Structure of liquid equiatomic KSn and CsSn

Reijers, H. T. J.; Saboungi, Marie‐Louise; Price, David L.; Lugt, W. van der

doi:10.1103/physrevb.41.5661

Cited by 26 publications

(15 citation statements)

References 33 publications

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“…Nevertheless we propose that this method of extracting chain lengths from RMC modeling of total scattering data may prove valuable for identifying other molten chemical species, especially if the cluster of interest is small. Early total scattering studies found signatures of Zintl polyanions in the A-Sn, and A-Te systems − (where A is an alkali metal), both of which are viable fluxes for crystal growth. ,, Constraints on the number of distinct anion coordinations might be gleaned from X-ray absorption spectroscopy or nuclear magnetic resonance, although the latter is not straightforward for sulfides …”

Section: Resultsmentioning

confidence: 99%

Understanding Fluxes as Media for Directed Synthesis: In Situ Local Structure of Molten Potassium Polysulfides

et al. 2012

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Rational exploratory synthesis of new materials requires routes to discover novel phases and systematic methods to tailor their structures and properties. Synthetic reactions in molten fluxes have proven to be an excellent route to new inorganic materials because they promote diffusion and can serve as an additional reactant, but little is known about the mechanisms of compound formation, crystal precipitation, or behavior of fluxes themselves at conditions relevant to synthesis. In this study we examine the properties of a salt flux system that has proven extremely fertile for growth of new materials: the potassium polysulfides spanning K(2)S(3) and K(2)S(5), which melt between 302 and 206 °C. We present in situ Raman spectroscopy of melts between K(2)S(3) and K(2)S(5) and find strong coupling between n in K(2)S(n) and the molten local structure, implying that the S(n)(2-) chains in the crystalline state are mirrored in the melt. In any reactive flux system, K(2)S(n) included, a signature of changing species in the melt implies that their evolution during a reaction can be characterized and eventually controlled for selective formation of compounds. We use in situ X-ray total scattering to obtain the pair distribution function of molten K(2)S(5) and model the length of S(n)(2-) chains in the melt using reverse Monte Carlo simulations. Combining in situ Raman and total scattering provides a path to understanding the behavior of reactive media and should be broadly applied for more informed, targeted synthesis of compounds in a wide variety of inorganic fluxes.

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Section: Resultsmentioning

confidence: 99%

Understanding Fluxes as Media for Directed Synthesis: In Situ Local Structure of Molten Potassium Polysulfides

et al. 2012

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“…In view of the difficulties associated with constant-pressure ab initio MD simulation, we decided to repeat both runs at the experimental atomic volume. Experimentally, the number density of the molten alloy has been estimated from the neutron diffraction data (essentially from the slope of the reduced radial distribution function G(R) = 4π Rn(g(R) − 1) at small R where g(R) is the total pair correlation function), leading to an atomic volume of L = 42.6 Å 3 [11] compared to S = 37.84 Å 3 for the crystalline compound at room temperature [39]. However, it is certainly legitimate to emphasize that the experimental densities determined in that way are subject to a rather large uncertainty.…”

Section: Simulation Historymentioning

confidence: 99%

“…Hightemperature phase transitions to plastic (rotor) phases with diffusive disorder of the alkali ions and rotational motion of the polyanions have been detected in NaSn and CsPb [3,4]. Diffraction experiments on molten alkali-Sn and alkali-Pb alloys have demonstrated the existence of a pronounced chemical and topological short-range order (CSRO and TSRO), which has been interpreted as evidence for the at least partial survival of the polyanions in the liquid phase [5][6][7][8][9][10][11][12][13]. This interpretation is supported by the analysis of the thermodynamic and electronic transport properties; see I for a more detailed discussion and references.…”

Section: Introductionmentioning

confidence: 99%

First-principles studies of the stability of Zintl ions in alkali-tin alloys: II. Liquid alloys

Genser

Häfner

2001

J. Phys.: Condens. Matter

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Following our preceding work on the structure and electronic properties of crystalline Zintl phases in alkali-tin systems, we have studied the structural, dynamic and electronic properties of these alloys in the molten state using ab initio local density functional molecular dynamics. Extended simulations (up to 124 atoms per cell, simulation times of up to 60 ps) have been performed for K-Sn, in which, according to the results for the crystalline compounds, the tetrahedral Sn4 polyanions can be expected to be most stable. Simulations at the experimental density and starting from configurations with no polyanions at all, but allowing for sufficient time for equilibration, lead to excellent agreement with the structure factor and radial distribution function measured by means of neutron diffraction. The analysis of the instantaneous multi-atom configurations leads to the conclusion that at least a certain fraction of the Sn atoms form polyanionic clusters. The existence of such clusters is also supported by the calculation of the electronic and vibrational spectra; the electronic structure in particular shows the signatures of tetrahedral polyanions. The precise percentage of Sn atoms forming polyanions depends, however, on density and on the ability of the system to simultaneously accommodate all An atoms in electronically saturated clusters. At a slightly higher density we find that a 64-atom ensemble condenses to a `plastic' or `rotor' phase in which almost all Sn atoms are arranged in tetrahedral polyanions performing only librational motions, whereas the K atoms continue to show liquid-like behaviour. Simulations for liquid Na-Sn and Li-Sn show a less complex behaviour: in the melt the Sn atoms form an entangled three-dimensional network instead of isolated polyanions. Again the calculated structure factors are in good agreement with diffraction measurements. The analysis of the vibrational and electronic spectra confirms the breakdown of polyanionic ordering. The trend in the series K, Na, Li-Sn is attributed to the decreasing size of the alkali atoms which leads to a less efficient screening of the polyanions by a surrounding shell of alkali atoms. The Zintl picture for the chemical bonding is supported insofar as we find that the electronic and chemical bonding properties are dominated by the strong attractive potential of the polyvalent Sn atoms resulting in the formation of at least partially covalent Sn-Sn bonds.

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“…The radial distribution functions each exhibit a peak at a distance equal to the tetrahedral Pb-Pb bond length. Similar experiments have been carried out for alkali-tin alloys [42]. No measurements of the partial structure factors, for instance by means of isotope substitution, have as yet been reported.…”

Section: The 'Perfect Zintl Model'mentioning

confidence: 64%

Polyanions in liquid ionic alloys: a decade of research

Lugt

1996

J. Phys.: Condens. Matter

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The occurrence of polyanions in a group of liquid ionic alloys, viz. alloys of the alkali metals with 13, 14, 15 and 16 elements (post-transition-metal groups 3, 4, 5 and 6), is discussed. It is shown that there are strong parallels with the corrresponding crystalline phases, in which polyanions such as (Pb 4 ) 4− , (Sb − ) ∞ and (Te 2 ) 2− exist, known for a long time as 'Zintl ions'. Little evidence exists for remnants of the diamond-lattice-type Zintl ion in liquid alkali-group-13 alloys, but in the alloys of Tl with K, Rb and Cs very long-range superstructures have been found, which are related to the occurrence of large, compact, polyhedral clusters in many crystalline phases.A stability rule, first proposed by Geertsma, relating the stability of the polyanions to the size of the cations, is universally observed. Furthermore it is shown that the range of the superstructure in the liquid is with remarkable precision proportional to the intercluster distance in the corresponding solids.The interpretation of the experimental data in terms of polyanion formation is discussed critically. There remains a paradox. Some sharp experimental features (superstructure peaks and maxima in the resistivities and stability functions) seem to indicate that the Zintl ions in the liquid are near perfect whereas specific heat results and ab initio computer simulations clearly show that the structure of the liquid is seriously blurred.

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Structure of liquid equiatomic KSn and CsSn

Cited by 26 publications

References 33 publications

Understanding Fluxes as Media for Directed Synthesis: In Situ Local Structure of Molten Potassium Polysulfides

Understanding Fluxes as Media for Directed Synthesis: In Situ Local Structure of Molten Potassium Polysulfides

First-principles studies of the stability of Zintl ions in alkali-tin alloys: II. Liquid alloys

Polyanions in liquid ionic alloys: a decade of research

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