Papers by Author: R. Muanghlua

Abstract: Multiferroics, which display simultaneous ferrimagnetic and ferroelectric properties, have been interesting recently because of their potentially significant applications in multifunctional devices such as magnetic resonance, drug delivery, high-density data storage, ferrofluid technology, etc. Composites combining BaTiO₃ with Co_0.5Ni_0.5Fe₂O₄ have influenced the interest of many researchers, due to their outstanding and distinguished character called magnetoelectric (ME). In this work, ferrimagnetic-ferroelectric composites of BaTiO₃ nanopowder and Co_0.5Ni_0.5Fe₂O₄ nanopowders were prepared by a conventional mixed oxide method. The multiferroic ceramics were compounded with the formula, (1-x)BaTiO₃-(x)Co_0.5Ni_0.5Fe₂O₄, in which x = 0, 0.05, 0.10, 0.20 and 0.35. All of the compositions were analyzed by an X-ray diffractometer (XRD) in order to reveal the phase of perovskite and spinal structure. Scanning electron microscopy (SEM) was used to examine the variation of morphology and grain size of the composited ceramics. The magnetism of all the ceramics was measured using a vibrating sample magnetometer (VSM). The results showed that microstructure and the amount of ferrite are related strongly with magnetization.

Abstract: A corundum-type structure of cobalt niobate (Co4Nb2O9) has been synthesized by a solid-state reaction. The formation of the Co4Nb2O9 phase in the calcined powders was investigated as a function of calcination conditions by differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Morphology and particle size have been determined by scanning electron microscopy (SEM). It was found that the minor phases of unreacted Co3O4 tend to form together with the columbite CoNb2O6 phase at a low calcination temperature and short dwell time. It seems that the single-phase of Co4Nb2O9 in a corundum phase can be obtained successfully at the calcination conditions of 900°C for 60 min, with heating/cooling rates of 20°C /min.

Abstract: This paper presents the diamond nucleation using combustion activation chemical vapor deposition (CACVD) by 0.95 volumetric ratio of O2 /C2H2 under atmospheric pressure. The main point of our work is to develop the CACVD technique for synthesize the semiconductor materials, which is developed for electronic devices application. The surface nucleation of substrate was studied by using surface pretreatment. The results of surface nucleation on mirror-silicon, polished silicon by diamond powder, silicon-dioxide (SiO2), and polished SiO2 by diamond powder, are significantly different. It can be concluded that the silicon-dioxide mask technique is useful for nucleated diamond protection whereas the polished silicon by diamond powder is suitable for nucleated diamond generation. These techniques are applied for the pattern fabrication.

Abstract: The piezoelectric ceramics of Pb(ZrxTi1−x)O3 – Pb(Zn1/3Nb2/3)O3 – Pb(Mn1/3Nb2/3)O3; PZT-PZN-PMN with Zr/Ti ratios of 48/52, 50/50 and 52/48 were fabricated in order to investigate the effect of compositional modifications on the ferroelectric properties of PZT-PZN-PMN ceramics. The phase structure of ceramics sintered at 1,150°C was analyzed. Results show that the pure perovskite phase was in all ceramic specimens, and the phase structure of PZT-PZN-PMN piezoelectric ceramics transformed from tetragonal to rhombohedral, with the Zr/Ti ratios increased in the system. The PZT-PZN-PMN ceramics with a Zr/Ti ratio of 50/50 exhibited the most promising properties including high remanent polarization and low coercive field of 25.95 µC cm−2 and 12.5 kV cm−1, respectively. Furthermore, the transition temperature decreased when the Zr/Ti ratio increased in the system.

Abstract: The phase transition behavior of the (1–x) PbZrO3-xPb(Co1/3Nb2/3)O3 (PZCN) solid solution system (0 ≤ x ≤ 0.30) has been investigated by X-ray diffraction and DSC. In the solid solution, for x ≤ 0.20, the transition shows a first-order phase transition behavior and its antiferroelectric (AFE) crystal structure is orthorhombic. The transition temperature gradually decreases with increased Co2+/Nb5+ concentration. On the composition range 0.20 ≤ x ≤ 0.30, a typical relaxor-like behavior is displayed. The low temperature crystal structure is pseudo-cubic in this composition range. With these data, the ferroelectric phase diagram between PZ and PCoN has been established.

Abstract: The binary system of (1-x)(K1/2Na1/2)NbO3–xBi(Zn1/2Ti1/2)O3; x = 0.0-0.30 ceramics was fabricated by conventionally mixed oxide and two-stage mixed oxide methods. Phase development of calcined powders and the crystal structure of sintered ceramics were analyzed by X-ray diffraction (XRD). The microstructure analyses were undertaken by scanning electron microscopy (SEM). In the conventional method, the perovskite phases were obtained for compositions containing only 10 mol % KNN. For compositions above this amount, a complex mixture of phases was observed. However, the complete solid solution of perovskite phase, prepared by two−stage mixed oxide, was retained up to 20 mole % BZT content. The experiments in this study suggest that the two-stage mixed oxide method helps to stabilize the perovskite phase better, when compared with the conventional method.

Abstract: he solid solution between the normal ferroelectric Pb(Zr1/2Ti1/2)O3 (PZT) and relaxor ferroelectric Pb(Co1/3Nb2/3)O3 (PCoN) was synthesized by the solid state reaction method. Sintered PZT-PCoN ceramics were annealed at temperatures ranging from 850 to 1,100°C for 4 h. X-ray diffraction patterns revealed changes of crystalline structure after annealing, which could be correlated to the accompanied changes in dielectric properties. Furthermore, significant improvements in the dielectric responses were observed in this system. After annealing, a huge increase of up to 200% occurred in the dielectric constants, especially near the temperature of maximum dielectric constant.