• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.313-313
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• 2010

$BiFeO_3$ (BFO), when forming a solid solution with $BaTiO_3$ (BTO), shows structural transformations over the entire compositional range, which not only gives a way to increase structural stability and electrical resistivity but also applies a means to have better ferromagnetic ordering. In this respect, we have prepared and studied 0.8 BFO-0.2 BTO thin films on Pt(111)/$TiO_2/SiO_2$/Si substrates by pulsed laser deposition. Various deposition parameters, such as deposition temperature and oxygen pressure, have been optimized to get better quality films. Based on the X-ray diffraction results, thin films were successfully deposited at the temperature of $700^{\circ}C$ and an oxygen partial pressure of 10mTorr and 330mTorr. The dielectric, ferroelectric, and magnetic properties have then been characterized. It was found that the films deposited under lower and higher oxygen pressure corresponded to lower leakage current. Magnetism measurement showed an induced ferromagnetism. The microstructures associated with the magnetic and dielectric properties of this mixed-perovskite solid solutions were observed by transmission electron microscopy, which revealed the existence of complicated ferroelectric domains, suggested that the weak spontaneous magnetization was closely associated with the decrease in the extent of rhombohedral distortion by a partial substitution of $BaTiO_3$ for $BiFeO_3$.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.307-311
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• 2011

Solid solutions of the (1-x)$BiFeO_3-xSrTiO_3$ ceramic system (x = 0~0.4) are explored here in attempts to obtain multiferroic properties in these systems. The polarization-electric field hysteresis, magnetization-magnetic field curves, and dielectric properties are also characterized. This solid-solution system shows a crystal structural transition from a noncentrosymmetric (R3c) structure to a centrosymmetric (Pm-3m) structure at 0.3 < x < 0.4. The solid solution ceramic shows unsaturated M-H behavior and low remanent magnetization over the composition region of 0.1 ${\leq}$ x ${\leq}$ 0.3. The $0.7BiFeO_3-0.3SrTiO_3$ system shows the largest value of $M_s$ at 0.17 emu/g and the smallest value of $H_c$ at 1.06 kOe. The P-E hysteresis curves were not saturated under an electric field as high as E = 70 kV/cm. This system is considered to have multiferroic characteristics in the composition range of 0.1 ${\leq}$ x ${\leq}$ 0.3.

• Proceedings of the Korean Magnestics Society Conference
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• 2017.05a
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• pp.123-123
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• 2017

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.30.1-30.1
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• 2009

PZT(Pb(Zr, Ti)$O_3$ 압전세라믹스는 뛰어난 압전 특성과 강유전 특성을 가지고 있어서 현재 널리 사용되고 있다. 하지만 PZT세라믹스는 큐리온도 이상에서 그 특성을 잃게 되고 높은 온도에서의 응용이 제한된다. 따라서 높은 큐리온도를 가지는 압전체를 개발하기 위한 연구가 많이 이루어지고 있다. $PbTiO_3$의 경우에는 $Bi(Zn_{0.5}Ti_{0.5})$, $BiFeO_3$등의 Bi계 세라믹스를 치환하면서 큐리온도가 올라가는 결과가 보고되고 있다. 하지만 이것은 PZT세라믹스 보다 압전 및 유전 특성이 상당히 낮다. 따라서 본 연구에서는 $(1-x)PbZrO_3-xPbTiO_3$조성에 Bi(Me)$O_3$(Me:Zn, Ti, Fe, Al)를 치환하여 압전특성 및 강유전 상전이 온도를 조사하였다. 모든 시편들은 고상반응법으로 제조하였고, 제조한 시편으로 조성에 따른 압전특성 및 유전특성의 변화를 측정하였다. 그리고 이를 통해 큐리온도는 PZT의 MPB조성근처에서 Bi계 세라믹의 치환은 $T_C$가 낮아 졌으나, Tetragonal 상을 가지고 있는 Ti-rich인 조성에서는 $T_C$가 높아지는 것을 관찰하였다.

• Journal of Magnetics
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• v.21 no.1
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• pp.29-34
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• 2016

Nd-doped $BiFeO_3$ materials were synthesized via a sol-gel method. The crystal structure, magnetic properties, and complex impedance spectroscopy of multiferroic $Bi_{1-x}Nd_xFeO_3$ (BNFO) materials were investigated by X-ray diffraction (XRD), Raman scattering, vibrating sample magnetometer (VSM), and complex impedance spectroscopy. Our results show that the lattice crystal constants (a, c) and the ratio c/a of BNFO materials decreased with increasing Nd concentration. All samples exhibited weak ferromagnetism at room temperature, and the magnetization of samples was enhanced by the presence of $Nd^{3+}$ ions. There was an enhancement in the spontaneous magnetization of BFO with increasing Nd concentration, which is attributable to the collapse of the spin cycloid structure.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.121-125
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• 2005

Magnetoelectric (ME) effects for lanthanum modified $BiFeO_3-PbTiO_3\;(BE-_xPT)$ solid solutions have been investigated. The value of magnetoelectric polarization coefficient, up is 10 times greater than that of $Cr_2O_3$. The results also show that up is due to a linear coupling between polarization and magnetization, and that up is independent of do magnetic bias and ac magnetic field. The ME effect is believed to be significantly enhanced due to breaking of the cycloidal spin state of a long-period spiral spin structure, via randomly distributed charged imperfections.

• Journal of the Korean Ceramic Society
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• v.54 no.4
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• pp.323-330
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• 2017

To understand the defect chemistry of multiferroic $BiFeO_3-based$ systems, we synthesized nonstoichiometric $Bi_{1+x}FeO_{3{\pm}{\delta}}$ ceramics by conventional solid-state reaction method and studied their structural, dielectric and high-temperature charge transport properties. Incorporation of an excess amount of $Bi_2O_3$ lowered the Bi deficiency in $BiFeO_3$. Polarization versus electric field (P-E) hysteresis loop and dielectric properties were found to be improved by the $Bi_2O_3$ addition. To better understand the defect effects on the multiferroic properties, the high temperature equilibrium electrical conductivity was measured under various oxygen partial pressures ($pO_2{^{\prime}}s$). The charge transport behavior was also examined through thermopower measurement. It was found that the oxygen vacancies contribute to high ionic conduction, showing $pO_2$ independency, and the electronic carrier is electron (n-type) in air and Ar gas atmospheres.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.64-67
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• 2002

The Physical and magnetic properties such as microstructure, permeability and power loss of Ni-Zn ferrite with composition of $Ni_{0.8}Zn_{0.2}Fe_2O_4$, were investigated as the function of $Bi_2O_3$ and CaO contents. The power loss increased in proportion to the amount of $Bi_2O_3$ up to 0.3 wt% but it decreased over than 0.3 wt% addition. The highest permeability of 134 was obtained to the specimen added 1.0 wt% $Bi_2O_3$ since $Bi_2O_3$ contents were strongly dominant to grain growth and size than that of CaO. $Bi_2O_3$ liquid phase created during sintering process promoted sintering and grain growth so that grain size and permeability increased compared to that of the specimens which were sintered with free-additive and CaO. Also, lots of pores existed in the specimen which was added $Bi_2O_3$ wt% with the biggest grain size.

• Journal of the Korean Magnetics Society
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• v.16 no.4
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• pp.201-205
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• 2006

The electromagnetic properties and microstructure of the basic composition of $(Ni_{0.2}Cu_{0.2}ZnO_{0.2})_{1.02}(Fe_{2}O_{3})_{0.98}$ were invested, changing the amount of the additives $Bi_2O_3$ and $ZrO_2$ and sintering temperature. The spinel structure of specimen was confirmed by the analysis of XRD patterns. Grain size and its density are increased by increasing the additive and the sintering temperature.However, the permeability increased with decreasing additive. It was also found that $Bi_2O_3$ had more effect on the increase of grain size and permeability rather than $ZrO_2$.

• Journal of the Korean Ceramic Society
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• v.34 no.10
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• pp.1074-1082
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• 1997

Microstructure and permeability as a function of sintering temperature and composition were studied on the Ni$\delta$Cu0.4-$\delta$Zn0.6Fe2O4 ($\delta$=0, 0.1, 0.2, 0.3, 0.4) which was prepared by Cu2+ substitution for Ni2+ in Ni.0.4Zn0.6Fe2O4, then followed by 8 wt% CuO and 1wt% Bi2O3 as sintering aids. It was found that NiCuZn ferrite in which Cu2+ is substituted for Ni2+ is more effective in reduction of sintering temperature than Ni.0.4Zn0.6Fe2O4, containing CuO as a sintering aid. The specimen $\delta$=0.2 sintered at 90$0^{\circ}C$ for 2hr exhibited the highest initial permeability value ($\mu$o=280 at 1Mhz), but the real permeability decreased at the frequency under 10 MHz. EPMA analysis showed that Ni$\delta$Cu0.4-$\delta$Zn0.6Fe2O4 ($\delta$=0.4), sintered at 95$0^{\circ}C$ for 2hrs consisted of three phase regions of Ni.0.3Cu0.1Zn0.6Fe2O4 region, Cu and Bi liquid existed at the 3-point boundary, although the stabilization energy of Ni2+ is higher than that of Cu2+ in B site.