Structural ordering in CdxPb1−xF2 alloys: A combined molecular dynamics and solid state NMR study

Abstract

Molecular dynamics (MD) simulations of binary Cd(x)Pb(1-x)F(2) alloys have been carried out, using a two-body Buckingham interaction potential, leading to a correct description of structural properties as a function of composition and pointing towards an understanding of the eutectic phenomenon. The simulation data can be analyzed in terms of five local fluorine environments Q((n)) (4> or =n> or =0), where n is the number of Pb nearest-neighbor environments. The results suggest a highly nonstatistical population distribution, suggesting an intrinsic phase segregation tendency in the undercooled melt, during the cooling process. This prediction has been tested experimentally for six representative compositions (0.2< or =x< or =0.7) on the basis of high-resolution (19)F solid state NMR data, revealing important similarities between theory and experiment. While the NMR data confirm that the population distribution is, indeed, nonstatistical for all compositions, the results are only found to be consistent with an intrinsic segregation tendency of PbF(2)-rich domains. This tendency manifests itself in substatistical populations of Q((3)) units, resulting in preferred Q((2)) and Q((4)) formations.

Fluoride solid electrolytes: investigation of the tysonite-type solid solutions La1−xBaxF3−x (x < 0.15)

“…19 F MAS NMR provides an ideal method to probe the local order in fluoride solid solutions. 50,[57][58][59][60][61][62][63][64] Nevertheless, the case of the La 1−x Ba x F 3−x solid solution seems to be, at first sight, unfavorable since there are three fluorine sites in LaF 3 and since the δ iso value of BaF 2 (−14.3 ppm, 56 CN = 4, 2.683 Å 65 ) is in the range of the δ iso values of LaF 3 . Moreover, local disorder, leading to a broadening of the NMR lines, is expected since the heterovalent substitution generates fluorine vacancies and that both cations have different ionic radii.…”

Charge compensation in RE3+ (RE = Eu, Gd) and M+ (M = Li, Na, K) co-doped alkaline earth nanofluorides obtained by microwave reaction with reactive ionic liquids leading to improved optical properties

“…This journal is © The Royal Society of Chemistry 2014 tentatively attributed to uoride ions next to one La 3+ species, while the resonance near À31 ppm might be assignable to interstitial uoride ions, resembling the F 1 and/or F 2 sites reported in ref. 26 and having proximity to two lanthanum species. Based on these assignments, we observe that the signal displacements relative to F n are generally larger here than those in Y-doped CaF 2 .…”

“…25 In contrast, clear segregation and clustering phenomena were observed in the PbF 2 -CdF 2 system. 26 Furthermore, a detailed 19 F MAS NMR study by Wang and Grey showed that aliovalent substitution in the CaF 2 -YF 3 system creates multiple uoride environments. 27 The quantitative concentrations of these environments have been discussed in relation to various defect cluster models originating from the necessary creation of interstitial uoride ions owing to charge balancing constraints.…”

Molecular Insights into the Eutectic Tripalmitin/Tristearin Binary System

“…It is also possible to obtain some information regarding the nature of the eutectic phenomenon by examining other research areas. The eutectic phenomenon has been studied in alloys, − glasses, biological compounds, and deep eutectic systems. , A common observation in these studies is that the lower melting point is indicative of greater molecular mobility . As well, the eutectic behavior of these systems has been attributed to differences in intermolecular interactions, particularly hydrogen bonds …”