(K0.5Na0.5)NbO3 (KNN) + x (= 1, 0.5, 0.05, and 0) wt%Co3O4 single crystals were fabricated by a solid-state crystal growth method with a KTaO3 seed crystal and a KNN atmosphere powder, and the ...effects of the sintering aid content x and the addition of Co3O4 to the atmosphere powder on the growth of the single crystals were investigated. The formation of pores in the single crystals was suppressed by a decrease of x, which, however, decreased the crystal growth length. On the other hand, dense and large KNN single crystals could be fabricated by sintering with a KNN + 5 wt%Co3O4 atmosphere at x = 0. The dielectric, ferroelectric, and piezoelectric properties of the KNN single crystals were comparable to those of reported (K,Na)NbO3 single crystals. These results would be useful for fabricating dense and large single crystals by the solid-state crystal growth method.
The origin of the significantly large piezoelectricity and ferroelectricity was investigated in the 0.67BiFeO3–0.33BaTiO3 ceramics. The crystal structure of 0.67BiFeO3–0.33BaTiO3, identified using ...the Rietveld method, suggested a cubic structure at 950 K and a rhombohedral structure at 300 K with small lattice distortion 89.94(4)°, which is close to 90° of cubic structure. Despite the small lattice distortion at 300 K, significantly large piezoelectricity and ferroelectricity was observed in the 0.67BiFeO3–0.33BaTiO3, which is associated Bi ion off-centering. The Bi3+ ions were off-centered from the corner of the Ba2+ position along the 〈100〉 directions at 300 K, occupying three equivalent neighboring sites in the 100, 010, and 001 directions. The occupancies of Bi ions could be changed, and partially ordered along the applied electric field direction. The off-centered Bi ions are attributed to the ferroelectricity and piezoelectricity in non-centrosymmetry structure with a small lattice distortion, i.e., pseudo-cubic structure, due to partial ordering under the electric field.
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Piezoelectric materials play a key role in applications, while there are physically open questions. The physical origin of piezoelectricity is understood as the sum of contributions from intrinsic ...effects on lattice dynamics and those from extrinsic effects on ferroic‐domain dynamics, but there is an incomplete understanding that all but intrinsic effects are classified as extrinsic effects. Therefore, the accurate classification of extrinsic effects is important for understanding the physical origin of piezoelectricity. In this work, high‐energy synchrotron radiation X‐ray diffraction is utilized to measure the response of BiFeO3−BaTiO3 piezoelectrics and the intrinsic/extrinsic contribution to electric fields. It is found from crystal structure and intrinsic/extrinsic contribution, using the analysis involving structure refinement with various structural model and micromechanics‐based calculations, that Bi3+‐ion disordering is important for realization of piezoelectricity and nanodomains. Here, an extrinsic effect on the rearrangement of nanodomains is suggested. The nanodomains, which are formed by the locally distorted structure around the A‐site by Bi‐ion disordering, can significantly deform the material in the BiFeO3−BaTiO3 system, which contributes to the piezoelectric actuation mechanism apart from the extrinsic effect on ferroic‐domain dynamics. Bi‐ion disordering plays an important role in realizing piezoelectricity and nanodomains and can provide essential material design clues to develop next‐generation Bi‐based lead‐free piezoelectric ceramics.
The piezoelectric actuation mechanism in pseudocubic structures is clarified by the calculation of extrinsic/intrinsic contribution. Although only intrinsic contributes to the piezoelectricity, it does not match the piezoelectricity of BiFeO3–BaTiO3. It is clarified that extrinsic effect on nanodomain rearrangements is revealed in BiFeO3–BaTiO3. Extrinsic effect on nanodomain rearrangement is involved in the actuation mechanism of piezoelectricity.
The lead-free x(Bi0.5K0.5)TiO3-0.23BaTiO3-0.02Bi(Mg0.5Ti0.5)O3-(0.75-x)BiFeO3 piezoelectric ceramics (x = 0.05, 0.07, 0.09, and 0.11) were prepared by solid-state reaction method. The increase of ...(Bi0.5K0.5)TiO3 concentration revealed a decrease of dielectric maximum temperature (Tm), however, the values were higher than 420 °C. The Rietveld structure refinement for each composition showed pseudo-cubic symmetry and the rhombohedral distortion (90 - αF) was gradually decreased from 0.27° to 0.09° for x = 0.05 and 0.11, respectively. The saturation and remanent polarization were increased and a coercive field was decreased, while the critical exponent (γ) was increased from 1.407 (x = 0.07) to 1.821 (x = 0.11) revealing more relaxor-like behavior with higher (Bi0.5K0.5)TiO3 content. The remanent polarization, coercive field, and piezoelectric strain constant of 31.9 μC/cm2, 23.6 kV/cm, and 315 pm/V, respectively, obtained in the composition with x = 0.11 are significantly higher than those reported previously for other Bi-based piezoelectric ceramics with Tm>250 °C.
BaTi1-2xMnxNbxO3 (x = 0, 0.05 and 0.10) ceramics were fabricated by either one-step calcination or two-step calcination with the first calcination of BaTi1-2xMnxO3-δ and the second calcination with ...Nb2O5 addition, and the effect of the calcinations on crystal structure, microstructure, and electrical properties was investigated. With the Mn and Nb substitution, the crystal system of BaTiO3 changed to a pseudo-cubic, the temperature dependence of the dielectric constant was flattened, and the polarization-electric field (P-E) loops became almost linear. At x = 0.10, compared with the one-step calcined ceramics with a remaining hexagonal phase and higher dielectric loss at high temperatures, the two-step calcined ceramics had a single-phase perovskite structure, the dielectric constants of 575–345 at temperatures between 25 and 150 °C with smaller dielectric loss, and the dielectric constants estimated from the slopes of the P-E loop of ∼650 at 0 kV/cm and ∼500 at 100 kV/cm at room temperature. BaTiO3+xMnO2+x/2Nb2O5 ceramics were also fabricated at x = 0.05 and 0.10, but they were less dense and had a secondary phase. These results suggest that the two-step calcined BaTi1-2xMnxNbxO3 ceramics with x = 0.10 can be a candidate material for temperature stable, DC-bias free capacitor applications.
Nanostructured porous zinc oxide electrodes for use in dye-sensitized solar cells (DSSCs) were coated with thin niobium oxide layers by using sol–gel transformation of niobium pentaethoxide in air. ...Coating solutions were prepared by mixing niobium pentaethoxide and ethanol. A dip-coating technique was adopted at a low withdrawal speed of 100μms−1. The coated electrodes were then heat-treated at temperatures between 400 and 600°C. The presence of niobium in the coated electrodes was confirmed by X-ray photoelectron spectroscopy. As expected, the niobium oxide layers worked as an energy barrier between the ZnO electrode and electrolyte. Open-circuit voltage (VOC) of the cells using the coated electrodes was then enhanced up to 0.768V, which was attributable to the suppression of the recombination of photogenerated electrons with oxidized species in electrolytes. An additional benefit of the coating was that grain growth of ZnO particles in the electrodes was hindered and short-circuit photocurrent density (JSC) was kept relatively high due to large amounts of adsorbed dye. An overall light-to-electricity conversion efficiency was increased to a maximum of 5.19%, indicating that the proper coating technique was the key for improving the performance of ZnO-based DSSCs.
Hybridization induced by human activities, such as crossbreeding between invasive and native species, can adversely affect the natural biodiversity of an ecosystem. In Japan, the endemic turtle ...species
is known to hybridize with the alien species
, and putative hybrids have been encountered in the wild. If
×
hybrids can readily crossbreed with
, the hybridization with
could lead to the extinction of pure
populations. However, information on the reproductive ability of
×
hybrids is limited. In this study, we collected wild-caught hybrids from across western Japan to assess their reproductive ability. We investigated the nesting season timing, clutch size, embryonic development, hatching success, and sperm viability. The results showed that female hybrids nested during the same months as the parental species and had similar clutch sizes and hatching success. No embryonic development abnormalities were detected, and viable sperm were observed in all hybrid male semen samples. In conclusion, the fertility of
×
hybrids appears to be similar to the fertilities of the parental species, posing a potential challenge for
conservation.
