• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.147-147
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• 2013

Multiferroic material $BiFeO_3$ (BFO) is a typical multiferroic material with a room-temperature magnetoelectric coupling in view of high magnetic- and ferroelectric-ordering temperatures (Neel temperature $T_N$ ~ 647 K and Curie temperature TC ~1,103 K). Rare-earth ion substitution at the Bi sites is very interesting, which induces suppressed volatility of the Bi ion and improved ferroelectric properties. At the same time, the Fe-site substitution with magnetic ions is also attracting, since the enhanced ferromagnetism was reported. In this study, BFO, $Bi_{0.9}Dy_{0.1}FeO_3$ (BDFO), $BiFe_{0.97}Co_{0.03}O_3$ (BFCO) and $Bi_{0.9}Dy_{0.1}Fe_{0.97}Co_{0.03}O_3 $ (BDFCO) compounds were prepared by conventional solid-state reaction and wet-mixing method. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ for 24 h. The samples were immediately put into an oven, which was heated up to 800oC and sintered in air for 1 h. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies). Dy and Co co-doping at the Bi and the Fe sites induce the enhancement of both magnetic and ferroelectric properties of $BiFeO_3$.

• ETRI Journal
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• v.33 no.1
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• pp.132-135
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• 2011

In this letter, we study the contemporary technologies for making ferroelectric films and the possibility of using the oscillator model of PZT-22 to analyze its ferroelectric properties. The material showed permittivity dispersion at 65 KHz and 88.5 KHz. We obtained relative attenuation ${\gamma}$, relaxation time ${\tau}$, and ${\varepsilon}_{max}$ of the material as 0.0008319, 0.5 s, and 603.438, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.3
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• pp.223-227
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• 2007

The effect of Eu contents on the ferroelectric properties of $Bi_{4-x}Eu_xTi_3 O_{12}$ (BET) thin films has been investigated. Bismuth Europium titanate thin films with a Eu contents were prepared on the $Pt/Ti/SiO_2/Si$ substrate by metal-organic decomposition technique. The structure and the morphology of the films were analyzed using X-ray diffraction (XRD) and field emission scanning microscopy (FE-SEM), respectively. From the XRD analysis, it was found that BET thin films have polycrystalline structure, and the layered-perovskite phase is obtained when the Eu contents exceeds 0.2 (x > 0.2). Also, the ferroelectric characteristics of the BET thin films were found to be dependent on the Eu content. Particularly, the BET films doped with x = 0.75 show better ferroelectric properties (remanent polarization 2Pr = 60.99 C/$cm^2$ and only a little polarization fatigue up to $3.5{\times}10^9$ bipolar switching cycling) than those doped with other Eu contents.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.620-624
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• 2016

Ferroelectric $Pb(Zr_{0.52}Ti_{0.48})O_3$ (PZT) films were deposited on SrTiO3(100) substrate by using conductive $SrRuO_3$ films as underlayer and their structural and ferroelectric properties were investigated. PZT films were grown in (00l) orientation on well lattice-matched pseudo-cubic $SrRuO_3$ films. Thickness dependence of ferroelectric and electrical properties of PZT films was investigated. PZT film with 400 nm thickness showed a remanent polarization ($P_r$) of $29.0{\mu}C/cm^2$ and coercive field ($E_c$) of 83 kV/cm, and $P_r$ decreased and $E_c$ increased with thickness reduction. The dielectric constant for PZT films showed gradual decrease with thickness reduction. Breakdown field of PZT films did not show the thickness dependence and displayed as high value as 1 MV/cm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.7
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• pp.541-545
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• 1998

(PZT, PST, PT)/ YBCO structured have been grown on single crystal $LaAlO_3$ using in-situ Nb:YAG pulsed laser deposition technique. The optimum conditions of fabrication for high quality films have been established under various oxygen pressure. TBCO was used as a metallic electrode for polarizing ferroelectric thin fillms. Lattice mismatch of these materials were found to be with in 3%. As a result XRD patterns and rocking curves, (PZT, PST, PT)/ YBCO multiayered thin films on $LaAlO_3$ substrates showed preferred orientation to c-axis. For invastigation on electrical properties of ferroelectric thin films, remanent polaiztion $P_r$ and coercive field $E_c$ were measured for three samples. At each optimum condition, they showed the values of P_r=60 \mu C/cm^2 and E_c=240kV/ cm for PT, 30\mu C/cm^2 and 105kV/cm for PZT, 1.5\mu C/cm^2$ and 15kV/cm for PST. Frequency dependence of dielectric properties of ferroelectric thin fillms was also investigated. As a result, it showed the frequency dependence was relatively small in the range of 10Hz~10kHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.290-291
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• 2006

The effect of praseodymium substitution on the ferroelectric properties of $Bi_4Ti_3O_{12}$ thin films have been investigated. Ferroelectric Pr-substituted $Bi_4Ti_3O_{12}$ thin films were fabricated by chemical solution deposition onto Pt/Ti/$SiO_2$/Si substrates. The structure and morphology of the films were analyzed using Xray diffraction, and scanning electron microscopy, respectively. About 200-nm-thick BPT films grown at $720^{\circ}C$ exhibited a polycrystalline structure and showed excellent ferroelectric properties with a remanent polarization ($2P_r$) of $28.21\;{\mu}C/cm^2$ at an applied voltage of 5 V. The films a1so demonstrate fatigue-free behavior up to $10^{11}$ read/write switching cycles with 1 MHz bipolar pulses at an electric field of ${\pm}5\;V$.

• Journal of Powder Materials
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• v.8 no.2
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• pp.131-135
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• 2001

The ferroelectric properties of barium titanate strongly depend on its microstructure, in particular, grain size and distribution. During sintering, $BaTiO_3$ usually exhibits abnormal grain growth, which deteriorates considerably the ferroelectric properties. A typical technique to suppress the abnormal grain growth is the addition of dopants. Dopant addition, however, affects the ferroelectric properties and thus limits the application of $BaTiO_3$. Here, we report a simple but novel technique to prevent the abnormal grain growth of $BaTiO_3$ and to overcome the limitation of dopant use. The technique consists of stepwise sintering in a reducing atmosphere and in an oxidizing atmosphere. The materials prepared by the present technique exhibit uniform grain size and high dielectric properties. The technique should provide opportunities of having $BaTiO_3$-based materials with superior ferroelectric properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.4
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• pp.265-271
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• 2003

Ferroelectric lanthanum-substituted Bi$_4$Ti$_3$O$_{12}$(BLT) thin films were fabricated by spin-coating onto a Pt/Ti/SiO$_2$/Si substrate by metalorganic decomposition technique. The grain size in BLT thin films were prepared with controlled by various drying process. The effect of grain size on the crystallization and ferroelectric properties were investigated by x-ray diffraction and field emission scanning electron microscope. The dependence of crystallization and electrical properties are related to the grain size in BLT thin films with different drying temperature. The remanent polarization of BLT thin film increases with the increasing grain size. The value of 2P$_{r}$ and E$_{c}$ of BLT thin film dried at 45$0^{\circ}C$ were 25.9 $\mu$C/$\textrm{cm}^2$ and 85 kV/cm, respectively. The BLT thin film with larger grain size has better fatigue properties. The fatigue properties revealed that small grained film showed more degradation of switching charge than large grained films.lms.s.

• Proceedings of the Materials Research Society of Korea Conference
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• 2000.11a
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• pp.39-39
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• 2000

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.412-420
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• 2019

In this study, the dielectric and polarization properties of manganese (Mn% = 0.0, 0.1, 0.2, 0.5) doped (Pb_0.93La_0.07)(Zr_0.82Ti_0.18)O₃ (PLZT 7/82/18) anti-ferroelectric ceramics were studied for energy storage capacitor and pyroelectric applications. A systematic investigation demonstrated that the electric properties of PLZT 7/82/18 ceramics are affected significantly by the Mn-doping content. A maximum dielectric constant of ~ 2,128 at 1 kHz was found for 0.1% Mn-doped PLZT ceramics with a low dielectric loss of 0.018. The bipolar polarization versus electric field (P-E) hysteresis loops were traced for all compositions showing a typical anti-ferroelectric nature. The breakdown field was found to decrease with Mn-doping. The energy storage density and efficiency were found to be 460 J/㎤ and ~ 63%, respectively, for 0.2% Mn-doped PLZT ceramics. The pyroelectric coefficient of PLZT ceramics shows an increase based on the amount of Mn-doping.