Crack path instabilities in DCDC experiments in the low speed regime

We studied the low speed fracture regime (10⁻⁴-10⁻⁹ m s⁻¹) in different glassy materials (soda-lime glass, glass ceramics) with variable but controlled length scale of heterogeneity. The chosen mechanical system enabled us to work in pure mode I (tensile) and at a fixed load on double cleavage drilled compression specimen. The internal residual stresses of studied samples were carefully relaxed by appropriate thermal treatment. By means of optical and atomic force microscopy techniques fracture surfaces have been examined. We have shown for the first time that the crack front line underwent an out-of-plane oscillating behavior as a result of a reproducible sequence of instabilities. The wavelength of such a phenomenon is in the micrometer range and its amplitude in the nanometer range. These features were observed for different glassy materials providing that a typical length scale characterizing internal heterogeneities was lower than a threshold limit estimated to few nanometers. This effect is the first clear experimental evidence of crack path instabilities in the low speed regime in a uniaxial loading experiment. This phenomenon has been interpreted by referring to the stability criterion for a straight crack propagation as presented by Adda-Bedia et al. [Phys. Rev. Lett. 76 (1996) 1497].     

Photo-stimulated long-lasting phosphorescence in Mn-doped zinc borosilicate glasses

In addition to long-lasting phosphorescence (LLP), photo-stimulated long-lasting phosphorescence (PSLLP) was also observed in Mn²⁺-doped zinc borosilicate glasses (ZSBM). When the bright red LLP induced by the irradiation of a ultraviolet (UV) lamp with λ_max=254 nm disappeared, the glass could re-emit this phosphorescence under the stimulation of lower energy light ranging from about 300 to 800 nm, while this phenomenon is not present without the pre-irradiation. The re-emitted phosphorescence was considerably bright and persistent after the removal of the stimulation light, hence called PSLLP. This PSLLP consists of two steps: the re-capture of the electrons photo-released from deep traps during the stimulation and the LLP process following the removal of the stimulation light. We demonstrated optical storage by using the ZSBM glass.     

Nanosized gold clusters formation in selected areas of soda-lime silicate glass

Nanosized gold clusters were developed in a gold-doped soda-lime silicate glass after X-ray irradiation followed by annealing, which provided an alternative way of forming metallic nanoclusters in glass to ion implantation. The formation of gold nanoclusters can be controlled by irradiation time or annealing time.     

High resolution patterning of silica aerogels

Three-dimensional metallic structures are fabricated with high spatial resolution in silica aerogels. In our method, silica hydrogels are prepared with a standard base-catalyzed route, and exchanged with an aqueous solution typically containing Ag⁺ ions (1 M) and 2-propanol (0.2 M). The metal ions are reduced photolytically with a table-top ultraviolet lamp, or radiolytically, with a focused X-ray beam. We fabricated dots and lines as small as 30 × 70 μm, protruding for several mm into the bulk of the materials. The hydrogels are eventually supercritically dried to yield aerogels, without any measurable change in the shape and spatial resolution of the lithographed structures. Transmission electron microscopy shows that illuminated regions are composed by Ag clusters with a size of several μm, separated by thin layers of silica.     

Structure and properties of Ge2.5PSx glasses

Ge_2.5PS_x glasses were studied with a combination of Raman spectroscopy, nuclear magnetic resonance, and neutron diffraction. From these experiments the distribution of bonding configurations was determined, and used to explain the compositional dependence of the index of refraction and the glass transition temperature. On reducing the sulfur content of these glasses below the stoichiometric amount, the sulfur deficit is accommodated by the progressive loss of the non-bridging sulfur of SPS_3/2 groups, followed by the conversion of the resultant PS_3/2 groups into species such as P₄S₃ characterized by P-P bonding. The presence of metal-metal bonds involving germanium, found in samples with the lowest sulfur content, was found to be the most important structural feature in determining the optical response.     

Random close packing of spheres in a round cell

The paper describes the method of construction of cells containing large numbers (10⁵-10⁶) of close packed spheres, ranging in packing fractions from 0.2 to 0.60. The cells are constructed in a round form, utilizing varying surface curvature to prevent ordered packing. The properties of the cells are described by a series of distributions: (i) polar angle of contact points, (ii) maximum displacement of loose spheres, (iii) and Voronoi volumes for individual spheres. The cells of varying density appear to show the liquid-to-solid transition. All cells described here contain loose spheres. It is proposed that cells with zero loose spheres are ideal amorphous solids. Ideal amorphous solids are characterized by a number of elements, described herein.     

Structural implications of water and boron dissolution in albite glass

A combined nuclear magnetic resonance, infrared and Raman spectroscopic study on the effect of water dissolution on the structure of B-bearing aluminosilicate glasses is presented. The base composition was albite (NaAlSi₃O₈) to which different amounts of B₂O₃ (4.8, 9.1, 16.7 wt%) were added. Hydrous glasses containing 4.4 ± 0.1 wt% water were synthesized at pressures of 2000 bar. The results show that B dissolves in both dry and hydrous glasses by forming predominantly trigonal BO₃ groups although some tetrahedral BO₄ is also present. In anhydrous glasses prepared at high pressures (above 10 kbar) the fraction of BO₄ increased. The hydrous glasses contain more BO₄ groups compared to the dry counterparts, suggesting that this species is stabilized by water. The Raman and NMR (¹⁷O, ²⁷Al, ²⁹Si) spectra show that B interacts with the aluminosilicate network by formation of Si-O-B and probably Al-O-B units. In the hydrous glasses the water speciation changes significantly towards higher hydroxyl concentrations with increasing B-content. The NIR peaks, which are related to OH groups and molecular H₂O, develop additional shoulders, suggesting that possibly B-OH complexes are formed.     

Potassium surface enrichment in mixed alkali glass irradiated with electrons

Sodium-potassium-silicate glass was irradiated with electrons of energy of 1600 eV. The changes in the surface composition were analyzed by means of the angular-resolved X-ray induced photoelectron spectroscopy (ARXPS). Low electron dose irradiation enriched the uppermost glass surface with alkali ions, considerably more with potassium than with sodium ions.     

Synthesis, crystal structures, and properties of two manganese(II)-nitroprusside complexes

Two new manganese(II)-1,10-phenanthroline-nitroprusside complexes, [Mn(phen)₃][Fe (CN)₅(NO)]⋯2H₂O⋯0.25CH₃OH (1) and [Mn(phen)₂(H₂O)₂][Fe(CN)₅(NO)]⋯H₂O (2) (where phen is 1,10-phenanthroline) have been synthesized and characterized by X-ray diffraction, electronic paramagnetic resonance (E.P.R.) and IR analyses. Complex 1 crystallizes in the monoclinic space group P2₁/n, with lattice parameters a = 10.0441(15) Å, b = 19.668(2) Å, c = 19.938(3) Å,  β =100.427(14)°, V = 3873.7(10) ų, Z = 4; complex (2) crystallizes in the monoclinic space group C2/c, with a = 17.120(2) Å, b = 13.7925(19) Å, c = 14.4362(17) Å, β = 107.962(12)°, V = 3242.6(7) ų, Z = 4. In the two compounds, three phen ligands 1, or two phen ligands and two cis-related aqua molecules 2, are in a distorted octahedral arrangement around the Mn(II) ion. The nitroprusside anion, [Fe(CN)₅(NO)]²⁻, acts as a counterion. It is intriguing that in complex 2 no cyano bridges are present with two water molecules coordinated to the Mn(II) ion considering that usually the cyano nitrogen atoms are strong donors and could readily replace the coordinating solvent water molecules. Abundant hydrogen bond interactions and π–π stacking between the phen rings in two complexes lead to three-dimensional supramolecular networks.     

On the character of local electric fields in amorphous semiconductors

On the basis of the agreement of calculated and measured parameters of some amorphous semiconductors, an argument is stated in favour of the central-symmetric type of random local electric fields. A possible mechanism of the transport of electrons is discussed.