INTERACTION OF THE LANTHANA, YTTRIA WITH ITERBIY AT TEMPERATURE 1100 °C

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Using the methods of physicochemical analysis (XRD, petrography, SEM, X–ray microprobe analysis) phase equilibria were firstly investigated in the ternary system La 2 O 3 –Y 2 O 3 –Yb 2 O 3 at 1100 °C. The specimens were prepared in step 1-5 mol % from nitrate solutions with their subsequent evaporation and decomposition at 800 °C for 2 h. Powders were pressed at 10 MPa into pellets of 5 mm in diameter and 4 mm in height. To study phase relationships in the ternary system La2О3 – Y2O3 – Yb2О3 thermal treatment of as-prepared samples was carried at 1100 °С. X-ray diffraction analysis of the samples was performed by a powder method at room temperature (CuKa radiation). The scanning speed of 0.05-0.1 ° 2q/min was employed in the 15° to 90 ° 2q range. The effective precision of the measurements was ± 0.0002 nm. Lattice parameters were refined by least squares fitting using the LATTIC program. The crystal-optic characteristics of the obtained phases were determined under polarized microscopes “МІН-8” and Leica. The refraction indісes were measured in immersion liquids (solution of arsenic tribromide in methylene iodide or alloys of sulfur with selenium) with accuracy ± 0.02. The solid solutions based on various polymorphous forms of constituent phases and ordered phase with a structure of the perovskite-type of LaYO3 (LaYbO3) were revealed in the system. The boundaries of mutual solubility and concentration dependences the lattice parameters for all phases have been determined. The isothermal sections of the phase diagrams for the La 2 O 3 –Y 2 O 3 –Yb 2 O 3 systems at 1100°C are characterized by the presence of one three-phase (B +C + R), four single-phase (A- La 2 O 3 , B- La 2 O 3 , R, C- Y 2 O 3 (Yb 2 O 3 )) and two-phase (A + B, B+ R, C + R, B + C) regions. The solid solutions are formed by the mechanism of the isovalent substitution. The stability of ordered phases and solid solutions are determined by the dimensional factor : in the LaYO 3 , the large size ions replace La 3+ ions, the smaller ions of the cerium series substitute both Y 3+ and La 3+ , where as all the mentioned rare earth ions may be replaced by Y 3+ ions. An ordered R-phase in the ternary system exists in the wider range of concentrations than in the binary system.