INVESTIGATION NATURE OF THIN FILMS FORMATION OF Pb-MeF2 BY X-RAY DIFFRACTION

Souchkov I.A.

Dept Physical and Marine Geology, Odessa State University, 2, Shampanskij per, Odessa, 270058,Ukraine.

Disproportionation of solid solution PbF₂-MeF₂ (Me=Sr, Ba) udder electron beam and thermal evaporation and formed thin films were investigated. These materials have cubic fluorite structure. Initial fluoride composite was obtained by annealing of this simple fluoride in the inert atmosphere at 1800-13000^oC. Thin film was condensed by the electron beam methods and thermal evaporation on the glass substrate heated up to 1500^oC.

Analysed the phase composition and the elementary cell parameters of the film-forming materials, their thin films and residue after evaporation.

Elementary cell parameters initial fluoride film-forming material change according to difference ionic radius of cations of the alkaline earth metals. Substitution Pb on the Ba ease lead to increasing of the elementary cell volume and substitution Pb-Sr to their decreasing. In the process of evaporator of the initial complex fluoride materials can be observed following. The vacuum evaporation multi-component fluoride material is accompanied by the enrichment of more volatile component (Pb) and residue less volatile (Ba and Sr). This phenomenon is reflected in changing of the elementary cell parameters and is confirmed by second ion mass-spectrometry data. For example by evaporation of the composition PbF₂-SrF₂ (10 mol%) the film contain 0,6% SrF₂ and with increasing of the content SrF₂ in the evaporated material to 50 mol% it content in the film increase to 13%.

The difference between phase contented elementary cell parameters in films obtained by different method is observed. The phase content of films obtained by electron beam evaporation correspondent to the phase content of initial material. In the process of thermal evaporation in films together with the metal fluoride is observed the admixture of the elementary lead and elementary cell volume decrease and their value in initial materials. These phenomenon may be explained by the presence in films of admixture the lead with valence more than 2+. The melting of the lead fluoride in vacuum lead to their decomposition up to appearance of independent phase - elementary lead. The present in films of lead more high valence than 2+ lead to decreasing of elementary cell volume. In the films obtained by electron beam evaporation these phenomenon is absent. Due to high-powered electron beam which head the evaporated material considerably over melting point the rate of evaporation of material so high what process of the PbF₂ decomposition didn't occur.

This the elementary cell volume of the vacuum condencate may be influence by two following process: 1 - by changing of the content of the alkaline earth metals (Ba, Sr); 2 - by compression of thin film elementary cell due to PbF decomposition.

Elementary cell parameters of the solid solution PbF₂-MeF₂.