Elasticity and structure of the compounds in the wollastonite (CaSiO3)-Na 2SiO 3 system: from amorphous to crystalline state.

The elastic properties and structure of four potential bioactive compounds in the CaSiO3-Na2SiO3 system were characterized by Raman and Brillouin spectroscopy at ambient conditions. The increase of Na2O content in the Na2O-CaO-SiO2 glass with the same silica content and hence polymerization was found to lower the elastic moduli with accompanied decrease of Q(0) and Q(2) species, increase of Q(1) species and negligible change of Q(3) species, corresponding to a lower and higher equilibrium constant for the disproportional reactions [Formula: see text] and [Formula: see text] (without balance), respectively. The composition-dependent variation in the shear modulus (G) of the Na2O-CaO-SiO2 glass can be attributed to the concentration change of Q(2) and probably Q(4) species; while bulk modulus (K) ascribed to the cohesion factor. The elastic moduli of the corresponding crystalline phases in this system also lower with the increase of Na2O content following two general criteria as a function of Na2O/CaO molar ratio: (1) K decreases faster than G for both the amorphous and crystalline phases and (2) both K and G decreases faster for the crystals than the glasses.

Pulse laser ablation in water fragmentation of amorphous silica in water with optional NaCI spiking.

Amorphous SiO2 powders having two kinds of medium range order (MRO) were subjected to pulse laser ablation in water (PLAL) for X-ray diffraction, transmission electron microscopy and spectroscopy characterization. The powders fragmented down to 10-20 nm in size are mainly hydrogenated amorphous phase retaining Si-2nd O but not Si-2nd Si MRO. There are minor co-existing crystallites of beta-cristobalite, H2Si2O5 as well as additional alpha-tridymite and Na2SiO3 when water is spiked with NaCI for PLAL. Na-signature also caused lower vibration frequency of the hydrogenated silica network. The opal-like hydrogenated phase assemblage of amorphous phase, cristobalite and tridymite thus formed have a minimum band gap at ca. 5 eV for potential optoelectronic and catalytic applications in UV range and shed light on natural occurrence in dynamic settings such as meteorite impact and lightening strike on silicate-enrich crustal rocks.

(Zn,H)-codoped copper oxide nanoparticles via pulsed laser ablation on Cu-Zn alloy in water.

Nanosized (5 to 10 nm) amorphous and crystalline nanocondensates, i.e., metallic α-phase of Zn-Cu alloy in face-centered cubic structure and (Zn,H)-codoped cuprite (Cu2O) with high-pressure-favored close-packed sublattice, were formed by pulsed laser ablation on bulk Cu65Zn35 in water and characterized by X-ray/electron diffractions and optical spectroscopy. The as-fabricated hybrid nanocondensates are darkish and showed photoluminescence in the whole visible region. Further dwelling of such nanocondensates in water caused progressive formation of a rice-like assembly of (Zn,H)-codoped tenorite (CuO) nanoparticles with (001), (100), and {111} preferred orientations, (111) tilt boundary, yellowish color, and minimum bandgap narrowing down to ca. 2.7 eV for potential photocatalytic applications.

Effects of CaO/P2O5 ratio on the structure and elastic properties of SiO2-CaO-Na2O-P2O5 bioglasses.

The evolution of elastic properties and structure upon the change of CaO/P(2)O(5) ratio in SiO(2)-CaO-Na(2)O-P(2)O(5) glasses (45S5-derived and 55S4-derived) at ambient conditions has been studied by using both Brillouin and Raman spectroscopy coupled with X-ray diffraction. Under the same SiO(2)/Na(2)O ratio, it is found that a decrease in CaO/P(2)O(5) molar ratio has caused a more-polymerized silicate network via a net consumption of Q(0), Q(1), and Q(2) species yet enriching in Q(3) and Q(4) species. Brillouin experiments revealed that all the bulk, shear and Young's moduli of the glasses studied increases with the increase of CaO/P(2)O(5) molar ratio. The unexpected variation trend in shear modulus can be correlated to the contribution from cohesion, the less-polymerized phosphate Q species, and density. Compared to the 45S5-derived, the more-polymerized 55S4-deived glass has a lower bulk but slightly higher shear modulus at the given CaO/P(2)O(5) ratio.

Size, composition and structural changes of TiO2 rutile nanoparticles by pulsed laser ablation in water.

The rutile-type TiO2 powders originally whitish and micrometer in size were successfully reduced in size with accompanied structure, composition and optical property change to become dark bluish by pulsed laser ablation in liquid under 532 nm excitation and 400 mJ per pulse at a specified water depth (5 or 15 mm) for up to 30 min. Transmission electron microscopic observations indicated the newly formed anatase nanoparticles are ca. 5 nm in size with spindle-like shape having well-developed {101} faces and -(001) facets for mutual coalescence into unity. The -(001)-specific coalescence twin of anatase was also observed. There are also amorphous nanoparticles in association with anatase, minor brookite and relic rutile with 2 x (110) superstructure. The resultant colloidal TiO2 nanoparticles are (Ti3+, Ti2+, H+) co-signified according to optical spectroscopic results and have a bimodal minimum band gaps 3.12 and 2.66 eV due to nanocrystals and amorphous phase, respectively, for potential optocatalytic applications in UV-visible range.

Formation of (H+, Al+, Al2+) co-doped bayerite and gamma-Al2O3 plates from spinel-type related nanocondensates in water.

The Al2O3 nanocondensates of spinel-type related structures, i.e., gamma- and theta-type with a significant internal compressive stress via pulsed laser ablation in water were subjected to prolonged dwelling in water to form columnar bayerite plates for further transformation as platy gamma-Al2O3. Transmission electron microscopic observations indicated the gamma-Al2O3 follows the crystallographic relationship (100)b//(011)gamma; [001]b//[111]gamma with relic bayerite (denoted as b). The gamma-Al2O3 also shows {111} twin/faults and rock salt-type domains due to dehydroxylation of bayerite which involves {1111} shuffling and disordering of the Al ions in the octahedral and tetrahedral sites. The combined evidences of X-ray photoelectron spectroscopy, vibrational spectroscopy and UV-visible absorbance indicated that the H+, Al+ and Al2+ co-doped bayerite and gamma-Al2O3 composite plates have a minimum band gap as low as approximately 5 eV for potential catalytic and electro-optical applications in water environment.

Nonstoichiometric Titanium Oxides via Pulsed Laser Ablation in Water.

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.

Tapered ZnO Whiskers: {hkil}-Specific Mosaic Twinning VLS Growth from a Partially Molten Bottom Source.

Zn particulates overlaid with wurtzite (W)-type ZnO condensates having nearly orthogonal {101̄1} and {112̄1} facets were found to self-catalyze unusual tapered W-ZnO whiskers upon isothermal atmospheric annealing, i.e., thermal oxidation, at 600 °C. Analytical electron microscopic observations indicated that such whiskers formed tapered slabs having mosaic {101̄1} and {21̄1̄1} twinned domains. The tapered whiskers can be rationalized by an alternative vapor-liquid-solid growth, i.e., {hkil}-specific coalescence twinning growth from the ZnO condensates taking advantage of a partially molten bottom source of Zn and the adsorption of atoms at the whisker tips and ledges under the influence of capillarity effect. The tapered whiskers having strong photoluminescence at 391 nm and with a considerable flexibility could have potential applications.

Water-Driven Assembly of Laser Ablation-Induced Au Condensates as Mesomorphic Nano- and Micro-Tubes.

Reddish Au condensates, predominant atom clusters and minor amount of multiply twinned particles and fcc nanoparticles with internal compressive stress, were produced by pulsed laser ablation on gold target in de-ionized water under a very high power density. Such condensates were self-assembled as lamellae and then nano- to micro-diameter tubes with multiple walls when aged at room temperature in water for up to 40 days. The nano- and micro-tubes have a lamellar- and relaxed fcc-type wall, respectively, both following partial epitaxial relationship with the co-existing multiply twinned nanoparticles. The entangled tubes, being mesomorphic with a large extent of bifurcation, flexibility, opaqueness, and surface-enhanced Raman scattering, may have potential encapsulated and catalytic/label applications in biomedical systems. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11671-009-9359-x) contains supplementary material, which is available to authorized users.

Mesomorphic lamella rolling of au in vacuum.

Lamellar nanocondensates in partial epitaxy with larger-sized multiply twinned particles (MTPs) or alternatively in the form of multiple-walled tubes (MWTs) having nothing to do with MTP were produced by the very energetic pulse laser ablation of Au target in vacuum under specified power density and pulses. Transmission electron microscopic observations revealed (111)-motif diffraction and low-angle scattering. They correspond to layer interspacing (0.241-0.192 nm) and the nearest neighbor distance (ca. 0.74-0.55 nm) of atom clusters within the layer, respectively, for the lamella, which shows interspacing contraction with decreasing particle size under the influence of surface stress and rolls up upon electron irradiation. The uncapped MWT has nearly concentric amorphous layers interspaced by 0.458-0.335 nm depending on dislocation distribution and becomes spherical onions for surface-area reduction upon electron dosage. Analogous to graphene-derived tubular materials, the lamella-derived MWT of Au could have pentagon-hexagon pair at its zig-zag junction and useful optoelectronic properties worthy of exploration.

Laser ablation condensation, coalescence, and phase change of dense gamma-Al(2)O(3) particles.

Dense gamma-Al(2)O(3)condensates, with residual stress up to 3 GPa and ranging from nanometer to an unexpected micrometer size, were formed by pulsed laser ablation on Al target under oxygen background gas for a very rapid heating and cooling effect. Analytical electron microscopic observations indicated such nanoparticles tended to coalesce over {111} facets to form multiple twin and tilt boundary. The micrometer-size particles changed, upon electron irradiation, into metastable orthorhombic delta form full of twin variants and faults parallel to {100}.

Directional/acidic dissolution kinetics of (OH,F,Cl)-bearing apatite.

Directional dissolution of a natural (OH,F,Cl)-bearing apatite has been studied at various solution pH values (0-3) and 30 degrees C. This apatite showed abnormally high O--H stretching frequencies due to the substitution of Cl for OH. The advance of dissolution front indicated that steady-state directional dissolution for pH = 0-2 followed an apparent rate law of Rate = ka(H+) (n) (in mole/m(2)h), where the rate constants (k) are 2.15 and 1.61; and the rate orders (n) are 1.44 and 1.30 for [0001] and <1,120> directions, respectively. Previous study, however, indicated a smaller n value (n = 0.55-0.70) for fluorapatite powders at higher pHs. A nonlinear pH dependence of logarithmic dissolution rate at a wide pH range implied that the surface active sites and/or rate-determining steps have changed when the acidity of solution and/or the composition of the apatite were changed. The opening of etch pits on basal planes further indicated that the dissolution rates along the three principal directions have the following relationship: [0001] > <1,120> > <1,010> for pH=0-1, but the order was reversed for pH > 3.

Condensation and relaxation/transformation of dense t-ZrO2 nanoparticles.

Dense tetragonal (t)-ZrO(2) nanocondensates were synthesized under very rapid heating and cooling by pulsed Nd-YAG (YAG--yttrium aluminum garnet) laser ablation with oxygen background gas and characterized by electron diffraction. The t-ZrO(2) nanoparticles with a residual stress up to about 5 GPa tended to form deformation twins/faults upon local electron dosage. By contrast, the t-ZrO(2) nanoparticles formed at an-order-of-magnitude higher power have a residual stress above 6 GPa and tended to transform into a metastable cubic (c) phase vulnerable to amorphization. The relaxation/transformation of the self-constrained t-ZrO(2) nanoparticles can be rationalized by a lowering of internal energy under the influence of resolved shear stress and local electron heating.

Density functional theory calculations of dense TiO2 polymorphs: implication for visible-light-responsive photocatalysts.

Structural parameters and electronic band gaps of dense TiO(2) polymorphs, i.e., alpha-PbO(2), baddeleyite, fluorite, and cotunnite types of structures, were calculated using a first-principles density functional method with local-density approximation. The ambient phases, i.e., rutile and anatase, with known theoretical and experimental data were used to ensure the validity of the calculations. The fluorite-type TiO(2) turned out to have the narrowest band gap, 1.08 or 2.18 eV after applying a very approximate band gap correction, due to highly symmetrical TiO(8) polyhedra with Ti(3d) and O(2p) orbitals in the most mixed state. Ti with eight coordinated oxygens, as feasible under high pressure or residual stress, may have potential applications as a visible-light-responsive photocatalyst.

Towerlike SBA-15: base and (10)-specific coalescence of a silicate-encased hexagonal mesophase tailored by nonionic triblock copolymers.

Hydrothermal templating of mesoporous molecular sieves by nonionic triblock copolymers [poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) (PEO-PPO-PEO)] at specific block lengths of EO(20)PO(70)EO(20) and selected 2 M HCl dosage (pH -0.3) caused the formation of micrometer-sized SBA-15 hexagons with well-ordered hexagonal pore channels (pore size and wall thickness of approximately 6 nm and pore-to-pore distance of approximately 12 nm) after template removal. For a beneficial lower surface energy, these {10} laterally coalesced hexagons tend to stack imperfectly over the base into towerlike entities, leaving dislocations and faults within the single domain thus formed. Evidence for the mechanism of Brownian motion/coalescence of the hexagonal-mesophase particulates, previously suggested for MCM-41 accretion in the presence of cationic surfactant, is more clearly identifiable in the present low-pH case of amphiphilic block copolymer templates and linear silica oligomers.

Polymorphic transformation of dense ZnO nanoparticles: implications for chair/boat-type Peierls distortions of AB semiconductor.

Peierls distortion path was proved experimentally for dense ZnO nanoparticles prepared by static compression. Electron irradiation caused rock salt (R) to wurtzite (W) transition, following preferential (111)(R)//(0111)(W); [011](R)//[1213](W) and then transformation strain induced (111)(R)//(1011)(W); [011](R)//[0111](W). The two relationships can be rationalized by specified extent of chair- and boat-type Peierls distortions accompanied with band gap opening and intermediate {111}R slip for energetically favorable {111}R/(0111)W match.

Laser ablation condensation of alpha-PbO(2)-type TiO(2).

A high-pressure phase of TiO(2) with an alpha-PbO(2)-type structure has been synthesized via very energetic Nd-YAG laser pulse irradiation of oxygen-purged Ti target. The nanometer-size alpha-PbO(2)-type particles were (11;0), (010), and (001) faceted but the larger ones were spherical. The combined effects of rapid heating and cooling, the nanophase effect, and dense surfaces account for the formation of coherently strained alpha-PbO(2) particles. The refined cell volume indicated a considerable residual stress to stabilize the dense structure to ambient condition.

Interdiffusion induced defect microstructures of Co(1-x)O near confined zirconia particles.

Diffusion couples of metal alloys were commonly used to study Kirkendall pore formation and amorphization near the interface of composition discontinuity. In this work, yttria-partially stabilized zirconia (Y-PSZ) powders mixed with Co(1-x)O (1:99 molar ratio, denoted as Z1C99) were sintered and annealed at 1600 degrees C for 1-75 h to study interdiffusion-induced defect microstructures of Co(1-x)O near confined Y-PSZ particles. Analytical electron microscopic analysis indicated a much larger flux of Co(2+) from Co(1-x)O into Y-PSZ compared to the reverse flux of Zr(4+) and Y(3+). In addition, there is a significant inward flux of oxygen from Y-PSZ into Co(1-x)O. A net vacancy flux in the opposite direction of ion flux then caused the formation of Kirkendall pores and dislocations in Co(1-x)O near corrugated Y-PSZ/Co(1-x)O interface. Amorphous regions and [111] faulting were also found in Co(1-x)O near Kirkendall pores, which can be rationalized by diffusion-induced amorphization and assembly of cation vacancies along close-packed [111] planes vulnerable to crystallographic shear, respectively. Y-PSZ particles were found to migrate-coalesce as corrugated slabs and rods at Co(1-x)O grain boundaries and junctions, respectively, when the composite with more Y-PSZ additive (Z(1)C(89)) was annealed.