X-ray and Raman study on coordination states of fluorite- and pyrochlore-type compounds in the system ZrO 2-Gd 2O 3

Abstract

Raman spectra were measured on the pyrochlore- and fluorite-type Zr 2Gd 7 ( x=0.50) in the system (1− x)ZrO 2− 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 Gd 3+ ion was coordinated by eight oxygens and oxygen vacancies were adjacent to Zr 4+ ion. A Raman spectrum of the fluorite-type Zr 2Gd 2O 7 was very similar to that of the pyrochlore-type, and had the line near 220 cm −1 attributed to the pyrochlore-type Gd 4O tetrahedra. Coordination states and stability of the pyrochlore- and fluorite-type structures are discussed based on the present results.