A Study of the Formation of Ln_{2 + x}Me_{2 x}O_{7 x/2}
(Ln = Gd, Dy; Me = Zr, Hf) Nanocrystals

V. V. Popov^a, Ya. V. Zubavichus^b, V. F. Petrunin^a, A. P. Menushenkov^a, O. V. Kashurnikova^a,
S. A. Korovin^a, R. V. Chernikov^a, and A. A. Yaroslavtsev^a

^a National Research Nuclear University “MIFI,” Kashirskoe sh. 31, Moscow, 115409 Russia

*e-mail: victorvpopov@mail.ru

^b National Research Centre “Kurchatov Institute,” pl. Akademika Kurchatova 1, Moscow, 123182 Russia

Received December 10, 2010

Abstract—It has been established that the process of producing the Ln_2+xMe_2–xO_7–x/2 (Ln = Gd, Dy; Me=
Zr, Hf) nanocrystals by calcination of hydroxides, which, in turn, have been produced by coprecipitation of
metal salts, includes several stages. At the beginning, the X-ray amorphous structure of the precursors remains
unchanged during dehydration; during subsequent heating to 600–700C, nanocrystals with a disordered fluo-
rite structure begin to be formed. An increase in the temperature above 700C leads to an increase in the size of
crystallites (coherent scattering regions). This process is accompanied by changes occurring in their local struc-
ture. In the nanocrystalline powders of Cd₂Hf₂O₇ and Gd₂Zr₂O₇ synthesized at 1200C (6 h), the pyrochlore-
type superstructure with the lattice parameters doubled relative to fluorite has been revealed. It has also been
found that, possibly, the Dy₂HfO₅ sample at 1600C (3 h) has a modulated structure.

Keywords: Ln_2+xMe_2–xO_7–x/2 (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals, fluorite, pyrochlore, coprecipitation,
local structure

DOI: 10.1134/S1087659611050117

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