Maeda, Takafumi, et al. “Hydrothermal (K1-XNax)NbO3 Lead-Free Piezoelectric Ceramics.”10.3938/jkps.57.924__Journal of Korean Physical Society, vol. 57, no. 4, 2010, pp. 924–28, doi:10.3938/jkps.57.924.

Maeda, Takafumi, et al. “(K,Na)NbO3 Lead-Free Piezoelectric Ceramics Synthesized from Hydrothermal Powders.”10.1016/j.matlet.2009.10.012__Materials Letters, vol. 64, no. 2, 2010, pp. 125–28, doi:10.1016/j.matlet.2009.10.012.