Maeda, T., Takiguchi, N., Morita, T., Ishikawa, M., &; Hemsel, T. (2010). Hydrothermal (K1-xNax)NbO3 Lead-free Piezoelectric Ceramics. Journal of Korean Physical Society, 57(4), 924–928.https://doi.org/10.3938/jkps.57.924 

Maeda, T., Takiguchi, N., Morita, T., Ishikawa, M., &; Hemsel, T. (2010). (K,Na)NbO3 lead-free piezoelectric ceramics synthesized from hydrothermal powders. Materials Letters, 64(2), 125–128.https://doi.org/10.1016/j.matlet.2009.10.012