Superstructure ordering in lanthanum doped lead zinc niobate

Single crystals of pure and lanthanum doped lead zinc niobate, Pb(Zn1/3Nb2/3)O-3, were studied by synchrotron radiation X-ray diffraction. Chemical ordering between the B-site ions of Zn and Nb results in superstructure peaks at the (h + 1/2, k + 1/2, l + 1/2)positions. In comparison with earlier work on lead magnesium niobate, we find that the chemically ordered regions of PZN are much smaller. Doping with La greatly increased their size, while causing a decrease and broader transition in the measurement of dielectric constant versus temperature. Crystallographic analysis of the superstructure peaks in 10% La-PZN revealed a similar structure to 10% La-PMN, only with a larger oxygen displacement. This reflects the larger size difference that exists between Zn and Nb compared with Mg and Nb. The oxygen displacement within the ordered regions was 0.055(6) Angstrom along a [100] direction towards the Nb ion. This result in 10% La-PZN is consistent with a "random layer" model of ordering between a B' site of Zn2/3Nb1/3 and a B " site of Nb. (C) 1999 Elsevier Science Ltd. All rights reserved.