Jin-Kyu Kang

Incipient piezoelectrics and electrostriction behavior in Sn-doped Bi1/2(Na0.82K0.18)1/2TiO3 lead-free ceramics

Dielectric, ferroelectric, piezoelectric, and strain properties of lead-free Sn-doped Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) were investigated. A crossover from a nonergodic relaxor to an ergodic relaxor state at room temperature, accompanied by a giant electric-field-induced strain, was observed at 5 at. % Sn doping. Switching dynamics monitored during a bipolar poling cycle manifested that the observed giant strain originates from incipient piezoelectricity. When Sn doping level reached 8 at. %, BNKT exhibited an electrostrictive behavior with a highly temperature-insensitive electrostrictive coefficient of Q11 = 0.023 m4 C−2.

Effect of Ta-Substitution on the Ferroelectric and Piezoelectric Properties of Bi 0.5 (Na 0.82 K 0.18 ) 0.5 TiO 3 Ceramics

The effect of Ta substitution on the crystal structure, ferroelectric, and piezoelectric properties of ceramics has been investigated. The Ta doping resulted in a transition from coexistence of ferroelectric tetragonal and rhombohedral phases to an electrostrictive pseudocubic phase, leading to degradations of the remnant polarization, coercive field, and piezoelectric coefficient . However, the electricfield-induced strain was significantly enhanced by the Ta substitution-induced phase transition and reached a highest value of

High strain in lead-free Nb-doped Bi1/2(Na0.84K0.16)1/2TiO3–SrTiO3 incipient piezoelectric ceramics

Lead-free 0.96[Bi1/2(Na0.84K0.16)1/2(Ti(1−x)Nbx)O3]–0.04SrTiO3 (BNKTN–ST, with x = 0–0.030) ceramics were synthesized by a conventional solid-state reaction technique. Polarization and strain hysteresis loops indicated a significant disruption of ferroelectric order accompanied by an enhanced field-induced strain (S = 0.438%) with a high normalized strain Smax/Emax of 876 pm/V at 5 kV/mm. Their reproducibility was confirmed by the fabrication of a 10-layered stack-type multilayer actuator, which demonstrated a normalized strain Smax/Emax of 720 pm/V.

Enhanced Low-Field Strain in Bi-Based Lead-Free Ferroelectric-Relaxor Composites

To improve the strain properties of Bi-based lead-free ceramics at lower electric fields, ferroelectric 0.82(Bi1/2Na1/2)TiO3-0.18(Bi1/2K1/2)TiO3 (BNKT) seed particles were embedded in Bi0.5(Na0.385K0.09Li0.025)(Ti0.975Ta0.025)O3 (BNKLTT) ceramics exhibiting relaxor behaviour using a conventional solid-state reaction. The unipolar strain versus electric field hysteresis loops of the BNKT-BNKLTT composites resulted in a maximum Smax/Emax of 761 pm/V at 4 kV/mm when 30 wt.% BNKT particles were added, which was higher than that of the single ferroelectric or relaxor phase.

Viscosity Sensor Using Piezoelectric Ceramic Resonators

A bolt-clamped ultrasonic viscometer was designed and fabricated using a pair of ring-shaped piezoelectric ceramic resonators. For its compactness and low operation frequencies, simulation of piezoelectric resonators was carried out using an ATILA program. Ring-shaped resonators using ceramics were prepared by a conventional ceramic processing, which were then clamped with a pair of metal caps. The fabricated sensor module with a small volume of less than 1 and an operation frequency as low as 26.5 kHz showed a good relationship between its quality factor and the viscosity of oil.

Tailoring Low-field Strain Properties of [0.97Bi 1/2 (Na 0.78 K 0.22 ) 1/2 TiO 3 -0.03LaFeO 3 ]-Bi 1/2 (Na 0.82 K 0.18 ) 1/2 TiO 3 Lead-Free Relaxor/Ferroelectric Composites

We investigated the effect of (BNKT) modification on the ferroelectric and electric-field-induced strain (EFIS) properties of lead-free (BNKTLF) ceramics as a function of BNKT content (x

Effect of Excess CuO on the Sintering Behavior and Piezoelectric Properties of Bi 0.5 (Na 0.82 K 0.18 ) 0.5 TiO 3 Ceramics

We investigated the effect of excess CuO on the sintering behavior, ferroelectric, and piezoelectric properties of lead-free (BNKT) ceramics. The addition of excess CuO was found to greatly contribute to the densification and grain growth, however, excess CuO over 3 mol% was precipitated at grain boundaries after sintering. BNKT with 1~2 mol% CuO in excess sintered at showed piezoelectric properties comparable to those of unmodified BNKT sintered at . These results seem meaningful for its application to low cost multilayer actuators (MLAs) because low firing ceramics make it possible to apply less expensive base metals to the inner electrode of MLAs.

Effect of Ta Doping on Piezoelectric Properties of Lead-Free (K 0.5 Na 0.5 )NbO 3 Ceramics

We investigated the effect of Ta doping on the dielectric and piezoelectric properties of lead-free (K0.5Na0.5)NbO3 ceramics prepared using a conventional ceramic processing. X-ray diffraction analysis revealed that Ta was perfectly substituted into Nb-sites in the range of 0 to 20 at%. As Ta content in the KNN increased, the sinterability of KNN ceramics was significantly degraded while the Ta doping enhanced the piezoelectric constant d33, planar mode piezoelectric coupling coefficient (kp), and electromechanical quality factor (Qm). The highest values for d33, kp, and Qm was found to be 156 pC/N, 0.37, and 155, respectively.

Electrical Properties of Multilayer Piezoelectric Transformer using PMN-PZN-PZT Ceramics

Dielectric and piezoelectric properties of PMN-PZT ceramics with a high mechanical quality factor and a low temperature sintering temperature were investigated as a function of PZN substitution in order to develop multilayer piezoelectric transformer for AC-DC converter. Multilayer piezoelectric transformers were subsequently manufactured using the PMN-PZN-PZT ceramic offering the optimal behavior and then the electrical performance were invetigated. At the sintering temperature of , density, electromechanical coupling factor, mechanical qualify factor and dielectric constant of 8 mol% PZN substituted specimen were , 0.524, 1573 and 1455, respectively. The PZN substitution caused a increase in the dielectric constant and the electromechnical coupling factor. The voltage step-up ratio of multilayer piezoelectric transformer showed the maximum value at near the resonant frequency of 76.55 kHz and increased according to the increase of load resistance. The multilayer piezoelectric transformer with the output impedance coincided with the load resistance showed the temperature increase of less than at the output power of 10 W. Based on the results, the manufactured multilayer transformer using the low temperature sintered PMN-PZN-PZT ceramics can be stably driven for both step-up and down transformers.