Amorphous KNbO (KN) films were grown on a TiN/SiO/Si substrate to synthesize a KN memristor as a potential artificial synapse. The Pt/KN/TiN memristor exhibited typical and reliable bipolar switching behavior with multiple resistance levels. It also showed the transmission properties of a biological synapse, with a good conductance modulation linearity. Moreover, the KN memristor can emulate various biological synaptic plasticity characteristics including short-term plasticity, long-term plasticity, spike-rate dependent plasticity, paired-pulse facilitation, and post-tetanic potentiation by controlling the number and rate of the potentiation spike. Spike-timing-dependent plasticity (STDP), which is an essential property of biological synapses, is also realized in the KN memristor. The synaptic plasticity of the KN memristor can be explained by oxygen vacancy movement and oxygen vacancy filaments. The metaplasticity of biological synapses was also implemented in the KN memristor, including the metaplasticity of long-term potentiation and depression, and of STDP. Therefore, the KN memristor could be used as an artificial synapse in neuromorphic computing systems.

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KNbO 3 (KN) nanowires having a tetragonal structure or a polymorphic phase boundary (PPB) structure, which contains both tetragonal (P4mm) and orthorhombic (Amm2) structures, are formed at low temperatures. The presence of tetragonal and PPB KN nanowires is attributed to the existence of OH À and H 2 O defects. Further, the tetragonal and PPB KN nanowires change to orthorhombic KN nanowires in the temperature range between 300 and 400 C owing to desorption of the lattice hydroxyl group. A composite consisting of polydimethylsiloxane (PDMS) and KN nanowires having a PPB structure shows large dielectric constant and low dielectric loss values of 9.2 and 0.5%, respectively, at 100 kHz.Moreover, a nanogenerator (NG) synthesized using the PPB KN nanowires exhibits the largest output voltage and current among NGs synthesized using the tetragonal or orthorhombic KN nanowires. In particular, the NG containing 0.7 g of PPB KN nanowires shows an output voltage of 10.5 V and an output current of 1.3 mA; these values are among the highest ever reported for NGs synthesized using a lead-free composite. In addition, this NG exhibited the maximum output power and energy conversion efficiency, which were 4.5 mW and 0.9%, respectively, for an external load of 1.0 MU.

K(Nb1−xMnx)O3 (KN1−xMx) ceramics with 0.005 ≤ x ≤ 0.015 were sintered at 1020°C through a normal sintering process without the formation of a liquid phase. They exhibited double polarization versus electric field (P–E) hysteresis and sprout‐shaped strain versus electric field (S–E) curves owing to the presence of a defect dipole (PD), which was formed between the acceptor Mn3+ ion and the oxygen vacancy. Moreover, the aging process was not required to develop the PD. The KN1−xMx ceramics exhibited a large strain of ~0.2% at 6.0 kV/mm. For the KN0.985M0.015 ceramic, this large strain was maintained after 104 cycles of an electric field of 6.0 kV/mm. This ceramic also maintained a double hysteresis curve at 200°C. Therefore, the KN0.985M0.015 ceramic has a large electric field‐induced strain, along with good thermal and fatigue properties for multilayer piezoelectric actuators.