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Tho, P.T.,Dang, N.V.,Nghia, N.X.,Khiem, L.H.,Xuan, C.T.A.,Kim, H.S.,Lee, B.W. Elsevier 2018 The Journal of physics and chemistry of solids Vol.121 No.-
<P><B>Abstract</B></P> <P>In this investigation, we have studied the crystal structure and magnetic properties of Zn doped Bi0.84La0.16FeO3 (<I>x</I> = 0.02–0.1) ceramics at the morphotropic phase boundary of rhombohedral and orthorhombic phases. Rietveld refinement of the obtained XRD patterns and Raman spectroscopy confirm the presence of multiphases crystal structure of <I>R3c</I> rhombohedral and <I>Pbam</I> orthorhombic. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization and coercivity with dominating of orthorhombic phase. The isothermal structural transition from <I>R3c</I> to <I>Pbam</I> is caused for the decrease in magnetization and the increase in coercivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The crystal structure of Bi<SUB>0.84</SUB>La<SUB>0.16</SUB>Fe<SUB>1-x</SUB>Zn<SUB>x</SUB>O<SUB>3</SUB> at the morphotropic phase boundary. </LI> <LI> The microstructure reveals the coexistence crystal phase and their phase boundary. </LI> <LI> The isothermal structural transition induces the change in magnetic properties. </LI> <LI> The vertical shift (exchange bias) is observed in compounds. </LI> </UL> </P>
Resonant Raman Scattering in ZnO Nanostructures Annealed at Different Temperatures
The Long Phan,N. X. Nghia,V. D. Lam,유성초 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.61
We studied resonant Raman scattering (RRS) in ZnO nanostructures annealed at various temperatures. Experimental samples, including nanorods, nanowires and thin films, were prepared by using a chemical aqueous solution (CAS) method, chemical vapor deposition (CVD), radio-frequency magnetron sputtering, and pulsed laser deposition (PLD). After prepared, the CAS-grown nanorods were annealed at temperatures (Tan) between 300 and 1000 ℃ while the other nanostructures were annealed at Tan = 500 - 850 ℃. RRS spectra revealed that the as-prepared ZnO samples usually exhibited three or four modes of the longitudinal optical (LO) phonon. The annealing introduced the fifth mode (5LO). The intensity ratio of I2LO to 1LO (I 2LO/I 1LO), reflecting the coupling strength of electron-phonon interaction, was found to be a function of Tan . With increasing Tan, I 2LO/I 1LO increased and reached a maximum value at about 800 ℃. At higher annealing temperatures, I 2LO/I 1LO decreased. This feature seemed to be universal for all the ZnO nanostructures investigated.
A quantitative analysis of the optical reflection properties of self-assembled opal films
Q.M. Ngo,S. Kim,H. Lim,P.T. Nga,P.T. Linh,N.X. Nghia,F. Rotermund,K. Kim,A. Avoine,A. Maître 한국물리학회 2011 Current Applied Physics Vol.11 No.3
The reflection spectra of self-assembled opal films on glass substrates are analyzed in detail, with an eye to employing the film as a tunable filter, using the photonic band diagram and the simulation on the reflectance corresponding to the real structure. The reflection peak commonly thought to be due to the photonic pseudogap formed by the (111) planes is found to be actually formed by two different pseudogaps by the (111) planes and the (200) planes. The small value for the photonic pseudogap in the <111> direction makes the corresponding light frequency propagate more than 40 SiO_2 layers in the <111> direction. Therefore, a reflectivity of larger than 65% is difficult to achieve with an opal film whose thickness is smaller than 25 SiO_2 layers in any direction with incident angles between 5° and 75°. The reflectivity of annealed opal film is found to be lower than that of the ideal film due to the reduction of the photonic pseudogaps and a microscopic wavy surface that is believed to be due to the variation of the SiO_2 sphere size and the deformation of the SiO_2 spheres caused by the contraction of the SiO_2 spheres during the annealing process.