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.
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.
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.
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