BiFeO₃-doped (Na_0.5K_0.5)NbO₃lead-free piezoelectric ceramics

Abstract

Lead-free piezoelectric ceramics (1 − x)(Na 0.5 K 0.5 )NbO 3 -xBiFeO 3 (x = 0 ∼ 0.07) were synthesized by the solid-state reaction. Differential scanning calorimetry (DSC) measurements revealed that an increase in the amount of BiFeO 3 dopant resulted in a decrease in the orthorhombic-tetragonal and tetragonal-cubic phase transition temperature of the material. One percent BiFeO 3 additive suppressed grain growth, which not only benefits the sintering of ceramics but also enhances the piezoelectric and ferroelectric properties, where d 33 = 145pC/N, k p = 0.31, Q m = 80, P r = 11.3 µC cm −2 and E c = 16.5 kV cm −1 . As x BF > 0.01, both piezoelectric and ferroelectric properties decreased rapidly with an increasing amount of dopant.

All-Ceramic Percolative Composites with a Colossal Dielectric Response

“…7 and 8 further confirms the perfect outgrowth of the PZT-Pb 2 Ru 2 O 6.5 , PMN-35PT-Pb 2 Ru 2 O 6.5 , and KNN-RuO 2 composites, with the dielectric constant near the percolation threshold being for two orders of magnitude higher than in the pure matrix (PZT, PMN-35PT, or KNN) ferroelectric ceramics -this hold true also for the PMN-35PT-Pb 2 Ru 2 O 6.5 and KNN-RuO 2 composites, where a significant fraction of porosity, which can clearly be seen in Fig. 3 (and is many times observed in KNN-based ceramic composites (Sun et al, 2008)) undoubtedly alters the dielectric response, i.e., decreases the dielectric constant. It should once again be stressed out that the effective conductivity, similar as the effective dielectric constant (Eq.…”

Efecto del BiFeO₃ en las propiedades del sistema ferroeléctrico libre de plomo K_0.5Na_0.5NbO₃

“…La primera fase que se forma en la pareja Na 2 CO 3 /Nb 2 O 5 es el Na 2 Nb 4 O 11 a 500 ºC, y la fase perovskita sólo se forma en la interfase Na 2 caracterizadas por espectroscopia de impedancia compleja. La parte real e imaginaria de la constante dieléctrica en función de la frecuencia se muestra en la figura 9 donde se observa la existencia de un mecanismo de relajación simple en el rango de frecuencias analizado, se observa que para frecuencias menores a 10 5 Hz la componente real disminuye monótonamente hasta alcanzar un comportamiento casi constante para frecuencias mayores a 10 5 Hz, mientras que la componente imaginaria pasa por un valor máximo.…”

“…A la fecha han sido identificados relativamente pocos materiales multiferroicos, y en los que se conocen, el mecanismo que subyace a su ferroelectricidad es a menudo poco convencional [1]. El niobato de potasio y sodio, K 0.5 Na 0.5 NbO 3 (KNN), se ha considerado un buen candidato para la fabricación de cerámicas ferroeléctricas libres de plomo debido a su buena respuesta piezoeléctrica y la relativamente alta temperatura de Curie ~420 ºC [2]. Sin embargo, es muy difícil sinterizar cerámicas piezoeléctricas basadas en KNN debido a la volatilidad del Na y del K y a su alta reactividad con la humedad.…”

Dielectric, ferroelectric and piezoelectric proprieties of GdCoO3 doped (K0.5Na0.5)NbO3

“…In order to further improve the piezoelectric properties of KNN, a series of methods have been proposed: compositional substitution -(K, Na)(Nb, Ta)O 3 [6] or [K,(Na, Li)]NbO 3 [7], use of sintering additive -CuO for [K, (Na, Li)](Ta, Sb, Nb)O 3 [8], alternative synthesis methods -hydrothermal [9] or hot pressing [10], and simple doping-CeO 2 doped KNN [11] or other perovskite structure doping: KNN + BaTiO 3 [12], KNN + BiFeO 3 [13] or KNN + BiScO 3 [14]. Recent finds in lead free piezoelectric materials, show that perovskite structure doping can be an effecting way of improving the electrical properties of potassium-sodium niobate, with a reported value of the piezoelectric constant close to that of commercial PZT: d 33 = 425 pCN À1 for [(K, Na), Li](Nb, Sb)O 3 -BaZrO 3 [15], d 33 = 366 pCN À1 for (K, Na)NbO 3 -0.005BiScO 3 -Bi(Na, K, Li)ZrO 3 [16], d 33 = 460 pCN À1 for (K, Na)(Nb, Ta, Sb)O 3 -(Bi, Na, K)ZrO 3 [17], d 33 = 388-465 pCN À1 for (K, Na)(Nb, Sb)O 3 -(Bi, Na, K)ZrO 3 [18] and a maximum ever recorded for KNN -based lead free piezoceramics reported by Wang et al [19] of d 33 = 490 pCN À1 .…”