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  1. Studies of Multiferroic Palladium Perovskites

    Pradhan, Dhiren K. ; Mishra, Ajay K. ; Kumari, Shalini ; ... - Scientific Reports
    Abstract We have studied the atomic force microscopy (AFM), X-ray Bragg reflections, X-ray absorption spectra (XAS) of the Pd L-edge, Scanning electron microscopey (SEM) and Raman spectra, and direct magnetoelectric tensor of Pd-substituted lead titanate and lead zirconate-titanate. A primary aim is to determine the percentage of Pd +4 and Pd +2 substitutional at the Ti-sites (we find that it is almost fully substitutional). The atomic force microscopy data uniquely reveal a surprise: both threefold vertical (polarized out-of-plane) and fourfold in-plane domain vertices. This is discussed in terms of the general rules for Voronoi patterns (Dirichlet tessellations) in two andmore » three dimensions. At high pressures Raman soft modes are observed, as in pure lead titanate, and X-ray diffraction (XRD) indicates a nearly second-order displacive phase transition. However, two or three transitions are involved: First, there are anomalies in c/a ratio and Raman spectra at low pressures (P = 1 − 2 GPa); and second, the c/a ratio reaches unity at ca. P = 10 GPa, where a monoclinic (M c ) but metrically cubic transition occurs from the ambient tetragonal P4 mm structure in pure PbTiO 3 ; whereas the Raman lines (forbidden in the cubic phase) remain until ca. 17 GPa, where a monoclinic-cubic transition is known in lead titanate.« less

  2. The Potential of Plutonium as a Fuel in Near-Thermal Burner Reactors

    Puechl, Karl H. - Nuclear Science and Engineering
    Here, the influence of plutonium as a fuel constituent on burner reactor behavior is examined. Both the SM-1 and the Shippingport seed lattices are investigated. It is found that the decrease in the effective absorption cross section of Pu240 with fuel burnup gives the plutonium the characteristic of a self-compensating fuel, thereby leading to the extension of core life with minimum shim control requirements. The illustrated behavior is similar to that which was previously shown to be possible for converter-type reactors.

  3. In search of the elusive IrB2: Can mechanochemistry help?

    Xie, Zhilin ; Blair, Richard G. ; Orlovskaya, Nina ; ... - Journal of Solid State Chemistry
    We produced hexagonal ReB2-type IrB2 diboride and orthorhombic IrB monoboride phases, that were previously unknown and saw them produced by mechanochemical syntheses. High energy ball milling of elemental Ir and B powder for 30 h, followed by annealing of the powder at 1050 °C for 48 h, resulted in the formation of the desired phases. Both traditional laboratory and high resolution synchrotron X-ray diffraction (XRD) analyses were used for phase identification of the synthesized powder. Additionally, scanning electron microscopy and transmission electron microscopy were employed, along with XRD, to further characterize the microstructure of the phases produced.

  4. Nonlinear Deflections of Shallow Spherical Shells

    Reiss, Edward L. ; Greenberg, Herbert J. ; Keller, Herbert B. - Journal of the Aeronautical Sciences
    The equations obtained by Chien for the nonlinear deflection of shallow spherical shells under uniform external pressure are solved by means of power series expansions following procedures introduced by Friedrichs and Stoker in their treatment of buckling of circular plates. These equations depend upon two parameters. One of these is related to the external pressure, while the other depends upon the dimensions of the shell. The equations are solved for several ranges of the parameters under boundary conditions corresponding to a fixed edge. The solution, carried out numerically on the Univac at New York University, yields a complete description ofmore » the stresses and deflections as functions of the polar angle over a wide range of values of the loading parameter and the dimensional parameter. Prediction of the upper buckling load is then made by means of a numerical criterion based on the load vs. deflection curve. For some cases, the post-buckling behavior is investigated. Finally, the results agree well with existing experimental and theoretical studies and cover a wide range of cases not previously treated.« less

  5. Oscillations of a Cylindrical Plasma

    Stix, Thomas H. - Physical Review
    The natural modes of oscillation of a cylindrical plasma of finite density at zero pressure in a longitudinal magnetic field are examined. When one considers frequencies well below the electron plasma and electron cyclotron frequencies, there appear in two limiting cases hydromagnetic waves, and waves whose natural frequencies are close to the ion cyclotron frequency. This cyclotron frequency resonance occurs when the wavelength of the oscillation in the z direction is short compared to the wavelength for light in vacuo corresponding to the root square sum of the ion plasma frequency and the ion cyclotron frequency.

  6. Measurements of Stacking Faults in Cold-Worked Alpha Brass

    Warren, B. E. ; Warekois, E. P. - Journal of Applied Physics
    Barrett has suggested that stacking faults on the (111) planes should contribute to the broadening of the x-ray reflections from a cold worked face centered cubic metal. Paterson's recent treatment of this problem predicts peak shifts as a result of stacking faults, and hence gives a method for uniquely proving their existence and measuring the probability of occurrence. The (111) reflection moves toward large angle and the (200) reflection toward small angle, so that the separation of these two peaks decreases as a result of stacking faults. Finally, for the (222)-(400) pair the opposite effect is predicted.

  7. Acoustic Wave Velocities, Elastic Constants, and Debye Characteristic Temperature for Polycrystalline MgCd

    Smith, Charles S. ; Wallace, W. E. - Journal of Chemical Physics
    The longitudinal and transverse acoustic wave velocities in a polycrystalline magnesium-cadmium alloy containing 50.6 atomic per cent cadmium were measured using the pulsed ultrasonic method. The alloy was prepared by fusing together spectroscopically pure magnesium and cadmium under a blanket of helium purified by evaporation. Experimental details concerning preparation and analysis of the alloy and the method employed in measuring the sound velocities are given elsewhere.

  8. The Thermal Decomposition of Ammonium Heptafluorozirconate(IV)1

    Haendler, Helmut M. ; Wheeler, Charles M. ; Robinson, Dean W. - Journal of the American Chemical Society
    A study has been made of the thermal decomposition of ammonium heptafluorozirconate, (NH4)3ZrF7, using the technique of differential thermal analysis. The decomposition proceeds in three distinct stages, (NH4)3ZrF7 → (NH4)2ZrF6 → NH4-ZrF5 → ZrF4. The temperature of decomposition is a function of the pressure.

  9. Powder metallurgy technique for the preparation of HoZn2 samples

    Michel, D.J. ; Ryba, E. - Journal of the Less Common Metals

  10. Magnesium-Cadmium Alloys. VI. Heat Capacities between 12 and 320°K. and the Entropies at 25° of Magnesium and Cadmium1,2

    Craig, R. S. ; Krier, C. A. ; Coffer, L. W. ; ... - Journal of the American Chemical Society
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