Shock Compression of Lead Fluoride at Room Temperature
Lead difluoride (PbF2) is known to occur in two distinct crystalline forms; namely, fluorite and PbCl2 structures. The fluorite structure has a cubic symmetry (Fm3m - O5 h) ancd PbCl2 has an orthorhomic symmetry (Pbnm — V16). The fluorite and orthorhombic forms of PbF2 are identified as β- and α-PbF2, respectively. The prevalent information about the stability of these two forms of PbF2 may be summarized as follows: (1) α-PbF2 is the stable form of PbF2 at ambient conditions; (2) α-PbF2 transforms to β-PbF2 at 583 ± 1K; (3) The reverse transformation of β;-PbF2 to α-PbF2 has not yet been observed; (4) The crystals of PbF2 grown from its melt are invariably in the form of β;-PbF2; (5) Even though unstable at ambient conditions, β-PbF2 needs to be subjected to a hydrostatic pressure of around 0.4 + 0.1 GPa to transform it into α-PbF2 form. This transformation has also been reported to be rather sluggish; (6) The rate of transformation of β- to α-PbF2 increases with an increase in temperature; (7) The pressure of transformation Pt of β- to α-PbF2 decreases with an increase in temperature T. The magnitude of dPt /dT is approximately -3.6 MPa/K; (8) There is some indication that the β- to α-PbF2 transformation proceeds readily under shearing stress conditions at room temperature.
KeywordsParticle Velocity Shock Compression Fluorite Structure Shock Velocity Shock Experiment
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