Search results for "defect"
showing 10 items of 879 documents
Structural and vibrational properties of CdAl2S4 under high pressure: Experimental and theoretical approach
2014
The behavior of defect chalcopyrite CdAl2S4 at high pressures and ambient temperature has been investigated in a joint experimental and theoretical study. High-pressure X-ray diffraction and Raman scattering measurements were complemented with theoretical ab initio calculations. The equation of state and pressure dependences of the structural parameters of CdAl2S4 were determined and compared to those of other AB(2)X(4) ordered-vacancy compounds. The pressure dependence of the Raman-active mode frequencies is reported, as well as the theoretical phonon dispersion curves and phonon density of states at 1 atm. Our measurements suggest that defect chalcopyrite CdAl2S4 undergoes a phase transit…
Linker depletion for missing cluster defects in non-UiO Metal-Organic Frameworks
2021
Defect engineering is a valuable tool to tune the properties of metal–organic frameworks. However, defect chemistry remains still predominantly limited to UiO-type MOFs. We describe the preferential formation of missing cluster defects in heterometallic titanium–organic frameworks of the MUV-10 family when synthesised in sub-stoichiometric linker conditions. Our results show the value of integrating experimental work, computational modelling and thorough characterization in rationalizing the impact of defects over the porosity and structure of this family of materials. Correlation of experiment with computational models reveals the dominance of missing cluster vacancies in the pore size dis…
Optimization of impurity profile for p-n junction in heterostructures
2005
We analyze the dopant diffusion in p-n-junction in heterostructure, by solving the diffusion equation with space-varying diffusion coefficient. For a step-wise spatial distribution we find the optimum annealing time to decrease the p-n-junction thickness and to increase the homogeneity of impurity concentration in p or n regions.
Kinetics of dimer F2 type center annealing in MgF2 crystals
2018
Authors are greatly indebted to V. Lisitsyn, A. Ch. Lushchik and R.Vila for stimulating discussions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The calculations were performed using facilities of the Stuttgart Supercomputer Center (project DEFTD 12939).
<title>Thermostimulated electronic and ionic processes in irradiated sapphire</title>
2003
Electronic and ionic thermostimulated (TS) relaxation (TSR) processes in nominally pure sapphire (α-Al2O3 grown with oxygen deficiency) have been investigated at 290 - 650 K by means of the TS current (TSC), ionic depolarization current (TSDC) and electron emission (TSEE) techniques. After thermal (ionic) polarization of the reduced sapphire wide (approximately 75 K) and asymmetric ionic dipolar TSDC peak at 590 K (disorientation of the anion vacancy-related dipoles) was detected. Above 450 - 500 K the anion vacancy hopping (migration) starts and their interaction with defects take place. This can lead to lattice dynamic disordering and anion vacancy diffusion-controlled processes in sapphi…
Immediate implants following tooth extraction. A systematic review
2012
Objectives: The aim of this article is to review the current state of immediate implants, with their pros and contras, and the clinical indications and contraindications. Material and Methods: An exhaustive literature search has been carried out in the COCHRANE library and MEDLINE electronic databases from 2004 to November 2009. Randomized clinical trials and clinical trials focused on single implants placed in fresh extraction sockets were included and compared. A meta-analysis could not be performed due to heterogeneity of the data. Results: Twenty studies out of 135 articles from the initial search were finally included, which summed up a total of 1139 immediate implants with at least a …
Hydration entropy of BaZrO3 from first principles phonon calculations
2015
The impact of phonons on the hydration and defect thermodynamics of undoped and acceptor (Sc, In, Y and Gd) doped BaZrO3 is addressed by means of first principles supercell calculations. In contrast to previous, similar investigations, we evaluate contributions from all phonon modes, and also pressure/volume effects on the phonon properties. The calculations are performed at the GGA-level with the PBE and RPBE functionals, both of which predict for BaZrO3 a stable cubic perovskite structure. For all dopants, the vibrational formation entropy of the doubly positively charged oxygen vacancy is significantly lower than that of the protonic defect , which therefore also is the dominant contribu…
The aristaless (Arx) gene: one gene for many "interneuronopathies".
2009
The ARX (Aristaless-related (X-linked) homeobox) gene is not only present in arthropods and their ancestors, but also in vertebrates including humans (ARX orthologs). The gene is composed of 5 coding exons and it is expressed predominantly in foetal and adult brain and skeletal muscle. In this review we report on our experience and review the existing literature on the genotype and phenotype heterogeneity associated with ARX abnormalities in humans ranging from severe neuronal migration defects (e.g., lissencephaly), to mild forms of X-linked mental retardation without apparent brain abnormalities. The ARX-related disorders are reviewed focusing on their clinical features and on the role of…
Behavior of gap solitons in anharmonic lattices
2017
International audience; Using the theory of bifurcation, we provide and find gap soliton dynamics in a nonlinear Klein-Gordon model with anharmonic, cubic, and quartic interactions immersed in a parametrized on-site substrate potential. The case of a deformable substrate potential allows theoretical adaptation of the model to various physical situations. Nonconvex interactions in lattice systems lead to a number of interesting phenomena that cannot be produced with linear coupling alone. By investigating the dynamical behavior and bifurcations of solutions of the planar dynamical systems, we derive a variety of exotic solutions corresponding to the phase trajectories under different paramet…
Solid-state diffusion phenomena in heterogeneous gas-solid reactions : Application to oxides sulfidation
2018
Phase transition phenomena involving the mobility of the reaction interface are involved in a wide variety of chemical reactions and applications. A good example is the sulfidation reaction experienced by the metal oxide-based materials used in the framework of gas purification or catalysts preparation applications. These reactions involve solid-state diffusion phenomena of the reactive species (atomic or ionic form) through the layer of product formed during the reaction (oxide, sulfide, or metal phase). In many cases, solid-state diffusion has a direct impact on the reaction mechanisms while determining the growth direction of the formed phases, as well as the overall kinetics of the reac…