Piezoelectric and Dielectric Properties of Ceramics in the System Potassium—Sodium Niobate

Abstract

From this it can be seen that in forming either the 3 : 5 or 2: 1 structures from the molten state or the oxides, the aluminum must decrease its coordination. On the other hand, the coordination of this ion in YAIOJ is the same or greater than in the oxides or in the molten state. As a result, YAlOa is readily formed from these starting materials even though it is a metastable compound under equilibrium conditions. The aluminum oxygen octahedra are, of course, the most important structural element of these structures and hence the yttrium plays a minor role in metastability.One of the most important results found from this study and another one1* involving the tetravalent ceramic oxides F. A. Mumpton and Rustum Roy, "Experimental Study of the Zircon-Thorite Group, Bull. Geol. Soc. Am., 68,1772 (1957).is that very great difficulty is encountered in attaining equilibrium or even in obtaining indications of the direction of equilibrium in systems which contain ions with high Z / r values because of the high bond strength between the cation and the surrounding oxygen ions. Previously this has been observed in silicate systems, but more recently it has also been found in aluminate, zirconate, and titanate systems. Indeed, the surprising fact is that the problem is even more acute in the latter systems than in silicates. Highradial coupling coefficients are observed for compositions having up to 50 mole % sodium niobate additions to potassium niobate. The activity diminishes with additional sodium niobate content and disappears beyond about 98 mole yo additions. Dielectric constants are relatively low, varying from 450 to 125, depending on composition. A.-c. losses are high and d.-c. resistivities are -lo1* ohm-cm. The low dielectric constants and high coupling obtained in certain regions of the system make these materials promising for solid ultrasonic delay line use, especially where thin sectioned plates are required, as in high-frequency thickness ertensional or thickness shear mode transducers.

Lead-Free Ferroelectric Ceramics with Perovskite Structure

“…The dielectric constant and dielectric losses are shown in Fig. 7, the T O-T and T C are clearly observed, the T O-T is close to 200°C as reported in several works (Du et al, 2006;Egerton & Dillon, 1959). The Curie temperature also agrees well with that reported previously which is near to 420°C (Ringgaard & Wurlitzer, 2005;Singh et al, 2001).…”

“…The conventional method is well-known and extensively used, and was the first method reported for the synthesis of KNN (Egerton & Dillon, 1959;Jaeger & Egerton, 1962;Shirane et al, 1954), since it is simple and low cost. Basically, it consists of mixing carbonates and oxide powders of the desired elements.…”

“…The method is simple and economic comparing with HP or SPS which will be described in the next sections. Most studies about KNN and related compositions use conventional sintering (Chang et al, 2007;Egerton & Dillon, 1959;Hao et al, 2009;Park et al, 2007;Saito & Takao, 2006;Y. Wang et al, 2007;Zuo et al, 2007), and just some papers report lead-free piezoceramics sintered by HP or SPS.…”

Review: environmental friendly lead-free piezoelectric materials

“…It was established that Ta substitution for Nb, changes the properties of KNbO 3 and the authors also demonstrated that small amounts of Ta for Nb could enhance the piezoelectric properties of KNN ceramics [72,91]. Saito et al [92] also developed a lead-free system containing a blend of alkaline niobate (T c = 415°C) based solid solution with LiTaO 3 (T c = 615°C).…”

“…It is a solid solution of ferroelectric KNbO 3 and antiferroelectric NaNbO 3 , exhibiting very high Curie temperature (T c = 420°C), good ferroelectric properties (P r = 33 lC/cm 2 ), and large electromechanical coupling (1-3x)NBT-2xKBT-xBt factors [72]. The phase diagram for the KNN system is shown in Fig.…”