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Microstructure and piezoelectric properties of the CuO-added (Na0.5K0.5)(Nb0.97Sb0.03)O3 lead-free piezoelectric ceramics

The presence of the Sb5+ ion increased the piezoelectric properties of the (Na0.5K0.5)NbO3 (NKN) ceramics by enhancing the poling state as identified by the increased phase angle (θ). The increased θ value was explained by the increased ferroelectricity due to the large electronegativity of the Sb5+ ion and the increased off centering of the cation due to the small ionic size of the Sb5+ ion. The (Na0.5K0.5)(Nb0.97Sb0.03)O3[NK(N0.97S0.03)] ceramics containing CuO were well sintered even at 960 °C. A small amount of the Cu2+ ions was incorporated into the matrix of the NK(N0.97S0.03) ceramic and behaved as a hardener. The kp, Qm, d33, and e3T/e0 values of the CuO-added NK(N0.97S0.03) ceramics were much higher than those of the CuO-added NKN ceramics due to the Sb5+ ion’s enhancement of the piezoelectric properties by increasing the poling state of the specimens. The high piezoelectric properties of kp=0.41, Qm=1333, d33=111 pC/N, and e3T/e0=324 were obtained from the 2.0 mol % CuO-added NK(N0.97S0.03) cera...

Piezoelectric nanogenerators synthesized using KNbO3 nanowires with various crystal structures

KNbO3 (KN) nanowires having a tetragonal structure or a polymorphic phase boundary (PPB) structure, which contains both tetragonal (P4mm) and orthorhombic (Amm2) structures, are formed at low temperatures. The presence of tetragonal and PPB KN nanowires is attributed to the existence of OH− and H2O defects. Further, the tetragonal and PPB KN nanowires change to orthorhombic KN nanowires in the temperature range between 300 and 400 °C owing to desorption of the lattice hydroxyl group. A composite consisting of polydimethylsiloxane (PDMS) and KN nanowires having a PPB structure shows large dielectric constant and low dielectric loss values of 9.2 and 0.5%, respectively, at 100 kHz. Moreover, a nanogenerator (NG) synthesized using the PPB KN nanowires exhibits the largest output voltage and current among NGs synthesized using the tetragonal or orthorhombic KN nanowires. In particular, the NG containing 0.7 g of PPB KN nanowires shows an output voltage of 10.5 V and an output current of 1.3 μA; these values are among the highest ever reported for NGs synthesized using a lead-free composite. In addition, this NG exhibited the maximum output power and energy conversion efficiency, which were 4.5 μW and 0.9%, respectively, for an external load of 1.0 MΩ.

Effect of the structural properties on the energy density of Pb(Zr0.47Ti0.53)O3-Pb[(Ni0.6Zn0.4)1/3Nb2/3]O3 ceramics

(1−x)Pb(Zr0.47Ti0.53)O3-xPb[(Ni0.6Zn0.4)1/3Nb2/3]O3 [(1−x)PZT-xP(NZ)N] ceramics with 0.22 ≤ x  ≤ 0.45232 have the tetragonal-pseudocubic morphotropic phase boundary (MPB). Their ɛ33T/ɛ0 values considerably decreased but their d33 values slowly decreased on the pseudocubic side of the MPB. Therefore, high d33 × g33 values were obtained from a composition on the pseudocubic of the MPB because g33 is given as d33/ɛ33T. In particular, a very high d33 × g33 value of 20 134 × 10−15 m2/N was observed from the 0.7PZT–0.3P(NZ)N ceramic sintered at 1000 °C for 2 h, which had a pseudocubic structure. The 0.7PZT–0.3 P(NZ)N ceramic sintered at 950 °C also exhibited a similar d33 × g33 value of 20 179 × 10−15 m2/N but it considerably decreased to 12 474 × 10−15 m2/N for the 0.7PZT–0.3P(NZ)N ceramic sintered at 1100 °C for 2 h, which can be explained by the increased ɛ33T value that resulted from the increased grain size. The grain size of this ceramic decreased as the sintering time decreased, resulting in an increase ...

Microstructure and piezoelectric properties of (Na 0.5 K 0.5 )NbO 3 lead-free piezoelectric ceramics with V 2 O 5 addition

Various amounts of Nb₂O₅ in the (Na_0.5K_0.5) NbO₃ (NKN) ceramic were replaced by V₂O₅ to decrease its sintering temperature to below 950°C. A small V₂O₅ content resulted in a dense microstructure with an increased grain size for the specimen sintered at 900°C due to the presence of a liquid phase. When V₂O₅ was added to the NKN ceramics, their orthorhombic-to-tetragonal transition temperature increased from 178°C to around 200°C. However, their Curie temperature decreased from 402°C to around 330°C. The k_p, _ε3 ^T/_ε0, and Q_m values increased with V₂O₅ addition, probably due to the increased density and poling state, which was identified by the phase angle. The specimen with x = 0.05, sintered at 900°C for 8 h, exhibited the following piezoelectric properties: k_p = 0.32, _ε3 ^T/_ε0 = 245, d₃₃ = 120 (pC/N), and Q_m = 232.

Resistive switching properties of amorphous Pr0.7Ca0.3MnO3 films grown on indium tin oxide/glass substrate using pulsed laser deposition method

Amorphous Pr0.7Ca0.3MnO3 (APCMO) films, which were grown on indium tin oxide (ITO)/glass at room temperature (RT), were n-type materials. The APCMO/ITO/glass device exhibited an average transparency of 77% in the visible range with a maximum transparency of 84% at a wavelength of 530 nm. The Pt/APCMO/ITO device showed stable bipolar resistive switching behavior over 200 cycles that did not degrade after 105 s at RT. The resistance of the APCMO film decreased in both low- and high-resistance states with increasing device area. The resistive switching behavior of the Pt/APCMO/ITO device can be explained by the trap-charged space-charge-limited current mechanism.

Structural variation of hydrothermally synthesized KNbO3 nanowires

KNbO3 (KN) nanowires were synthesized using various process conditions and their structures and morphologies were investigated. Homogeneous KN nanowires were formed in specimens synthesized at 130 °C for 24.0–48.0 h. These KN nanowires have a tetragonal structure that is known to be stable at high temperatures in the range of 225–435 °C. Tetragonal KN nanowires changed to orthorhombic KN nanoplates when the process time increased and homogeneous orthorhombic KN nanoplates existed for specimens synthesized for 144.0 h. In addition, tetragonal and orthorhombic structures coexisted in KN nanoplates synthesized at 130 °C for 72.0 h. For specimens synthesized at 100 °C, a long process time of 144.0 h was required to develop homogeneous KN nanowires that were also considered to have both tetragonal and orthorhombic structures. On the other hand, for specimens synthesized at 150 °C for 8.0 h, KN nanowires and a cube-shaped KN phase coexisted. Furthermore, a K4Nb6O17 second phase was formed in specimens synthesized for short periods of time (<8.0 h), indicating that the formation of homogeneous KN nanowires is difficult at 150 °C. Therefore, homogeneous KN nanowires with a tetragonal structure can be obtained at a low temperature of 130 °C with a short process time in the range of 24.0–48.0 h.KNbO3 (KN) nanowires were synthesized using various process conditions and their structures and morphologies were investigated. Homogeneous KN nanowires were formed in specimens synthesized at 130 °C for 24.0–48.0 h. These KN nanowires have a tetragonal structure that is known to be stable at high temperatures in the range of 225–435 °C. Tetragonal KN nanowires changed to orthorhombic KN nanoplates when the process time increased and homogeneous orthorhombic KN nanoplates existed for specimens synthesized for 144.0 h. In addition, tetragonal and orthorhombic structures coexisted in KN nanoplates synthesized at 130 °C for 72.0 h. For specimens synthesized at 100 °C, a long process time of 144.0 h was required to develop homogeneous KN nanowires that were also considered to have both tetragonal and orthorhombic structures. On the other hand, for specimens synthesized at 150 °C for 8.0 h, KN nanowires and a cube-shaped KN phase coexisted. Furthermore, a K4Nb6O17 second phase was formed in specimens synthesiz...

Synthesis of highly tetragonal BaTiO3 nanopowders using acetone as a solvent by alkoxide-hydroxide route

BaTiO3 (BT) nanopowders were synthesized in acetone to remove the TiO2 second phase, which was formed in the specimens synthesized in the 2-methoxyethanol solvent at above 100 °C due to H2O evaporation. No TiO2 second phase was formed in the specimens synthesized in acetone, even at 260 °C, due to the low boiling temperature of acetone which evaporated at above 55 °C and suppressed the H2O evaporation by increasing the vapor pressure in the vessel. However, for the BT nanopowders synthesized at 250 °C for 60 h, TiO2 second phase was formed at a Ba/Ti ratio of ≤1.5 and the BT nanopowders were agglomerated at a ratio of ≥3.0. Homogeneous BT nanopowders were obtained at a ratio of 2.0 and they exhibited a high c/a ratio of 1.0082 with a small size of 95.2 nm. Therefore, these nanopowders can be a good candidate for future multi-layer ceramic capacitor.