X-RAY AND RAMAN-STUDY ON COORDINATION STATES OF FLUORITE-TYPE AND PYROCHLORE-TYPE COMPOUNDS IN THE SYSTEM ZRO2-GD2O3

Raman spectra were measured on the pyrochlore- and fluorite-type Zr2Gd7 (x=0.50) in the system (1-x)ZrO2-xGdO 1.5 and structure refinements were carried out for both structure types with a composition of x=0.43 by means of single crystal X-ray diffraction. Bond distances in the fluorite-type structure with x=0.43 were in good agreement with those calculated from the effective ionic radii, assuming that Gd3+ ion was coordinated by eight oxygens and oxygen vacancies were adjacent to Zr4+ ion. A Raman spectrum of the fluorite-type Zr2Gd2O7 was very similar to that of the pyrochlore-type, and had the line near 220 cm-1 attributed to the pyrochlore-type Gd4O tetrahedra. Coordination states and stability of the pyrochlore- and fluorite-type structures are discussed based on the present results. © 1990.