Study on the K3Li2Nb5O15 formation during the production of (Na0.5K0.5)1-xLixNbO3 lead-free piezoceramics at the morphotropic phase boundary

Abstract

Because of the environmental concerns, the manufacture of ceramics based on lead titanate zirconate [Pb(Zr1−xTix)O3−PZT] has been condemned because of the lead toxicity. In this context, the electromechanical properties of sodium, potassium and lithium niobate [(Na0.5−x/2K0.5−x/2Lix)NbO3−NKLN] at the morphotropic phase boundary granted these materials the position of most suitable candidate to replace PZT. However, the production of these ceramics is rather critical mainly because of a natural tendency of forming secondary phases. To help with the studies of the synthesis of this lead-free piezoceramic, this work presents an evaluation of the crystallization of the (Na0.47K0.47Li0.06)NbO3 phase by solid-state reactions. TG-DTA, XRD, dilatometric and ferroelectric hysteresis analyses indicated that a secondary phase (K3Li2Nb5O15) crystallizes at temperatures above 850 C and also during the sintering of the powders compacts at 1080 C. To prevent the formation of this phase, the addition of Na2Nb2O6.nH2O microfibers obtained through a microwave hydrothermal synthesis was performed in the sintering process. After to this addition, the suppression of the K3Li2Nb5O15 phase occurred and an increase of the NKLN electrical properties was then obtained.