• Current Applied Physics
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• v.18 no.12
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• pp.1473-1479
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• 2018

Recently multiferroic materials have attract great interest for the applications on memorial, spintronic and magneto-electric sensor devices for their spontaneous magneto-electric coupling properties. Research and development of the various kinds of multiferroics are indispensable factor for a new generation multifunctional materials. In this research, mechanical, electronic, magnetic and nonlinear optical properties of La modified $BiLaFe_2O_6$ (BLFO) and Mn modified $Bi_2FeMnO_6$ (BFMO) were studied as new members of multiferroic $BiFeO_3$ (BFO) series by first-principles calculations, and compared with the pure BFO to discover the optimized properties. Our results show that BLFO and BFMO have good mechanical stability as revealed by elastic constants that satisfy the stability criteria. All these compounds exhibit anisotropic and ductile nature. The enhanced properties by La and Mn substitution, such as increased hardness, improved magnetism, decreased band gap and comparable second harmonic generation responses reveal that the new multiferroic members of BLFO and BFMO would get wider application than their BFO counterpart. Our study is expected to providing an appropriate mechanical reference data as guidance for engineering of high efficiency multifunctional devices with the BFO series.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.21.1-21.1
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• 2007

• Proceedings of the Korean Ceranic Society Conference
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• 2003.04a
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• pp.163.1-163
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• 2003

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.949-955
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• 2010

Nd and Ti co-doped bismuth ferrite $(Bi_{1-x}Nd_x)(Fe_{1-y}Ti_y)O_3$ (x, y = 0, 0.05, 0.1, 0.2) ceramics and thin films were synthesized through the conventional mixed-oxide process and pulsed laser deposition (PLD), respectively. Nd and Ti co-doping effect was examined with emphasis on how these impurities affect phase formation behavior as there could be the improvement in leakage current problems often associated with multiferroic $BiFeO_3$ (BFO) thin films. The lattice constants of BFO ceramics decreased with Nd doping concentration up to 10mol%, while they further decreased with Nd and Ti co-doping to about 20%. BFO thin films obtained by the PLD process revealed random polycrystalline structure. Similar to bulk BFO ceramic, Nd and Ti co-doping effectively suppressed the formation of unwanted secondary phase and thus stabilized the perovskite phase in BFO thin films.

• Journal of Magnetics
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• v.14 no.2
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• pp.62-65
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• 2009

The multiferroic $BiFeO_3$ has been investigated extensively in both thin film and ceramic form. However, the synthesis of a perfect sample with high resistivity is a prerequisite for examining its properties. This paper reports the synthesis of multiferroic $BiFeO_3$ along with its structural, electrical and magnetic properties in ceramic form. Polycrystalline ceramic samples of $BiFeO_3$ were synthesized by solid-state reaction using high purity oxides and carbonates. The formation of a single-phase compound was confirmed by x-ray diffraction and its lattice parameters were determined using a standard computer program. The microstructural studies and density measurement confirmed that the prepared samples were sufficiently dense for an examination of its electrical and magnetic properties. The dc electrical conductivity studies show that the sample was resistive with an activation energy of ${\sim}0.81\;eV$. The magnetization measurement showed a linear ($M{\sim}H$) curve indicating antiferromagnetic characteristics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.5
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• pp.406-411
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• 2002

Ni-Zn ferrite is required to have predominant and stable characteristics in the range of high frequency for the power line communication, so that microstructures and magnetic properties such as power loss and initial permeability in $Ni_{0.8}Zn_{0.2}Fe_2O_4$ were investigated in terms of variable $Bi_2O_3,CaO$ and $V_2O_5$ contents. $Bi_2O_3$ and $V_2O_5$ liquid phase created during sintering process promoted sintering and grain growth but much of the closed pore existed in the grains. The grain size of the specimens with $V_2O_5$ of over 0.5 wt% decreased as the result of "pinning effect"and the resonance frequency increased with CaO of 0.3we%. The high initial permeability of 81.52%, resonance frequency of 17.05 MHz and low power loss of 17,858 kW/$\textrm{m}^3$ were obtained from the samples with $Bi_2O_3$ of 0.5, CaO of 0.3, and $V_2O_5$ of 0.7 wt%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.9
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• pp.555-560
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• 2014

In this paper, in order to develop outstanding Pb-free composition ceramics, the $Fe_2O_3$-doped ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ + 0.3 wt% $Bi_2O_3$ + x wt% $Fe_2O_3$ (x= 0~1.0 wt%)(abbreviated as NKL-NST) lead-free piezoelectric ceramics have been synthesized using the ordinary solid state reaction method. The effect of $Fe_2O_3$-doping on their microstructure and electrical properties were investigated. XRD diffraction pattern studies confirm that $Fe_2O_3$ completely diffused into the NKL-NST lattice to form a new stable soild solution with $Fe^{3+}$ entering the $Nb^{5+}$, $Sb^{5+}$ and $Ta^{5+}$ of B-site. And, phase structure of all the ceramics exhibited pure perovskite phase and no secondary phase was found in the ceramics. The ceramics doped with 0.6 wt% $Fe_2O_3$ have the optimum values of piezoelectric constant($d_{33}$), planar piezoelectric coupling coefficient($k_p$) and mechanical quality factor($Q_m$) : $d_{33}$ = 233 [pC/N], $k_p$= 0.44, $Q_m$= 95. These results indicate that the ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ +0.3 wt% $Bi_2O_3$ + 0.6 wt% $Fe_2O_3$ ceramic is a promising candidate for lead-free piezoelectric ceramics.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.10a
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• pp.146.2-146
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• 2000

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.88-88
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• 2009

$BiFeO_3$(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 0.7BFO-0.3BTO 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 $600^{\circ}C$ and an oxygen partial pressure of 10mTorr. The dielectric, ferroelectric, and magnetic properties have then been characterized. It was found that the films deposited under lower 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 $BiFeO_3$.

• Korean Journal of Materials Research
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• v.19 no.5
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• pp.253-258
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• 2009

Mn-substituted $BiFeO_3$(BFO) thin films were prepared by r.f. magnetron sputtering under an Ar/$O_2$ mixture of various deposition pressures at room temperature. The effects of the deposition pressure and annealing temperature on the crystallization and electrical properties of BFO films were investigated. X-ray diffraction patterns revealed that BFO films were crystallized for films annealed above $500^{\circ}C$. BFO films annealed at $550^{\circ}C$ for 5 min in $N_2$ atmosphere exhibited the crystallized perovskite phase. The (Fe+Mn)/Bi ratio decreased with an increase in the deposition pressure due to the difference of sputtering yield. The grain size and surface roughness of films increased with an increase in the deposition pressure. The dielectric constant of BFO films prepared at various conditions shows $127{\sim}187$ at 1 kHz. The leakage current density of BFO films annealed at $500^{\circ}C$ was approximately two orders of magnitude lower than that of $550^{\circ}C$. The leakage current density of the BFO films deposited at $10{\sim}30\;m$ Torr was about $5{\times}10^{-6}{\sim}3{\times}10^{-2}A/cm^2$ at 100 kV/cm. Due to the high leakage current, saturated P-E curves were not obtained in BFO films. BFO film annealed at $500^{\circ}C$ exhibited remnant polarization(2Pr) of $26.4{\mu}C/cm^2$ at 470 kV/cm.