Search results for "Frenkel defect"
showing 10 items of 15 documents
Long-term stability of alpha particle damage in natural zircon
2005
Abstract We report the first discovery of radiation damage haloes generated by alpha particles in zircon. Proterozoic zircon crystals from a potassium-rich leucogranite from the Adirondack Mountains, New York State, have interior regions that are generally low in actinide elements (UO 2 + ThO 2 ≤ 0.02 wt.%) but show a remarkable pattern of heterogeneous metamictisation. The degree of radiation damage in these regions is not uniformly low, as would be expected if it corresponded to the observed actinide distribution patterns and age of the crystals. Rather, radiation damage is significantly increased in the outermost micro-areas of the low-actinide regions. The additional radiation damage …
Ab initio simulations on Frenkel pairs of radiation defects in corundum
2015
Large scale first principles periodic calculations based on the density functional theory within the localized atomic orbital approach (DFT-LCAO) using the hybrid exchange- correlation potential B3PW have been performed in order to study the structural and electronic properties of radiation-induced Frenkel pairs Oi+VO in corundum crystal. As an initial approach, we have used conventional 2x2x1 supercell for defective α-Al2O3 lattice containing 120 atoms. After relaxation of the ideal supercell structure, the optimized doi-vo distance has been found to be ~4.5 A while the formation energy of Frenkel pair has achieved 11.7 eV. The interstitial Oi atom, both single and a component of Oi+VO pai…
Giant Mechanocaloric Effects in Fluorite-Structured Superionic Materials
2016
Mechanocaloric materials experience a change in temperature when a mechanical stress is applied on them adiabatically. Thus, far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic species undergoes a sudden increase in mobility. Using first-principles and molecular dynamics simulations, we found that the superionic transition in fluorite-structured FIC, which is characterized by …
Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review
2008
This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO 2 (a-SiO 2 ). The most common form of interstitial oxygen species is oxygen molecule (O 2 ), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial 0 2 provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O 2 in long-range oxygen transport in a-SiO 2 ; formation of the Frenkel defect pair (Si-Si bond and interstitial oxygen atom, 0°) by dense electronic excitation; efficient photolysis of interstitial O 2 into O° with F 2 laser light (λ= 157…
Microscopic theory of colloid formation in solids under irradiation
1996
Results of the first-principles study of diffusion-controlled aggregation of Frenkel defects-interstitial atoms-under irradiation of solids are presented. Conditions of the efficient radiation-induced aggregation of vacancies and interstitials are studied and the scenario of this process is presented.
<title>High-excitation-density luminescence as probe of mixed silver halides</title>
1992
Two kinds of intrinsic luminescence in mixed AgBr1-xClx (1 io. Dependence of the parameters of this process on crystal composition has been investigated in terms of spatially well correlated Frenkel defect recombinations. The main effect found was the linear increase of the Agio migration energy with the crystal composition x. The second kind of luminescence arising due to exciton molecules has been shown to be sensitive to the solid solution composition and the quality of a crystal. It is shown that this luminescence correlates with the optical losses of the fibers studied.
First-principles calculations of iodine-related point defects in CsPbI3
2019
Many thanks to A. Lushchik, A. Popov and R. Merkle for numerous fruitful discussions. This study was partly supported by the Latvian Council for Science (grant LZP-2018/1-0147 to EK). R.A.E acknowledges the assistance of the University Computer Center of Saint-Petersburg State University for high-performance computations.
Intrinsic defect formation in amorphousSiO2by electronic excitation: Bond dissociation versus Frenkel mechanisms
2008
Two competing mechanisms of intrinsic defect formation in amorphous ${\text{SiO}}_{2}$ $(a{\text{-SiO}}_{2})$, i.e., the vacancy-interstitial (Frenkel) mechanism and Si-O bond dissociation to form silicon and oxygen dangling bonds, were compared under $\ensuremath{\gamma}$-ray electronic excitation. The Frenkel mechanism was found to be dominant. The concentrations of both kinds of defects strongly correlate with the degree of the structural disorder of $a{\text{-SiO}}_{2}$, providing experimental evidence that both types of intrinsic defect pairs are formed mainly from the strained Si-O-Si bonds. The bond dissociation mechanism is more susceptible to the structural disorder than the vacanc…
Frenkel defect process in amorphous silica
2011
Point defects strongly influence optical properties of synthetic amorphous silica (synthetic a-SiO2) used in excimer laser photolithography and their properties are intensively studied. Decomposition of an Si-O-Si bond into a pair of oxygen vacancy and interstitial oxygen species is an intrinsic defect process in a-SiO2. It is similar to the creation of vacancy-interstitial pairs in crystalline materials and is regarded as "Frenkel defect process" in an amorphous material. Oxygens are also known to be emitted from a-SiO2 surfaces under irradiation with vacuumultraviolet (VUV) light or electron beam. However, the anion part of the Frenkel pair in a-SiO2, interstitial oxygen atom, lacks relia…
Discrete-lattice theory for Frenkel-defect aggregation in irradiated ionic solids
1998
Institut fu ¨r Physikalische und Theoretische Chemie, Technische Universitat Braunschweig, D-38106 Braunschweig, Germany~Received 11 September 1997; revised manuscript received 6 April 1998!A microscopic theory of diffusion-controlled aggregation of radiation Frenkel defects—called in ionic solidsH and F centers—is presented. This is based on a discrete-lattice formalism for the single defect densities~concentrations! and the coupled joint densities of similar and dissimilar defects treated in terms of a modifiedKirkwood superposition approximation. The kinetics of defect aggregation is studied in detail; the cooperativecharacter of this process for both types of complementary defects is sho…