Kenta Yamashita

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.

Crystal Structure of BaTiO3?KNbO3 Nanocomposite Ceramics: Relationship between Dielectric Property and Structure of Heteroepitaxial Interface

High-energy synchrotron radiation powder diffraction experiments have been carried out to investigate the crystal structure of solvothermally synthesized KNbO3 (KN)/BaTiO3 (BT) nanocomposite ceramics in which a ceramic grain consists of a BT nanoparticle thinly coated with KN crystals through the heteroepitaxial interface. Rietveld analysis reveals that the ceramic grain has the core/multishell structure consisting of a BT core and distorted BT and KN multishells. BT is gradually distorted in the large region to form the interface with KN from the tetragonal structure at the core toward the cubic structure at the boundary between BT and KN. The variations of the volume of the distorted interface region of BT and the dielectric property of the ceramics show similar trends to the variation of KN/BT molar ratio, which suggests that the electrically soft interface of BT nanoparticles governs the dielectric properties of the ceramics.

Nanostructure Control of Barium Titanate--Potassium Niobate Nanocomplex Ceramics and Their Enhanced Ferroelectric Properties

Barium titanate (BaTiO3,BT)–potassium niobate (KNbO3,KN) nanocomplex ceramics with various KN/BT molar ratios were prepared by a solvothermal method. From a transmission electron microscopy (TEM) observation, it was confirmed that the KN layer thickness on BT particles was controlled from 5 to 40 nm by controlling KN/BT molar ratios. Their dielectric constants were measured at room temperature and 1 MHz, and the maximum dielectric constant of 370 was measured for the BT–KN nanocomplex ceramics with a KN thickness of 22 nm. TEM observation revealed that at a KN thickness below 22 nm, the BT/KN heteroepitaxial interface was assigned as a strained interface, while at 40 nm, the interface was assigned as a relaxed one. These results suggested that the strained heteroepitaxial interface could be responsible for the enhanced dielectric properties.

Microstructure Control of Potassium Niobate Porous Ceramics and their Sensor Properties

Porous potassium niobate (KNbO3, KN) system ceramics were prepared by spark plasma sintering (SPS) method using carbon black (CB, 5 μm). First, the powders of raw materials were mixed in ethanol by ball milling, and then calcined. Obtained KN powders with CB were sintered by SPS in argon atmosphere. Their piezoelectric properties were measured and a relationship between porosity, pore size, and sensor properties was studied. It was found that d33 increased as pore size decreased. Thus, pore size was important for the improvement of value of g33/ρ.

Grain Size Dependence of the Microstructure and Dielectric Properties of Potassium Niobate-Barium Titanate Ceramics

In this study, 0.8 KNbO3 (KN) -0.2 BaTiO3 (BT) ceramics were prepared using KN powder with the diameter of 100 nm and BT powders with the diameter of 100, 300, or 500 nm. The relative densities were more than 96 % of the theoretical densities of the samples. The dielectric constant of the samples was temperature-stable at temperatures between-50 and 300 °C and it was found that the dielectric constant of the 0.8KN-0.2BT ceramics increased as the BT diameter increased.

Preparation of Potassium Niobate/Barium Titanate Nanocomposite Ceramics with a Wide Barium Titanate Particle Size Distribution and their Dielectric Properties

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.

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.

Piezoelectric and Dielectric Enhancement of New Nano-structured Ceramics with Heteroepitaxial Interfaces

Barium titanate (BT) - potassium niobate (KN) nano-structured ceramics with an artificial morphotropic phase boundary (MPB) structure were prepared by a solvothermal method at temperatures below 230 °C. Various characterizations of the BT-KN nano-structured ceramics revealed that the BT/KN molar ratio was 1, the porosity was around 30 %, and the interface between BT particles and KN crystals was heteroepitaxial. The apparent piezoelectric constant d33* was 136 pC/N, which was three times larger than that of 0.5BT-0.5KN dense composite ceramics. The concept proposed in this study can be useful to create piezoelectric ceramics with artificial MPB regions.

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.