A Modulated Structure in a Fluorite-Type Fast-Ion-Conductor δ-(Bi2O3)1-x(Nb2O5)x

Abstract
The modulated structure of the fluorite-related δ-(Bi2O3)1-x (Nb2O5) x compounds was investigated by electron diffraction, high-resolution electron microscopy and X-ray powder diffraction. It was described by the substitutional and displacing waves with a common wave number vector q k 111. The value of q increased from 0.360 to 0.383 with increasing x from 0.13 to 0.24. The substitutional waves were expressed by 0.2–0.042·cos 2πq x/d 111 for cations and 0.15+0.039·cos 2πq x/d 111 for anions. The displacing waves were expressed by 0.0029d 111·sin 2πq x/d 111 and 0.171d 111·sin 2πq x/d 111 for cations and anions, respectively. The Debye-Waller factor for O2- ions was determined as about 10 Å and 4.2 Å2 with O2- ions to occupy the 8(c) and 32(f) sites, respectively.

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