Ferroelectric Properties of BiFeO3 Ceramics Sintered under Low Oxygen Partial Pressure

김아영,Ye Ji Lee,김정석,한승호,강형원,이형규,천채일 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.1

BiFeO3 ceramics were prepared in various atmospheres with hydrothermally-synthesized BiFeO3crystalline powders, and their dielectric and ferroelectric properties were investigated. The single BiFeO3 phase was formed when the sample was sintered at 800 C under air, and a minor Bi2Fe4O9phase was observed when it was sintered under a N2 or an Ar atmosphere. The BiFeO3 ceramic sintered under N2 showed a dense microstructure and superior electric properties: a dielectric constant of 75, a low loss tangent of 0.01 at 100 kHz and a high resistivity of 1.37 × 1011 ·cm. A pinched and asymmetric P-E hysteresis and a typical butterfly-shaped S-E loop were observed in the BiFeO3 ceramic sintered under N2. The electric properties of BiFeO3 ceramics sintered in various atmospheres are discussed on the basis of defect chemistry. BiFeO3 ceramics were prepared in various atmospheres with hydrothermally-synthesized BiFeO3crystalline powders, and their dielectric and ferroelectric properties were investigated. The single BiFeO3 phase was formed when the sample was sintered at 800 C under air, and a minor Bi2Fe4O9phase was observed when it was sintered under a N2 or an Ar atmosphere. The BiFeO3 ceramic sintered under N2 showed a dense microstructure and superior electric properties: a dielectric constant of 75, a low loss tangent of 0.01 at 100 kHz and a high resistivity of 1.37 × 1011 ·cm. A pinched and asymmetric P-E hysteresis and a typical butterfly-shaped S-E loop were observed in the BiFeO3 ceramic sintered under N2. The electric properties of BiFeO3 ceramics sintered in various atmospheres are discussed on the basis of defect chemistry.

Characterization of Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer thin films prepared by a sol-gel method

Seo-Hyeon Jo 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.5

Multiferroic Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer thin films were fabricated by the spin-coating method on Pt/Ti/SiO2/p-Si(100) substrates alternately using Pb(Zr0.52Ti0.48)O3 and BiFeO3 metal alkoxide solutions. The PZT/BFO multilayer thin films show the formation of layers and a change of lattice constant caused by different structure of each other. The coating and heating procedure was repeated several times to form Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without the presence of a second phase such as Bi2Fe4O3. Pb(Zr0.52Ti0.48)O3/ BiFeO3 multilayer films showed a uniform and small grain size rather than pure Pb(Zr0.52Ti0.48)O3 and BiFeO3 films. We think that the crystal growth of the upper BiFeO3 layers can be influenced by the lower Pb(Zr0.52Ti0.48)O3 layers, and choosing the initial Pb(Zr0.52Ti0.48)O3 layer or a seeding layer has controlled the microstructural behavior of the resultant film. Leakage current density of the Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer film was 5.74 × 10-6 A/cm2 at 150 kV/cm.

상자성 불순물이 도핑된 BiFeO$_3$ 물질에 대한 전기적 자기적 성질

이수형,염태호,김상수 한국물리학회 2008 새물리 Vol.57 No.1

BiFeO$_3$ powders doped with Cr (3 mol\%) or Mn (3 mol\%) were synthesized. The two kinds of powders turned out to have ferromagnetic properties based on the electron magnetic resonance signal and the M-H hysteresis loop obtained by using a vibrating sample magnetometer. When BiFeO$_3$ doped with Cr was coated on a Si substrate by using a chemical solution deposition method, however, the BiFeO$_3$ thin film doped with Cr had antiferromagnetic, instead of ferromagnetic, properties. The spectroscopic splitting factors, g, of the ferromagnetic signals for the two kinds of powders were obtained. Cr (3 mol\%)과 Mn (3 mol\%)이 도핑된 BiFeO$_3$ 분말 시료를 합성하였다. 이 시료에 대한 전자 자기 공명 실험의 공명 흡수선과 시료진동 자기력계 (VSM) 실험의 M-H 이력곡선으로부터 이들 분말 시료가 강자성 성질을 갖고 있다는 것을 알았다. 그러나 Cr 이온이 도핑된 BiFeO$_3$를 화학용액 증착 (CSD) 방법을 사용하여 Si 기판위에 박막으로 입혀 전자 자기 공명 실험을 한 결과 이 BiFeO$_3$ 박막시료는 BiFeO$_3$ 분말에서 갖고 있던 강자성 성질을 갖는 것이 아니라, 박막 성장 시 결정화 과정 등을 거치면서 반강자성 성질로 변한다는 것을 알아내었다. 그리고 위의 두 Cr과 Mn이 도핑된 시료에 대한 강자성 공명 신호의 분광학적 분리인자 g 값을 각각 구하였다.

Single BiFeO3 and mixed BiFeO3/Fe2O3/Bi2Fe4O9 ferromagnetic photocatalysts for solar light driven water oxidation and dye pollutants degradation

Tanveer A. Gadhi,Simelys Hernández,Micaela Castellino,Angelica Chiodoni,Thomas Husak,Gabriele Barrera,Paolo Allia,Nunzio Russo,Alberto Tagliaferro 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.63 No.-

A simple synthesis route is presented to obtain single BiFeO3 and mixed BiFeO3/Fe2O3/Bi2Fe4O9 photocatalysts. The obtained samples were characterized to analyze their structural, magnetic, optical and physical–chemical properties. The role of additional phases, i.e. Bi2Fe4O9 and Fe2O3 in the BiFeO3 structure, was analyzed by investigating sunlight-driven water oxidation and degradation of different dye pollutants. The achieved results suggest formation of BiFeO3/Fe2O3/Bi2Fe4O9 heterojunction-like interfaces, that induce lower e−/h+ recombination rate, thus enhancing photoactivity than bare BiFeO3. Additionally, BiFeO3/Fe2O3/Bi2Fe4O9 has exclusive feature of being magnetically separated from treated media and its stability was demonstrated for at least 3 cycles of dye degradation.

화학용액 증착법으로 제조된 희토류 금속으로 치환한 Bi(Fe0.975Cu0.025)O3-δ 박막의 전기적 특성

배유리,김진원,김상수 한국물리학회 2012 새물리 Vol.62 No.8

Pure 순수한 BiFeO_3(BFO),(Bi_(0.9)Dy_(0.1))(Fe_(0.975)Cu_(0.025))O_(3-δ)(BDFC) and (Bi_(0.9)Eu_(0.1))(Fe_(0.975)Cu_(0.025))O_(3-δ)(BEFC) thin films were prepared on Pt(111)/Ti/SiO_2/Si(100) substrates by using a chemical solution deposition method. The coated thin films were annealed at 550℃C for 30 min under a nitrogen atmosphere by using a conventional annealing process and the changes in the micro-structure and the electrical properties with doping were investigated. The micro-structure of the thin films was characterized by means of X-ray diffraction, Raman scattering spectroscopy and scanning electron microscopy. The BDFC and the BEFC thin films exhibited good hysteresis characteristics. The values of the remnant polarizations (2P_r) and the coercive fields(2E_c)of the BDFC and the BEFC thin films were 52 μ/C㎠ and 849kV/cm and 49 μC/㎠ and 981 kV/cm at an electric field of 935kV/cm, respectively. The leakage current densities of the BFO, BDFC and BEFC thin films were 2.60 × 10^-3 A/㎠, 2.07× 10^-4 A/㎠ and 4.45 × 10^-5 A/㎠ at an electric field of 100 kV/cm, respectively. Also the values of the dielectric constants and the dielectric loss of the BFO, BDFC and BEFC thin films were 121 and 0.049, 140 and 0.037, and 135 and 0.040at a frequency of 1 kHz, respectively. The improved electrical properties could be explained by the reduction of oxygen vacancies due to the substitution of Dy^3+, Eu^3+ and Cu^2+ions into BFO and by a change in the micro-structure. 순수한 BiFeO_3(BFO) 박막과 BiFeO_3의 Bi^(3+)이온 일부를Dy^(3+)또는 Eu^(3+)이온으로 치환하고 Fe^(3+)이온일부를Cu^(2+) 이온으로 동시에 치환한(Bi_(0.9)Dy_(0.1))(Fe_(0.975)Cu_(0.025))O_(3-δ)(BDFC),(Bi_(0.9)Eu_(0.1))(Fe_(0.975)Cu_(0.025))O_(3-δ)(BEFC)박막을 Pt(111)/Ti/SiO_2/Si(100) 기판 위에 화학 용액 증착법으로성장시켰다. 성장시킨 박막들은 550℃의 질소 분위기에서 통상적인방법으로 열처리 하였으며 치환에 따른 박막의 미세구조와 전기적 특성변화를 측정, 비교 분석 하였다. BDFC와 BEFC 박막의 전기적 특성이순수한 BFO 박막에 비해 크게 향상되었는데 외부 전기장이 935 kV/cm 일때 잔류 분극(2P_r)과 항전기장(2E_c) 값은 각각 52 μC/㎠과 849 kV/cm, 49 μC/㎠ 과 981 kV/cm이었다. 또 외부 전기장이100 kV/cm 일 때 BFO와 BDFC, BEFC 박막의 누설 전류 밀도는 각각 2.60× 10^{-3} A/㎠과 2.07× 10^-4 A/㎠, 4.45× 10^-5} A/㎠이었으며, 1 kHz에서 측정한 유전상수와유전 손실 값은 각각 121과 0.049, 140과 0.037, 135와 0.040이었다. 이처럼 동시 치환한 박막들이 좋은 전기적 특성을 보이는 것은 치환에의해 산소 빈자리 수의 감소가 일어났기 때문이라고 보여진다.

비스무스 페라이트계 무연 압전 세라믹스

최진홍,김현아,한승호,강형원,이형규,김정석,천채일,Choi, Jin-Hong,Kim, Hyun-Ah,Han, Seung-Ho,Kang, Hyung-Won,Lee, Hyeung-Gyu,Kim, Jeong-Seog,Cheon, Chae-Il 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.9

Recently, many lead-free piezoelectric materials have been investigated for the replacement of existing Pb-based piezoelectric ceramics because of globally increasing environmental interest. There has been remarkable improvement in piezoelectric properties of some lead-free ceramics such as $(Bi,Na)TiO_3-(Bi,K)TiO_3-BaTiO_3$, $(Na,K)NbO_3-LiSbO_3$, and so on. However, no one still has comparable piezoelectric properties to lead-based materials. Therefore, new lead-free piezoelectric ceramics are required. $BiFeO_3$ has a rhombohedrally distorted perovskite structure at room temperature and a very high Curie temperature ($T_C$= 1,100 K). And a very large electric polarization of 50 ~ 60 ${\mu}C/cm^2$ has been reported both in epitaxial thin film and single crystal $BiFeO_3$. Therefore, a high piezoelectric effect is expected also in a $BiFeO_3$ ceramics. The recent research activities on $BiFeO_3$ or $BiFeO_3$-based solid solutions are reviewed in this article.

펄스 레이저 증착법을 이용한 BiFeO3BaTiO3 고용체의 강유전 및 누설전류 특성

이명환,김다정,박진수,김명호,송태권,도달현,김원정 한국물리학회 2015 새물리 Vol.65 No.6

A polycrystalline 0.67BiFeO3-0.33BaTiO3 solid-solution thin film was prepared on a Pt(111)/Ti/SiO2/Si(100) substrate by using pulsed laser deposition (PLD) at different pressure, such as 10 mTorr, 30 mTorr, 50 mTorr, and 100 mTorr, and the crystal structure, the microstructure, the leakage current, and the ferroelectric properties were investigated. The 0.67BiFeO3-0.33BaTiO3 thin film deposited at 30 mTorr exhibited good ferroelectric properties with a large remnant polarization (2Pr = 28 μC/cm2) and a low coercive field (2Ec = 342 kV/cm), which were due to the high (111) preferred orientation and the uniform large grain size. 펄스 레이저 증착법을 이용하여 Pt(111)/Ti/SiO2/Si(100) 기판 위에 0.67BiFeO3-0.33BaTiO3 박막을 10 mTorr, 30 mTorr, 50 mTorr, 100 mTorr의 다양한 산소 분위기에서 540 ℃의 온도에서 제작하여 결정구조, 미세구조, 강유전 및 누설전류 특성을 연구하였다. 30 mTorr의 산소 분위기에서 제작한 0.67BiFeO3-0.33BaTiO3 박막에서 우수한 잔류분극 (2Pr = 28 μC/cm2) 과 낮은 항전계장 (2Ec = 342 kV/cm)을 나타내었으며 이와 같은 결과는 X-선 회절패턴에서 나타나는 높은 (111) 방향으로 우선배향과 균일하고 큰 낟알에 기인하고 있다.

Characterization of the Co film deposited by MOCVD using dicobalt (Hexacarbonyl) tert-butylacetylene and the CoSi2 film formed by a two-step annealing process with a Ti capping layer

Jaesang Lee 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.5

Multiferroic Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer thin films were fabricated by the spin-coating method on Pt/Ti/SiO2/p-Si(100) substrates alternately using Pb(Zr0.52Ti0.48)O3 and BiFeO3 metal alkoxide solutions. The PZT/BFO multilayer thin films show the formation of layers and a change of lattice constant caused by different structure of each other. The coating and heating procedure was repeated several times to form Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without the presence of a second phase such as Bi2Fe4O3. Pb(Zr0.52Ti0.48)O3/ BiFeO3 multilayer films showed a uniform and small grain size rather than pure Pb(Zr0.52Ti0.48)O3 and BiFeO3 films. We think that the crystal growth of the upper BiFeO3 layers can be influenced by the lower Pb(Zr0.52Ti0.48)O3 layers, and choosing the initial Pb(Zr0.52Ti0.48)O3 layer or a seeding layer has controlled the microstructural behavior of the resultant film. Leakage current density of the Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer film was 5.74 × 10-6 A/cm2 at 150 kV/cm.

Crystal Structure and Piezoelectric Properties of KNbO3-BiFeO3 Ceramics

최진홍,김정석,홍석범,채기웅,천채일 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.6

The crystal structure, microstructure, and piezoelectric properties of 1-wt% MnO-doped (1 - x)KNbO₃-xBiFeO₃ (x = 0 ∼ 0.05) ceramics were investigated. The crystal structure changed from orthorhombic to pseudo-cubic around x = 0.005 in the (1 - x)KNbO₃-xBiFeO₃ ceramics. The addition of BiFeO₃ to KNbO₃ reduced the grain size and led to poor densification. The Dielectric constant showed a maximum at x = 0.005 where the crystal structure changed. The KNbO₃ ceramic had a pinched P-E hysteresis loop. KNbO₃-BiFeO₃ ceramics had lower remanent polarizations (P_r) than KNbO₃, probably due to the effect of small grain size. The KNbO₃ ceramic showed good piezoelectric properties; a planar electromechanical factor (k_p) of 0.304, a mechanical quality factor (Q_m) of 281, and a piezoelectric constant (d₃₃) of 121 pC/N. The KNbO₃-BiFeO₃ ceramic, however, had inferior piezoelectric properties compared to KNbO₃ due to the incomplete poling resulting from the small grain size, low density, and low insulating resistance.

천이원소(Ni, Cr, Ti)를 첨가한 Bi0.9Dy0.1FeO3 박막의 성장과 전기적 특성

김은선,김상수,김진원,김해진 한국물리학회 2012 새물리 Vol.62 No.7

Pure BiFeO$_3$ (BFO) and Dy^3+- and transition-metal (Ni^2+,Cr^3+, Ti^4+)-ion co-doped (Bi_0.9Dy_(0.1))(Fe_(0.975)_(0.025))O_(3±, (B = Ni^2+, Cr^3+ and Ti^4+, denoted by BDFNi, BDFCr and BDFTi), respectively thin films were prepared on Pt(111)/Ti/SiO_2/Si(100) substrates by using a chemical solution deposition method. The coated thin films were annealed at 550℃ for 30 min by using a conventional annealing process under a nitrogen atmosphere, and the changes in the microstructure and the electrical properties with doping were investigated. The thin films were well crystallized and randomly oriented, with no detectable impurity and secondary phases. The values of the remnant polarization (2P_r) and the coercive field (2E_c) of the BDFNi,BDFCr and BDFTi thin films were 38 μC/㎠ and 937 kV/cm, 39 μC/㎠ and 954 kV/cm, and 49 μC/㎠ and 1070 kV/cm at an electric field of 1000 kV/cm, respectively. The leakage current densities of the BFO, BDFNi, BDFCr and BDFTi thin films were 2.58× 10^-3 A/㎠, 8.62 × 10^-5 A/㎠, 1.91× 10^-5 A/㎠, and 5.71× 10^-5 A/㎠ at an electric field of 100 kV/cm, respectively. The dielectric constants of the BFO, BDFNi, BDFCr and BDFTi thin films were 121,130, 145, and 124 at a frequency of 1 kHz, respectively, and at the same frequency, the dielectric losses were 0.049, 0.042, 0.039, and 0.043, respectively. The improved electrical properties for the co-doped thin films could be explained by a reduction of oxygen vacancies due to the substitution of Dy and transition-metal (Ni,Cr, Ti) ions and the change in the microstructure. 화학 용액 증착법으로 순수한 BiFeO_3 (BFO) 박막과 BiFeO_3의Bi^3+이온 일부를 Dy^3+ 으로 치환하고 Fe^3+이온 일부를Ni^2+, Cr^3+, Ti^4+이온으로 동시에 치환한(Bi_(0.9)Dy_(0.1))(Fe_(0.975)B_(0.025))O_(3±(B =Ni^2+, Cr^3+, Ti^4+, BDFNi, BDFCr, BDFTi라 함) 박막들을Pt(111)/Ti/SiO_2/Si(100)기판 위에 성장시켜 박막의 구조와 전기적특성 변화를 측정, 비교 분석하였다. 성장시킨 박막들은 550℃의질소 분위기에서 통상적인 방법으로 열처리 하였다. 박막들은 잘결정화되어 있으며 어떤 축 방향으로도 정렬되어 있지 않았고 눈에 띄는이차상이나 불순물상도 발견되지 않았다. 외부 전기장이 1000 kV/cm 일때, BDFNi, BDFCr, BDFTi 박막에 대한 잔류 분극(2P_r)과항전기장(2E_c) 값은 각각 38 μC/㎠ 과 937 kV/cm, 36 μC/㎠과 954 kV/cm, 49 μC/㎠과 1070 kV/cm 이었다. 또외부 전기장이 100 kV/cm일 때 BFO와 BDFNi, BDFCr, BDFTi 박막의 누설전류 밀도는 각각 2.58 × 10^-3 A/㎠, 8.62×10^-5 A/㎠, 1.91 × 10^-5 A/㎠, 5.71 ×10^-5 A/㎠ 이었으며, 주파수가 1 kHz일 때 BFO와 BDFNi, BDFCr,BDFTi 박막의 유전율은 각각 121과 130, 145, 124 이었으며, 같은주파수에서 유전 손실은 각각 0.049, 0.042, 0.039, 0.043 이었다. 이와같이 동시 치환한 박막들이 좋은 전기적 특성을 보이는 것은 치환에의해서 산소 빈자리 수의 감소와 미세 구조의 변화가 일어났기때문이라고 보여진다.