Dae Su Lee

Antiferroelectric Thin-Film Capacitors with High Energy-Storage Densities, Low Energy Losses, and Fast Discharge Times

We demonstrate a capacitor with high energy densities, low energy losses, fast discharge times, and high temperature stabilities, based on Pb(0.97)Y(0.02)[(Zr(0.6)Sn(0.4))(0.925)Ti(0.075)]O3 (PYZST) antiferroelectric thin-films. PYZST thin-films exhibited a high recoverable energy density of U(reco) = 21.0 J/cm(3) with a high energy-storage efficiency of η = 91.9% under an electric field of 1300 kV/cm, providing faster microsecond discharge times than those of commercial polypropylene capacitors. Moreover, PYZST thin-films exhibited high temperature stabilities with regard to their energy-storage properties over temperatures ranging from room temperature to 100 °C and also exhibited strong charge-discharge fatigue endurance up to 1 × 10(7) cycles.

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...

Antiferroelectric characteristics and low frequency dielectric dispersion of Pb1.075La0.025(Zr0.95Ti0.05)O3 thin films

Abstract La-modified lead zirconate titanate Pb 1.075 La 0.025 (Zr 0.95 Ti 0.05 )O 3 , antiferroelectric thin films are fabricated by excimer laser ablation technique on Pt/Ti/SiO 2 /Si substrates. The measured dielectric constant and dissipation factor are 642 and 0.021 at room temperature, respectively, and Curie temperature is 196 °C. The antiferroelectric double hysteresis loops of Pb 1.075 La 0.025 (Zr 0.95 Ti 0.05 )O 3 film are confirmed by measuring the polarization vs. the electric field. With increasing temperature, the double hysteresis loop behavior is reduced and gradually becomes a loose single ferroelectric hysteresis loop. The complex dielectric constants and a.c. conductivities are measured as a function of frequency (10 −2 –10 6 Hz) and temperature (25–250 °C) in order to investigate the influence of microstructure on the charge transport mechanism. We observe the strong low-frequency dielectric dispersion due to migration of thermally activated oxygen vacancies at higher temperature above 175 °C. The activation energy calculated from the a.c. conductivity is 0.63 eV.

An advanced ferroelectric properties of the Mn doped Na0.5Bi4.5Ti4O15 ceramics fabricated by hot-forging method

Mn doped Na0.5Bi4.5Ti4O15 (NBTM) ceramics were fabricated by ordinary firing (OF) and hot forging (HF) method. The HF(//) sample is strongly oriented to the c-axis which is confirmed by the X-ray diffraction. Dielectric constant of HF(⊥) sample at Curie temperature is about 5176 which is larger than that (416) of the HF(//) sample. The value of the remnant polarization Pr and coercive field Ecof HF(⊥) samples at 200°C are 17.8 μC/cm2 and 28.5 kV/cm, respectively. From the temperature dependence of conductivity, the activation energy of the HF(⊥) sample is 1.65 eV in the temperature range of 520°C ∼750°C.

Advanced Dielectric Properties of Li2O Doped 0.2[Pb(Mg1/3Nb2/3)]-0.8[PbTiO3-PbZrO3] Ceramics

0.2Pb(Mg 1/3 Nb 2/3 )O 3 -0.8Pb(Zr 0.475 Ti 0.525 )O 3 [PMNZT] ceramics doped with various contents of Li 2 O (0, 0.05, 0.1, 0.2, 0.3 wt.%) are fabricated by columbite precursor method. The lithium doping effect on the PMNZT ceramics is discussed in the relation to the piezoelectric properties and conduction behavior. The ferroelectricity is confirmed by polarization-electric field hysteresis loop. Remnant polarization P r reached a maximum value of 27.16 μC/cm 2 when a 0.1 wt% Li 2 O was doped. Coercive field E c reached a maximum value of 8.27 kV/cm for 0.1 wt% Li 2 O and decreased again as Li 2 O ratio increased. The PMNZT + 0.1 wt.% Li 2 O ceramic attain the sufficient densification with large dielectric constant (ϵ r = 1448) and low dielectric loss (tan δ = 0.022) at room temperature. The maximum values of the longitudinal electromechanical coupling factor (k 33 ) and piezoelectric coefficient (d 33 ) of PMNZT + 0.1 wt.% Li 2 O ceramics are 78% and 565pC/N, respectively. The incorporation of Li+1 in the PMNZT ceramics has led to an appreciable reduction in conductivity throughout the temperature range of 30∼400°C. The activation energy of PMNZT + xLi 2 O ceramics calculated from the Arrhenius relation were (x = 0, 0.05, 0.1, 0.2, 0.3) were 1.05, 1.25, 1.27, 1.38 and 1.41 eV, respectively.

Thermally Activated Low Frequency Dielectric Dispersion of Antiferroelectric Pb 1.075 La 0.025 Zr 0.95 Ti 0.05 O 3 Thin Film

Antiferroelectric Pb 1.075 La 0.025 Zr 0.95 Ti 0.05 O 3 (PLZT) thin films on Pt/Ti/SiO 2 /Si substrate have been fabricated by pulsed laser deposition technique. The temperature dependent dielectric constant and polarization-electric field (P-E) hysteresis loops of PLZT film demonstrate the phase transition from antiferroelectric to ferroelectric. The Curie temperature (T c ) and dielectric constant at T c are 196C and 2065, respectively. The maximum saturated polarization reaches nearly 50 w C/cm 2 , corresponding to a maximum induced charge of 12.5 nC. The complex dielectric constants and ac conductivities of PLZT thin film are measured as a function of frequency (0.01Hz∼1 MHz) and temperature (25∼200C) in order to investigate dielectric dispersions and conduction mechanisms. We also observe the strong low-frequency dielectric dispersion at high temperature above 125C due to the migration of thermally activated oxygen vacancies. The estimated activation energy for conduction is 0.76 eV. The conduction mechanism seems more complicated than simple hopping model. Consequently, understanding of oxygen vacancy transfer in the antiferroelectric PLZT thin film is important for practical applications in high charge storage and actuator devices.