Relaxation of Impurity-Defect Complexes in Fluorite Crystals
This paper summarizes recent contributions to the understanding of the structure and the reorientation kinetics of various impurity-defect complexes in alkaline earth fluroides. For the most part the relevant investigations involve relaxation of electric polarization as revealed by the ionic thermo-current (ITC) method on CaF2, SrF2 and BaF2 crystals doped with a variety of trivalent rare earth (RE3+) ions. In the absence of contaminating oxygen the extra positive charge is compensated by an interstitial fluoride ion (Fi -) which except at elevated temperature forms a complex with the In CaF2 the (dominant form of the complex as revealed by EPR and ITC is tetragonal with the Fi - located in the nearest neighboring interstitial site (Type I complex). In BaF2 the dominant form is trigonal with the situated in a next nearest site along a ‹111› direction (Type II complex). In SrF2 both Type I and Type II complexes are clearly evident in the ITC relaxation peak structure. In a crystal of CaF2:Gd3+ treated to introduce oxygen the Type I relaxation at 131 K is replaced almost quantitatively by a new peak at 166 K. Comparison with EPR behavior reveals that the new peak is associated with the relaxation of the CaF2:Gd3+O4 complex (Type T1) which had been previously identified by ENDOR.
KeywordsTrivalent Rare Earth Fluorite Crystal Alkaline Earth Fluoride BaF2 Crystal Dipolar Complex
Unable to display preview. Download preview PDF.
- 1.For a review of the relaxation modes and defect structures see A. S. Nowick, in Point Defects in Solids, J.H. Crawford and L.M. Slifkin, eds., Plenum Press, New York (1972) ch. 3.Google Scholar
- 4.J.H. Chen, M.S. McDonough, Phys. Rev. 185–453 (1969).Google Scholar
- 6.A.D. Franklin, S. Marzullo, J. Phys. Chem. 3, L171 (1970).Google Scholar
- 10.B. Bleaney, P.M. Llewellyn, D.A. Jones, Proc. Phys. Soc. B69 858 (1956) U. Ranon, W. Low, Phys. Rev. 132 1609 (1963).Google Scholar
- 11.J,M. Baker, E.R. Davis, J.P. Hurrell, Proc. Roy. Soc, A308 403 (1968).Google Scholar
- 12.J. Sierro, Phys. Lett. 4 178 (1963).Google Scholar
- 13.U, Ranon, A. Yaniv, Phys. Lett. 9 17 (1964).Google Scholar
- 17.G.D. Jones, S. Peled, S. Rosenwaks, S. Yatsiv, Phys. Rev. 183, 353 (1969).Google Scholar
- 18.We are indebted to G.D. Jones and A. Edgar, University of Canterbury, Christ church., New Zealand, for providing these EPR measurements.Google Scholar