Arrays of ultrathin monocrystalline submicrometer-sized Fe dots: Néel–Brown relaxation and activation volume

1999 ◽  
Vol 86 (2) ◽  
pp. 1028-1034 ◽  
Author(s):  
J.-E. Wegrowe ◽  
O. Fruchart ◽  
J.-P. Nozières ◽  
D. Givord ◽  
F. Rousseaux ◽  
...  
Keyword(s):  
Activation Volume ◽  
Brown Relaxation

Under Pressure: Mechanochemical Effects on Structure and Ion Conduction in the Sodium-Ion Solid Electrolyte Na3PS4

2020 ◽  
Author(s):  
Theodosios Famprikis ◽  
O. Ulas Kudu ◽  
James Dawson ◽  
Pieremanuele Canepa ◽  
François Fauth ◽  
...  
Keyword(s):  
Ionic Conductivity ◽  
Mechanochemical Synthesis ◽  
Activation Volume ◽  
External Pressure ◽  
Sodium Ion ◽  
Variable Pressure ◽  
Ion Conductor ◽  
Ceramic Synthesis ◽  
Solid State Batteries ◽  
Fast Ion

<div> <p>Fast-ion conductors are critical to the development of solid-state batteries. The effects of mechanochemical synthesis that lead to increased ionic conductivity in an archetypical sodium-ion conductor Na<sub>3</sub>PS<sub>4</sub> are not fully understood. We present here a comprehensive analysis based on diffraction (Bragg, pair distribution function), spectroscopy (impedance, Raman, NMR, INS) and <i>ab-initio</i> simulations aimed at elucidating the synthesis-property relationships in Na<sub>3</sub>PS<sub>4</sub>. We consolidate previously reported interpretations about the local structure of ball-milled samples, underlining the sodium disorder and showing that a local tetragonal framework more accurately describes the structure than the originally proposed cubic one. Through variable-pressure impedance spectroscopy measurements, we report for the first time the activation volume for Na<sup>+</sup> migration in Na<sub>3</sub>PS<sub>4</sub>, which is ~30% higher for the ball-milled samples. Moreover, we show that the effect of ball-milling on increasing the ionic conductivity of Na<sub>3</sub>PS<sub>4</sub> to ~10<sup>-4</sup> S/cm can be reproduced by applying external pressure on a sample from conventional high temperature ceramic synthesis. We conclude that the key effects of mechanochemical synthesis on the properties of solid electrolytes can be analyzed and understood in terms of pressure, strain and activation volume.</p> </div>

Electrical conductivity studies on silica phases and the effects of phase transformation

2019 ◽  
Vol 104 (12) ◽  
pp. 1800-1805
Author(s):  
George M. Amulele ◽  
Anthony W. Lanati ◽  
Simon M. Clark
Keyword(s):  
Electrical Conductivity ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Hydrogen Charge ◽  
Charge Compensation ◽  
Composition Analysis ◽  
Conductivity Measurements ◽  
Pressure System ◽  
Electrical Conductivities ◽  
Silica Phases

Abstract Starting with the same sample, the electrical conductivities of quartz and coesite have been measured at pressures of 1, 6, and 8.7 GPa, respectively, over a temperature range of 373–1273 K in a multi-anvil high-pressure system. Results indicate that the electrical conductivity in quartz increases with pressure as well as when the phase change from quartz to coesite occurs, while the activation enthalpy decreases with increasing pressure. Activation enthalpies of 0.89, 0.56, and 0.46 eV, were determined at 1, 6, and 8.7 GPa, respectively, giving an activation volume of –0.052 ± 0.006 cm3/mol. FTIR and composition analysis indicate that the electrical conductivities in silica polymorphs is controlled by substitution of silicon by aluminum with hydrogen charge compensation. Comparing with electrical conductivity measurements in stishovite, reported by Yoshino et al. (2014), our results fall within the aluminum and water content extremes measured in stishovite at 12 GPa. The resulting electrical conductivity model is mapped over the magnetotelluric profile obtained through the tectonically stable Northern Australian Craton. Given their relative abundances, these results imply potentially high electrical conductivities in the crust and mantle from contributions of silica polymorphs. The main results of this paper are as follows:The electrical conductivity of silica polymorphs is determined by impedance spectroscopy up to 8.7 GPa.The activation enthalpy decreases with increasing pressure indicating a negative activation volume across the silica polymorphs.The electrical conductivity results are consistent with measurements observed in stishovite at 12 GPa.

scholarly journals Dislocation-mediated shear amorphization in boron carbide

2021 ◽  
Vol 7 (8) ◽  
pp. eabc6714 ◽  
Author(s):  
Kolan Madhav Reddy ◽  
Dezhou Guo ◽  
Shuangxi Song ◽  
Chun Cheng ◽  
Jiuhui Han ◽  
...  
Keyword(s):  
Boron Carbide ◽  
Structural Transition ◽  
Activation Volume ◽  
Structural Evolution ◽  
Dislocation Nucleation ◽  
Superhard Materials ◽  
Rate Dependent ◽  
Transmission Electron ◽  
Lower Activation ◽  
Underlying Mechanisms

The failure of superhard materials is often associated with stress-induced amorphization. However, the underlying mechanisms of the structural evolution remain largely unknown. Here, we report the experimental measurements of the onset of shear amorphization in single-crystal boron carbide by nanoindentation and transmission electron microscopy. We verified that rate-dependent loading discontinuity, i.e., pop-in, in nanoindentation load-displacement curves results from the formation of nanosized amorphous bands via shear amorphization. Stochastic analysis of the pop-in events reveals an exceptionally small activation volume, slow nucleation rate, and lower activation energy of the shear amorphization, suggesting that the high-pressure structural transition is activated and initiated by dislocation nucleation. This dislocation-mediated amorphization has important implications in understanding the failure mechanisms of superhard materials at stresses far below their theoretical strengths.

scholarly journals Activation volume for arsenic diffusion in germanium

1996 ◽  
Vol 69 (7) ◽  
pp. 922-924 ◽  
Author(s):  
Salman Mitha ◽  
Michael J. Aziz ◽  
David Schiferl ◽  
David B. Poker
Keyword(s):  
Activation Volume

THE STRUCTURE OF AGGREGATES AND THE MOLECULAR KINEMATICS OF THE VISCOSITY OF A BERNAL LIQUID

1964 ◽  
Vol 42 (2) ◽  
pp. 304-320 ◽  
Author(s):  
F. W. Smith
Keyword(s):  
Coordination Number ◽  
Free Volume ◽  
Activation Volume ◽  
Molecular Volume ◽  
3 Dimensional ◽  
Theory Of Liquids ◽  
Kinetic Pressure ◽  
Steel Balls ◽  
Set Of Points ◽  
Structure Of Aggregates

The structure of 3-dimensional aggregates is discussed as a set of points on which graphs are constructed. By constructing the Voronoi honeycomb (Dirichlet regions) for the points and applying a small "irregularizing transformation", a "simplicial graph" and a "primitive coordination number" (whose value is close to 14 for all aggregates) can be defined universally for both regular and irregular aggregates. Recent studies of the geometry of irregular aggregates (of steel balls, crystal grains, etc.) are reviewed. The theory of liquids of J. D. Bernal is discussed and the simplicial graph is used to show that the "activation volume" of a Bernal liquid is about one-tenth of the molecular volume. The kinematics of flow of aggregates is discussed in terms of their graphs and in terms of a process of "volume exchange"—the production and destruction of free volume. Using these concepts, an equation is derived for the viscosity of a Bernal liquid as a product of five terms expressing respectively the kinematic, stoichiometric, kinetic, pressure-dependent, and shear-dependent factors.

Towards constraining Mars' thermal evolution using machine learning

2021 ◽  
Author(s):  
Siddhant Agarwal ◽  
Nicola Tosi ◽  
Pan Kessel ◽  
Sebastiano Padovan ◽  
Doris Breuer ◽  
...  
Keyword(s):  
Activation Energy ◽  
Enrichment Factor ◽  
Activation Volume ◽  
Initial Conditions ◽  
Thermal Evolution ◽  
Diffusion Creep ◽  
Dynamic Simulations ◽  
Mixture Density ◽  
Lithospheric Thickness ◽  
Mantle Temperature

&lt;p&gt;The thermal evolution of terrestrial planets depends strongly on several parameters and initial conditions that are poorly constrained. Often, direct or indirect observables from planetary missions such as elastic lithospheric thickness, crustal thickness and duration of volcanism are inverted to infer the unknown parameter values and initial conditions. The non-uniqueness and non-linearity of this inversion necessitates a probabilistic inversion framework. However, due to the expensive nature of forward dynamic simulations of thermal convection , Markov Chain Monte Carlo methods are rarely used. To address this shortcoming, some studies have recently shown the effectiveness of Mixture Density Networks (MDN) (Bishop 1995) in being able to approximate the posterior probability using only the dataset of simulations run prior to the inversion (Meier et al. 2007, de Wit et al. 2013, K&amp;#228;ufl et al. 2016, Atkins et al. 2016).&lt;/p&gt;&lt;p&gt;Using MDNs, we systematically isolate the degree to which a parameter can be constrained using different &amp;#8220;present-day&amp;#8221; synthetic observables from 6130 simulations for a Mars-like planet. The dataset &amp;#8211; generated using the mantle convection code GAIA (H&amp;#252;ttig et al. 2013)- is the same as that used by Agarwal et al. (2020) for a surrogate modelling study.&lt;/p&gt;&lt;p&gt;The loss function used to optimize the MDN (log-likelihood) provides a single robust quantity that can be used to measure how well a parameter can be constrained. We test different numbers and combinations of observables (heat flux at the surface and core-mantle boundary, radial contraction, melt produced, elastic lithospheric thickness, and duration of volcanism) to constrain the following parameters: reference viscosity, activation energy and activation volume of the diffusion creep rheology, an enrichment factor for radiogenic elements in the crust, and initial mantle temperature. If all observables are available, reference viscosity can be constrained to within 32% of its entire range (10&lt;sup&gt;19&lt;/sup&gt;&amp;#8722;10&lt;sup&gt;22&lt;/sup&gt; Pa s), crustal enrichment factor (1&amp;#8722;50) to within 15%, activation energy (10&lt;sup&gt;5&lt;/sup&gt;&amp;#8722;5&amp;#215;10&lt;sup&gt;5&lt;/sup&gt; J mol-1 ) to within 80%, and initial mantle temperature (1600&amp;#8722;1800K) to within 39%. The additional availability of the full present-day temperature profile or parts of it as an observable tightens the constraints further. The activation volume (4&amp;#215;10&lt;sup&gt;-6&lt;/sup&gt; &amp;#8722;10&amp;#215;10&lt;sup&gt;-6&lt;/sup&gt;&amp;#160; m&lt;sup&gt;3&lt;/sup&gt; mol&lt;sup&gt;-1&lt;/sup&gt;) cannot be constrained and requires research into new observables in space and time, as well as fields other than just temperature. Testing different levels of uncertainty (simulated using Gaussian noise) in the observables, we found that constraints on different parameters loosen at different rates, with initial temperature being the most sensitive. Finally, we present how the marginal MDN proposed by Bishop (1995) can be modified to model the joint probability for all parameters, so that&amp;#160; the inter-parameter correlations and the associated degeneracy can be capture, thereby providing a more comprehensive picture of all the evolution scenarios that fit given observational constraints.&lt;/p&gt;

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