Shigehito Shimizu

Enhanced piezoelectric response of BaTiO3–KNbO3 composites

The piezoelectric response of solvothermally synthesized BaTiO3 (BT)–KNbO3 (KN) composites (the nominal BT/KN ratio was 1) with distinct interfaces was investigated. The x-ray diffraction pattern showed two distinct peaks began to merge into a singular broad peak at a two-theta position between (200) and (002) tetragonal-related peaks of BT. The transmission electron microscopy observation showed a heteroepitaxial interface region between BT single-crystal particles and deposited KN crystals. The large-field piezoelectric constant was 136 pC/N, which was three times larger than that of a sintered 0.5BT–0.5KN composite. The enhanced piezoelectric response was attributed to the strained epitaxial interface region.

Preparation of Barium Titanate–Potassium Niobate Nanostructured Ceramics with Artificial Morphotropic Phase Boundary Structure By Solvothermal Method

Barium titanate (BaTiO3, BT)–potassium niobate (KNbO3, KN) (BT–KN) nanostructured ceramics with a distorted interface region, i.e., artificial morphotropic phase boundary (MPB) structure, were prepared by the solvothermal method. The results of the optimization of reaction conditions showed that the metastable region of only KN crystal growth was obtained using a mixture of KOH and K2CO3 as the K source and Nb2O5 as the Nb source in ethanol. Moreover, KN formation under the metastable region using a particle compact composed of a mixture of BT and Nb2O5 particles as substrates resulted in the successful preparation of BT–KN nanostructured ceramics with an artificial MPB region and a porosity of around 35%. This is the first report on the preparation of ceramics with a heteroepitaxial interface between BT and KN below 230 °C.

Microstructure Control of Barium Titanate – Potassium Niobate Solid Solution System Ceramics by MPB Engineering and their Piezoelectric Properties

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.

Enhanced Piezoelectric Properties of Barium Titanate-Potassium Niobate Solid Solution System Ceramics by MPB Engineering

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.

Piezoelectric Properties of Porous Potassium Niobate System Ceramics

Porous potassium niobate (KNbO3, KN) system ceramics were prepared by a conventional sintering method using carbon black (CB) nanoparticles. First, KN nanoparticles with a size of 100 nm was mixed with CB nanoparticles and binder using ball milling with ethanol. The mixture was dried, and pressed into pellets using uniaxial pressing. After binder burnout, these ceramics was sintered in air. Their piezoelectric properties were measured and discussed a relationship between porosity and piezoelectric properties. As the results, with increasing porosity, piezoelectric g33 constant increased significantly, which suggested that porous ceramics were effective for stress sensor application.

Enhanced Piezoelectric Properties of Lead-Free Piezoelectric Materials by Microstructure Control

Barium titanate (BaTiO3, BT)—potassium niobate (KNbO3, KN) solid solution system (0.5BT-0.5KN) ceramics with various microstructures were prepared by two-step sintering method, and their piezoelectric properties were investigated. For 0.5BT-0.5KN ceramics, two phases, ferroelectric tetragonal and ferroelectric orthorhombic, coexisted in different grains at room temperature, owing to the limited solid solution system. The volume fraction of interface region between BT-rich tetragonal and KN-rich orthorhombic grains was controlled by sintering temperatures, and increased with decreasing sintering temperatures. Apparent piezoelectric constant d 33* was measured using slope of strain vs. electric field curves. As the results, the d 33* increased with decreasing sintering temperatures, which revealed that interface region between tetragonal and orthorhombic grains could contribute to enhancement of piezoelectric properties.

Preparation of Potassium Niobate-Coated Barium Titanate Accumulation Ceramics by Solvothermal Synthesis and Enhancement of Piezoelectric Property

Barium titanate (BaTiO3, BT) - potassium niobate (KNbO3, KN) nanostructured ceramics with artificial morphotropic phase boundary (MPB) structure were successfully prepared at temperatures below 230 °C by solvothermal method. Various characterizations suggested that the BT-KN nanostructured ceramics exhibited a porosity of around 30 % and heteroepitaxial interface between BT and KN. Their dielectric and piezoelectric properties were measured at room temperature, and the dielectric constant and apparent piezoelectric constant estimated from slope of strain and electric field curve was 370 and 136 pm/V, respectively.

Preparation of Potassium Niobate–Barium Titanate Ceramics Using Well-Dispersed Nanoparticles and their Dielectric Properties

ANbO3 – BaTiO3 (A=K, Na, or K0.5Na0.5) system ceramics were prepared using a conventional sintering method, and their dielectric properties were investigated. It was found that the dielectric constant of KNbO3-BaTiO3 and (K0.5Na0.5) NbO3- BaTiO3 system ceramics did not strongly depend on temperature between 20 and 400 °C, making them useful for capacitor application.

Porosity Dependence of Piezoelectric Properties for Porous Potassium Niobate System Ceramics

Porous potassium niobate (KNbO3, KN) system ceramics were prepared by a conventional sintering method using carbon black (CB) nanoparticles. First, KN nanoparticles with a size of 100 nm was mixed with CB nanoparticles and binder using ball milling with ethanol. The mixture was dried, and pressed into pellets using uniaxial pressing. After binder burnout, these ceramics was sintered in air. Their piezoelectric properties were measured and discussed a relationship between porosity and piezoelectric properties. As the results, with increasing porosity, piezoelectric g33 constant increased significantly, which suggested that porous ceramics were effective for stress sensor application.

Microstructure Control of Barium Titanate - Potassium Niobate Solid Solution System Ceramics by MPB Engineering and Their Piezoelectric Properties

KBaTiNbO6, i.e., 0.5BT-0.5KN complete solid solution ceramics and barium titanate (BaTiO3, BT) - potassium niobate (KNbO3, KN) system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method. The 0.5BT-0.5KN with diffusion of BT and KN completely were paraelectrics. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM). KBaTiNbO6 at room temperature was assigned to cubic Pm3m symmetry. For the 0.5BT-0.5KN patially solid solution system ceramics, the control of the interface area between two phases was important to enhance piezoelectric property. Their piezoelectric property was measured, and the apparent piezoelectric constant d33* increased with increasing interface area.