Masaki Fukada

The effect of SrTiO3 substrate orientation on the surface morphology and ferroelectric properties of pulsed laser deposited NaNbO3 films

Orientated NaNbO3 (NN) films were grown on SrRuO3/(001)SrTiO3 [SRO/(001)STO], SRO/(110)STO, and SRO/(111)STO substrates by pulsed laser deposition. Scanning electron microscopy images showed that the surface morphologies of the NN/SRO/(001)STO, NN/SRO/(110)STO, and NN/SRO/(111)STO took the form of a stepped structure, a striped pattern, and trigonal pyramidal-like structures, respectively. The dielectric and ferroelectric properties of the films were characterized. The NN/SRO/(110)STO film showed the lowest relative dielectric constant and the largest remanent polarization of 30.8 μC/cm2 among all films. These were interpreted as being due to the orientation direction of the NN film grown on (110)STO being parallel to the polarization direction of NN.

Fabrication of lead-free piezoelectric (Na 0.5 K 0.5 )NbO 3 ceramics by a modified solid-state reaction method

Sodium potasium niobate, (Na_0.5K_0.5)NbO₃ fine powder has been successfully synthesized at a low temperature of 550degC through a modified solid state reaction, in which urea [CO(NH₂)₂] plays an important role. High-density (Na_0.5K_0.5)NbO₃ ceramics can be obtained by a conventional sintering with an addition of 0.03 mol% Co₃O₄. Their crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na_0.5K_0.5)NbO₃ ceramics show a comparatively saturated P-E hysteresis loop. The (Na_0.5K_0.5)NbO₃ ceramics also show piezoelectricity with a piezoelectric constant, d₃₃, of 126 pC/N and a planar electromechanical coupling factor, k_p, of 33%..

Fabrication of Lead-Free (Na0.52K0.44Li0.04)(Nb0.84Ta0.10Sb0.06)O3 Piezoelectric Ceramics by a Modified Solid-State Reaction Method

(Na0.52K0.44Li0.04)(Nb0.84Ta0.10Sb0.06)O3 (LF4) ceramics have been successfully prepared by a combination of a modified solid-state reaction and a conventional sintering method. LF4 fine powder with a perovskite structure was obtained by the modified solid-state reaction and continuous re-calcination treatment at low temperatures of 500–600 °C. The obtained fine powders had good sinterability and high-density LF4 ceramics with relative density more than 94% could be easily obtained by a conventional sintering. The obtained LF4 ceramics showed excellent piezoelectricity. The Curie temperature of LF4 ceramics was about 280 °C. The leak current measurements exhibited that the insulation property of the LF4 was improved by sintering in the oxygen atmosphere due to the decrease in the oxygen vacancies. The LF4 ceramics sintered in the oxygen atmosphere, which showed a larger saturated P–E hysteresis loop, also showed larger piezoelectricity than those sintered in the air. Additionally, we found that the LF4 ceramics after P–E hysteresis measurement exhibited larger piezoelectric properties than those without P–E hysteresis measurement. The largest piezoelectric constant d33 was 352 pC/N and the planar electromechanical coupling factor kp was 44%. This would be due to the effect on the domain motion by applying an AC bias field.

Fabrication of Lead-Free (Na0.5K0.5)NbO3–BaZrO3–(Bi0.5Li0.5)TiO3 Ferroelectric Thin Films on (111)Pt/Ti/SiO2/(100)Si Substrate by Pulsed Laser Deposition

0.92(Na0.5K0.5)NbO3–0.06BaZrO3–0.02(Bi0.5Li0.5)TiO3 (NKN–BZ–BLT) thin films were fabricated on a (111)Pt/Ti/SiO2/(100)Si substrate by pulsed laser deposition (PLD). The quality of the NKN–BZ–BLT thin films was improved by introducing an NKN–BZ–BLT buffer layer, which was deposited at a high substrate temperature of 850 °C. An X-ray diffraction pattern (XRD) showed that the 100pt preferential-oriented NKN–BZ–BLT thin films [on the basis of a pseudotetragonal perovskite (pt) structure] were obtained without and with buffer layers. From the rocking curves, the crystallinity of the film was slightly improved by introducing the buffer layer. SEM images showed that the grain size was increased and cracks were eliminated by introducing the buffer layer. The dielectric constant of the films was comparable to that of NKN–BZ–BLT ceramics. The P–E hysteresis loops showed that the remanent polarization and spontaneous polarization of the films increased with the increase in the thickness of the buffer layer. The NKN–BZ–BLT film with a 0.8-µm-thick buffer layer exhibited a remanent polarization of 6.7 µC/cm2 and a spontaneous polarization of 28.0 µC/cm2. This improvement of the ferroelectric properties would be due to the relaxation of the tensile stress in the presence of the buffer layer.

Fabrication of (K,Na)NbO 3 thin films on Si substrate by pulsed laser deposition

We fabricated (Na,K)NbO<inf>3</inf> (NKN) thin films on (111)Pt/Ti/SiO<inf>2</inf>/(001)Si substrates at substrate temperature of 750°C in O<inf>2</inf> gas pressure of 200 mTorr by pulsed laser deposition (PLD). The ferroelectric properties of the NKN thin films were improved by the insertion of a thin NKN or NN buffer layer. These buffer layers had an influence on composition control of the NKN films. The remanent polarization and the coercive electric field of the NKN films with the NN buffer layer were 15 µC/cm² and 40 kV/cm, respectively.

Fabrication of Lead-Free Piezoelectric (Na 0.5 K 0.5 )NbO 3 Ceramics by Modified Solid State Reaction Method

Sodium potassium niobate, (Na_0.5K_0.5)NbO₃, fine powder has been successfully synthesized at the low temperature of 550degC through a modified solid-state reaction method, in which urea [CO(NH₂)₂] plays an important role. High-density (Na_0.5K_0.5)NbO₃ ceramics could be obtained by conventional sintering of the synthesized (Na_0.5K_0.5)NbO₃ fine powder with the addition of 0.03 mol% Co₃O₄ as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na_0.5K_0.5)NbO₃ ceramic showed a comparatively saturated P-E hysteresis loop. The (Na_0.5K_0.5)NbO₃ ceramic also displayed piezoelectricity with a piezoelectric constant d₃₃ of 126 pC/N and a planar electromechanical coupling factor k_p of 33%.