Oxides and the high entropy regime: A new mix for engineering physical properties

MRS Advances ◽  
2020 ◽  
Vol 5 (64) ◽  
pp. 3419-3436 ◽  
Author(s):  
P. B. Meisenheimer ◽  
J. T. Heron
Keyword(s):  
Physical Properties ◽  
Degrees Of Freedom ◽  
Equilibrium Phase ◽  
Configurational Entropy ◽  
Oxide Materials ◽  
Spin Orbital ◽  
Metal Insulator ◽  
High Entropy ◽  
Thin Film Epitaxy

AbstractHistorically, the enthalpy is the criterion for oxide materials discovery and design. In this regime, highly controlled thin film epitaxy can be leveraged to manifest bulk and interfacial phases that are non-existent in bulk equilibrium phase diagrams. With the recent discovery of entropy-stabilized oxides, entropy and disorder engineering has been realized as an orthogonal approach. This has led to the nucleation and rapid growth of research on high-entropy oxides – multicomponent oxides where the configurational entropy is large but its contribution to its stabilization need not be significant or is currently unknown. From current research, it is clear that entropy enhances the chemical solubility of species and can realize new stereochemical configurations which has led to the rapid discovery of new phases and compositions. The research has expanded beyond studies to understand the role of entropy in stabilization and realization of new crystal structures to now include physical properties and the roles of local and global disorder. Here, key observations made regarding the dielectric and magnetic properties are reviewed. These materials have recently been observed to display concerted symmetry breaking, metal-insulator transitions, and magnetism, paving the way for engineering of these and potentially other functional phenomena. Excitingly, the disorder in these oxides allows for new interplay between spin, orbital, charge, and lattice degrees of freedom to design the physical behavior. We also provide a perspective on the state of the field and prospects for entropic oxide materials in applications considering their unique characteristics.

scholarly journals Settling the matter of the role of vibrations in the stability of high-entropy carbides

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Marco Esters ◽  
Corey Oses ◽  
David Hicks ◽  
Michael J. Mehl ◽  
Michal Jahnátek ◽  
...  
Keyword(s):  
Chemical Stability ◽  
Nearest Neighbor ◽  
Configurational Entropy ◽  
New Materials ◽  
Decomposition Products ◽  
Thermodynamic Characterization ◽  
High Entropy ◽  
Significant Interest ◽  
The Stability

AbstractHigh-entropy ceramics are attracting significant interest due to their exceptional chemical stability and physical properties. While configurational entropy descriptors have been successfully implemented to predict their formation and even to discover new materials, the contribution of vibrations to their stability has been contentious. This work unravels the issue by computationally integrating disorder parameterization, phonon modeling, and thermodynamic characterization. Three recently synthesized carbides are used as a testbed: (HfNbTaTiV)C, (HfNbTaTiW)C, and (HfNbTaTiZr)C. It is found that vibrational contributions should not be neglected when precursors or decomposition products have different nearest-neighbor environments from the high-entropy carbide.

Molecular Theories of Rubberlike Elasticity and Polymer Viscoelasticity

1972 ◽  
Vol 45 (3) ◽  
pp. 638-666 ◽  
Author(s):  
Mitchel Shen ◽  
William F. Hall ◽  
Roger E. Dewames
Keyword(s):  
Physical Properties ◽  
Configurational Entropy ◽  
Polymer Chains ◽  
Elastic Response ◽  
Linear Polymers ◽  
Polymer Molecules ◽  
Recent Developments ◽  
Conformational Statistics ◽  
Polymer Viscoelasticity

Abstract The foundation for nearly all the molecular theories of the physical properties of polymers was laid in 1934 when Guth and Mark and Kuhn first recognized the role of configurational entropy of polymer chains. By virtue of ability of their segments to rotate with respect to each other along the chain backbone, macromolecules are capable of assuming a myriad of conformations. It is this long, flexible chain nature of polymer molecules that provides us a link in interpreting the macroscopic physical properties in terms of microscopic molecular dynamics. In this review we shall demonstrate the utilization of conformational statistics in the formulation of molecular theories for two important aspects of the mechanical properties of polymers. The first part deals with the equilibrium elastic response of a crosslinked rubberlike network. A simplified derivation will be given on the basis of the entropic approach. Some of the underlying assumptions will then be examined, and the contribution of internal energy to rubber elasticity scrutinized. The second part describes the transient viscoelastic properties of linear polymers in solution and in bulk. Limitations of the model will be assessed and its applications to experimental data explored. It should be pointed out that a number of reviews are available in the literature both for elasticity and viscoelasticity of polymers. The present work is not an exhaustive review of these fields, but rather concentrates on the more recent developments not previously discussed. The emphasis will be placed upon polymers in the bulk state, although solution properties will be mentioned where appropriate.

scholarly journals Is Configurational Entropy the Main Stabilizing Term in Rock-Salt Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O High-Entropy Oxide?

2021 ◽  
Author(s):  
Martina Fracchia ◽  
Mauro Coduri ◽  
Maela Manzoli ◽  
Paolo Ghigna ◽  
Umberto Anselmi-Tamburini
Keyword(s):  
Solid Solution ◽  
Rock Salt ◽  
Single Phase ◽  
Configurational Entropy ◽  
Rock Salt Structure ◽  
High Entropy ◽  
Reversible Transformation ◽  
Salt Structure ◽  
Cubic Structure

We question the conclusions reported in the paper "Entropy-stabilized Oxides, by C. Rost et al., by looking into the role of configurational entropy as the stabilization of the rock-salt cubic structure of the Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (HEO) solid solution (SS). First, we demonstrate that configurational entropy can be reduced from 1.61R for HEO to 0.5R for a two-member SS, still obtaining a single-phase material if the molar fractions of ZnO and CuO are 0.2. These SSs behave identically as HEO regarding the reversible transformation between a multi- and single-phase states when temperatures are cycled between 800 and 1000 °C. Second, we demonstrate that the different SSs presenting a configurational entropy significantly lower than HEO, are less prone to the cubic to tetragonal structural distortion, suggesting that the configurational entropy has not the central role as stabilizing factor of the rock-salt structure.<br>

scholarly journals Is Configurational Entropy the Main Stabilizing Term in Rock-Salt Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O High-Entropy Oxide?

2021 ◽  
Author(s):  
Martina Fracchia ◽  
Mauro Coduri ◽  
Maela Manzoli ◽  
Paolo Ghigna ◽  
Umberto Anselmi-Tamburini
Keyword(s):  
Solid Solution ◽  
Rock Salt ◽  
Single Phase ◽  
Configurational Entropy ◽  
Rock Salt Structure ◽  
High Entropy ◽  
Reversible Transformation ◽  
Salt Structure ◽  
Cubic Structure

We question the conclusions reported in the paper "Entropy-stabilized Oxides, by C. Rost et al., by looking into the role of configurational entropy as the stabilization of the rock-salt cubic structure of the Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O (HEO) solid solution (SS). First, we demonstrate that configurational entropy can be reduced from 1.61R for HEO to 0.5R for a two-member SS, still obtaining a single-phase material if the molar fractions of ZnO and CuO are 0.2. These SSs behave identically as HEO regarding the reversible transformation between a multi- and single-phase states when temperatures are cycled between 800 and 1000 °C. Second, we demonstrate that the different SSs presenting a configurational entropy significantly lower than HEO, are less prone to the cubic to tetragonal structural distortion, suggesting that the configurational entropy has not the central role as stabilizing factor of the rock-salt structure.<br>

scholarly journals Review on quasi-2D square planar nickelates

CrystEngComm ◽  
2021 ◽  
Author(s):  
Junjie Zhang ◽  
Xutang Tao
Keyword(s):  
Physical Properties ◽  
Degrees Of Freedom ◽  
Insulator Transition ◽  
Strongly Correlated ◽  
Metal Insulator Transition ◽  
Metal Insulator ◽  
Strongly Correlated Materials ◽  
Square Planar ◽  
Magnetic Resistance

In strongly correlated materials, lattice, charge, spin and orbital degrees of freedom interact with each other, leading to emergent physical properties such as superconductivity, colossal magnetic resistance and metal-insulator transition....

Layered High-Entropy Oxide Structures for Reversible Energy Storage

2020 ◽  
Author(s):  
Junbo Wang ◽  
Yanyan Cui ◽  
Qingsong Wang ◽  
Kai Wang ◽  
Xiaohui Wang ◽  
...  
Keyword(s):  
Energy Storage ◽  
Cathode Material ◽  
Spray Pyrolysis ◽  
Lattice Structure ◽  
Oxide Materials ◽  
High Entropy ◽  
New Class ◽  
Nebulized Spray Pyrolysis

<p>Layered Li<i><sub>x</sub></i>MO<sub>2</sub> materials, a new class of high-entropy oxides, have been synthesized by nebulized spray pyrolysis. Specifically, the lattice structure of Li(Ni<sub>1/3</sub>Mn<sub>1/3</sub>Co<sub>1/3</sub>)O<sub>2</sub> (NCM111) cathode material has been replicated successfully while increasing the number of cations in equimolar proportions, thereby allowing transition to high-entropy oxide materials.</p>

On the Use of Quantum Thermal Bath in Unimolecular Fragmentation Simulations

2019 ◽  
Author(s):  
Riccardo Spezia ◽  
Hichem Dammak
Keyword(s):  
Degrees Of Freedom ◽  
Molecular Simulations ◽  
Zero Point ◽  
Thermal Bath ◽  
Unimolecular Dissociation ◽  
Point Energy ◽  
Rotational Degrees Of Freedom ◽  
The Difference ◽  
Nuclear Effects

<div> <div> <div> <p>In the present work we have investigated the possibility of using the Quantum Thermal Bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is aimed in introducing quantum nuclear effects with a com- putational time which is basically the same as in newtonian simulations. At this end we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model a microcanonical algorithm which monitor zero-point energy of products, and eventually modifies tra- jectories, was recently proposed. We have thus compared classical and quantum rate constant with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study unimolecular fragmentation of much complex systems with molecular simulations. The role of QTB thermostat on rotational degrees of freedom is also analyzed and discussed. </p> </div> </div> </div>

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