Jong Hoo Paik

Effect of BaCu(B2O5) Additive on the Sintering Temperature and Microwave Dielectric Properties of BaTi4O9 Ceramics

BaCu(B2O5) (BCB) additive was used to decrease the sintering temperature of the BaTi4O9 ceramics. The amount of Ba4Ti13O30 second phase increased with the addition of BCB, whereas that of the BaTi4O9 phase decreased. The bulk density and dielectric constant (er) considerably increased with the addition of BCB. An increase in the Q-value was also observed for the BaTi4O9 ceramics with a small amount of BCB. Good microwave dielectric properties with values of er=32, Q ×f=10800 GHz and τf=32 ppm/°C were obtained in the BaTi4O9 ceramics with 12.0 mol % of BCB sintered at 875 °C for 2 h.

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 ...

Crystal structure of La(Mg2/3Nb1/3)O3 ceramics

The crystal structure of La(Mg2/3Nb1/3)O3 has been analyzed by high-resolution transmission electron microscopy (HRTEM) and Rietveld refinement using X-ray and neutron powder diffraction patterns. According to our analysis, La(Mg2/3Nb1/3)O3 has the 1:1 ordered monoclinic P21/n structure, contrary to the results of previous works which suggest a 1:1 ordered rhombohedral R3 or orthorhombic Pbnmstructure. The lattice parameters of La(Mg2/3Nb1/3)O3 are a = 5.6052, b = 5.6482, c = 7.9414 A, and β = 89.9501°. Monoclinic La(Mg2/3Nb1/3)O3 is distorted by the inphase and the antiphase tilting of octahedra with the a−a−c+ tilting system. The antiparallel shift of A-site cations was also found in La(Mg2/3Nb1/3)O3.

Performance Enhancement of Elastic-Spring-Supported Piezoelectric Cantilever Generator by a 2-Degree-of-Freedom System

A piezoelectric cantilever generator using elastic springs as a supporting mechanism was fabricated for vibration-based energy harvester application. The optimum load resistance of 82 kΩ was selected to obtain the most effective output power. Two strong power peaks for the generator were obtained, being as high as 3.8 and 5.7 mW for frequencies of 68 and 79 Hz, respectively. This implies that the generator is controlled by a 2 degree-of-freedom system, which can induce a wide resonance frequency bandwidth. Therefore, the performance of the piezoelectric cantilever generator can be enhanced with the aid of the elastic spring for broadband energy harvesting.

Ferroelectric domain morphology and structure in Li-doped (K,Na)NbO3 ceramics

We prepared Li0.02(K0.45Na0.55)0.98NbO3 (KNN) ceramics using a conventional solid-state sintering method and investigated the domain structure and morphology using a piezoresponse force microscope in these material systems. The abnormal grain consisted of nano-sized subgrains, which were an elementary unit of the domain formation, with a size of approximately 100 nm. They were self-assembled and grew along the 〈001〉o directions. In the orthorhombic KNN ceramics, the 90° domains were dominantly distributed and all wedges were 60° wedges. The polarization vectors and geometrical configurations were analyzed and suggested in the banded twins. The observation of angles between (010)o and (011)o showed that the large grains experienced severe stress resulting in the deformation of the unit cell configuration during the phase transition. The S-walls were preferred as 120° domain walls and were assigned to (1/0.27/1)c.

Ferroelectric and Piezoelectric Properties of 0.72Pb(Zr0.47Ti0.53)O3?0.28Pb[(Zn0.45Ni0.55)1/3Nb2/3]O3 Thick Films for Energy Harvesting Device Application

The Ferroelectric and piezoelectric properties of 0.72Pb(Zr0.47Ti0.53)O3–0.28Pb[(Zn0.45Ni0.55)1/3Nb2/3]O3 (PZT–PZNN) piezoelectric thick films were investigated for application to energy harvesting devices. The PZT–PZNN thick films were fabricated by a conventional tape casting process. The sintered PZT–PZNN thick film was highly dense and flat when the annealed temperature was 1100 °C. It exhibited substantial ferroelectric and piezoelectric properties of Pr = 20.6 µC/cm2, d33 = 370 pC/N, eT33/e0 = 1185, and kp = 0.44. Moreover, its d33g33, which can characterize high energy density material, is as large as approximately 13050×10-15 m2/N. Therefore, the PZT–PZNN thick film can be a potential piezoelectric material for application to energy harvesting devices.

Energy harvesting characteristics from water flow by piezoelectric energy harvester device using Cr/Nb doped Pb(Zr,Ti)O3 bimorph cantilever

A water flow energy harvester, which can convert water flow energy to electric energy, was fabricated for its application to rivers. This harvester can generate power from the bending and releasing motion of piezoelectric bimorph cantilevers. A Pb(Zr0.54Ti0.46)O3 + 0.2 wt % Cr2O3 + 1.0 wt % Nb2O5 (PZT–CN) thick film and a 250-µm-thick stainless steel were used as a bimorph cantilever. The electrical impedance matching was achieved across a resistive load of 1 kΩ. Four bimorph cantilevers can generate power from 5 to 105 rpm. The output powers were steadily increased by increasing the rpm. The maximum output power was 68 mW by 105 rpm. It was found that the water flow energy harvester can generate 58 mW by a flow velocity of (2 m/s) from the stream with the four bimorph cantilevers.

Structural and Piezoelectric Properties of (1-x)(Na0.5K0.5)NbO3–xBa(Ti0.9Sn0.1)O3 Lead-Free Ceramics

Lead-free (1-x)(Na0.5K0.5)NbO3–xBa(Ti0.9Sn0.1)O3 ceramics doped with 1 mol % MnO2 [(1-x)NKN–xBTS] were prepared by the conventional solid state method and their structural and piezoelectric properties were investigated. The (1-x)NKN–xBTS ceramics were well synthesized and a dense microstructure was achieved when sintered at 1050 °C for 8 h. The phase transition temperature of the tetragonal–cubic (TC) peaks became broadened with increasing x, suggesting that a diffuse phase transition was induced and that the ceramic was changed gradually from a normal ferroelectric to a relaxor ferroelectric. The significantly enhanced piezoelectric properties of d33=256 and kp=42% were obtained for the 0.94NKN–0.06BTS ceramics.

Crystal structure of (Ba1−xLax) [Mg(1 + x)/3Nb(2−x)/3]O3 ceramics

The crystal structure of (Ba1−xLax)[Mg(1 + x)/3Nb(2−x)/3]O3 (BLMN) ceramics with 0 ≤ x ≤ 1 was investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). When the La content, x, was above 0.1, the 1:2 ordered hexagonal structure found in Ba(Mg1/3Nb2/3)O3 (BMN) was transformed into the 1:1 ordered cubic structure. The 1:1 ordered cubic structure was maintained up to x = 0.7. When x exceeded 0.7, however, BLMN exhibited a 1:1 ordered monoclinic structure, rather than a 1:1 ordered cubic structure. La(Mg2/3Nb1/3)O3 (LMN) has a 1:1 ordered monoclinic P21/n structure with a = 5.6004 Å, b = 5.6414 Å, c = 7.9346 Å, and β = 89.9819°. The monoclinic LMN has the in-phase and the anti-phase tilt of oxygen octahedra. The anti-parallel shift of A-site cations was also found in LMN.

Development of Stretchable PZT/PDMS Nanocomposite Film with CNT Electrode

The piezoelectric composite film of ferroelectric PZT ceramic (PbZrxTi1-xO3) and polymer (PDMS, Polydimethylsiloxane) was prepared to improve the flexibility of piezoelectric material. The bar coating method was applied to fabricate flexible nanocomposite film with large surface area by low cost process. In the case of using metal electrode on the composite film, although there is no problem by bending process, the electrode is usually broken away from the film by stretching process. However, the well-attached, flexible CNT electrode on PZT/PDMS film improved flexibility, especially stretchability. PZT particles was usually settled down into polymer matrix due to gravity of the weighty particle, so to improve the dispersion of PZT powder in polymer matrix, small amount of additives (CNT powder, Carbon nanotube powder) was physically mixed with the matrix. By stretching the film, an output voltage of PZT(70 wt%)/PDMS with CNT (0.5 wt%) was measured.