Disordered matter under extreme conditions: X-ray diffraction,electron spectroscopy and electroresistance measurements

In the last decade, we have developed a set of experimental techniques for in-house X-ray diffraction measurements under high-temperature (up to about 2300 K) and high-pressure (up to 10 GPa and 1500 K, up to 100 GPa and 700 K) conditions, electron energy-loss and Auger measurements for surface electronic structure measurements at high-temperature (up to about 1800 K), and electrical resistance measurements covering both low-temperatures (2 K) and high-temperatures/high-pressures (1500 K, 7 GPa) conditions. In this paper we discuss some important technical features and possibilities of these new equipments and present novel data collected for phase transitions and structural modifications occurring in liquid and solid systems. In particular, we present new results about phase transitions and undercooling of bismuth under pressure, extreme undercooling and metastable states in gallium films, and surface phase transitions of Si at high-temperatures. The relevance of these experiments to the exploitation of the potential of equipments available at synchrotron radiation facilities is emphasized.     

Effect of surface treatment methods on the shear bond strength between resin cement and all-ceramic core materials

This study compared the influence of various surface treatments on the shear bond strength between resin cement and lithium disilicate glass-ceramics. A series of 120 lithium disilicate ceramic samples were prepared to compare the effect of different surface treatments on the shear strength of a luting cement bonded to two all-ceramic systems. IPS Empress 2 and IPS e.max Press ceramic samples were fabricated according to the manufacturer's instructions. The ceramic samples were divided into the following 6 surface treatment groups for each ceramic system: 1—no treatment (C), 2—airborne-particle abrasion (A), 3—acid etching (E), 4—airborne-particle abrasion + acid etching (AE), 5—Nd:YAG laser (L), 6—Nd:YAG laser + acid etching (LE). Resin cement was then bonded to the treated ceramic surfaces and light polymerized. The shear bond strengths of the specimens were measured using a universal testing machine. Two-way ANOVA and Tukey HSD (α = 0.05) test were used to determine differences in shear bond strength between the groups. The ANOVA revealed significant differences between the treatment groups and ceramic types (p < 0.05). The shear bond strengths of IPS Empress 2 were significantly higher than those of IPS e.max Press.     

New observations on scratch deformations of soda lime silica glass

In spite of the wealth of literature, the role of the scratching speed in affecting the material removal mechanism in soda lime silica (SLS) glass is yet to be comprehensively understood. Here we report the surface and sub‐surface deformation mechanisms of SLS glass scratched under three different normal loads of 5, 10 and 15 N at various speeds in the range of 100–1000 μm/s with a diamond indenter of ~ 200 μm tip radius. The results show that at any given applied normal load, the width, depth, wear volume of the scratch grooves and wear rate of the SLS glass decreased with an inverse power law dependence on the applied scratching speed. The surface damage also reduced with the increase in scratching speed. A new, simple model was developed to explain these observations. The significant contributions of the time of contact, the tensile stress behind the indenter and the shear stress active just underneath the indenter in governing the material removal mechanisms of the SLS glass were discussed.     

Finite element analysis of auxetic plate deformation

The paper deals with computer simulations of mechanical behavior of a thick elastic plate. The plate, made of isotropic material, has been clamped at two lateral surfaces, loaded at the front and back walls and left free at the upper and lower walls. Simulations have been done for Poisson’s ratio from interval ?1 < ν < 0.5 using the finite element method. An anomalous feature of the plate deformation for negative Poisson’s ratio values compared to classical positive values has been observed: at extremely negative Poisson’s ratios the displacement vector has components which are anti-parallel to the direction of loading.     

Initiation and propagation of shear bands in Zr-based bulk metallic glass under quasi-static and dynamic shear loadings

The effect of strain rate on the initiation and propagation of shear bands in the Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass under shear loading was investigated. The quasi-static (at a strain rate of 1.5 × 10⁻³ s⁻¹) and the dynamic shear tests (at a strain rate of 1.4 × 10³ s⁻¹) were conducted at room temperature using a GATAN Microtest-2000 instrument and a split Hopkinson pressure bar (SHPB) with a specially designed ‘Plate-shear’ specimen, respectively. The complete process of shear band initiation, propagation, and shear band unstable propagation-induced fracture was revealed. The experimental results demonstrated that the macroscopic shear strength is relatively insensitive to the strain rate, whereas shear band initiation and fracture are significantly dependent on strain rate. A dimensionless Deborah number was introduced to characterize the effect of the strain rate on the formation of shear bands. Additionally, the observed numerous liquid droplets and melted belts on the fracture surface at high-strain rates demonstrate that the adiabatic heating exerts a significant effect on fracture behavior of the material.     

Internal stresses induced by plastic shear deformation of Zr–(Cu,Ag)–Al bulk metallic glasses

Effective internal shear stress σ_i induced by torsional deformation of Zr₄₆(Cu_4/5Ag_1/5)₄₆Al₈ and Zr₄₆Cu₄₆Al₈ bulk metallic glasses different by the glass-forming ability of the maternal melts has been determined by measurements of stress relaxation upon stepwise unloading. It has been found that the ratio σ_i/σ₀ (σ₀ is the initially applied shear stress) decreases upon increasing the temperature from ≈ 0.8 at T = 450K (T ≈ 0.64 × T_g) to ≈ 0.08 at T = 638K (T ≈ 0.91 × T_g) independently of σ₀ and glass composition. The obtained result is in good agreement with earlier data obtained on ribbon metallic glasses. The origin of deformation-induced internal stresses and their connection with deformation mechanisms of metallic glasses has been briefly discussed.     

Roughness of glass surfaces formed by sub-critical crack growth

This paper presents a study on the roughness of glass fracture surfaces formed as a consequence of sub-critical crack growth. Double-cantilever-beam specimens were used in these studies to form fracture surfaces with areas under well-defined crack velocities and stress intensity factors. Roughness depends on crack velocity: the slower the velocity, the rougher the surface. Ranging from approximately 1 × 10⁻¹⁰ m/s to approximately 10 m/s, the velocities were typical of those responsible for the formation of fracture mirrors in glass. Roughness measurements were made using atomic force microscopy on two glass compositions: silica glass and soda lime silica glass. For silica glass, the RMS roughness, R_q, decreased from about 0.5 nm at a velocity of 1 × 10⁻¹⁰ m/s to about 0.35 nm at a velocity of 10 m/s. For soda lime silica glass, the roughness decreased from about 2 nm to about 0.7 nm in a highly non-linear fashion over the same velocity range. We attributed the roughness and the change in roughness to microscopic stresses associated with nanometer scale compositional and structural variations within the glass microstructure. A theory developed to explain these results is in agreement with the data collected in the current paper. The RMS roughness of glass also depends on the area used to measure the roughness. As noted in other studies, fracture surfaces in glass exhibit a self-affine behavior. Over the velocities studied, the roughness exponent, ζ, was approximately 0.3 for silica glass and varied from 0.18 to 0.28 for soda lime silica glass. The area used for these measurements ranged from (0.5 μm)² to (5.0 μm)². These values of the roughness exponent are consistent with values obtained when the scale of the measurement tool exceeds a critical size, as reported earlier in the literature.     

Local photoconductivity of microcrystalline silicon thin films excited by 442 nm HeCd laser measured by conductive atomic force microscopy

Microcrystalline silicon (μc-Si:H) thin films were studied by photo-conductive atomic force microscopy (PC-AFM) under top side illumination by HeCd 442 nm laser and/or by scattered light of AFM detection diode. In order to make the top side illumination possible, so called “nose” type cantilevers, with the tip at the end of cantilever, were used for local photo-current map measurements. Local current intensity under different illumination is discussed mainly from a point of view of the absorption depth of the used light. Diffusion length of charge carriers ~ 300 nm was estimated from comparison of the current levels under different illumination.     

Thermodynamic properties of amorphous solids: The electrochemical approach

In the present contribution are critically analyzed and reexamined the possibilities to determine the thermodynamic properties of amorphous solids, of defect crystals and of glasses by means of electrochemical methods. After detailed theoretical considerations performed in the framework of the thermodynamics of irreversible processes it is demonstrated how the most significant thermodynamic parameters of amorphous systems with frozen-in structure—their configurational enthalpy and entropy ΔH_g and ΔS_g—can be electrochemically measured, when the systems under investigation are first order (electron) conductors, capable of forming the electrodes in a glass → crystal Galvanic cell. We refer here to existing classical experimental results with two such systems: vitreous Sb (so-called explosive antimony) and glassy carbon resins both used to demonstrate the applicability of the theoretical considerations developed. Results with several Metglass alloy systems (Ni/P, Fe, Ni/P, B, Co/B and Cu/Ti), obtained via corrosion potentio-dynamic electrochemical measurements are also summarized and used to estimate the thermodynamic properties of variously treated glass-forming systems. The electrochemical evidence analyzed clearly demonstrates in its integrity the particular, frozen-in nature of the basic thermodynamic parameters in the considered glass systems (ΔHg ≈ const > 0, ΔSg ≈ const > 0) as this is expected to be both from classical theory and from known calorimetric measurements. The contribution of direct glass/crystal Voltaic contacts to the thermodynamic properties of electrochemical cells with glassy or vitro-crystalline electrodes is also considered in details. Possible technical applications of Galvanic and Voltaic potentials, determined by glassy or vitro-crystalline electrode materials, including existing conventional battery systems and other horizons, opened to discussion by the present theoretical approach are also outlined.     

Morphology and dispersion state of Ba2TiSi2O8 nanocrystals in transparent glass-ceramics and their nanoindentation behavior

The morphology and dispersion state of Ba₂TiSi₂O₈ (BTS) nanocrystals in transparent glass-ceramics (composition: 40BaO–20TiO₂–40SiO₂) were examined from high resolution transmission electron microscope observations, and their nano-scale deformation behavior was examined using Berkovich nanoindentation technique (standard-type and continuous stiffness measurement (CSM)-type). In the early stage of crystallization, BTS crystalline layers with a thickness of ~ 120 nm were formed at the surface and ellipsoid-shaped crystallites with a diameter of 100–200 nm were dispersed in the glass matrix. In the late stage, BTS crystals with a diameter of 200–400 nm were formed densely, but a glassy phase was present between BTS crystals. The Young's modulus evaluated from CSM-type nanoindentation measurements for a deformation scale of about 100 nm shows the values of 98 GPa for the glass and 110 GPa for the glass-ceramics with nanocrystals. It was suggested that CSM-type measurements are very sensitive in the nano-scaled homogeneity in the heat-treated samples.     

A comparison of rheology,dielectric response,and calorimetry within indane-based glass-formers

We report dynamics data on a family of indane glass-forming liquids. Although structural variations make the glass transition vary over a 77 K range, the fragility and width of the relaxation time distribution from oscillatory shear measurements are quite similar for all 14 indanes studied. In contrast, the measured width of the primary relaxation time distribution from dielectric measurements varies considerably for different indanes. The temperature dependence of relaxation time can be described using either Vogel–Fulcher or dynamic scaling, but only the latter allows both mechanical and dielectric data sets to have the same divergence temperature. The consequences of this observation for the thermodynamic significance of such a divergence temperature are discussed.     

Synthesis and characterization of nanocrystalline Fe60X20B10P10 (X = Co,Ni) alloys

In this work, two nanocrystalline alloys, Fe₆₀Ni₂₀P₁₀B₁₀ and Fe₆₀Co₂₀P₁₀B₁₀, were produced by mechanical alloying processing them at milling times of 5, 40 and 100 h. Structural properties were determined by X-ray diffraction and transmission Mössbauer spectroscopy. The 100-h milled alloys consisted primarily of metastable bcc Fe(Co, Ni) nanocrystals (11–17 nm) with different Fe-rich environments. Differential scanning calorimetry measurements were performed in order to study the thermal stability of the nanocrystalline phases and their crystalline growth. The values for the apparent activation energy of the main crystallization processes were 2.1 ± 0.1 and 2.4 ± 0.1 eV, respectively, which were associated with grain growth mechanisms.     

Effect of reducing sintering atmosphere on Ce-doped sol–gel silica glasses

The effect of sintering atmosphere on the optical and structural properties of Cerium doped sol–gel silica was investigated. Two sets of xerogels with Ce concentration from 0 to 10 mol% were prepared and densified in different conditions. The effect of a post-densification rapid thermal treatment was also considered. Optical absorption measurements evidenced that in oxidizing conditions Cerium is preferably incorporated inside the silica matrix as Ce⁴⁺ while the trivalent state is favoured by reducing conditions. Transmission electron microscopy images show rare-earth clusters formation whose nature was investigated by means of Raman, EDS and microdiffraction measurements. In order to evaluate the efficiency of the glasses as scintillating materials radio-luminescence measurements were carried out. A numerical fit of RL spectra showed the presence of two components peaking at 2.7 and 3.1 eV. After RTT, the relative intensity of the 3.1 eV component increases with Ce concentration.     

Measurement of diffusion coefficients of Au in liquid Ag with the shear cell technique

Diffusion coefficients of Au in liquid Ag were measured at the temperatures 1300 K and 1500 K by using the shear cell technique. The adopted technique was a modified long capillary method which had a diffusion couple configuration. Obtained diffusion coefficients of Au in liquid Ag were respectively 2.30 × 10⁻⁹ m² s⁻¹ at 1300 K and 3.16 × 10⁻⁹ m² s⁻¹ at 1500 K, which were in good agreement with calculations based on the hard sphere mixture model.     

Contactless molding of arrayed chalcogenide glass lenses

The moldable chalcogenide glass material has been developed recently. This study developed a new process to produce an arrayed chalcogenide glass lenses by a contactless molding process, which is considered to have a great potential for the mass production of arrayed glass lenses with low cost, ease of manufacture and free of surface defects. The stainless steel plate with arrayed through holes was employed as the molds. The selenium based chalcogenide glass plate was put on the mold and nitrogen gas was introduced into the closed chamber to allow gas pressure up to 4 kg/cm². IR heating allows the chalcogenide glass plate to approach the soft point, and forces glass flows into the arrayed through holes to form the arrayed glass lenses by viscoelastic deformation. A higher forming temperature, pressure and longer time duration tend to produce the arrayed lenses with a higher peak height and a smaller radius of curvature. The arrayed chalcogenide glass lenses with a peak height of 430 μm can be obtained at a forming temperature of 305 °C, a gas pressure of 1 kg/cm² and a time duration of 110 s. The contactless gas assisted molding system can avoid contact induced glass sticking and gas bubble problems. The surface qualities of molded lenses are much better than that of lenses molded by the traditional contact molding process.     

Preparation and characterization of ZnO particles embedded in organic–inorganic planar waveguide by sol–gel route

Hybrid organic–inorganic waveguides based on ZnO-(3-glycidoxypropil)trimethoxisilane (GPTS) have been fabricated by sol–gel route. A transparent sol of ZnO was added to the GPTS host and the resulting sol was deposited on silica substrates by spin coating technique. Waveguides with different molar composition (100?x)GPTS?xZnO (x = 10, 20, 30) were investigated by different diagnostic techniques. Morphological measurements were carried out by means of an AFM apparatus, and a roughness of few nanometers was estimated for all the waveguides. Optical properties such as refractive index, thickness, number of propagating modes and attenuation coefficient were measured at 632.8, 543.5, 1319 and 1542 nm by the prism coupling technique as a function of the ZnO content. Photoluminescence measurements, upon excitation at 325 nm, showed a large luminescence band in the region between 350 and 600 nm with a main peak centered at about 380 nm, due to the presence of ZnO nanoparticles.     

Fabrication and direct bonding of photosensitive multicomponent silicate glasses for lossless planar waveguide splitters

In this paper the fabrication, characterization, and thermal assisted bonding of two photosensitive silicate glasses is presented, as part of a wider process aiming to obtain a planar waveguide lossless splitter for telecom applications. Two glass compositions are investigated: an Er–Yb doped silicate glass, which amplifies the signals when pumped at 980 μm and a matchable passive glass, which is designed to host the waveguide splitter. The two parts were bonded successfully using direct bonding technique at 605 ± 20 °C for 240 min under a pressure of 28 kPa. Vickers hardness measurements were made on the bulk glasses and at the bonded interface, which showed no cracks propagating along the interface.     

Determination of carrier mobility in MEH-PPV thin-films by stationary and transient current techniques

Charge transport and shelf-degradation of MEH-PPV thin-films were investigated through stationary (e.g. current versus voltage — JxV) and transient (e.g. Time-of-Flight — ToF, Dark-Injection Space-Charge-Limited Current — DI-SCLC, Charge Extraction by Linearly Increasing Voltage — CELIV) current techniques. Charge carrier mobility in nanometric films was best characterized through JxV and DI-SCLC. It approaches 10^? 6 cm²/Vs under a SCLC regime with deep traps for light-emitting diode applications. ToF measurements performed on micrometric layers (i.e. ~ 3 μm) confirmed studies in 100 nm-thick films as deposited in OLEDs. All results were comparable to a similar poly(para-phenylene vinylene) derivative, MDMO-PPV. Electrical properties extracted from thin-film transistors demonstrated mobility dependence on carrier concentration in the channel (~ 10^? 7–10^? 4 cm²/Vs). At low accumulated charge levels and reduced free carrier concentration, a perfect agreement to the previously cited techniques was observed. Degradation was verified through mobility reduction and changes in trap distribution of states.     

Microstructure and stored energy evolutions during rolling of Cu60Zr20Ti20 bulk metallic glass

The microstructure and stored energy of Cu₆₀Zr₂₀Ti₂₀ bulk metallic glass rolled at cryogenic temperature in a wide strain rate range 1.0 × 10^?4 ? 5.0 × 10^?1 s^?1 have been investigated. As the specimen is rolled to be thinner, the stored energy first increases linearly, and then saturates above a critical thickness reduction at lower strain rates, or decreases at high strain rates. At the initial stage of rolling, no phase transformation except shear bands appears in the glass. Phase transformation occurs only when the specimen is severely deformed at strain rates higher than 1.0 × 10^?4 s^?1. As strain rate increases, the critical strain for the stored energy to saturate increases, but the critical strain for phase separation to occur decreases, and meanwhile the type of the phase transformation changes from phase separation to nanocrystallization. The stored energy does not change with the occurrence of phase separation, but decreases due to nanocrystallization. It is proposed that coalescence of more free volume in shear bands into nano-voids should be principally responsible for the saturation of the stored energy, which balances the results from the increase in shear band number at higher strains.     

Effects of Fe2O3 replacement of ZnO on elastic and structural properties of 80TeO2–(20 − x)ZnO–xFe2O3 tellurite glass system

Ternary tellurite glasses with the chemical formula 80TeO₂–(2 ? x)ZnO–xFe₂O₃ (x = 0–15 mol%) have been prepared by the melt-quenching method. Elastic and structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap method at 5 MHz and Fourier transform infrared (FTIR) spectroscopy, respectively. Both longitudinal and shear velocity showed a large increase of 3.40% and 4.68%, respectively, at x = 5 mol% before a smaller increase for x > 5 mol%. Interestingly, longitudinal modulus (L), shear modulus (G), bulk modulus (K) and Young's modulus (E) recorded similar trends with increase in Fe₂O₃. The initial large increases in shear and longitudinal velocity and related elastic moduli observed at x = 5 mol% are suggested to be due to structural modification which enhances rigidity of the glass network. FTIR analysis showed increase in bridging oxygen (BO) as indicated by the relative intensity of the TeO₄ assigned peaks and increase in intensity of the FeO₆ assigned peak (~ 451 cm^? 1) which indicates that Fe acts as a modifier in the glass network. The increase in rigidity of the glass system is suggested to be due to the increase of BO together with the formation of strong covalent FeO bond. Quantitative analysis based on the bulk compression and ring deformation models showed that the k_bc/k_exp value decreased gradually from 2.41 (x = 0 mol%) to 2.02 (x = 15 mol%) which infers that the glass system became a relatively more open 3D network as Fe₂O₃ was increased.