Configurational entropy of binary silicate solid solutions

Abstract Rock-salt scandium nitride has gained interest due to its thermoelectric properties including a relatively high Seebeck coefficient. This motivates research for other semiconductor materials that exhibit similar electronic structure features as ScN. Using density functional theory calculations, we have studied disordered solid solutions of (Zr0.5, Mg0.5)N and (Hf0.5, Mg0.5)N using the special quasi-random structure model. The results show that within a mean-field approximation for the configurational entropy, the order–disorder phase transformation between the monoclinic LiUN2 prototype structure and the rock-salt cubic random alloy of these mentioned solid solutions occur at 740 K and 1005 K for (Zr0.5, Mg0.5)N and (Hf0.5, Mg0.5)N, respectively. The density-of-states for the two ternary compounds is also calculated and predicts semiconducting behavior with band gaps of 0.75 eV for (Zr0.5, Mg0.5)N and 0.92 eV for (Hf0.5, Mg0.5)N. The thermoelectric properties of both compounds are also predicted. We find that in the range of a moderate change in the Fermi level, a high Seebeck coefficient value at room temperature can be achieved.

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The configurational entropy of mixing of interstitials solid solutions

Applied Physics Letters ◽

10.1063/1.3400221 ◽

2010 ◽

Vol 96 (16) ◽

pp. 161904 ◽

Cited By ~ 7

Author(s):

Jorge Garcés

Keyword(s):

Solid Solutions ◽

Configurational Entropy ◽

Entropy Of Mixing

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Thermodynamic and Structural Modelling of Non-Stoichiometric Ln-Doped UO2 Solid Solutions,Ln = {La, Pr, Nd, Gd}

Frontiers in Chemistry ◽

10.3389/fchem.2021.705024 ◽

2021 ◽

Vol 9 ◽

Author(s):

Victor L. Vinograd ◽

Andrey A. Bukaemskiy ◽

G. Modolo ◽

G. Deissmann ◽

D. Bosbach

Keyword(s):

Solid Solutions ◽

Thermodynamic Model ◽

Structural Model ◽

Chemical Potential ◽

Configurational Entropy ◽

Lattice Parameter ◽

Lattice Contraction ◽

Coordination Numbers ◽

Ideal Mixing ◽

The One

Available data on the dependence of the equilibrium chemical potential of oxygen on degrees of doping, z, and non-stoichiometry, x, y, in U1-zLnzO2+0.5(x-y) fluorite solid solutions and data on the dependence of the lattice parameter, a, on the same variables are combined within a unified structural-thermodynamic model. The thermodynamic model fits experimental isotherms of the oxygen potential under the assumptions of a non-ideal mixing of the endmembers, UO2, UO2.5, UO1.5, LnO1.5, and Ln0.5U0.5O2, and of a significant reduction in the configurational entropy arising from short-range ordering (SRO) within cation-anion distributions. The structural model further investigates the SRO in terms of constraints on admissible values of cation coordination numbers and, building on these constraints, fits the lattice parameter as a function of z, y, and x. Linking together the thermodynamic and structural models allows predicting the lattice parameter as a function of z, T and the oxygen partial pressure. The model elucidates contrasting structural and thermodynamic changes due to the doping with LaO1.5, on the one hand, and with NdO1.5 and GdO1.5, on the other hand. An increased oxidation resistance in the case of Gd and Nd is attributed to strain effects caused by the lattice contraction due to the doping and to an increased thermodynamic cost of a further contraction required by the oxidation.

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Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle

Minerals ◽

10.3390/min10040330 ◽

2020 ◽

Vol 10 (4) ◽

pp. 330

Author(s):

Wendy R. Panero ◽

Razvan Caracas

Keyword(s):

Solid Solutions ◽

Lower Mantle ◽

Density Functional ◽

Bulk Composition ◽

Site Occupancy ◽

Configurational Entropy ◽

Density Functional Theory Calculations ◽

Earth’S Mantle ◽

Stability Structure ◽

The Stability

The degree to which the Earth’s mantle stores and cycles water in excess of the storage capacity of nominally anhydrous minerals is dependent upon the stability of hydrous phases under mantle-relevant pressures, temperatures, and compositions. Two hydrous phases, phase D and phase H, are stable to the pressures and temperatures of the Earth’s lower mantle, suggesting that the Earth’s lower mantle may participate in the cycling of water. We build on our prior work of density functional theory calculations on phase H with the stability, structure, and bonding of hydrous phases D, and we predict the aluminum partitioning with H in the Al 2 O 3 -SiO 2 -MgO-H 2 O system. We address the solid solutions through a statistical sampling of site occupancy and calculation of the partition function from the grand canonical ensemble. We show that each phase has a wide solid solution series between MgSi 2 O 6 H 2 -Al 2 SiO 6 H 2 and MgSiO 4 H 2 -2 δ AlOOH + SiO 2 , in which phase H is more aluminum rich than phase D at a given bulk composition. We predict that the addition of Al to both phases D and H stabilizes each phase to higher temperatures through additional configurational entropy. While we have shown that phase H does not exhibit symmetric hydrogen bonding at high pressure, we report here that phase D undergoes a gradual increase in the number of symmetric H-bonds beginning at ∼30 GPa, and it is only ∼50% complete at 60 GPa.

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The Poly-Substituted M-Type Hexaferrite Crystals Growth

Materials Science Forum ◽

10.4028/www.scientific.net/msf.946.186 ◽

2019 ◽

Vol 946 ◽

pp. 186-191 ◽

Cited By ~ 6

Author(s):

O.V. Zaitseva ◽

D.A. Vinnik ◽

Evgeny A. Trofimov

Keyword(s):

Solid Solutions ◽

Configurational Entropy ◽

Crystalline Solid ◽

Structural Stabilization ◽

High Entropy ◽

Crystal Matrix ◽

Composition And Structure ◽

Ferrite Structure ◽

Oxide Phases ◽

Matrix Components

In the presented article the possibility analysis of highly entropic oxide phases composition and structure formation was performed. Moreover, the studies devoted to the production of substituted single crystals with the M-type hexa-ferrite structure were carried out. The experiments were conducted to studying the possibility of obtaining oxide high-entropy crystalline solid solutions with the M-type hexa-ferrites structure. As the result of the crystallized samples investigation, the microcrystalline highly entropic Ba (Fe,Mn,Ni,Ti,Al)12O19 and (Ba,Pb,Sr)(Fe,Mn,Ti,Ni,Al)12O19 phases appearing was detected. Based on the obtained data, it is possible to consider that the poly-substituted crystals growth with M-type hexa-ferrite structure. The structural stabilization is promoted by high values of the configurational entropy of the crystal matrix components mixing.

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