Pyrochlore phase and microstructure development in lead magnesium niobate materials

Microstructure characteristics of powder and sintered samples of lead magne sium niobate (PMN) have been compared and related to the presence or nor of pyrochlore phase. Two kinds of samples obtained from two different hatches of powders, batch A and B, containing 1 and 0 vol.% of pyrochlore phase re spectively, were analysed. The two powders show the same morphology. The si ntered samples, with pyrochlore content around 13 vol.% for samples from ba tch A and 0 vol.% for samples from batch B. exhibit totally different micro structures The grain size increases drastically from about 1 mum for sample s with pyrochlore to 4-5 mum for pyrochlore free samples although starting from powders with same granulometry. The maximum dielectric constant uf sam ples as fired, ground and annealed were measured and related to microstruct ures and amount of pyrochlore. On the basis of these results and data repor ted in literature, mostly relating dielectric properties to stoichiometry o f the starting powder, it has been hypothesised that different sintering me chanisms come into play and govern the microstructure. Consequently the die lectric properties obtained were correlated to the sintering mechanism occu rred rather than to the absolute value of pyrochlore phase present, as it's commonly accepted. (C) 2001 Elsevier Science Ltd. All rights reserved.