N, P, As, Sb, Bi, S, Se, Te) is studied using the all-electron full potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximation (GGA) for the exchange and correlation potential. The calculated equlibrium lattice parameters and bulk moduli, as well as the equations of state agree well with experimental results. New experiments are reported for ThBi and ThN. Calculations are performed for the Th X compounds in the NaCl- and CsCl-type crystal structures, and structural phase transitions from NaCl to CsCl are found in ThP, ThAs, ThSb and ThSe at pressures of 26.1, 22.1, 8.1 and 23.2 GPa, respectively, in excellent agreement with experimental results. ThC, ThN and ThS are found to be stable in the NaCl structure, and ThBi and ThTe in the CsCl structure, for pressures below 50 GPa. The electronic structures of the Th X compounds are studied using the quasiparticle self-consistent GW method ( G: Green function, W: dynamically screened interaction). [ABSTRACT FROM AUTHOR]

Abstract: In this work, multilayered perceptron neural networks (MLPNNs) were presented for the computation of the gamma-ray energy absorption buildup factors (B A ) of seven thermoluminescent dosimetric (TLD) materials [LiF, BeO, Na2B4O7, CaSO4, Li2B4O7, KMgF3, Ca3(PO4)2] in the energy region 0.015–15MeV, and for penetration depths up to 10 mfp (mean-free-path). The MLPNNs have been trained by a Levenberg–Marquardt learning algorithm. The developed model is in 99% agreement with the ANSI/ANS-6.4.3 standard data set. Furthermore, the model is fast and does not require tremendous computational efforts. The estimated B A data for TLD materials have been given with penetration depth and incident photon energy as comparative to the results of the interpolation method using the Geometrical Progression (G-P) fitting formula. [Copyright &y& Elsevier]

Abstract: Using the theory of solvatochromism, the difference in the excited-state (μ e) and ground-state (μ g) dipole moments was determined from Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet, and McRae equations for three 1,2-diazines (pyrrolo-pyridazine derivatives). All of these equations are based on the variation of Stokes shift with solvent's relative permittivity and refractive index. Further, the change in dipole moment value (Δμ) was also calculated using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter. Theoretical μ g values were evaluated by quantum chemical calculations using the DFT method by adopting B3LYP/6-31G* level of theory (Gaussian 03) and using the AM1 method (Chem3D Ultra 8.0). It was observed that, dipole moments of diazines in the excited-state (μ e) were greater than the corresponding ground-state values (μ g), indicating a substantial redistribution of the π-electron densities in a more polar excited-state. Also, with the increase in the polarity of the solvent, the fluorescence emission peak undergoes a red-shift, confirming a π → π* transition. [Copyright &y& Elsevier]

High-pressure powder x-ray diffraction experiments using synchrotron radiation are performed on the yttrium monochalcogenides YS, YSe, and YTe up to a maximum pressure of 23 GPa. The ambient NaCl structure is stable throughout the pressure range covered. The bulk moduli are determined to be 93, 82, and 67 GPa for YS, YSe, and YTe, respectively. First-principles total energy calculations are carried out using the full-potential linear muffin-tin orbital method. The calculated and measured lattice constants and bulk moduli are in good agrement. Under applied pressure, the yttrium monochalcogenides are predicted to undergo a structural transition. Assuming that the high-pressure phase corresponds to the CsCl crystal structure, transition pressures of 53, 36, and 14 GPa are found for YS, YSe, and YTe, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The effective atomic number, Z eff, has been calculated for fatty acids and cysteine. It is shown that Z eff is a useful parameter for low-Z materials at any energy above 1keV. Absorption edges of medium-Z elements may complicate the energy dependence of Z eff below 10keV. The notion of Z eff is perhaps most useful at energies where Compton scattering is dominating, and where Z eff is equal to the mean atomic number, 〈Z〉, over a wide energy range around 1MeV. [Copyright &y& Elsevier]

Abstract: A comprehensive and consistent set of formulas is given for calculating the effective atomic number and electron density for all types of materials and for all photon energies greater than 1keV. The formulas are derived from first principles using photon interaction cross sections of the constituent atoms. The theory is illustrated by calculations and experiments for molecules of medical and biological interest, glasses for radiation shielding, alloys, minerals and liquids. [Copyright &y& Elsevier]

Abstract: The high-pressure, high-temperature structural behaviour of Cd3P2 has been studied using electrical resistance measurements, differential thermal analysis, thermo baric analysis and X-ray diffraction. At room temperature, a phase transformation is observed at 4.0GPa in compression. The experimental zero-pressure bulk modulus of the low-pressure phase is 64.7(7)GPa, which agrees quite well with the calculated value of 66.3GPa using the tight-binding linear muffin-tin orbital method within the local density approximation. Tentatively, the high-pressure phase has an orthorhombic crystal structure with space group Pmmn (#59). The relative volume change at the phase transition is ΔV/V =−5.5%. Amorphization of the sample occurs above 25GPa. A P–T phase diagram of Cd3P2 has been constructed. A metastable phase is observed at ambient conditions after heating the sample to above 600K at about 3GPa. A hexagonal unit cell can describe the crystal structure of the metastable phase. [Copyright &y& Elsevier]

Abstract: Microstructure and crystallization of a Cu50Zr45Al5 metallic glass have been investigated by differential scanning calorimetry, X-ray diffraction and extended X-ray absorption fine structure (EXAFS) using synchrotron radiation. The width of the supercooled region is ΔT x = T x − T g =67K, where T x and T g are the crystallization and the glass transition temperature, respectively; the reduced glass transition temperature is T rg = T g/T l =0.65, where T l is the liquid temperature; and γ = T x/(T g + T l)=0.41. After crystallization of the as-prepared Cu50Zr45Al5 metallic glass, crystalline phases are identified as tetragonal CuZr2 and orthorhombic Cu10Zr7. The local atomic structures deduced from EXAFS reveal that Zr atoms in the as-prepared Cu50Zr45Al5 metallic glass are surrounded by about 5 Cu atoms at a distance of 2.70Å and about 5 Zr atoms at 3.14Å. [Copyright &y& Elsevier]

Abstract: Effects of gamma-ray irradiation on some optical properties of xZnO·2xPbO·(1–3x)B2O3 glasses have been studied in the wavelength range 300–800nm. Decrease in transmittance indicates the formation of color-center defects. Values for the energy-band gap, the width of the energy tail above the mobility gap and the cut-off wavelength have been measured before and after irradiation. Changes in the optical properties are explained in terms of radiation-induced structural defects and the composition of the glass. [Copyright &y& Elsevier]

The structure of ReO3 has been studied over the pressure range from 1.27 to 8.01 GPa by neutron powder time-of-flight diffraction as well as by X-ray diffraction up to 41 GPa using Fluorinert as the pressure-transmitting medium. The cubic Irn3 phase was found to be stable in the pressure range 0.5 to 13.2 GPa and to be highly compressible with a zero-pressure bulk modulus of Bo = 43 (1) GPa. The neutron data were used in least-squares refinements, showing that the ReO6 octahedra remain almost undistorted, while the Re—O—Re bond angle decreases from 166.5 (1) to 146.4 (3)° within the investigated pressure range of 1.27 to 8.01 GPa. The compression mechanism is also described in terms of sphere-packing models of the oxygen anions. [ABSTRACT FROM AUTHOR]

Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, while the wurtzite phase was retained up to 60 GPa in the case of nanocrystalline GaN. The bulk moduli for the wurtzite phases were determined to be 187 (7) and 319 (10) GPa for the bulk- and nanocrystalline phases, respectively, while the respective NaCl phase were found to have very similar bulk moduli [208 (28) and 206 (44) GPa]. [ABSTRACT FROM AUTHOR]

The attenuation of gamma rays in some fatty acids, viz. formic acid (CH2O2), acetic acid (C2H4O2), propionic acid (C3H6O2), butyric acid (C4H8O2), n-hexanoic acid (C6H12O2), n-caprylic acid (C8H16O2), lauric acid (C12H24O2), myristic acid (C14H28O2), palmitic acid (C16H32O2), oleic acid (C18H34O2) and stearic acid (C18H36O2), has been measured at the photon energies 81, 356, 511, 662, 1173 and 1332 keV. Experimental values for the molar extinction coefficient, the effective atomic number and the electron density have been derived and compared with theoretical calculations. There is good agreement between experiment and theory. [Copyright &y& Elsevier]

In the present work, we report an X-ray powder diffraction study of TbN up to an applied hydrostatic pressure of 43 GPa. TbN was found to be stable in the B1 (NaCl structure) within the examined pressure interval, and the zero pressure bulk modulus was determined to be 176(7) GPa. The electronic structure of ferromagnetic TbN has been studied using the linearized augmented plane-wave method. The calculated equilibrium volume and equation of state (EOS) for TbN agree poorly with experiment when the LDA and GGA versions of DFT were used. The agreement between the experimental and theoretical EOS is greatly improved by introducing an orbital dependent U term into the energy-functional. The 4f electrons in TbN-B1 are atomic like and highly correlated, and ferro-magnetic TbN-B1 is found to be a magnetic half-metal. Calculations find the spin-down f-electrons in a hypothetical TbN-B2 (CsCl) structure to be itinerant and well described by standard DFT functionals. No pressure-induced phase transitions were found below 250 GPa with the LDA+U and GGA+U methods. [Copyright &y& Elsevier]

Novel nanocomposites, consisting of conducting poly(3,4-ethylenedioxythiophene) [PEDOT] and graphene nanoplatelets [GNPs], were successfully synthesized by in-situ chemical-oxidative polymerization of 3,4-ethylenedioxythiophene [EDOT] using ammonium peroxydisulfate as an oxidizing agent. The formation of PEDOT and its incorporation onto the surface of GNPs were confirmed by scanning electron microscopy, Fourier-transform infrared-spectroscopy, and X-ray diffraction. The optical energy band gap, E g opt, was determined by UV–Vis spectroscopy. Dielectric constant and loss as well as AC electrical conductivity, σ AC , were determined in the frequency range from 10 Hz to 8 MHz. The PEDOT-GNP nanocomposites were found to have extremely large dielectric constant, ε ′, significantly high σ AC , and narrow E g opt values. In particular, PEDOT-GNP nanocomposite with 10 wt% GNP has a gigantic dielectric constant of the order of 9 × 105 at 1 kHz and a narrow optical energy band gap of 1.26 eV. The ε ′ values (108 to 105 in the frequency range from 10 Hz to 5 MHz) of PEDOT-10 wt% GNP are the highest among those reported in the literature for carbon based polymer nanocomposites. The massive quantity of micro-capacitors formed in the nanocomposites, prior to the creation of conductive networks, leads to the gigantic dielectric properties. The ε ′ and σ AC values of PEDOT-10 wt% GNP nanocomposite were about 90 and 400 times larger than those of pure PEDOT. Our method should be particularly promising in the development of new materials for high energy storage applications. • PEDOT-GNP nanocomposites are synthesized by in-situ chemical oxidative polymerization. • Dielectric constant, ε ′, band gap, E g opt, and AC conductivity, σ AC , vary with GNP content and frequency. • PEDOT-10 wt% GNP nanocomposite has a gigantic ε ′ of the order of 9 × 105 at 1 kHz and a narrow E g opt of 1.26 eV. • ε ′ and σ AC values of PEDOT-10 wt% GNP nanocomposite are 90 and 400 times larger than those of pure PEDOT. • PEDOT-10 wt% GNP nanocomposite has shown highest ε ′ values for carbon based polymer nanocomposites. [ABSTRACT FROM AUTHOR]

Basic polyhedral clusters have been derived from intermetallic compounds at near-eutectic composition by considering a dense packing and random arrangement of atoms at shell sites. Using such building units, bulk metallic glasses can be formed. This strategy was verified in the Cu–Zr binary system, where we have demonstrated the existence of Cu8Zr5 icosahedral clusters in Cu61.8Zr38.2, Cu64Zr36, and Cu64.5Zr35.5 amorphous alloys. Furthermore, ternary bulk metallic glasses can be developed by doping the basic Cu–Zr alloy with a minority element. This hypothesis was confirmed in systems (Cu0.618Zr0.382)100-xNbx, where x=1.5 and 2.5 at. %, and (Cu0.618Zr0.382)98Sn2. The present results may open a route to prepare amorphous alloys with improved glass forming ability. [ABSTRACT FROM AUTHOR]

Quasicrystals with a primitive icosahedral structure and a quasilattice constant of 5.1215 Å have been synthesized in a binary Cd-Ca system. The thermal stability of the quasicrystal has been investigated by in situ high-temperature x-ray powder diffraction using synchrotron radiation. It is demonstrated that the binary CdCa quasicrystal is thermodynamic stable up to its melting temperature. The linear thermal expansion coefficient of the quasicrystal is 2.765x10[sup -5] K[sup -1]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]