Estimates for Diffusion Barriers and Atomic Potentials in Mgo: Cndo/2 Calculations for the Study of Microwave Effects in Sintering

1990 ◽  
Vol 189 ◽  
Author(s):  
L. Skala ◽  
V.M. Kenkre ◽  
M.W. Weiser ◽  
J.D. Katz
Keyword(s):  
Microwave Sintering ◽  
Activation Energies ◽  
Diffusion Barriers ◽  
Electron Densities ◽  
Self Consistent ◽  
Interstitial Atoms ◽  
Microwave Effects

ABSTRACTAs part of a program of investigation of microwave sintering, self-consistent CNDO/2 calculations are presented for diffusion barriers and potentials for the motion of interstitial atoms and vacancies in MgO. Clusters of 30 atoms are used in the calculations. Activation energies, diffusion barriers, shape of the potentials and electron densities are obtained.

scholarly journals The features of deformation-stimulated RbI luminescence

2021 ◽  
Vol 5 (4) ◽  
pp. 218-228
Author(s):  
L. N. Myasnikova ◽  
A. G. Maratova ◽  
K. Sh. Shunkeyev
Keyword(s):  
Elastic Deformation ◽  
Thermal Activation ◽  
Spectral Composition ◽  
Activation Energies ◽  
Luminescence Spectra ◽  
Radiation Defects ◽  
Thermally Stimulated Luminescence ◽  
Radiative Relaxation ◽  
Interstitial Atoms

This paper studies deformation-stimulated features of radiative relaxation of self-trapped excitons and recombination assembly of exciton-like luminescence in RbI crystal. Methods of research were luminescence and thermal activation spectroscopy. The identity of the mechanism of manifestation of the X-ray luminescence, tunnel luminescence and thermally stimulated luminescence spectra were found in the elastically deformed RbI crystal, interpreted by the luminescence of self-trapped exciton, tunnel recharge of F′, VK -pairs and thermally stimulated recombination of e−, VK -centres, respectively.The temperatures of the maximum destruction peaks of thermally stimulated luminescence, their spectral composition and activation energies were determined experimentally, on the basis of which the mechanisms of recombination assembly of exciton-like luminescences in a RbI crystal were interpreted. Uniaxial elastic deformation leads to the effective formation of point radiation defects ( F′, HA, VK -centers) in comparison with an unbroken lattice, where the predominant mechanism is the association of interstitial atoms ( H -centres) with the formation of I3−-centres.

scholarly journals Impedance and Electrical Modulus Study of Microwave-Sintered Ceramic

ISRN Ceramics ◽  
2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
V. Senthil ◽  
T. Badapanda ◽  
A. Chandra Bose ◽  
S. Panigrahi
Keyword(s):  
Microwave Sintering ◽  
Fatigue Property ◽  
Activation Energies ◽  
Nyquist Plot ◽  
Sintered Pellet ◽  
X Ray Diffraction ◽  
Sintered Ceramic ◽  
Solid State Route ◽  
Conventional Sintering ◽  
Single Arc

Bismuth layered structure SrBi2Ta2O9 ceramic is prepared by the microwave sintering technique via solid state route at 1100°C for 30 mins. X-ray diffraction analysis is used to analyze the phase purity, which identifies the orthorhombic structure with A21am space group. The fracture surface of the sintered pellet is visualized by scanning electron microscopy. Impedance spectroscopy is used to analyze the sample behavior as a function of frequency and temperature. Impedance and modulus study reveals the temperature-dependent non-Debye type relaxation phenomenon. The Nyquist plot shows a single arc representing the grain effect in the material, and the conductivity increases with increase in temperature. The Nyquist plot is fitted with an equivalent circuit, and the simulated parameters are well agreed with the calculated parameters. Arrhenius plot shows two different activation energies at below and above 300°C which identifies the phase transition of SrBi2Ta2O9 ceramic. The fatigue property is explained by the basis of activation energies, which shows that SBT sintered by microwave technique is more fatigue resistant than conventional sintering.

Self-consistent electron densities in metal vacancies

1975 ◽  
Vol 16 (7) ◽  
pp. 831-834 ◽  
Author(s):  
R. Nieminen ◽  
M. Manninen ◽  
P. Hautojärvi ◽  
J. Arponen
Keyword(s):  
Electron Densities ◽  
Self Consistent ◽  
Metal Vacancies
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