Soon Jong Jeong

Electric field-induced deformation behavior in mixed Bi0.5Na0.5TiO3 and Bi0.5(Na0.75K0.25)0.5TiO3-BiAlO3

In this study, a method in which an electric field-induced phase transition in bismuth-based ceramics is used at a relatively low field of 40 kV/cm is proposed. This study investigated the electrical properties and electric field-induced strain of Bi0.5Na0.5TiO3 (BNT) single particle-added Bi0.5(Na0.75K0.25)0.5TiO3-BiAlO3 (BNKT-BA) ceramics. Strains of 0.27% and 0.29%, for 0.94BNKT-0.06BA with 10% BNT and 0.93BNKT-0.07BA with 20% BNT, were observed, respectively. These strains were attributed to the transition from non-polar to ferroelectric phases in BNKT-BA small grains with ferroelectric BNT large grains during external electric field execution.

Electric field induced polarization and strain of Bi-based ceramic composites

The ferroelectric properties and strain behaviors of 0-3-type-ceramic composites were investigated. (100-x)Bi0.5(Na0.75K0.25)TiO3-xBiAlO3 (x = 5, 6, and 7: abbreviated as 95BNKT-5BA, 94BNKT-6BA, and 93BNKT-7BA, respectively, and the three compositions are altogether designated as BNKT-BA) were chosen as a matrix materials, and ferroelectric Bi0.5Na0.5TiO3 (f-BNT), Bi0.5(Na0.8K0.2)0.5TiO3 (f-BNKT), and 98.5Bi0.5(Na0.8K0.2)0.5TiO3-1.5BiAlO3 (f-BNKTBA) grains as inclusions. Large f-BNT, f-BNKT, and f-BNKTBA grains strongly affect the ferroelectric properties and strain behaviors of the BNKT-BA matrix in the composite. In 95BNKT-5BA with f-BNT and f-BNKT, negative strain was observed, indicating that the ferroelectric phase is formed and stabilized. 93BNKT-7BA with f-BNT, f-BNKT and f-BNKTBA showed an increase in positive strain, which is associated with low field-induced phase transition. It was found from the strain curve that two contributions, ferroelectric phase stabilization and phase transition activat...

Effect of Sintering Time on Strain in Ceramic Composite Consisting of 0.94Bi0.5(Na0.75K0.25)0.5TiO3?0.06BiAlO3 with (Bi0.5Na0.5)TiO3

The ferroelectric and electric field-induced strain properties of a ceramic composite comprising relaxor 0.94Bi0.5(Na0.75K0.25)0.5TiO3–0.06BiAlO3 (94BNKT–6BA) phase and ferroelectric (Bi0.5Na0.5)TiO3 (BNT) phase were investigated as a function of sintering time ranging 4 to 48 h at 1150 °C. Large strains were observed with an increase in the sintering time up to 36 h. The 36-h-sintered 94BNKT–6BA+BNT composite exhibited a large piezoelectric strain of 0.372% (4 kV/mm) and a high dynamic d33* of 930 pm/V as compared with conventional Pb(Zr,Ti)O3 (PZT) and other lead-free ceramics. With further sintering up to 48 h, the strain was decreased. The changes in the strain and the ferroelectric properties are thus attributed to the enlargement of ferroelectric grains and the variation of grains compositions. At sintering times below 36 h, the enlarged ferroelectric grains caused a low field-induced phase transition in the relaxor matrix. At sintering time longer than 36 h, the low strain behavior occurred due to the composition variations in ferroelectric and relaxor grains resulting in diffusion of K and Al elements.

Comparative Analysis of Li2CO3 Doped (Ba,Sr)TiO3 and ZnBO Doped (Ba,Sr)TiO3 Ceramics for the Low Temperature Sintering Applications

For the research on the LTCC(Low Temperature Co-fire Ceramic) applications, low temperature sintered ceramics have been extensively investigated. In this study, we have focused on the Li 2 CO 3 doped (Ba,Sr)TiO 3 and ZnBO doped (Ba,Sr)TiO 3 ceramics which have moderate dielectric properties such as high dielectric permittivity and low loss tangent. Until now, B 2 O 3 has been commonly employed as the low temperature sintering aid. However, in this paper, we suggest Li 2 CO 3 and ZnBO as alternative sintering aids to the B 2 O 3 . 1∼5 wt% of Li 2 CO 3 or ZnBO was added to BST ceramics in order to reduce the sintering temperature. Li 2 CO 3 doped BST and ZnBO doped BST ceramics were respectively sintered from 700°C to 1050°C and 750°C to 1250°C by 50°C to confirm the sintering temperature with different dopants concentrations. By adding Li 2 CO 3 to the BST ceramics, the sintering temperature of BST ceramics was drastically lowered down to 900°C, whereas by introducing ZnBO dopants to BST, the loss tangent was decreased. From the XRD analysis, ZnBO doped BST ceramics have no pyro phase. 3 wt% Li 2 CO 3 doped BST ceramics, which sintered at 900°C, have moderate relative dielectric permittivity of 1451 at 1 kHz, while 5 wt% ZnBO doped BST ceramics, sintered at 1100°C, have decreased dielectric permittivity of 1180 at 1 kHz. The loss tangent of ZnBO doped BST was decreased compared with that of BST. The loss tangent of ZnBO (1 wt%) doped BST was decreased down to 2.71 × 10−3 at 1 MHz.

Electromechanical Properties of NKN-5LT Multilayer Actuator

Li2O excess 0.95(Na0.5K0.5)NbO3-0.05LiTaO3 (NKN-5LT) ceramics were developed by conventional sintering method. Abnormal grain growth in NKN-5LT ceramics was observed with varying Li2O content during sintering. In the 1 mol% Li2O excess NKN-5LT samples sintered at 1000 oC for 4h in air, electromechanical coupling factor and piezoelectric constant of NKN-5LT ceramics were found to reach the highest values of 0.37 and 250 pC/N, respectively. Lead-free piezoelectric of the composition 1 mol% Li2O excess NKN-5LT were fabricated. 10×10×3 mm3 size multilayer ceramic actuators (MLCA) were fabricated by conventional tape casting method. The displacement of the MLCA was ~ 1 μm at 150 V. These results show that the NKN-5LT ceramics with reasonable good piezoelectric properties have the potential to become the next generation material for a wide range of electro-mechanical transducer applications.

Dielectric properties of Ta2O5 thin films deposited onto Ti and TiO2 layer

The present study describes the dielectric properties of RF sputtered Ta2O5 thin films as a function of the buffer layer and annealing condition. The buffer layers were Ti or TiO2. And the thin film was annealed in various conditions. The X-ray pattern results showed that the phase of the RF sputtered Ta2O5 thin films was amorphous and this state was kept stable to RTA (rapid thermal annealing) even at 700°C. Measurements of the electrical and dielectric properties of the reactive sputtered Ta2O5 fabricated in two simple metal insulator semiconductor (MIS) structures, (Cu/Ta2O5/Ti/Si/Cu and Cu/Ta2O5/TiO2/Si/Cu) indicated that the amorphous Ta2O5 grown on Ti possesses a high dielectric constant (30–70) and high leakage current (10−1–10−4 A/cm2), whereas a relatively low dielectric constant (−10) and low leakage current (−10−10 A/cm2) were observed in the amorphous Ta2O5 deposited on the TiO2 buffer layer. In addition, the leakage current mechanisms of the two amorphous Ta2O5 thin films were investigated by plotting the relation of current density (J) vs. applied electric field (E). The Ta2O5/Ti film exhibited three dominant conduction mechanism regimes contributed by the Ohmic emission at low electrical field, by the Schottky emission at intermediate field and by the Poole-Frenkel emission at high field. In the case of Ta2O5/TiO2 film, the two conduction mechanisms, the Ohmic and Schottky emissions, governed the leakage current density behavior. The conduction mechanisms at various electric fields applied were related to the diffusion of Ta, Ti and O, followed by the creation of vacancies, in the rapid thermal treated capacitors.

Low temperature sintering in 95 (Na0.5K0.5)NbO3-5LiTaO3 ceramics

Na2O excess 95(Na0.5K0.5)NbO3-5LiTaO3 (NKN-5LT) ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding Na2O as a sintering aid. Grain growth behaviors with Na2O addition were explained in terms of the effect of Na2O on interface reaction - controlled grain growth and the critical driving force. The electrical properties of NKN-5LT ceramics were investigated as a function of Na2O concentration. In the 1 mol% Na2O excess NKN-5LT samples sintered at 1000oC for 4h in air, electromechanical coupling factor (kP) and piezoelectric coefficient (d33) of NKN-5LT ceramics were found to reach the highest values of 0.43 and 190 pC/N, respectively.

Effect of Li2O Addition on Piezoelectric Properties of NKN-5LT Ceramics

Recently alkali oxide materials, such as sodium - potassium niobate have drawn much attention due to their ultrasonic applicability and are also considered as promising candidates for a piezoelectric lead-free system. However, it is difficult to sinter such NKN-based materials via conventional sintering process. Therefore, in this study, dense 0.95(Na0.5K0.5)NbO3-0.05LiTaO3 (NKN-5LT) ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding Li2O as a sintering aid. The electrical properties of NKN-5LT ceramics were investigated as a function of Li2O concentration. At the addition of 1 mol% Li2O, electromechanical coupling factor (kP) and piezoelectric coefficient (d33) of NKN-5LT ceramics were found to reach the highest values of 0.37 and 250 pC/N, respectively.

Effect of A-site ions additions on abnormal grain growth and piezoelectric properties in NKN 5LT systems

Dense 0.95(Na0.5K0.5)NbO3-0.05LiTaO3 (NKN-5LT) ceramics, as a candidate for leadfree piezoelectric materials, were developed by conventional sintering process. The effect of additions with A-site ions in perovskite structure on abnormal grain growth and piezoelectric properties in NKN-5LT ceramics was investigated. Sintering temperature was lowered by adding A-site ions as a sintering aid. Abnormal grain growth in NKN-5LT ceramics was observed with varying additions. This grain growth behavior was explained in terms of interface reactioncontrolled nucleation and growth. The electrical properties of NKN-5LT ceramics were investigated as a function of concentration of additions. The electromechanical coupling factor and piezoelectric constant of NKN-5LT ceramics were improved in the samples with A-site ions excess NKN-5LT. These results show that the piezoelectric properties of NKN-5LT samples can be improved by control of the microstructures.

Effect of Aging and Microstructure on Mechanical Rolling CuAlNi Shape Memory Alloy

CuAlNi shape memory alloy with Cu-13.5Al-4.5Ni(wt%) composition was prepared by cross-rolling method and the aging effect, phase transformation characteristics, microstructural variation were investigated. Transformation temperature was greatly increased in aged specimens at 250°C. Transformation temperature was not changed after the second reversed transformation, and Ms point was same in most specimens with third reversed transformation cycle. The variation of Ms point was not seen with aging at 100°C, but it was decreased with aging at 250°C. Transformation temperatures appear to be constant, to an measurable extent, in specimens prepared by both hotrolling and cross-rolling at 900°C. Plate shaped-specimen with the thickness of about 1mm was prepared by cross-rolling treatment at 350°C. The transformation temperatures did not change after the second transformation-reverse transformation cycling, and specially transformation start temperature was the same in most specimens experiencing third thermal cycle and thereafter. Undesirable tweed-like structure was observed in 250°C-aged specimen after a cross-rolling at 350°C. On aging the specimen prepared by cross-rolling, G.P zone was formed easier than that of γ2 phase. This phase was transformed to plate-like θ phase during aging.