Browsing by Author "Kim, Yong Soo"

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Enhancement of piezoelectric and ferroelectric properties of BaTiO3 ceramics by aluminum doping
(ELSEVIER SCI LTD, 2013) Ali, Ahmed I.; Ahn, Chang Won; Kim, Yong Soo
Ferroelectric and piezoelectric properties of BaTiO3 and Al-doped BaTiO3 ceramics were investigated. The ferroelectric study demonstrated that, by doping Al3+ ions in the A-site of BaTiO3, the polarization electric field loop exhibited enhanced remnant polarization (from 12 to 17.5 mu C/cm(2)), saturation and switching. In addition, the piezoelectric constant (d(33)) increased with Al-doping for both static and dynamic strain values (from 75 to 135 and from 29.2 to 57.9 pC/N, respectively, at a maximum applied electric field of 16 kV/cm). Furthermore, the dielectric constant values increased and both the dielectric loss factor and leakage current decreased, even though the transition temperature shifted to lower temperature (from 121 to 113 degrees C) for the Al-doped sample. Therefore, the Aldoped BaTiO3 has adjustable piezoelectric and ferroelectric properties. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Hall mobility, electrical resistivity, and dielectric properties of reduced La0.01Ba0.99TiO3
(KOREAN PHYSICAL SOC., 2013) Ali, Ahmed. I.; Moez, A. Abdel; Kim, Yong Soo
The La0.01Ba0.99TiO3 sample was reduced at 1380 A degrees C under about a 10(-14)-atmosphere oxygen partial pressure. After the sample had been reduced under these conditions, the resistivity and the Hall mobility of the reduced La0.01Ba0.99TiO3 were investigated experimentally within a temperature range of 300 to 600 K. The electrical resistivity decreased linearly with increasing measurement temperature, indicating that the conduction mechanism in this system was thermally activated. Evidence of an excess of charge carriers was observed at high temperatures. The dielectric property data showed that the known phase-transition temperature shifted to a higher temperature (425 K). Thus the reduction of the sample has an influence on both the dielectric constant and the transition temperature. In-situ high-temperature electrical-conductivity and Hall measurements are useful tools for establishing the donor-doping effect in perovskite La0.01Ba0.99TiO3 and for screening it for more industrial applications.
The influence of SrTiO3 buffer layer on ferroelectric properties of Al-doped BaTiO3 thin films
(SPRINGER INTERNATIONAL PUBLISHING, 2014) Ali, Ahmed; Senthikuma, , V; Kim, Yong Soo
Fabrication of Al0.01Ba0.99TiO3 (Al-BTO) thin films on SrTiO3/MgO/TiO2/SiO2/Si (STO/MgO) and MgO/TiO2/SiO2/Si (MgO) substrates were comparatively prepared using pulsed laser deposition (PLD). The structures of the prepared thin films were studied using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The SrTiO3 buffer layer between Al-BTO thin film and MgO substrate enhanced the ferroelectric, electrical properties. Moreover, the P-E loops showed a dramatic enhancement in the polarization values from 18 mu C/cm(2) at 600 kV/cm to 52 mu C/cm(2) at 780 kV/cm for Al-BTO thin films on SrTiO3/MgO and MgO substrates, respectively. In addition, the dielectric SrTiO3 buffer layer decreased the leakage current from 3 x 10(-3) to 12 x 10(-6) A/cm(2) and increased breakdown electric field from 10 to 30 kV/cm. The electric properties revealed that, the dielectric SrTiO3 buffer layer also decreased the conductivity, mobility and carrier concentrations. The data of Al-BTO thin films on SrTiO3/MgO substrate exhibited remarkably adjusted polarization and leakage current indicating a good ferroelectric property for non-volatile ferroelectric random access memory (FERAM) applications.
Room Temperature Ferromagnetism in Sm0.5Sr0.5CoO3 Thin Films Deposited by Pulsed Laser Deposition
(AMER SCIENTIFIC PUBLISHERS, 2017) Ali, Ahmed; Kim, Yong Soo
Ferromagnetic Sm0.5Sr0.5CoO3 thin films were deposited on MgO/TiO2/SiO2/Si (MgO) and Pt/InO2/SiO2/Si (Pt) substrates by pulsed laser deposition. The crystallinity and morphology of the films were characterized by X- ray diffraction and field emission scanning electron microscopy, respectively. The electrical properties revealed metallic- like behavior at room temperature, confirming the transition from the metallic state to the insulating state at T > 300 K. The magnetization as a function of the temperature under the zero-field-cooled and field cooled modes for the Sm0.5Sr0.5CoO3 confirm that the Curie temperature higher than 300 K for the films deposited on the MgO substrate. The M-H hysteresis loops show that both films exhibit hard ferromagnetic behavior at 10 K independent of substrate type. However, the films deposited on the MgO substrate show a soft ferromagnetic state, whereas those on the Pt substrate exhibit an antiferromagnetic state at 300 K. The correlation between the ferromagnetic and metal states depending on the double exchange interaction and spin states transition at low and high temperatures is discussed.