Acetate Sol-Gel Synthesis of PMN Ceramics from Nb-Ethyleneglycol-Tartarate Complex

PbMgNb(OAc) _x (OR) _y precursor was prepared from Pb and Mg acetates by dissolution in acetic acid (AcOH) and by mixing with Nb-ethyleneglycol-tartarate (Pechini) complex. The sol was formed after hydrolysis by various addition of water at 80°C and it was transformed by polycondensation to PMN two-phase gel. By the calcination of gel at the temperature of 500°C for 2 hours, the two-phase system was created with perovskite and undesirable pyrochlore phases. The content of the Pb(Mg _1/3 Nb _2/3 )O ₃ perovskite phase in PMN calcinates was increased from 0 to 60 vol.% by decreasing of water addition as it results from DTA, TG analysis, IR spectroscopy and XRD analysis. The Pb _1.83 (Mg _0.29 Nb _1.71 )O _6.39 pure pyrochlore phase was found in the calcinate prepared from gel with higher addition of water and hydrolyzing factor (h) equals 43. The content of perovskite phase in calcinate was approximately 60 vol.% at h = 21 and without water addition to sol. The partial decomposition of the pyrochlore phase with transformation into the perovskite phase (the maximal volume fraction of perovskite phase ∼ 70 vol.%) was observed above the sintering temperature of 1100°C. Densities of PMN ceramics sintered at 1200°C decreased with the content of py phase in PMN calcinates. The maximal value of ϵ _r = 4200 (at 1 kHz) was found in the ceramic sample with the highest content of perovskite phase and density.

Keywords:

• Sol
• gel
• PMN
• pyrochlore
• perovskite phase
• dielectric properties

Acknowledgments

This work was supported by the Slovak Grant Agency of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences, Project. No. 2/2084/22.