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Phan, T. L.,Thanh, T. D.,Ho, T. A.,Thang, P. D.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.4
<P>We prepared BaTi<SUB>1-x</SUB>Mn<SUB>x</SUB>O<SUB>3</SUB> samples (x = 0 and 0.05) by standard solid-state reaction at 700°C and 900°C in an Ar ambient to change oxidation number of Mn dopants. The fabricated samples were then studied structural characterization and electronic structures by means of X-ray diffraction and absorption, and Raman scattering and electron-spin-resonance spectrometers. We found oxidation numbers 2+ and 3+ of Mn ions coexisting in BaTi<SUB>1-x</SUB>Mn<SUB>x</SUB>O<SUB>3</SUB> with x = 0.05, where the Mn<SUP>2+</SUP>/Mn<SUP>3+</SUP> ratio is about one for the sample annealed at 700°C. These Mn ions prefer locating at the Ti site in the tetragonal BaTiO<SUB>3</SUB> host lattice. In particular, there is a change in the oxidation number of Mn<SUP>2+</SUP> → Mn<SUP>3+</SUP> when the annealing temperature changes from 700°C to 900°C. Their magnetic properties are accordingly changed. Meanwhile, annealing pure BaTiO<SUB>3</SUB> in an Ar ambient at 700°C and 900°C does not lead to ferromagnetic (FM) order; they are almost diamagnetic. With the obtained results, we believe that FM order in Mn-doped BaTiO<SUB>3</SUB> annealed in an Ar ambient is associated with exchange interactions of Mn<SUP>2+</SUP> ions mediated by oxygen vacancies rather than associated with Mn<SUP>3+</SUP> ions.</P>
Solid State Dye-Sensitized Solar Cells Based on Polymeric Ionic Liquid with Free Imidazolium Cation
Thanh-Tuan Bui,Tarik Matrab,Vincent Woehling,Justine Longuet,Cédric Plesse,Giao T.M. Nguyen,Frédéric Vidal,Fabrice Goubard 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.1
A polymeric ionic liquid issued from an ionic liquid monomer composed of a methacrylate polymerizable group, a polar tri(ethylene oxide) spacer, a trifluoromethane sulfonic anion and a free imidazolium cation was employed as a solid electrolyte for dye-sensitized solar cells. The simple device configuration based on dip-coated nanoporous TiO2 electrode sensitized by N3 ruthenium-based dye gave the conversion efficiency of up to 1.74% under AM 1.5 simulated solar light illumination. Effect of TiO2 porous film thickness on overall energy conversion efficiency was discussed. It has been found that the most appropriate thickness for the polymeric ionic liquid based electrolyte dye sensitized solar cell is around 7 μm.
Thanh, Tran Dang,Xuan Hau, Kieu,Huyen Yen, Pham Duc,Manh, T. V.,Yu, S. C.,Phan, T. L.,Telegin, A.,Telegin, S.,Naumov, S. IEEE 2018 IEEE transactions on magnetics Vol.54 No.11
<P>In this paper, we present a detailed analysis on the critical behavior of La<SUB>1.2</SUB>Sr<SUB>1.8</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB> single crystal via isothermal magnetization measured at different temperatures around the paramagnetic–ferromagnetic phase transition at <TEX>$T_{C} = 85$</TEX> K. Using the Landau–Lifshitz coefficients, the Arrott plots ( <TEX>$H/M = a(T) + b(T)M^{2}$</TEX>) of sample have been analyzed. It showed that a(T) changed from positive to negative values at different temperatures in the field ranges of <TEX>$H = 0$</TEX>–10, 10–30, and 30–50 kOe, indicating that the critical behavior could not be described with a single model under different applied fields. Through the modified Arrott plots method, the Kouvel–Fisher method, and the critical isotherm analysis, we determined the values of the critical exponents for La<SUB>1.2</SUB>Sr<SUB>1.8</SUB>Mn<SUB>2</SUB>O<SUB>7</SUB> around its magnetic phase transition over different magnetic field ranges. The critical exponent <TEX>$\beta $</TEX> value is found to be 0.501, 0.417, and 0.371 under field ranges of <TEX>$H = 0$</TEX>–10, 10–30, and 30–50 kOe, respectively. This means that the <TEX>$\beta $</TEX> value depends strongly on the strength of the applied field, shifting from the value approaching that of the mean field model ( <TEX>$\beta = 0.5$</TEX>) to the 3-D-Heisenbeg model ( <TEX>$\beta = 0.365$</TEX>). Meanwhile, its <TEX>$\gamma $</TEX> value is quite stable ( <TEX>$\gamma =0.973$</TEX>–1.074), almost independent on the choice of field fitting range. In addition, using the reduced temperature <TEX>$\varepsilon = (T-T_{C}$</TEX>)/ <TEX>$T_{C}$</TEX> and the obtained critical exponents, almost <TEX>$M(H, T$</TEX>) data measured near <TEX>$T_{C}$</TEX> obey the scaling equation <TEX>$M(H, \varepsilon) = \varepsilon ^{\boldsymbol {\beta }}f_{\pm }(H/\varepsilon ^{\boldsymbol {\beta +\gamma }}$</TEX>), where <TEX>$f_{+}$</TEX> and <TEX>$f_{-}$</TEX> are regular analytic functions corresponding to data at <TEX>$T > T_{C}$</TEX> and <TEX>$T < T_{C}$</TEX>, respectively.</P>
Thanh, T.D.,Nan, W.Z.,Nam, G.,Van, H.T.,You, T.S.,Phan, T.L.,Yu, S.C. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.10
A systematic study of the conventional and inverse magnetocaloric effects, and critical behaviors in an alloy ingot of Ni<SUB>43</SUB>Mn<SUB>46</SUB>Sn<SUB>8</SUB>In<SUB>3</SUB> has been performed. Our results reveal the sample exhibiting structural and magnetic phase transitions at temperatures T<SUB>C</SUB><SUP>M</SUP> = 166 K (T<SUB>C</SUB> of the martensitic phase), T<SUB>M-A</SUB> = 260 K (the martensitic-to-austenitic phase transformation) and T<SUB>C</SUB><SUP>A</SUP> = 296 K (T<SUB>C</SUB> of the austenitic phase). The large values of refrigerant capacity (RC) around T<SUB>M-A</SUB> and T<SUB>C</SUB><SUP>A</SUP> are found to be RC<SUB>M-A</SUB> = 172.6 and RC<SUB>A</SUB> = 155.9 J kg<SUP>-1</SUP>, respectively, under an applied field change of 30 kOe. Our critical analyses near the T<SUB>C</SUB><SUP>M</SUP> and T<SUB>C</SUB><SUP>A</SUP> reveal that a coexistence of the long- and short-range ferromagnetic order in the martensitic phase, while the long-range ferromagnetic order exists in the austenitic phase. Interestingly, at around T<SUB>C</SUB><SUP>A</SUP>, the maximum magnetic entropy change (|ΔS<SUB>max</SUB>|) versus magnetic field H obeys a power law, |ΔS<SUB>max</SUB>| = a.H<SUP>n</SUP>, where the exponent n is found to be about 0.66.
Tran Dang Thanh,Phan, T. L.,Pham Thi Thanh,Nguyen Hai Yen,Nguyen Huy Dan,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.4
<P>This paper presents the magnetocaloric effect and critical behavior of alloy ingot and ribbon samples of Ni<SUB>50</SUB>Mn<SUB>37</SUB>Sn<SUB>13</SUB> doped with 8% Ag, which were prepared by an arc-melting and rapidly quenched melt-spinning methods, respectively. Experimental results reveal that a partial replacement of Ag for Ni leads to stamping out the antiferromagnetic martensitic phase. This means that there is only the austenitic phase with a ferromagnetic-paramagnetic (FM-PM) phase-transition temperature of T<SUB>C</SUB> ≈ 295 K. Detailed studies and analyses around the phase transition region prove both samples undergoing a second-order magnetic phase transition. Basing on magnetic field dependences of magnetization, we have determined the magnetic-entropy change (ΔS<SUB>m</SUB>) of the samples. Under a field change of 10 kOe, the maximum magnetic-entropy change (|ΔS<SUB>max</SUB>|) reaches values 0.54 and 0.69 J · kg<SUP>-1</SUP> · K<SUP>-1</SUP> for the alloy ingot and ribbon, respectively. Using Landau's phase-transition theory, and careful analyses of the magnetic data around the FM-PM transition region, we have determined the critical parameters (T<SUB>C</SUB>, β, γ, and δ) in the low field range (below 10 kOe) with T<SUB>C</SUB> = 294.8 K, β = 0.469 ± 0.011, γ = 1.149 ± 0.060, and δ = 3.4 ± 0.1 for the alloy ingot, and with T<SUB>C</SUB> = 294.4 K, β = 0.449 ± 0.005, γ = 1.319 ± 0.040, and δ = 3.9 ± 0.1 for the alloy ribbon. One can see that β values fall in between those expected for the 3-D Heisenberg model (β = 0.365) and mean-field theory (β = 0.5). This indicates a coexistence of short-range and long-range FM interactions in both the samples. The nature of changes in value related to the critical parameters and maximum ΔS<SUB>m</SUB> is thoroughly discussed by means of structural analyses.</P>
Thanh, Tran Dang,Huyen Yen, Pham Duc,Hau, Kieu Xuan,Bau, Le Viet,Yu, S. C. IEEE 2018 IEEE transactions on magnetics Vol.54 No.11
<P>In this paper, we have investigated the critical properties in the vicinity of the ferromagnetic (FM)–paramagnetic (PM) phase transition in a polycrystalline sample of La<SUB>0.75</SUB>Ca<SUB>0.2</SUB>Ag<SUB>0.05</SUB>MnO<SUB>3</SUB>, which was prepared by a solid-state reaction method. Temperature dependence of the inverse of the susceptibility <TEX>$\chi ^{-1}$</TEX> ( <TEX>$T$</TEX>) proves an existence of the Griffiths phase well above Curie temperature ( <TEX>$T_{C} = 230$</TEX> K). Detailed analyses of the isothermal magnetization <TEX>$M$</TEX>( <TEX>$H$</TEX>, <TEX>$T$</TEX>) data reveal the sample exhibiting a second-order magnetic phase transition, and its temperature dependences of the saturation magnetization and the initial susceptibility obey the asymptotic relations. Using the modified Arrott plots method, the Kouvel–Fisher method, and the critical isotherm analysis, the critical parameters ( <TEX>$\beta$</TEX>, <TEX>$\gamma$</TEX>, <TEX>$\delta$</TEX>, and <TEX>$T_{C}$</TEX>) of La<SUB>0.75</SUB>Ca<SUB>0.2</SUB>Ag<SUB>0.05</SUB>MnO<SUB>3</SUB> compound have been estimated. Using these critical exponent values, almost <TEX>$M$</TEX>( <TEX>$H$</TEX>, <TEX>$T$</TEX>) data measured at different temperatures around FM–PM phase transition are collapsed onto two universal curves of <TEX>$M/\vert \varepsilon \vert ^{\boldsymbol {\beta }}$</TEX> versus <TEX>$H/\vert \varepsilon \vert ^{\boldsymbol {\beta }+\boldsymbol {\gamma }}$</TEX> corresponding to the regular functions for <TEX>$T > T_{C}$</TEX> and <TEX>$T < T_{C}$</TEX>, respectively.</P>
Thanh C., Nguyen,An T., Dang,Khuong N.T., Tran Techno-Press 2022 Ocean systems engineering Vol.12 No.4
Annually, about 48-60% of sediment discharge of the Mekong River is delivered near the mouths of the Mekong River branches which is mostly coinciding with the southwest (SW) monsoon. This sediment budget in turn will be southwestwardly transported along the coast of the Mekong Delta (MD) during the northeast (NE) monsoon. Analysis of monsoonal changes in grain-size distribution (GSD) of surface sediment contributes to a better understanding of erosion and deposition processes along the MD. This study aims to figure out changes in GSD and sediment textures along the MD between SW and NE monsoons based on 183 surficial sediment samples collected along the MD during two field surveys carried-out in October 2016 and February-March 2017. Compared to the GSD during the SW and NE monsoon, the GSD along the MD changed significantly, especially in the estuary areas and along the coast of Bac Lieu and Ganh Hao. Whereas, in the west coast of the MD, GSD seem no changes between the two seasons. These changes in seabed sediment suggest that sediment with grain-sizes ranging from silt to fine sand can be transported during only a NE season.