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were measured at concentrations covering almost whale region of the C a~-~I a f~, solid solution formatian. They are characterized by increasing conducti ty an decreasing activation energy with increasing LaF3 concentrations. In aamples with x > 0 , l l an increase of electrical conductivity due to aging was observed.solid solutions in the CaF2 -Both dc / from 20 to 450 O C / and ac / from 450 to 600 oc / electrical $onductivities

The 0,ions appear as an unwanted impurity that contaminates the crystals of alkaline and rare earth fluorides during their preparation. The easy incorporation into the lattice and difficulties with their detection make the measurement of electrical properties problematical. I n order to elucidate the influence of oxygen on CaF, crystals we have measured electrical conductivity. The crystals were prepared from a raw material of various moisture content, or they were doped by CaO, respectively. The measured courses exhibit equal activation energy E = 0.64 eV in the middle range. We thus conclude that synthetizing the crystal contaminated by moisture yields incorporation of 02-ions only. We proved that even a two hours delay of melted raw material in gaseous products of Teflon pyrolysis does not suffice to remove oxygen. The method is effective only when applied after drying of raw material in vacuum.02--Ionen treten als unerwunschte Beimengung auf, die Alkali-und Seltenerd-Fluorid-Kristalle wahrend ihrer Herstellung verunreinigen. Der leichte Einbau in das Gitter und die Schwierigkeiten bei ihrem Nachweis machen die Messung ihrer elektrischen Eigenschaften problematisch. Zur Aufkliirung des Einflusses des Sauerstoffs auf CaF,-Kristalle haben wir die elektrische Leitflhigkeit gemessen. Die Kristalle wurden aus Rohstoffen verschiedenen Feuchtigkeitsgehalts hergestellt, oder sie wurden mit CaO dotiert. Die gemessenen Verlaufe zeigen gleiche Aktivierungsenergie von E = 0,64 eV im mittleren Gebiet. Wir schlieaen daraus, dal3 die Herstellung von Kristallen in Anwesenheit von Feuchtigkeit allein den Einbau von 02--Ionen verursacht. Wir konnten nachweisen, da13 sogar ein zweistundiger Verbleib des geschmolzenen Rohmaterials in den gasformigen Produkten der Teflonpyrolyse nicht ausreichen, den Sauerstoff zu entfernen. Die Methode ist nur dann wirksam, wenn sie nach der Trocknung des Rohmaterials im Vakuum angewendet wird.

This work completes our previous results on the measurement of electrical conductivity in fluorite solid solutions Cal-,Ln,Fz+, (MAFXANI et al.), SVANTNER et al.) and gives new results for Cal-,Gd,FZ+, and Cal-,Er,Fz+,. The main characteristic of the measured In (I vs 1/T dependences is an increase of electrical conductivity and decreases of activation energy with increasing concentration of LnF,. The preexponential terms in the Arrhenius formula for electrical conductivity are constant for z > 0.01. I n the interpretation of measured results the existence of regions with high concentration of defects is assumed in agreement with structural views.