The structural inhomogeneity of lead–cadmium fluoride systems and its implications

Abstract

In this paper we present a detailed study of structural and dynamical properties of the CdF(2)-PbF(2) systems. Particular attention is devoted to the processes involving the phase separation, a phenomenon of fundamental importance in the correct description of some dynamical properties, as introduced in our previous works. We show here, that the phase separation trend is observed in the undercooled melt, whether by cooling the liquid below its melting point, or by heating a homogeneous glass at temperatures above T(g). The degree of phase separation depends on the procedure employed to obtain the crystalline materials, and the simplest way to determine this property is by performing an isothermal treatment in the undercooled melt region. The local fluorine environments Q((n)), corresponding to fluorine surrounded by nPb and 4-nCd neighbors, is used as a probe in the average local composition. We demonstrate that the increase in the structural inhomogeneity around the composition with x = 0.35 is the factor which leads to a better fluorine conducting property for the Cd(0.35)Pb(0.65)F(2) solid solution, in addition to providing a correct determination of the melting temperature of the Cd(x)Pb(1-x)F(2) compositions.

PbF2–CdF2–SrF2 Ternary Solid Solution: Crystal Growth and Investigation

“…The nature of the ionic conductivity of the fluorite-type solid solution Pb0.552Cd0.273Sr0.175F2 is due to fluorine anions. This is directly indicated by the results of the F 19 NMR study of Pb0.67Cd0.33F2 crystals, in which a high diffusion of Fions was found [45,46], and theoretical calculations using molecular dynamics and quantum chemistry methods [47,48]. In an equivalent AC circuit, the resistor R b determines the bulk resistance of the crystal associated with the process of electrotransfer, P b (ω) and P el (ω) frequency-dependent elements with a constant phase angle (constant phase elements, CPE) [34], model polarization processes in the bulk of the crystal, and the electrode/crystal interface.…”

“…The nature of the ionic conductivity of the fluorite-type solid solution Pb 0.552 Cd 0.273 Sr 0.175 F 2 is due to fluorine anions. This is directly indicated by the results of the F 19 NMR study of Pb 0.67 Cd 0.33 F 2 crystals, in which a high diffusion of Fions was found [45,46], and theoretical calculations using molecular dynamics and quantum chemistry methods [47,48].…”