Abstract
(Na0.55K0.45)NbO3 (NKN) and acceptor-doped (Na0.55K0.45)(Nb1-xZr5x/4)O3 (NKNZ; x = 0.005 and 0.01) piezoelectric ceramics were fabricated by the conventional solid-state reaction method. Both ceramics were applied to a fatigue test for 106 cycles under an electric field at 3 kV/mm with unipolar drive. After the fatigue test, the maximum polarization of NKN and NKNZ (x = 0.005) was decreased by approximately 15 and 5%, respectively. Therefore, we found that the fatigue resistance properties of NKNZ ceramics, which substituted the Nb5+ ion with the Zr4+ ion, were improved. To study fatigue phenomena in piezoelectric ceramics, the chemical bond strength of both ceramics before and after the fatigue test was analyzed by soft X-ray emission spectroscopy (SXES), which has high energy resolution and is suitable for the evaluation of light elements in a local region with the micrometer order. We evaluated the formation of oxygen vacancies in as-sintered, poled, and fatigued ceramics by analyzing a chemical shift of the O Ka(3) peak appeared at approximately 175 eV in the SXES spectra. In NKN ceramics, the O Ka(3) peak was shifted to the higher energy side by the poling treatment and fatigue test. The peak position of fatigued NKN ceramics was close to that of the standard SrTiO3 sample. It was considered that the oxygen vacancies of the fatigued NKN ceramics had accumulated at grain boundaries instead of the oxygen moving. The improvement of the fatigue resistance for the NKNZ ceramics was attributed to the formation of a defect dipole connected with the oxygen vacancy and acceptor Zr ion.
Highlights
Many dielectric- and piezoelectric devices using perovskitetype ferroelectrics sustain the comfort and safety of our lives and are indispensable for maintaining our lives in the future
(Na0.55K0.45)NbO3 (NKN) and acceptor-doped (Na0.55K0.45)(Nb1-xZr5x/4)O3 (NKNZ; x = 0.005 and 0.01) piezoelectric ceramics were fabricated by the conventional solid-state reaction method
We considered that the Zr4+ ion was doped to the B-site of NKNZ ceramics, since the Zr4+ ion cannot have a coordination number of 12 in the A-site of the perovskite structure
Summary
Many dielectric- and piezoelectric devices using perovskitetype ferroelectrics sustain the comfort and safety of our lives and are indispensable for maintaining our lives in the future. In the case of the displacement sustainable type and the precision displacement type in a high electric field, the fatigue mechanism has been considered electric damage caused by the accumulation of oxygen vacancies at grain boundaries and domain walls.. In the case of the displacement sustainable type and the precision displacement type in a high electric field, the fatigue mechanism has been considered electric damage caused by the accumulation of oxygen vacancies at grain boundaries and domain walls.3–5 This is because, in the perovskite-type structure, the oxygen ion has an activation energy. In NKN-series ceramics, the relationship between oxygen vacancies and grain boundaries has already been reported by using a polarization-electric field (P-E) hysteresis loop, an electric-field-induced strain measurement, a thermally stimulated depolarization current measurement, and impedance analysis.. We investigated the role of oxygen vacancies in the electric fatigue properties of NKN-series piezoelectric ceramics by using SXES and showed that the formation of a defect dipole for NKN-series ceramics is effective for suppressing the fatigue properties
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