Study of charge transfer in FeTi

1983 ◽  
Vol 41 ◽  
pp. 296-297
Author(s):  
J. Taft∅
Keyword(s):  
Charge Transfer ◽  
Charge Distribution ◽  
Electron Scattering ◽  
Periodic System ◽  
Electron Distribution ◽  
Scattering Amplitude ◽  
Transition Elements ◽  
Hartree Fock ◽  
Cscl Structure ◽  
The Right

It is well known that for reflections corresponding to large interplanar spacings (i.e., sin θ/λ small), the electron scattering amplitude, f, is sensitive to the ionicity and to the charge distribution around the atoms. We have used this in order to obtain information about the charge distribution in FeTi, which is a candidate for storage of hydrogen. Our goal is to study the changes in electron distribution in the presence of hydrogen, and also the ionicity of hydrogen in metals, but so far our study has been limited to pure FeTi. FeTi has the CsCl structure and thus Fe and Ti scatter with a phase difference of π into the 100-ref lections. Because Fe (Z = 26) is higher in the periodic system than Ti (Z = 22), an immediate “guess” would be that Fe has a larger scattering amplitude than Ti. However, relativistic Hartree-Fock calculations show that the opposite is the case for the 100-reflection. An explanation for this may be sought in the stronger localization of the d-electrons of the first row transition elements when moving to the right in the periodic table. The tabulated difference between fTi (100) and ffe (100) is small, however, and based on the values of the scattering amplitude for isolated atoms, the kinematical intensity of the 100-reflection is only 5.10-4 of the intensity of the 200-reflection.

On the hyperfine structure of paramagnetic resonance: the s -electron effect

1955 ◽  
Vol 230 (1181) ◽  
pp. 169-187 ◽  
Keyword(s):  
Neutral Atoms ◽  
Transition Elements ◽  
Paramagnetic Resonance ◽  
Electron Effect ◽  
Hartree Fock ◽  
Full Explanation ◽  
Unpaired Spin ◽  
Paramagnetic Ions ◽  
The Right ◽  
Open Question

Unpaired s -electrons play an important part in hyperfine spectra, even when the nominal spectroscopic configuration contains no unpaired s -electrons. This situation occurs in paramagnetic resonance and optical spectra. A survey of the experimental evidence for the effect is given in relation to the paramagnetic ions and the neutral atoms of the 3 d transition elements. It appears that the central density of unpaired spin is nearly the same in all the ions of the group for which experimental data are available, while for the neutral atoms it is more variable, but of the same general magnitude. A calculation of the magnitude of the effect is attempted from first principles, starting from the Hartree–Fock self-consistent wave functions as a first approximation, and adding configurations in which 3 s -, 2 s - and 1 s -electrons are promoted. The promotion of a 3 s -electron is described by an integro-differential equation, which has been solved numerically in one particular case. The contribution turns out of the right sign but ten times smaller than the observed value. Promotion of 2 s - and l s -electrons yield similar equations, which, however, have not been solved, owing to the excessive labour involved. There is no reason to believe that they would not give smaller contributions still. The full explanation of the s -electron effect is thus still an open question.

Single Atom Image Contrast in Fixed Beam Dark Field Electron Microscopy

1974 ◽  
Vol 32 ◽  
pp. 366-367
Author(s):  
Wah Chi
Keyword(s):  
Scattering Amplitude ◽  
Present Report ◽  
Dark Field ◽  
Image Contrast ◽  
Single Atom ◽  
Optical Theorem ◽  
Hartree Fock ◽  
Heavy Atoms ◽  
Beam Stop ◽  
Fixed Beam

Resolution and contrast are the important factors to determine the feasibility of imaging single heavy atoms on a thin substrate in an electron microscope. The present report compares the atom image characteristics in different modes of fixed beam dark field microscopy including the ideal beam stop (IBS), a wire beam stop (WBS), tilted illumination (Tl) and a displaced aperture (DA). Image contrast between one Hg and a column of linearly aligned carbon atoms (representing the substrate), are also discussed. The assumptions in the present calculations are perfectly coherent illumination, atom object is represented by spherically symmetric potential derived from Relativistic Hartree Fock Slater wave functions, phase grating approximation is used to evaluate the complex scattering amplitude, inelastic scattering is ignored, phase distortion is solely due to defocus and spherical abberation, and total elastic scattering cross section is evaluated by the Optical Theorem. The atom image intensities are presented in a Z-modulation display, and the details of calculation are described elsewhere.

Direct imaging of charge transfer

1996 ◽  
Vol 54 ◽  
pp. 680-681
Author(s):  
Yimei Zhu ◽  
J. Tafto
Keyword(s):  
Charge Transfer ◽  
Electron Diffraction ◽  
Scattering Amplitude ◽  
High Temperature Superconductors ◽  
Charge Carriers ◽  
Image Charge ◽  
Net Charge ◽  
Long Time ◽  
Electron Holes ◽  
First Time

The electron holes confined to the CuO2-plane are the charge carriers in high-temperature superconductors, and thus, the distribution of charge plays a key role in determining their superconducting properties. While it has been known for a long time that in principle, electron diffraction at low angles is very sensitive to charge transfer, we, for the first time, show that under a proper TEM imaging condition, it is possible to directly image charge in crystals with a large unit cell. We apply this new way of studying charge distribution to the technologically important Bi2Sr2Ca1Cu2O8+δ superconductors.Charged particles interact with the electrostatic potential, and thus, for small scattering angles, the incident particle sees a nuclei that is screened by the electron cloud. Hence, the scattering amplitude mainly is determined by the net charge of the ion. Comparing with the high Z neutral Bi atom, we note that the scattering amplitude of the hole or an electron is larger at small scattering angles. This is in stark contrast to the displacements which contribute negligibly to the electron diffraction pattern at small angles because of the short g-vectors.

New Polaronic-Type Excitons in Ferroelectric Oxides: INDO-Calculations and Experimental Manifestation

2001 ◽  
Vol 677 ◽  
Author(s):  
Valentin S. Vikhnin ◽  
Roberts I. Eglitis ◽  
Eugene A. Kotomin ◽  
Siegmar Kapphan ◽  
Gunnar Borstel
Keyword(s):  
Charge Transfer ◽  
Theoretical Knowledge ◽  
Strongly Correlated ◽  
Hartree Fock ◽  
Indo Calculations ◽  
Photoluminescence Studies ◽  
Ferroelectric Oxides ◽  
New Phase

ABSTRACTThe current experimental and theoretical knowledge of new polaronic-type excitons in ferroelectric oxides – charge transfer vibronic excitons (CTVE) – is discussed. It is shown that Hartree-Fock-type INDO calculations as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE-concept. Single CTVE as well as a new phase of strongly correlated CTVEs are analysed.

SCF Dirac-Hartree-Fock calculations in the periodic system

1973 ◽  
Vol 31 (2) ◽  
pp. 137-153 ◽  
Author(s):  
Jarom�r Mal� ◽  
Michel Hussonnois
Keyword(s):  
Periodic System ◽  
Hartree Fock
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