A homovalent doping in PMN ceramics by using lithium and scandium cations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The Mg(2+) homovalent substitution by Li(+)/Sc(3+) cations at the B-site sub-lattice of the lead magnesium niobate (PMN) perovskite structure was studied in this work. Through structural and electrical analyses, it was observed that the dopant pair effectively substituted the Mg cation, although an addition limit close to 2.5 mol% of dopants was observed. Up to this concentration level, the dopant pair does not affect the perovskite phase stability, and thus, pyrochlore free ceramics with a T(m) value of -6 degrees C and 19,000 of electric permittivity were obtained. As a consequence of the substitution, the 1:1 chemical ordering at the B-site was changed, leading to a less diffuse ferroelectric-paraelectric phase transition even despite the increase of the relaxor character. However, a 5.0 mol% addition of Li/Sc provoked the precipitation of a small quantity of pyrochlore phase that caused a deterioration of the ceramic electrical properties. (C) 2008 Elsevier B.V. All rights reserved.