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Long, Phan The,Manh, T.V.,Ho, T.A.,Dongquoc, Viet,Zhang, P.,Yu, S.C. Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.13
<P><B>Abstract</B></P> <P>We have prepared rhombohedral La<SUB>1-x</SUB>Sr<SUB>x</SUB>CoO<SUB>3-δ</SUB> (<I>x</I> = 0.2–0.5) compounds with a mass density <I>ρ</I> ≈ 5.5 g/cm<SUP>3</SUP>. Their magnetocaloric (MC) effect is studied via the magnetic-entropy change (Δ<I>S</I> <SUB>m</SUB>) and relative cooling power (<I>RCP</I>), which are calculated from initial magnetization data recorded at different temperatures. Results reveal that the Δ<I>S</I> <SUB>m</SUB> magnitude is maximum (Δ<I>S</I> <SUB>max</SUB>) around the ferromagnetic-paramagnetic phase transition and dependent on both the applied-field (<I>H</I>) magnitude and Sr content (<I>x</I>). For <I>H</I> = 50 kOe, |Δ<I>S</I> <SUB>max</SUB>| can be tuned in the range of 1.6–2.7 J/kg K, corresponding to <I>RCP</I> values of 89–141 J/kg. Among the studied La<SUB>1-x</SUB>Sr<SUB>x</SUB>CoO<SUB>3-δ</SUB> samples, the samples with <I>x</I> = 0.3–0.5 have the largest |Δ<I>S</I> <SUB>max</SUB>| values. If combining these samples as MC blocks in refrigeration application, the working temperature range of a cooling device could range from 204 to ~280 K, with |Δ<I>S</I> <SUB>max</SUB>| stable at ~2.6 J/kg K and <I>RCP</I> ≈ 198 J/kg. We have also assessed the phase-transition type and magnetic order and found La<SUB>1-x</SUB>Sr<SUB>x</SUB>CoO<SUB>3-δ</SUB> undergoing a second-order phase transition. Magnetic order tends to change from the long-range type to the short-range one when <I>x</I> varies from 0.2 to 0.5. This is in good agreement with the results obtained from the analysis of critical behavior.</P>
Ha, Quang-Khai,Choi, Seunghyun,Phan, Nam-Long,Kim, Kangjoo,Phan, Chu-Nam,Nguyen, Viet-Ky,Ko, Kyung-Seok Elsevier 2019 Science of the Total Environment Vol.654 No.-
<P><B>Abstract</B></P> <P>Acidic groundwaters enriched with heavy metals are frequently observed in the coastal plain aquifers. The acidic pHs are observed even in the deep confined aquifers in southern Vietnam. This study geochemically explores the causes of these acidic groundwaters by investigating 41 groundwater samples, 4 soil samples and a 54 m long sediment core and the long-term monitoring data (4189 observations) obtained from 178 wells of the National Groundwater Monitoring Network for the South of Vietnam (NGMNS). The groundwater data show elevated Fe, Mn, Al, Pb, and Zn concentrations as the pH becomes acidic and suggest pyrite oxidation be the major cause for the groundwater acidification. This is further confirmed by pyrite framboids observed in the sediment or soil samples taken from the sites where strongly acidic groundwaters were observed. Results of leaching experiments using sediment and soil samples indicate that high metal concentrations in the acidic pH are associated with the increased metal solubility and mineral dissolution kinetics. The acidification of deep groundwaters is revealed to be associated with well installation, indicating the importance of proper well-installation techniques to protect water quality of deep confined aquifers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Metal-rich, acidic groundwaters are commonly observed in Mekong Delta area. </LI> <LI> Pyrite oxidation is the major reason for groundwater acidification in the area. </LI> <LI> The pyrite oxidation in deep confined aquifer was induced by well installation. </LI> <LI> Well installation techniques minimizing aquifer disturbance are required. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Tran Dang Thanh,Dinh Chi Linh,Le Viet Bau,Thi Anh Ho,Tien Van Manh,The-Long Phan,Seong-Cho Yu IEEE 2015 IEEE transactions on magnetics Vol.51 No.1
<P>Four samples of La<SUB>0.7</SUB>Sr<SUB>0.3</SUB>Mn<SUB>0.92</SUB>Co<SUB>0.08</SUB>O<SUB>3</SUB> (LSMCO) with different crystallite sizes were prepared by the combination of solid-state reaction and mechanical milling methods. Based on isothermal magnetization data, M(H), temperature dependences of magnetic entropy change, ΔS<SUB>m</SUB>T, of the samples under a magnetic field change of 10 kOe were calculated. The maximum values of magnetic entropy change (|ΔS<SUB>max</SUB>|) at room temperature are in the range of 0.9-1.4 J · kg<SUP>-1</SUP> · K<SUP>-1</SUP>, corresponding to ferromagnetic (FM)-paramagnetic phase transition. In addition, M<SUP>2</SUP> versus H/M curves at temperatures around TC prove the samples exhibiting a second-order magnetic phase transition. The critical exponents β, γ, and δ were determined using the modified Arrott plot method and critical isotherm analysis. Here, these exponent values are located in between those expected for the mean-field theory and 3-D Heisenberg model. It means the coexistence of short-range and long-range FM interactions in LSMCO nanoparticles.</P>
Phan, The-Long,Ho, T.A.,Thang, P.D.,Tran, Q.T.,Thanh, T.D.,Phuc, N.X.,Phan, M.H.,Huy, B.T.,Yu, S.C. Elsevier 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.615 No.-
<P><B>Abstract</B></P> <P>We have determined the values of critical exponents of two polycrystalline samples (Nd<SUB>1−</SUB> <I> <SUB>x</SUB> </I>Y<I> <SUB>x</SUB> </I>)<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> (<I>x </I>=0 and 0.07) from the magnetization data versus temperature and magnetic field, <I>M</I>(<I>H</I>, <I>T</I>), to learn about their magnetic and magnetocaloric (MC) properties. The results reveal the samples exhibiting the crossover of first-order and second-order phase transitions, where the exponent values <I>β </I>=0.271 and <I>γ </I>=0.922 for <I>x </I>=0, and <I>β </I>=0.234–0.236 and <I>γ </I>=1.044–1.063 for <I>x </I>=0.07 determined by using modified Arrott plots and static-scaling hypothesis are close to those expected for the tricritical mean-field theory (<I>β </I>=0.25 and <I>γ </I>=1.0). Particularly, the <I>T</I> <SUB>C</SUB> of <I>x </I>=0 and 0.07 can be any value in the temperature ranges of 240–255K and 170–278K, respectively, depending on the magnitude of applied magnetic field and determination techniques. Around the <I>T</I> <SUB>C</SUB>, studying the MC effect of the samples has revealed a large magnetic-entropy change (Δ<I>S</I> <SUB>m</SUB>) up to ∼8J/kgK for the applied field interval Δ<I>H </I>=50kOe, corresponding to refrigerant capacity values of 200–245J/kg. These phenomena are related to the crossover nature and the persisting of FM/anti-FM interactions even above the <I>T</I> <SUB>C</SUB>, as further confirmed by electron-spin-resonance data, Curie–Weiss law-based analyses, and an exponential parameter characteristic of magnetic order <I>n </I>=dLn|Δ<I>S</I> <SUB>m</SUB>|/dLn<I>H</I>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Tricritical point in Y-doped Nd<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> manganites. </LI> <LI> A large magnetic-entropy change. </LI> <LI> Magnetic inhomogeneity and phase separation. </LI> </UL> </P>