The potassium sodium niobate (KxNa1−x)NbO3 (KNN) family with the perovskite structure is a technologically important lead-free piezoelectric material. This paper reviews the ferroelectric and structural phase transitions of KNN and related materials. The nature of end members, the physical properties, and phase transitions of simple alkali niobate materials MNbO3 (M=Li, Na, K, Rb, and Cs) are reviewed. The binary solid solution's phase diagram, KNN, is introduced concerning the morphotropic phase boundary (MPB). To understand the phase transitions near the MPB composition, the temperature dependences of lattice dynamical properties of KNN single crystals on optical modes and acoustic modes are reviewed by Raman and Brillouin scattering studies, respectively. Physical properties and phase transitions of KNN-based solid solutions were also reviewed.

Tactile technology is becoming increasingly important due to robotics applications and the use of the metaverse. However, there is few research on tactile technologies that can provide information on two-point discrimination thresholds at the human sensory level, and practical application has not progressed. This is due to the fact that the devices are complex and cannot be compactly mounted in key locations such as fingertips. This research aims to develop thin, flexible piezoelectric resin devices and put them into practical use. Here, it is important to miniaturize the drive circuits that drive such piezoelectric devices, so we developed a drive system that uses a piezoelectric driver IC that utilizes serial communication, and is capable of generating a wide range of tactile sensations, including multi-tone gradations.