Pouyan Shen
National Sun Yat-sen University
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Featured researches published by Pouyan Shen.
Earth and Planetary Science Letters | 2001
Shyh-Lung Hwang; Pouyan Shen; Hao-Tsu Chu; Tzen-Fu Yui; Chung-Cherng Lin
Abstract The common association of microdiamonds with the phase assemblage: phlogopite, apatite, paragonite and α-quartz (containing amorphous Na–Al silicate inclusions), as inclusions in garnets of quartzofeldspathic rocks from the Saxonian Erzgebirge, Germany, was studied by analytical electron microscopy. The assemblage implies a precedent melt, which coexisted with the microdiamonds before and after entrapment in the garnet host, and subsequently crystallized. The formation of microdiamonds in this metamorphic rock could be explained by cotectic-induced partial melting of a subducted continental slab at about 4–6 GPa and 1000°C, as constrained by the occurrence of TiO 2 with an α-PbO 2 -type structure at the peak metamorphic conditions, and by the catalytic effect of siderophile and chalcophile elements.
Journal of Non-crystalline Solids | 1994
Chung-Cherng Lin; Pouyan Shen
Abstract A two-step sol-gel process between a nucleophilic addition on zinc by the SiOH group was explored to prepare Zn 2 SiO 4 powders from organometallic compounds. Hydrolysis of tetraethyl orthosilicate under ⩽ 3N HNO 3 followed by reaction with diethylzinc and then condensation under 0.1 to ∼ 15M NH 4 OH resulted in the formation of amorphous Zn 2 SiO 4 particles ∼ 10–20 nm in size. Infrared and Raman spectroscopic results suggest that this Zn 2 SiO 4 consists mainly of a SiOZn network which remained amorphous to 600°C. Heating (10°C/min) above ∼ 700 and 900°C caused the formation of β- and α-Zn 2 SiO 4 powders, respectively, which appeared to coalesce but not sinter. A high concentration of NH 4 OH is preferred for the synthesis of a high-density gel which transforms at lower temperatures to crystalline polymorphs.
Nanoscale Research Letters | 2010
Chang-Ning Huang; Jong-Shing Bow; Yuyuan Zheng; Shuei-Yuan Chen; New Jin Ho; Pouyan Shen
Titanium oxide compounds TiO,Ti2O3, and TiO2 with a considerable extent of nonstoichiometry were fabricated by pulsed laser ablation in water and characterized by X-ray/electron diffraction, X-ray photoelectron spectroscopy and electron energy loss spectroscopy. The titanium oxides were found to occur as nanoparticle aggregates with a predominant 3+ charge and amorphous microtubes when fabricated under an average power density of ca. 1 × 108W/cm2 and 1011W/cm2, respectively followed by dwelling in water. The crystalline colloidal particles have a relatively high content of Ti2+ and hence a lower minimum band gap of 3.4 eV in comparison with 5.2 eV for the amorphous state. The protonation on both crystalline and amorphous phase caused defects, mainly titanium rather than oxygen vacancies and charge and/or volume-compensating defects. The hydrophilic nature and presumably varied extent of undercoordination at the free surface of the amorphous lamellae accounts for their rolling as tubes at water/air and water/glass interfaces. The nonstoichiometric titania thus fabricated have potential optoelectronic and catalytic applications in UV–visible range and shed light on the Ti charge and phase behavior of titania-water binary in natural shock occurrence.
Materials Science and Engineering | 1986
Pouyan Shen; Dershin Gan; C.C. Lin
Abstract Scanning transmission electron microscopy analyses of aluminized coatings on superalloy Rene 80 were used to characterize the microstructures, crystallographic relationships and qualitative compositions of various phases within the coatings. In the diffusion zone, elongated precipitates which extend from the β phase to the γ phase were identified to be σ phase and, in the outer region of the diffusion zone, M23C6 and σ grains were identified. The crystallographic relationships of γ, β and σ phases at the interface between the coating and the substrate were identified as 001] σ [111] γ, [110] σ [01 1 ] γ [001] σ [001] γ, [110] β [010] β [0 1 0] β [1 4 0] σ, (1 ° off) However, the β phase located away from the coating-substrate interface has no simple relationship with the σ phase and the M23C6. The results of an energy-dispersive X-ray analysis of various phases are also presented.
European Journal of Mineralogy | 2003
Shyh-Lung Hwang; Pouyan Shen; Tzen-Fu Yui; Hao-Tsu Chu
Submicron metal sulfides, randomly oriented microdiamonds and phlogopite have been identified as multiphase inclusions in garnet of a garnet-clinopyroxene-quartz crustal rock from the Kokchetav Massif in Kazakhstan. Analytical electron microscopy shows that metal sulfides are entrapped among diamond aggregates away from infiltration cracks and do not exhibit any specific crystallographic relationship with associated microdiamonds, thus implying a possible syngenetic nucleation of microdiamonds from a precursive fluid containing dissolved metal sulfides. The diamonds increased in size via a spiral growth mechanism, as manifested by dislocations radiating from nuclei toward faceted surface outcrops.
Materials Science and Engineering | 1986
Pouyan Shen; Dershin Gan; C.C. Lin
Abstract Electron and X-ray diffraction studies of aluminized coatings on Rene 80 indicate that the β phase has an L21 structure rather than a B2 structure in the diffusion zone. The L21-type superlattice is mainly due to the ordering of aluminum and titanium on the aluminium sublattice. However, in the outer zone the β phase is of a B2 structure. Anomalies including diffuse streaks, diffuse intensities or extra spots in the electron diffraction patterns of the β phase are observed in both the B2 and the L21 structure.
American Mineralogist | 2008
Shyh-Lung Hwang; Tzen-Fu Yui; Hao-Tsu Chu; Pouyan Shen; Yoshiyuki Iizuka; Houng-Yi Yang; Jingsui Yang; Zhiqin Xu
Abstract Analytical electron microscopic observations have been carried out on a garnet peridotite from the Maobei area, Sulu ultrahigh-pressure terrane. The results showed that olivine in this garnet peridotite (5.3-6.6 GPa; 853-957 °C), contains precipitates of chromian magnetite and chromian-titanian hematite at dislocations and (001) faults. Specific crystallographic relationships were determined between these precipitates and the olivine host, viz. [101]Mt//[001]Ol, [110]Mt//[01̄1]Ol, and [01̄1]Mt//[011]Ol; and [0001]Hm//[100]Ol and [101̄0]Hm//[001]Ol. These oriented oxides are not associated with silicate/silica phases and therefore cannot be accounted for by the mechanism of olivine oxidation. It is postulated that these magnetite and hematite precipitates most likely have resulted from dehydrogenation-oxidation of nominally anhydrous mantle olivine during rock exhumation. In view of the contrasting diffusion rates of H and Fe in the olivine lattice, it is suggested that the formation process might actually take place in steps. Hydrogen diffusion with concomitant quantitative oxidation of Fe2+ to Fe3+ in olivine occurred early during initial rock exhumation and was followed by slow Fe diffusion forming magnetite/hematite at stacking faults and dislocations within the olivine lattice. Two requirements are essential under such a scenario: an ample amount of H content of the olivine, and an appropriate exhumation rate, probably in the range of 6-11 mm/year, of the host rock. It is also noted that such dehydrogenation-oxidation processes may hamper a correct estimate of the actual P-T conditions and mantle oxidation state based on mineral chemistries present in mantle eclogite/peridotite. The present study demonstrates that oriented mineral inclusions may not necessarily form through exsolution processes sensu stricto, but may form through a series of more complicated reaction mechanisms.
Journal of Solid State Chemistry | 2004
Wen-Hsu Lee; Pouyan Shen
Abstract Paracrystalline array of defect clusters ca. five times the lattice spacing of the average Co 3− δ O 4 spinel structure occurred more or less in a relaxed manner when the sintered Co 1− x O polycrystals were air-quenched below the Co 1− x O/Co 3− δ O 4 transition temperature to activate oxy-precipitation of cube-like Co 3− δ O 4 at dislocations. The same paracrystalline spacing was obtained for Co 3− δ O 4 when formed via oxidizing/sintering the Co 1− x O powders at 800°C in air, suggesting a nearly constant δ value for Co 3− δ O 4 in the T – P O 2 conditions encountered. The extra cobalt vacancies and Co 3+ interstitials, as a result of δ value, may form additional 4:1-derived defect clusters for further paracrystalline distribution in the spinel lattice. The nanosize defect clusters self-assembled by columbic interactions and lattice relaxation in ionic crystal may have potential applications as step-wise sensor of oxygen partial pressure at high temperatures.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing | 2000
Li-Ying Kuo; Pouyan Shen
Abstract Laser ablation (420–1200 W for 1–8 s in air) of CeO 2 -rich targets (CeO 2 , Z 4 C 6 and A 12 Z 40 C 48 where A, Z and C denote Al 2 O 3 , ZrO 2 and CeO 2 , respectively and subscripts in mol.%) resulted in the CeO 2 condensation. Transmission electron microscopic observations indicated the CeO 2 crystallites thus produced were predominantly {111} octahedra and cubo-octahedra ({111}+{100}), having {111} as the preferred rest plane and contact plane for coalescence. X-ray diffraction of the CeO 2 crystallites deposited on surface oxidized Si(100) and soda-lime glass showed preferred orientation {111} in accordance with the habit plane of the crystallites. Thus, the shape of crystalline condensates is an important factor of preferred orientation regardless of the type of the substrates. Post-deposition annealing (1200°C in air) of CeO 2 film on surface oxidized Si(100) caused orientation change from {111} to {100}, which can be ascribed to shape change and accompanied rotation-coalescence of the CeO 2 crystallites.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing | 2000
Li-Ying Kuo; Pouyan Shen
Abstract The condensates formed by reacting Ti plasma with C2H2 gas (75 sccm) under relatively low vacuum (1×10−3 Torr) and collected on carbon-coated collodion film were characterized by transmission electron microscopy to be TiC nanocrystals in random crystallographic orientation. The TiC condensates showed preferred orientation (200) when assembled on polycrystalline and amorphous substrates at ca. 150°C, and changed further into (111) when the substrate was subject to voltage bias (−120 V) with or without preheating to 450°C. The α-Ti co-deposited, with the TiC at a relatively low flow rate of C2H2 (25 sccm), followed the crystallographic relationship: (0001)α-Ti//(111)TiC; [1120]α-Ti//[110]TiC, in accordance with the TiC (111) preferred orientation. On the other hand, the amorphous carbon formed at a high flow rate of C2H2 (250 sccm) hindered the preferred orientation (111) of TiC. The effects of applied electric field, substrate temperature and second phase on the accumulation and reorientation of the TiC condensates in the coating can be rationalized by surface charge of the TiC crystallites, Brownian rotation–coalescence of the crystallites, and atom configuration specification at the interphase interface, respectively.