Superstructure ordering in lanthanum doped lead zinc niobate Original Research Article

Single crystals of pure and lanthanum doped lead zinc niobate, Pb(Zn1/3Nb2/3)O3, 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) Å 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.