PHASE RELATION STUDIES IN THE ZrO2-CeO2-Dy2O3 SYSTEM AT 1500 °С

Abstract

The systems containing ceria, dysprosium and zirconia are perspective for the development of energy saving technological solutions and solid oxide fuel cells (SOFC). Ceramics based on ZrO 2 is used as a high temperature electrolyte for SOFC. The solid solutions based on CeО 2 are the most perspective electrolytes, operating at moderate temperatures, because of their ionic conductivity and high sensitivity to changes of oxygen partial pressure is much higher than ones of ZrO 2 stabilized with Y 2 O 3 (YSZ). In the present work, first the phase equilibria and physicochemical properties for solid solutions in the ternary ZrО 2 -CeО 2 -Dy 2 O 3 system at temperature 1500 °С (150 h) in air were studied by X-ray diffraction in the overall concentration range of compositions. Cerium oxide nitrate Ce(NO 3 ) 3 ∙6H 2 O and zirconium oxide nitrate ZrO(NO 3 ) 2 ×2Н 2 О of grade «ch» (above 98%, dysprosium oxide (99.99 % produced by Merck Corp.) and analytical-grade nitric acid were used as the starting materials. Samples were prepared with a concentration step of 1-5 mol % from nitrate solutions with subsequent evaporation and decomposіtion of nitrates into oxides through annealing at 1200 °С for 2 h. Powders were pressed in pellets (diameter 5 mm, height 4 mm) under a pressure of 10-30 MPа. XRD analysis of samples was performed by powder procedure on a DRON-3 apparatus at ambient temperature under CuКa radiation. Scanning step was 0.05-0.1 degrees in the range 2θ = 15–90°. Lattice parameters were calculated by the least square method using the LATTIC computer code with an error of not lower than 0.0001 nm for the cubic phase. Any new phase in the ternary system was revealed at 1500 °С. The structure of the boundary binary systems defines the phase equilibria in the ZrО 2 -CeО 2 -Dy 2 O 3 system. Solid solutions based on tetragonal (Т) modification ZrО 2 , cubic (С) modification Dy 2 O 3 and cubic with fluorite-type structure (F) modifications СеО 2 (ZrО 2 ) were determined.