Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Mössbauer-Effect Studies Of The Phase Transitions In Antiferroelectric Pbzro₃ And Ferroelectric Pbti₀.₀₂Zr₀.₈O₃, James P. Canner, C. M. Yagnik, Robert Gerson, William Joseph James
Mössbauer-Effect Studies Of The Phase Transitions In Antiferroelectric Pbzro₃ And Ferroelectric Pbti₀.₀₂Zr₀.₈O₃, James P. Canner, C. M. Yagnik, Robert Gerson, William Joseph James
Physics Faculty Research & Creative Works
The Mössbauer spectra were studied for the antiferroelectric compound PbZrO3 and for the closely related ferroelectric PbTi0.2Zr0.8O3. In both cases, a substitution of 5-mol% BiFeO3 was made to permit the Mössbauer measurements. Little difference was found in the isomer shift in these compounds, whether they were in the ferroelectric, antiferroelectric, or cubic state, indicating that the bonding character is not affected by the transitions among the states. There was a pronounced and approximately equivalent dip in the recoil-free fraction at the Curie points of both the antiferroelectric and ferroelectric materials, associated with …
Excitation Of The 2s State Of Atomic Hydrogen By Electron Impact In The Distorted-Wave Approximation - Angular Distributions, W. Neil Shelton, E. S. Leherissey, Don H. Madison
Excitation Of The 2s State Of Atomic Hydrogen By Electron Impact In The Distorted-Wave Approximation - Angular Distributions, W. Neil Shelton, E. S. Leherissey, Don H. Madison
Physics Faculty Research & Creative Works
The excitation of ground-state hydrogen atoms to the 2s state by the impact of electrons with energies of 1 to 50 Ry (13.6 to 680.3 eV) has been calculated in the distorted-wave approximation with exchange included. The angular distributions of the scattered electrons at 1 and 4 Ry are compared with those derived from the close-coupling calculations by Burke, Schey, and Smith, and are compared with four different plane-wave theories at all energies calculated. Taking the close-coupling results as a standard, it is found that the distorted-wave angular distributions represent an improvement over those of the plane-wave theories.
Collision Cross Sections For The Excitation Of The Schumann-Runge Dissociation Continuum In Molecular Oxygen By 20-110-Kev Protons, John T. Park, F. D. Schowengerdt, D. R. Schoonover
Collision Cross Sections For The Excitation Of The Schumann-Runge Dissociation Continuum In Molecular Oxygen By 20-110-Kev Protons, John T. Park, F. D. Schowengerdt, D. R. Schoonover
Physics Faculty Research & Creative Works
Absolute cross sections for the excitation of the Schumann-Runge dissociation continuum of molecular oxygen have been obtained from inelastic energy-loss spectra induced by 20-110-keV protons incident on gaseous targets of molecular oxygen. Apparent differential energy loss cross sections, ionization cross sections, and total inelastic cross sections are also obtained from the energy-loss spectra. The proton energy-loss spectra have an energy resolution of about 2 eV. The energy location of the first peak in the energy-loss spectra of O2 is in general agreement with the findings of photo absorption and electron energy-loss-spectra measurements. The cross section for the Schumann-Runge dissociation continuum …
Heisenberg Ferromagnet With Biquadratic Exchange, Harry A. Brown
Heisenberg Ferromagnet With Biquadratic Exchange, Harry A. Brown
Physics Faculty Research & Creative Works
The usual Heisenberg Hamiltonian with bilinear exchange -2JS→1•S→2 has been extended to include a biquadratic term -2αJ(S→1•S→2)2, with an adjustable parameter α. A method equivalent to constant coupling was employed to calculate the effect of the biquadratic exchange term on the Curie temperature, magnetization, susceptibility, specific heat, and entropy for lattices with spin-1 atoms. As α goes from 0 to 1, the Curie temperature falls by a factor 2 to 3, while the asymptotic Curie temperature is reduced by the factor 2. The magnetization rises much more rapidly below TC, and the specific heat has a peak and discontinuity several …
Mössbauer Studies Of Bifeo₃-Pbtio₃ Perovskite-Type Solid Solutions, C. M. Yagnik, Robert Gerson, William Joseph James
Mössbauer Studies Of Bifeo₃-Pbtio₃ Perovskite-Type Solid Solutions, C. M. Yagnik, Robert Gerson, William Joseph James
Physics Faculty Research & Creative Works
The Mössbauer spectra of the ferroelectric solid solutions (BiFeO3)x(PbTiO)1-x have been studied as a function of temperature, mainly between room temperature and 600°C, using 57Fe in the solutions as an absorber. The quadrupole splitting increased and the isomer shift decreased between x = 0.05 and x = 0.70, a range in which the solutions are tetragonal and paramagnetic, and in which the unit cell volume increases with increasing x. The isomer shift, in particular, was primarily determined by the unit cell volume. Data are presented on the internal magnetic field of the antiferromagnetic …
Surface Plasmons And The Reflectivity Of N-Type Insb, William E. Anderson, Ralph William Alexander, Robert John Bell
Surface Plasmons And The Reflectivity Of N-Type Insb, William E. Anderson, Ralph William Alexander, Robert John Bell
Physics Faculty Research & Creative Works
The Reflectivity of N-Type InSb Has Been Measured in the Far Infrared. the Doping of the Samples Was Such that the Free-Carrier Plasma Frequency Was Near the LO Mode Frequency. the Results Suggest that Samples with a Sufficiently Thick Damage Layer Show Effects Due to Surface Plasmons. Use of a Simple Model Indicates that the Surface-Plasma Excitations Are Coupled to the Phonons. © 1971 the American Physical Society.
Second- And Third-Order Elastic Constants Of Aluminum And Lead, Tetsuro Suzuki
Second- And Third-Order Elastic Constants Of Aluminum And Lead, Tetsuro Suzuki
Physics Faculty Research & Creative Works
The second- and third-order elastic constants of Al and Pb are calculated as the second and third derivatives of the binding energy with respect to the finite deformation parameter. The binding energy is derived from a local pseudopotential by use of second-order perturbation theory. It is shown that the binding energy satisfied not only the diagonal equilibrium condition, but also the off-diagonal equilibrium condition, i.e., the first derivative of the binding energy with respect to a volume change as well as with respect to shear deformations is zero. Accordingly, the present method of calculation is based on a stable lattice …
Calculation Of Anisotropic Hyperfine Constants For Lattice Nuclei Near A Shallow Donor, Edward B. (Boyd) Hale, Robert Lee Mieher
Calculation Of Anisotropic Hyperfine Constants For Lattice Nuclei Near A Shallow Donor, Edward B. (Boyd) Hale, Robert Lee Mieher
Physics Faculty Research & Creative Works
A method is presented for calculating the magnetic anisotropic (dipolar) hyperfine constants for lattice nuclei near a shallow-donor impurity. The method assumes that the wave function of the donor electron can be expressed in an effective-mass form, i.e., a slowly varying envelope function times conduction-band Bloch functions. For each dipolar hyperfine constant, two separate calculations are performed. One calculation is for a local region about the lattice nucleus of interest. The greatest part of the interaction occurs in this region (about 85 ± 10%). The second calculation is for the more distant region. The dipolar constants in the distant region …
Magnetostriction And Magnetic Breakdown In Cadmium, J. M. Carter, Don M. Sparlin
Magnetostriction And Magnetic Breakdown In Cadmium, J. M. Carter, Don M. Sparlin
Physics Faculty Research & Creative Works
Studies of the monotonic magnetostriction of cadmium at 4.2 °K in applied magnetic fields to 70 kG have shown that the angular variation of an extremal point Hm is proportional to secθ. The magnitude of Hm is in close agreement with the onset of a breakdown orbit γ13 observed for the applied field within 35 °of the c axis. The range of observation of Hm coincides with the range of the orbit γ. © 1971 The American Physical Society.
Electron-Impact Excitation Of Auto-Ionizing Levels In Cesium, Yu Bong Hahn, Kaare J. Nygaard
Electron-Impact Excitation Of Auto-Ionizing Levels In Cesium, Yu Bong Hahn, Kaare J. Nygaard
Physics Faculty Research & Creative Works
Auto-ionizing states in Cs between 12 and 20 eV have been studied by electron impact. The retarding-potential-difference method was used to obtain an electron beam with energy spread of about 0.1 eV. To determine the threshold energies, inelastically scattered electrons were analyzed by the trapped-electron method. We have been able to identify about 20 levels, and the agreement with spectroscopic data is excellent. A peak appearing at 12.80 eV is probably due to the quartet states observed by Feldman and Novick. © 1971 The American Physical Society.
Absolute Excitation Cross Sections Of He+ In 20-100-Kev He+-He Collisions Using Energy-Loss Spectrometry, D. R. Schoonover, John T. Park
Absolute Excitation Cross Sections Of He+ In 20-100-Kev He+-He Collisions Using Energy-Loss Spectrometry, D. R. Schoonover, John T. Park
Physics Faculty Research & Creative Works
Application of positive-ion energy-loss spectrometry has been extended to include experimental determination of absolute excitation cross sections of ground-state helium ions. Helium ion-atom collisions were studied for impact energies ranging between 20-100 keV, in 10-keV intervals. The data were taken with an apparatus resolution between 0.6-0.8 eV full width at half-maximum (FWHM). Cross sections for transitions from ground state to the second and third principal quantum levels of the ion plotted as a function of impact energy were still rapidly increasing at 100 keV. The cross sections at this energy were (1.64 ± 0.28) x 10-18 cm2 for He+(1s122)→He+ (n=2) …
Experimental And Theoretical Study Of The Sign Preference In The Nucleation Of Water Vapor, Daniel R. White, James L. Kassner
Experimental And Theoretical Study Of The Sign Preference In The Nucleation Of Water Vapor, Daniel R. White, James L. Kassner
Physics Faculty Research & Creative Works
The nucleation of water vapor on ions in atmospheres of helium and argon was studied using an expansion type cloud chamber. Separation of the positive and negative ions was achieved so that the nucleation could be studied as a function of both the sign of the ionic charge and the supersaturation. A semiphenominological theory was developed as an extension of the classical liquid drop theory to include the effects of the ionic charge on the nucleation process. The theoretical model of the prenucleation embryo was assumed to possess an oriented dipole surface layer with the direction of orientation dependent on …
Scattering Of Waves In Many Dimensions, I. Adawi
Scattering Of Waves In Many Dimensions, I. Adawi
Physics Faculty Research & Creative Works
Scattering by a spherical potential is discussed in all dimensions by one formulation using the partial-wave expansion method. The optical theorem relating the total scattering cross section σ to the forward scattering amplitude f(0) is derived.