Synthesis and microstructure/optical property analyses of Zr/Ti oxide and carbide by laser pulses in water or tetraethyl orthosilicate

• Main Authors: Chao-Hsien Wu, 伍昭憲
• Other Authors: Pouyan Shen
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/62698758512456844035

博士 === 國立中山大學 === 材料與光電科學學系研究所 === 101 === This thesis is divided into seven chapters dealing with the synthesis and phase/microstructure characterizations of the condensates fabricated by pulsed laser ablation (PLA) of some bulk targets in liquid. In chapter 2 and 3, PLA of bulk Zr in water and a specific organic solvent (i.e. tetraethyl orthosilicate, TEOS) were comparatively studied, which triggered further researches on PLA of bulk graphite (chapter 4) versus Ti (chapter 5 to 7) in TEOS, for novel synthesis of organic/inorganic composites with special structures, compositions and optical properties as addressed in turn. In chapter 2, PLA of Zr plate in water under Q-switch mode and a fluence of 700 and 800 mJ/pulse for a rather high power density of 1.5×1011 and 1.7 × 1011 W/cm2, respectively was employed to fabricate ZrO2 nanocondensates. X-ray diffraction and transmission electron microscopic observations indicated such nanocondensates are full of {111} and {100} facets and predominantly in monoclinic (m-) rather than cubic- (c) and/or tetragonal (t-) crystal symmetry in particular when fabricated at 700 mJ/pulse. The hydrogenated ZrO2 nanocondensates underwent martensitic t→m transformation at a rather small critical size (ca. 20 nm) due to H+ signature and hence oxygen vacancy deficiency in the lattice. The resultant m-phase was free of twin and fault due to site saturation and rather limited growth of the nanosized particles. Spectroscopic characterizations indicated that the nanocondensates have a significant internal compressive stress, (H+, Zr2+, Zr3+) co-signature and hence a smaller band gap of 5.2-5.3 eV for potential applications in UV region. By comparison, a turbostratic C-Si-H lamellar phase with 0.35~0.39 nm interspacing and ZrO2 condensates having c-, t- and m- structure stabilized by increasing particle size were synthesized by PLA of Zr plate in TEOS and characterized by X-ray/electron diffraction and optical spectroscopy in chapter 3. The c-ZrO2 phase ca. 10% denser than the ambient lattice was stabilized as 3-10 nm sized cubo-octahedral nanoparticles but as abnormal large-sized (up to 30 nm) ones when encapsulated by the C1-xSix:H multiple shell with defective graphite-like structure units to exert an effective compressive stress. The potential application of such core-shell nanostructure with enhanced binding of Zr and O ions and implication for natural dynamic occurrence of the C1-xSix:H phase are addressed. The reidite-type ZrSiO4 occasionally occurred as nanoparticle with (010) and (11-2) facets shedding light on the dense compound formation in natural dynamic settings. In chapter 4, polyynes and graphene-based lamellae doped with both Si and H were synthesized simultaneously by PLA of bulk graphite in TEOS for optical spectroscopy and X-ray/electron diffraction characterizations. The polyyne molecules have long carbon chains (up to C16H2) to give multiple ultraviolet absorptions. The graphene-based lamellae were assembled as nanoribbons having hierarchical folds and dislocations due to wrinkle-to-fold transitions and imperfect attachment growth of the lamellae. A rather high fraction of sp3 bonds in the nanoribbons, as manifested by Raman shift, can be ascribed to capillarity force and Si-H solute trapping under the influence of particle size and lattice imperfections. The implications of the present composite phases on the natural dynamic occurrence and potential engineering applications are discussed. By comparison as endeavored in chapter 5, titanium oxides doped with C and H were fabricated by pulsed laser ablation of Ti in tetraethyl orthosilicate and characterized by transmission electron microscopy. The doped titanium oxides showed bimodal size distribution, the finer faceted ones being TiCxOy of rock salt-type structure encapulated with turbostratic graphene lamellae, and the larger spherical ones, anatase with (hkl)-specific ordering and faulting/twinning due to solute (Ti2+, C and H) trapping, phase transformation and/or deformation. The defective anatase was stabilized and nucleated from paracrystalline β-Ti and TiCxOy nuclei following specific crystallographic relationships. The colloidal suspension containing such composite condensates showed visible absorbance for potential photocatalytic applications. The anatase nanocondensates with commensurate superstructure as prepared by pulsed laser ablation of Ti in tetraethyl orthosilicate were identified by transmission electron microscopy to have special grain boundaries, i.e. symmetrical [100] tilt boundaries with (001) or (01-1) interface and asymmetrical [1-10] tilt boundary with (11-2)/(001) heterointerface. The [100] tilt boundaries are in fact about basal twinning with a coherent (001) and a semi-coherent (01-1) interface, respectively, both following the Burgers vector =1/2[0-10]+1/4[00-1]. The (11-2)/(001) heterointerface is decorated with {101} ledges, both having a primitive coincidence site lattice for fair lattice coherency. These special grain boundaries can be rationalized by the (hkl)-specific rotation/coalescence of the crystalline nanocondensates. Finally, in chapter 7, titania nanocondensates as fabricated by pulsed laser ablation of Ti in tetraethyl orthosilicate were occasionally characterized by transmission electron microscopy to have a rutile-brookite (Rt-Brk) core-shell structure. Lattice imaging of the core-shell showed a definite crystallographic relationship [001]Brk//[111]Rt; (0-20)Brk//(2-1-1)Rt, which is different from that inferred from the reported anatase/rutile and anatase/brookite relationships. The real relation has fair +/- mixed match for multiple lattice plane pairs across a spherical interface to minimize strain energy and interfacial energy. The nucleation and growth of rutile single crystal, with 2x(10-1) and 2x(1-21) superstructure, from the core of brookite nanoparticle can be rationalized by the capillarity effect under the influence of radiant heating upon laser pulses in liquid.