Electronic structure and magnetic properties of BaTi_1-xMn_xO₃

Dang, N.V.,Dang, N.T.,Ho, T.A.,Tran, N.,Phan, T.L. Elsevier 2018 CURRENT APPLIED PHYSICS Vol.18 No.2

<P>The electronic structure and magnetic properties of polycrystalline BaTi1-xMnxO3 (x = 0-0.1) compounds prepared by solid-state reactions were studied. The results revealed that the increase in Mn content (x) did not change the oxidation numbers of Ba (+2) and Ti (+4) in BaTi1-xMnxO3. However, there is the change in Mn valence that Mn-3+,Mn-4+ ions coexist in the samples with x = 0.01-0.04 while Mn4+ ions are almost dominant in the samples with x = 0.06-0.1. We also point out that Mn3+ and Mn4+ ions substitute for Ti4+ and prefer locating in the tetragonal and hexagonal BaTiO3 structures, respectively, in which the hexagonal phase constitutes soon as x = 0.01. Particularly, all the samples exhibit room-temperature ferromagnetism. Ferromagnetic order increases with increasing x from 0 to 0.02, but decreases as x >= 0.04. We think that ferromagnetism in BaTi1-xMnxO3 is related to lattice defects and/or exchange interactions between Mn3+ and Mn4+ ions. (C) 2017 Elsevier B.V. All rights reserved.</P>

Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds

N.T. Dang,D.P. Kozlenko,Kim Gareoung,손원혁,이종수,Dimitar N. Petrov,T. V. Manh,Phan The Long 한국물리학회 2020 Current Applied Physics Vol.20 No.6

Orthorhombic La0.7-xEuxCa0.3MnO3 samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm3 prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (TC) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around TC reaches the maximum (|ΔSmax|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔSmax| values are about 5.88, 4.93, and 4.71 J/ kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔSmax| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around TC have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La0.7Ca0.3MnO3 materials for magnetic refrigeration below room temperature.

Electronic structure and magnetic properties of BaTi1-xMnxO3

N.V. Dang,N.T. Dang,T.A. Ho,N. Tran,T. L. Phan 한국물리학회 2018 Current Applied Physics Vol.18 No.2

The electronic structure and magnetic properties of polycrystalline BaTi1-xMnxO3 (x ¼ 0e0.1) compounds prepared by solid-state reactions were studied. The results revealed that the increase in Mn content (x) did not change the oxidation numbers of Ba (þ2) and Ti (þ4) in BaTi1-xMnxO3. However, there is the change in Mn valence that Mn3þ,4þ ions coexist in the samples with x ¼ 0.01e0.04 while Mn4þ ions are almost dominant in the samples with x ¼ 0.06e0.1. We also point out that Mn3þ and Mn4þ ions substitute for Ti4þ and prefer locating in the tetragonal and hexagonal BaTiO3 structures, respectively, in which the hexagonal phase constitutes soon as x ¼ 0.01. Particularly, all the samples exhibit roomtemperature ferromagnetism. Ferromagnetic order increases with increasing x from 0 to 0.02, but decreases as x 0.04. We think that ferromagnetism in BaTi1-xMnxO3 is related to lattice defects and/or exchange interactions between Mn3þ and Mn4þ ions.

Ferromagnetism-to-Paramagnetism Transition in the ZnMnO System

V. S. Dang,Y. Y. Song,N. Q. Hoa,유성초,Y. G. Yoo 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5

The magnetic properties of Mn- and P-doped ZnO prepared by using the solid state reaction and pulsed laser deposition (PLD) were investigated by measuring the magnetization and the absorption derivative of the electron paramagnetic resonance (EPR). The film's thickness was about 0.3 μm. The X-ray diraction pattern indicated a single-phase polycrystalline ZnO structure without any MnO₂ phase in both the polycrystalline samples and the thin lms. The magnetic behaviors of the samples were determined by using an alternating gradient magnetometer (AGM) at room tempera- ture. All the bulk samples showed ferromagnetism at room temperature. Mn-doped ZnO films with Zn₃P₂ added also showed ferromagnetism at room temperature. A transition from ferromagnetism to paramagnetism with increasing in sintering temperature was detected in the EPR experiments. The absorption derivative of the EPR signal showed hyperne splitting for the samples sintered at 800 and 900℃ due to a spin degeneracy of Mn²+, the hyperfine splitting disappeared for the samples sintered at 1000℃ due to a superposition of the six lines of hyperfine splitting.

Utilization of AZO/Au/AZO multilayer electrodes instead of FTO for perovskite solar cells

Dang, Tran-Van,Pammi, S.V.N.,Choi, Jihoon,Yoon, Soon-Gil Elsevier 2017 Solar energy materials and solar cells Vol.163 No.-

<P><B>Abstract</B></P> <P>Aluminum (3at%)-doped ZnO (AZO)/Au/AZO multilayer films with low resistivity and high transmittance are in situ deposited at room temperature via facing-target sputtering for AZO and direct current (DC) sputtering for Au. The optical and electrical properties of multilayer films are compared with conventionally (<I>on</I>-axis) sputtered and facing-target sputtered (FTS) AZO films. The FTS samples show better crystallinity than that of <I>on</I>-axis sputtered samples, and the lowest value for resistivity is 7.9×10<SUP>−5</SUP> Ω-cm at an Au layer thickness of 8nm, which is compared with that of a conventional FTO electrode. The photo-conversion efficiencies (PCE) of the perovskite solar cells based on the AZO multilayer electrodes deposited via FTS and <I>on</I>-axis sputtering are 9.5% and 8.2%, respectively. Although the PCE of AZO multilayer-based-solar cells exhibit a lower efficiency than that of the FTO based-devices (~12.3%), the perovskite solar cell performance based on the FTS AZO multilayer electrodes is very attractive for applications to flexible planar-structured solar cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Utilization of the AZO/Au/AZO multilayer electrodes for perovskite solar cells. </LI> <LI> Low resistivity and high transmittance of AZO/Au/AZO deposited at room temperature via FTS. </LI> <LI> Damage-free FTS method from the plasma for multilayer electrodes. </LI> <LI> Achievement of high photo-conversion efficiency (~9.5%) using multilayer electrodes deposited via FTS. </LI> </UL> </P>

Ferromagnetic Resonance of Soft Magnetic CoFeAlO Thin Films

V. S. Dang,T.L. Phan,N.D. Ha,C.O.Kim,S.C. Yu 한국자기학회 2007 한국자기학회 학술연구발표회 논문개요집 Vol.- No.-

Antifungal activity of sterols and dipsacus saponins isolated from Dipsacus asper roots against phytopathogenic fungi

Choi, N.H.,Jang, J.Y.,Choi, G.J.,Choi, Y.H.,Jang, K.S.,Nguyen, V.T.,Min, B.S.,Le Dang, Q.,Kim, J.C. Academic Press 2017 Pesticide biochemistry and physiology Vol.141 No.-

<P>The in vivo antifungal activity of crude extracts of Dipsacus asper roots was evaluated against the phytopathogenic fungi Botrytis cinerea, Colletotrichum coccodes, Blumeria graminis f. sp. hordei, Magnaporthe grisea, Phytophthora infestans, Puccinia recondite and Rhizoctonia solani using a whole-plant assay method. Ethyl acetate and acetone extracts, at 1000 mu g/mL, suppressed the development of tomato gray mold (TGM) and tomato late blight (TLB) by 90%. Through bioassay-guided isolation, five antifungal substances were isolated from the D. asper roots and identified as beta-sitosterol (1), campesterol (2), stigmasterol (3), cauloside A (4) and a novel dipsacus saponin, named colchiside (3-O-beta-D-xylopyranosyl-23-O-beta-D-glucopyranosyl-28-O-beta-D-(6-O-acetyl)-glucopyranosyl hederagenin) (5). Of those, cauloside A (4) displayed the greatest antifungal efficacy against rice blast, TGM and TLB. Colchiside (5) moderately suppressed the development of TLB, but exhibited little effect against the other diseases. The synergistic effects of the isolated compounds against TLB were also assessed. Synergistic and additive interactions were observed between several of the sterol compounds. This study indicated that the crude extracts of, and bioactive substances from, the roots of D. asper suppress TGM and TLB. In addition, cauloside A (4) and colchiside (5) could be used as antifungal lead compounds. (C) 2016 Elsevier Inc. All rights reserved.</P>

Second-order phase transition with coexistence of short-range and long-range ferromagnetic interactions in Ba1.7La0.3FeMoO6 compound

Tran Dang Thanh,오석근,김동현,유성조,S.E. Demyanov,N.A. Kalanda,M.V. Yarmolich,L.V. Kovalev 한국물리학회 2014 Current Applied Physics Vol.14 No.6

In this work, the magnetic properties and critical behavior around ferromagneticeparamagnetic (FM ePM) phase transition in Ba1.7La0.3FeMoO6 compound have been investigated in detail. This compound exhibits a second-order magnetic phase transition with Curie temperature TC ¼ 345 K. The critical exponents b, g, and d that are determined by using the modified Arrott plots (MAP), the KouveleFisher (KF) and the critical isotherm analysis agree very well. Our results indicate a coexistence of short-range and long-range ferromagnetic (FM) interactions in Ba1.7La0.3FeMoO6 compound. The existence of long-range FM interactions in this compound can be associated with the crystal structure of materials with longrange Fe/Mo ordering parameter and strength of double-exchange interaction, whereas the existence of the short-range FM interactions can be explained by magnetic inhomogeneity and FM clusters.

Transfer-free graphene electrodes for super-flexible and semi-transparent perovskite solar cells fabricated under ambient air

Tran, Van-Dang,Pammi, S.V.N.,Park, Byeong-Ju,Han, Yire,Jeon, Cheolho,Yoon, Soon-Gil Elsevier 2019 Nano energy Vol.65 No.-

<P><B>Abstract</B></P> <P>Graphene has shown many advantages over the metal oxide transparent materials that serve as conventional electrodes in solar cells because graphene is more transparent, has greater stability, and is more mechanically flexible. Flexibility and semi-transparency of the perovskite solar cells are challenged to integrate with the flexible electronic devices since the perovskite solar cells have discovered. Herein, we provide the first report of transfer-free, large-scale monolayer graphene employed as a transparent and flexible bottom electrode. High-quality graphene without transfer process was directly synthesized at 150 °C on a polymer substrate <I>via</I> plasma assisted thermal chemical vapor deposition (PATCVD). Additionally, a highly transparent AZO/Ag/AZO (AAA) multilayer was utilized as a top counter electrode to create semi-transparent perovskite solar cells with a remarkable degree of mechanical flexibility. The 300 nm-thick perovskite solar cells with PATCVD-Graphene revealed a high transmittance of ~26% at a wavelength of 700 nm. The highest level of power conversion efficiency (PCE) (~14.2%) was recorded by an illumination from the bottom graphene side. After 1000 bending cycles under a tensile strain of 1.5%, the graphene-based devices maintained a level of PCE that was more than 90% greater than the initial reading. This superior bending robustness highlights the potential for non-transfer, graphene-based, perovskite photovoltaic material to establish a tandem structure for a foldable solar cell.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High-quality graphene without transfer process was directly synthesized at 150 °C on a polymer substrate as transparent electrode. </LI> <LI> The smooth surface with grain size upon 700 nm of MAPbI<SUB>3</SUB> perovskite has been obtained by CVD process. </LI> <LI> Solar-cell devices with PATCVD-graphene electrodes demonstrated a PCE of 14.2% with a transmittance ~26% at a wavelength of 700 nm. </LI> <LI> PSC devices demonstrated a great flexibility, maintaining 90% of the original PCE value after 1000 bending cycles under a tensile strain of 1.5%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Chemical vapor deposition in fabrication of robust and highly efficient perovskite solar cells based on single-walled carbon nanotubes counter electrodes

Tran, Van-Dang,Pammi, S.V.N.,Dao, Van-Duong,Choi, Ho-Suk,Yoon, Soon-Gil Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.747 No.-

<P><B>Abstract</B></P> <P>This study presents a strategy of fabricating a perovskite layer through chemical vapor deposition (CVD) method and applying it as an efficient absorber in PSCs based on SWCNT counter electrode. As the results, the CVD method produced smooth and void-free perovskite films, which reduced the moisture absorption at the grain boundaries then delayed the degradation of the organic/inorganic composition. Furthermore, the smooth surface of the dye layer enhances charge collection at the interface with counter electrodes. Thus, the efficiency of cell fabricated by CVD method was 7.9%, which is improved by 29.5% as compared with cells using the conventional spin-coating method. Furthermore, the cell fabricated by CVD method gave an excellent stability. Accordingly, the efficiency was lost only 17% after 500 h performances. This approach could pave the way to develop low-cost PSCs with long-term stability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Smooth surface with grain size upon 2 μm of MAPbI<SUB>3</SUB> via CVD. </LI> <LI> Degradation of MAPbI<SUB>3</SUB> films by moisture absorption depends on surface morphology. </LI> <LI> Single-wall carbon nanotube for hybrid hole-transporter and counter electrode. </LI> <LI> A small linear efficiency loss of SWCNT-based devices under illumination of 500 h. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>