Synthesis of lead-free piezoelectric powders by ultrasonic-assisted hydrothermal method and properties of sintered (K0.48N.52)NBO3 ceramics
G. Isobe, T. Maeda, P. Bornmann, T. Hemsel, T. Morita, Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions On 61 (2014) 225–230.

Synthesis of piezoelectric materials by ultrasonic assisted hydrothermal method
G. Isobe, R. Ageba, T. Maeda, P. Bornmann, T. Hemsel, T. Morita, in: B. B. J. Linde, J. Paczkowski, N. Ponikwicki (Eds.), AIP Conference Proceedings, AIP, 2012, pp. 569–572.