Search results for "composition"

Mechanisms for the Dynamics of Phase Transformations

1984

An introductory review of the dynamics of (first- order) phase transitions is given. Concepts describing the initial stages of the transition, such as nucleation, spinodal decomposition (in the case of unmixing) are introduced, and their validity is critically discussed. The theoretical results are compared to recent computer simulations and pertinent experiments. Then the scaling concepts describing the late stages of domain growth are discussed, and open problems are outlined.

Alkaline cavities and tetrahedra in and solid solutions

1997

Seven different crystals were grown with 0 < x < 2 while seven different crystals were grown with , the limit value x = 1 corresponding to the clearly defined compound. A crystallographic study of these solid solutions was performed by comparison with the pure crystal. Structures were solved in the Pnma space group for the rubidium solid solutions and in the space group for the potassium ones. It was shown that the distribution of Cs and Rb, or Cs and K, among the two cationic sites called and was not random: Rb and K exhibit a higher affinity for the smallest cavity, the site. While the phase transition of and can be interpreted as rotations of the rigid tetrahedra mainly around the a dire…

Formation of Layers of Diverse Stoichiometric and Phase Composition in Lithium Tantalate Crystals at Treatment by Vapour Transport Equilibration

2012

Layers from tens to hundreds of microns thick of a different phase composition and stoichiometry are shown to form in lithium tantalate crystals subjected to treatment by vapor transport equilibration in lithium vapour. The 500 microns thick stoichiometric (Li/Ta ≈ 1) layers have ten times lower values of the coercive field compared with congruent lithium tantalate. As electrical measurements suggest, a new polar structure of phase transition at ∼120°C is possibly formed within a thin (30 μm) surface layer of the lithium tantalate sample after vapour transport equilibration treatment.

High Pressure Raman, Optical Absorption, and Resistivity Study of SrCrO4

2018

We studied the electronic and vibrational properties of monazite-type SrCrO4 under compression. The study extended the pressure range of previous studies from 26 to 58 GPa. The existence of two previously reported phase transitions was confirmed at 9 and 14 GPa, and two new phase transitions were found at 35 and 48 GPa. These transitions involve several changes in the vibrational and transport properties with the new high-pressure phases having a conductivity lower than that of the previously known phases. No evidence of chemical decomposition or metallization of SrCrO4 was detected. A tentative explanation for the reported observations is discussed.

Concurrent molecular dynamics simulation of spinodal phase transition on transputer arrays

1990

Abstract We describe a concurrent implementation on cost-effective transputer arrays of a molecular dynamics program to efficiently simulate physical systems consisting of thousands of mobile particles with an interaction range much shorter than the system dimensions. This program, which uses a geometric decomposition strategy and includes a distributed dynamic load balancer, has been extensively tested by simulating the two-dimensional spinodal phase separation of a large Lennard-Jones system.

Direct determination of total mercury in phosphate rock using alkaline fusion digestion

2014

The aim of this work was to develop a new method to determine the mercury (Hg) concentrations in phosphate rock using a dedicated analytical instrument (the DMA80 Tricell by Milestone) that employs an integrated sequence of thermal decomposition followed by catalyst conversion, amalgamation and atomic absorption spectrophotometry. However, this instrument underestimates Hg concentrations when phosphorite and apatite rocks are investigated with a classic thermal decomposition treatment that complies with US EPA method 7473. Therefore, to improve the recovery of total Hg, we performed alkaline fusion digestion (AFD) directly inside the furnace of the instrument, using BCR(32) as a certified r…

Photocurrent Spectroscopy Applied to the Characterization of Compositionally and Structurally Graded Materials: from Thin Films to Nanostructures

2010

Optical characterization of Mg-doped GaN films grown by metalorganic chemical vapor phase deposition

2000

Scanning electron microscopy, micro-Raman, and photoluminescence (PL) measurements are reported for Mg-doped GaN films grown on (0001) sapphire substrates by low-pressure metalorganic chemical vapor phase deposition. The surface morphology, structural, and optical properties of GaN samples with Mg concentrations ranging from 1019 to 1021 cm−3 have been studied. In the scanning micrographs large triangular pyramids are observed, probably due to stacking fault formation and three-dimensional growth. The density and size of these structures increase with the amount of magnesium incorporated in the samples. In the photoluminescence spectra, intense lines were found at 3.36 and 3.31 eV on the tr…

A new discretization for the polarizable continuum model within the domain decomposition paradigm

2016

International audience; We present a new algorithm to solve the polarizable continuum model equation in a framework compatible with the strategy previously developed by us for the conductor-like screening model based on Schwarz’s domain decomposition method (ddCOSMO). The new discretization is systematically improvable and is fully consistent with ddCOSMO so that it reproduces ddCOSMO results for large dielectric constants.

Implementation of analytic gradients for CCSD and EOM-CCSD using Cholesky decomposition of the electron-repulsion integrals and their derivatives: Th…

2019

We present a general formulation of analytic nuclear gradients for the coupled-cluster with single and double substitution (CCSD) and equation-of-motion (EOM) CCSD energies computed using Cholesky decomposition (CD) representations of the electron repulsion integrals. By rewriting the correlated energy and response equations such that the storage of the largest four-index intermediates is eliminated, CD leads to a significant reduction in disk storage requirements, reduced I/O penalties, and an improved parallel performance. CD thus extends the scope of the systems that can be treated by (EOM-)CCSD methods, although analytic gradients in the framework of CD are needed to extend the applicab…