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Журнал структурной химии  / №2 2016

PEROVSKITE SOLID SOLUTIONS — A MONTE CARLO STUDY OF THE DEEP EARTH ANALOGUE (K, Na)MgF3 (300,00 руб.)

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Первый авторTealdi
АвторыLavrentiev M.Yu., Mohn C.E., Allan N.L.
Страниц9
ID364677
АннотацияUnderstanding the behaviour of solid solutions over wide ranges of temperature and pressure remains a major challenge to both theory and experiment. Here we report a detailed exchange Monte Carlo study using a classical ionic model of the model perovskite parascandolaiteneighborite (K,Na)MgF3 solid solution and its end-members for temperatures in the range 300—1000 K and pressures from 0—8 GPa. Full account is taken of the local environment of the individual cations, clustering and thermal effects. Properties considered include the crystal structure, phase transitions, the thermodynamics of mixing and the non-ideality of the solid solution. Clustering of the potassium ions is examined via a short-range order parameter. Where experimental data are available for comparison, agreement is very good.
PEROVSKITE SOLID SOLUTIONS — A MONTE CARLO STUDY OF THE DEEP EARTH ANALOGUE (K, Na)MgF3 / C. Tealdi [и др.] // Журнал структурной химии .— 2016 .— №2 .— С. 45-53 .— URL: https://rucont.ru/efd/364677 (дата обращения: 08.12.2021)

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Here we report a detailed exchange Monte Carlo study using a classical ionic model of the model perovskite parascandolaiteneighborite (K,Na)MgF3 solid solution and its end-members for temperatures in the range 300—1000 K and pressures from 0—8 GPa. <...> Full account is taken of the local environment of the individual cations, clustering and thermal effects. <...> Properties considered include the crystal structure, phase transitions, the thermodynamics of mixing and the non-ideality of the solid solution. <...> Clustering of the potassium ions is examined via a short-range order parameter. <...> INTRODUCTION Solid solutions and phase stability continue to present considerable challenges for theory. <...> Energy differences between different phases can be small and subtle cation ordering effects can be often crucial in determining phase stability and thermodynamic and chemical properties. <...> This solution is not only an excellent test of any theoretical model, but also serves as a useful analogue for the silicate perovskite (Mg, Fe)(Al,Si)O3, which is a dominant phase under the conditions of the lower mantle of the Earth (pressure > 25 GPa, temperature > 2000 K) [ 1—4]. <...> Neighborite NaMgF3 [ 11 ] is isoelectronic and isostructural with MgSiO3; the ratios of the formal cation charges are the same in both compounds (1:2) and the ratio of their ionic radii are about the same. <...> KMgF3 was until very recently known only as a synthetic crystal but has now been identified as the new mineral parascandolaite, found as a volcanic sublimate at Vesuvius [ 12 ]. <...> KMgF3 is a cubic perovskite (Fig. 1, a), while in NaMgF3 there is an orthorhombic distortion such that the Mg—F—Mg bridges linking the MgF6 octahedra are not linear (Fig. 1, b). <...> Cubic perovskite structure AMF3 (a), Representative tilting of MF6 octahedra in an orthorhombic perovskite (b) rules (the so-called ™tolerance factor™) is possible [ 13, 14 ]. <...> The Na+ cation is too small to touch the twelve neighbouring anions in a cubic structure and the Mg—F—Mg links bend, tilting the MgF6 octahedra to bring further anions into contact with the A cations. <...> An extensive NMR and X-ray diffraction study of the effect of the A-site cation radius on the ordering of BX6 octahedra in (K,Na)MgF3 <...>