Influence of mechanochemical activation on the synthesis and properties of (K,Na)NbO3-based piezoceramics

The improvement of piezoelectric properties of chemically modified (K,Na)NbO3 (KNN) solid solutions has been recognized as a promising direction for the development of efficient lead-free piezoelectric ceramics [1]. However, a... [ view full abstract ]

The improvement of piezoelectric properties of chemically modified (K,Na)NbO₃ (KNN) solid solutions has been recognized as a promising direction for the development of efficient lead-free piezoelectric ceramics [1]. However, a set of common difficulties accompanying the processing of such compositions needs to be considered as these issues can significantly affect the reproducibility of electromechanical properties and thus hinder their practical application [2].

One of the major challenges, achieving a high degree of compositional homogeneity with a low level of contamination, can be overcome by mechanochemically activating the powder mixture prior the calcination step [3]. In this study, mechanochemical activation is employed to assist the solid-state synthesis of Li- and Ta-modified (K,Na)NbO₃-CaZrO₃ (KNLNT-CZ) with MnO₂ addition, which was reported as a promising KNN-based lead-free piezoceramic material with remarkable temperature stability and enhanced strain behavior [4]. The starting powders were high-energy milled. The formation of a transitional amorphous carbonato complex was observed during activation as followed by IR spectroscopy. A single calcination at 800 °C and subsequent sintering at 1150 °C yielded a dense KNLNT-CZ ceramic with a fine-grained microstructure and good electrical properties (room temperature permittivity and dielectric losses measured at 1 kHz ~2000 and ~0.03, respectively; piezoelectric coefficient d₃₃ ~150 pC/N). The overall advantage related to this approach will be discussed and compared to the conventional solid-state synthesis route.

[1] Y. Saito et al., Nature, 432, 84–87, 2004.

[2] B. Malič et al., Materials, 8, 8117–8146, 2015.

[3] T. Rojac, A. Benčan and M. Kosec, J. Amer. Ceram. Soc., 93, 1619–1625, 2010.

[4] K. Wang et al., Adv. Funct.Mat., 23, 4079–4086, 2013.