PHYSICAL PROPERTIES AND STRUCTURE OF OXYFLUORIDE MELTS

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The dependence of oxygen partial pressure(OPP)on electrical conductivity have been studied for MO-MF_2(M=Ca,Sr,Ba) melts and discussed the newly observed phenomena caused by the liquid lattice of fluorite-like structure.Electrical conductivities of MO-MF_2 melts (MO<17mass%) varied with the one-quarter power of OPP in argon and oxygen atmosphere.The dependence of OPP on electrical conductivity kappa can be expressed as kappa^0_<ion>exp(-E/RT)+kappa^0_pP_<0^21/4>exp(-E'/RT), where kappa^0_<ion>exp(-E/RT) and kappa^0_pP_<O^21/4>exp(-E'/RT) are partial conductivity for ions and positive holes.The reversible change in transparency of these melts with OPP was directly observed by the hot-thermocouple method. The crystal structure of fluorite such as CaF_2,SrF_2,and BaF_2 has a high Madelung constant,therefore,the relative long range order is maintained even in liquid state. We call this state "liquid lattice". When oxide MO is added,oxide MO is incorporated into the liquid lattice.The ions M^<2+> and O^<2-> of MO are located on the M^<2+>-site and F^--site,respectively,in the liquid lattice formed by MF_2.The unequal charges of O^<2-> and F^- causes the anion vacancy in the melts. The gaseous oxygen is ionized and dissolved into the melts above a critical OPP in the atmosphere and the oxygen reacted with the anion vacancy and results in the formation of positive holes.The positive holes make the melts to be opaque by the absorption of light and contribute to the conduction.