Papers by Author: Daisuke Tanaka

Abstract: Denser, solvothermally synthesized KNbO₃ (KN) / BaTiO₃ (BT) composites with heteroepitaxial interfaces were prepared using the barium titanate powder with a wide particle size distribution. The relative density was 68 - 80 %, which was larger than that of the composites prepared using the barium titanate powder with a narrow particle size distribution. The dielectric constant was 300 450 and it was maximized at the KN/BT molar ratio of 0.5. The origin was discussed with the microstructure and crystal structure.

Abstract: Effect of the microstructural homogeneity of 0.5 BaTiO₃ - 0.5 KNbO₃ (0.5BT-0.5KN) solid solution ceramics on the dielectric and piezoelectric properties was investigated. Microstructure of a sample prepared by a conventional sintering method was homogenous, and the room temperature crystal structure was assigned to cubic Pm3m symmetry and therefore the sample was paraelectric. On the other hand, microstructure of samples prepared by a two-step sintering method was inhomogeneous, that is, it was made of BT and KN grains. The large electric field piezoelectric constant d₃₃* increased with increasing interface area.

Abstract: Barium titanate (BaTiO3, BT) - potassium niobate (KNbO3, KN) solid solution system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method using BT and KN nanoparticles. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM), and it was confirmed that two ferroelectric phases, i.e., BT-rich tetragonal and KN-rich orthorhombic phases, always coexisted for all ceramics, which suggested that 0.5BT-0.5KN ceramics had “pseudo-morphotropic phase boundary (MPB)” structure. Thus, the control of the interface area between two phases was important to enhance piezoelectric property. Finally, their piezoelectric property was measured, and the apparent piezoelectric constant d33* increased with increasing interface area.

Abstract: Barium titanate (BaTiO3, BT) and potassium niobate (KNbO3, KN) ceramics were prepared by normal sintering process. Phase diagram of BT-KN system was investigated using high-temperature XRD and dielectric measurement, and two phases coexistence between tetragonal and orthorhombic was observed at room temperature. Transmission electron microscope (TEM) observation confirmed that the microstructure of the ceramics with KN contents below 30 molar% was composed of only tetragonal BT-rich grain, while those with KN contents above 40 molar% were composed of two kinds of grains, i.e., tetragonal BT-rich and orthorhombic KN-rich grains. Phase boundary between two phases for BT-KN ceramics was grain boundary. Thus, we named two phases coexistence region for BT-KN ceramics “wide-band morphotropic phase boundary (MPB)”. Finally, dielectric and piezoelectric properties were investigated, and both dielectric and apparent d33 maximum were observed at the 0.5BT-0.5KN ceramics.