A LOW-TEMPERATURE EXTENDED X-RAY-ABSORPTION STUDY OF THE LOCAL ORDER IN SIMPLE AND COMPLEX PEROVSKITES .2. PMN (PBMG1/3NB2/3O3)

EXAFS study of lead magnesium niobate was performed at the Nb K edge and at the Pb L(III) edge between 300 and 4.5 K. Two Nb-O bond lengths of 1.95 and 2.16 angstrom are observed and there is no significant modification of the local environment of the Nb atoms with temperature. The distribution of these two bonds in both polar nanodomains and 1-1 Nb-Mg ordered nanodomains is discussed in relation to results obtained previously by other techniques. It is shown that the ordered nanodomains could occupy about one third of the whole volume. The results obtained for the Nb-Nb and Nb-Mg distances confirm the structural results and particularly point to an increasing correlation of the Nb shift at their site, when the temperature is lowered to below 300 K. The weak EXAFS signal obtained at the Pb L(III) edge and the small backscattered contribution of Pb at the Nb K edge reveal a strong static disorder of the Pb positions.