Keiichi Hatano

Rayleigh Behavior in the Lead Free Piezoelectric Lix(Na0.5K0.5)1-xNbO3 Ceramic

The nonlinear behavior of piezoelectric response in Lix(Na0.5K0.5)1-xNbO3 ceramics with x=0.00–0.08 was investigated by Rayleigh analysis. These ceramics exhibited a linear dependence of the piezoelectric coefficient, d33, with the applied electric field. This data was then analyzed in accordance to the Rayleigh model for poled ceramic materials. The intrinsic contribution was found to be maximized at x=0.06, where this system has a polymorphic phase boundary at room temperature. The extrinsic contribution, which is the origin of the nonlinearity of piezoelectric response, had a maximum value at x=0.03–0.04 and is considered to be strongly affected by the crystal symmetry and domain structures.

Polarization System and Phase Transition on (Li,Na,K)NbO3 Ceramics

The polarization system and phase transition on Li0.055(Na0.50K0.50)0.945NbO3 (LNKN) ceramics were investigated to determine the piezoelectric properties, relative permittivities and X-ray diffraction (XRD). The piezoelectric properties and relative permittivities were strongly dependent on the poled state, which poling temperatures were 25 or 150 °C. The XRD did not exhibit orthorhombic–tetragonal phase transition around the phase transition temperature because no orthorhombic phase was observed below the phase transition temperature. The LNKN ceramics had multiple poled states, the origin of the multiple poled states was considered to be attributable to the multiple spontaneous polarization (Ps) direction on perovskite structure. From these results, we proposed that the phase transition on LNKN was not an orthorhombic–tetragonal phase transition but a monoclinic-tetragonal phase transition. The monoclinic perovskite structure [Z=1, Pm, a=3.9825(5) A, b=3.9438(4) A, c=4.0217(5) A, β=90.292(3)°] can provide multiple Ps directions, such as [101]pc and [001]pc.

Piezoelectric Properties of (Li, Na, K)NbO3 Ceramics with Monoclinic System

The Relationship between the Piezoelectric Properties and Crystal Lattice Deformation and Distortion Resulting from the Li Substitution in LiXNa0.52K0.48-XNbO3, Alkaline Niobate-Based Perovskite Ceramics of (Li, Na, K)NbO3, Was Investigated. the Lattice Parameters of the Sample with a Li Content X = 0.05 and Having a Monoclinic System with Space Group PM Were a = 3.9789(6) Å, B = 3.9385(5) Å, C = 4.0134(6) Å, and B = 90.305(4)º. the ET33/e0, Kr, and -D31 Values of the Sample by Poling in the Monoclinic System Were 450, 44.6%, and 57 PC/N, Respectively. on the other Hand, the ET33/e0, Kr, and -D31 Values of the Sample by Poling in the Tetragonal System Were 600, 38.7%, and 56 PC/N, Respectively. the Remarkable Piezoelectric Properties of these Ceramics Can Be Attributed only to the Low Symmetry of their Monoclinic System, which Is a Subgroup of aMm2 and P4mm. Li0.05Na0.52K0.43NbO3 Ceramics with a Monoclinic System Were Observed to Have the Unique Piezoelectric Characteristics.

Ferroelastic behavior across the orthorhombic-to-tetragonal phase transition region of NKN-based lead-free ferroelectrics

In this study, the macroscopic mechanical behavior was characterized as a function of temperature (−150 °C to 400 °C) for polycrystalline (Na0.5K0.5)NbO3 with three dopant concentrations. Dopants can improve certain electromechanical properties and, in the case of NKN and Li+, shift the orthorhombic-to-tetragonal phase transition temperature to lower temperatures. In this study, the mechanical behavior of undoped NKN, LNKN6 with 6 mol. % Li+, and LNKN6 with additional dopants was characterized and compared with the temperature dependent dielectric response and crystal structure. During mechanical loading, the samples showed a nonlinear hysteretic response. At low temperatures, this is understood to be due to ferroelasticity. At temperatures in the vicinity of the orthorhombic-tetragonal phase transition temperature, a closed hysteresis behavior was observed, corresponding to a local maximum of the critical ferroelastic stress and a minimum in the remanent strain. The observed closed hysteresis behavior is...

High-power impedance spectroscopy for lead-free alkali niobate piezoceramics

Impedance spectroscopy for piezoceramics under high-power application was investigated. Impedance spectra under bipolar high electric field were completely different below and above T C. Below T C, high-power impedance spectra could be successfully fitted to a three resistance-constant phase element (3 R-CPE) equivalent circuit. Above T C, however, a 2 R-CPE equivalent circuit was sufficient to fit with high-power impedance spectra. For this reason, there was another relaxation factor caused by high-power application in the ferroelectric phase. From the high-power impedance spectra below T C, the nonlinear response of capacitance under a high electric field was calculated. Hence, domain wall motion would appear as a relaxation factor. Subsequently, high-power impedance spectra before and after cyclic unipolar fatigue treatment were compared. Considering the assumption that domain wall motion appeared as a relaxation factor, the capacitance caused by domain wall motion was decreased after cyclic fatigue. In conclusion, we believe that domain wall pinning could be evaluated by separating other electrical properties. In this work, the measurement possibility by impedance spectroscopy for high-power application for piezoceramics was investigated.

Investigation of displacement property and electric reliability of (Li,Na,K)NbO3-based multilayer piezoceramics

In this study, lead-free multilayer piezoceramics with Pd inner electrodes were fabricated, and their displacement properties and electric reliabilities were investigated. The Li0.06Na0.52K0.42NbO3 multilayer piezoceramic exhibited a high displacement (S max/E max = 350 pm/V at 5 kV/mm) but a low resistivity (1.3 × 108 Ωcm at 100 °C). On the other hand, the additive-modified Li0.06Na0.52K0.42NbO3 multilayer piezoceramic exhibited both high displacement (S max/E max = 330 pm/V at 5 kV/mm) and high resistivity (1.2 × 1012 at 100 °C), and the breakdown voltages of the two piezoceramics were 4 and 16 kV/mm, respectively, at 100 °C. The observed improvement in electric reliability can be attributed to the refinement of the microstructure of Li0.06Na0.52K0.42NbO3 after the use of additives. Furthermore, the additive-modified Li0.06Na0.52K0.42NbO3 multilayer piezoceramic also showed a markedly higher resistivity than previously reported multilayer piezoceramics with Ag/Pd, Cu, and Ni inner electrodes, since the dispersion of elemental Ag and the generation of oxygen vacancies during the sintering process was prevented in the former case.