MODIFICATION OF THE NANOSTRUCTURE AND DIELECTRIC-PROPERTIES OF LEAD MAGNONIOBATE CERAMICS BY DOPING

Undoped as well as Ti and La-doped PbMg1/3Nb2/3O3 (PMN) ceramics were elaborated and characterized by dielectric measurements and by neutron and X-ray diffraction. At 20-degrees-C, they exhibit an average cubic structure (space group Pm3m) with important atomic shifts off the special positions of the perovskite structure. Some broad X-ray diffraction lines are only due to the polar nanoregions and thus give direct information about their nucleation and their growth when the temperature is decreased. In Ti-doped PMN, the polar nanodomains, related to a less diffuse dielectric behaviour, are greater than in undoped PMN, whereas in La-doped PMN, inverse features are observed. The polar domain growth seems to be related to the size of the Mg/Nb 1-1 ordered nanodomains originating strong random electric fields in the materials.