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 or dering 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 wo rk on lead magnesium niobate, we find that the chemically ordered regions o f 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 superstructur e 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 tha t 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 t owards the Nb ion. This result in 10% La-PZN is consistent with a "random l ayer" model of ordering between a B' site of Zn2/3Nb1/3 and a B " site of N b. (C) 1999 Elsevier Science Ltd. All rights reserved.