2022-12

Ukrainian Journal of Physical Optics (Issue : 1) (Volume : 23)

Inorganic halide-based perovskites are of great interest as materials for photo-voltaic and optoelectronic devices. Here we present a first-principles study of the structural, electronic, elastic and optical properties of alkali-metal lead iodides MPbI3 (M = Li, Na, K), with the emphasis on the role of their first cation M. In particular, this work is the first investigation of the elastic and optical properties of MPbI3 (M = Na, K). Our results show that the first cation has insignificant effect on the properties mentioned above, although there is some increase in the lattice constant when we pass from Li to Na. The energy band gap values calculated for our perovskites in a generalized gradient approximation agree with the available theoretical data but not with the experimental results. A better agreement with the experiment can be achieved with the approaches of Green’s function and screened Coulomb interaction approximation. We demonstrate that our compounds have a direct band gap. The optical properties of MPbI3 are calculated using a density-functional perturbation theory. Our data shows that MPbI3 (M = Na, K) have a weak response to electromagnetic radiation at high photon energies and a strong response at low energies.

2016-06

International Journal of Astronomy (Issue : 2169) (Volume : 5)

Craters occur when an objects like Asteroids, Comets and Meteorites hits onto the surfaces of Moon and Planets and their impact has became a major geological process. The objective of the project is to investigate how the size of a Meteorite and Asteroid on the Moon and Planets is related to the size of impact crater. We started with a two round stone of different mass and size covered slightly with a layer of a viscous mud fluid as a fragmentation were dropped at variable height onto the flour. However, we have used a layer of sprinkles as a mineral diversity of the surface impacted. We have measured the diameter, depth and the Ejecta distance of the crater each time, there were three trails for each stone drop height. The results shows that, the crater diameter and the crater depth increased as the height and mass of the ball drop increased in addition of increasing Ejecta distance. .