Vitreous Solids Research Articles

Disorder-tuned conductivity in amorphous monolayer carbon.

Correlating atomic configurations-specifically, degree of disorder (DOD)-of an amorphous solid with properties is a long-standing riddle in materials science and condensed matter physics, owing to difficulties in determining precise atomic positions in 3D structures1-5. To this end, 2D systems provide insight to the puzzle by allowing straightforward imaging of all atoms6,7. Direct imaging of amorphous monolayer carbon (AMC) grown by laser-assisted depositions has resolved atomic configurations, supporting the modern crystallite view of vitreous solids over random network theory8. Nevertheless, a causal link between atomic-scale structures and macroscopic properties remains elusive. Here we report facile tuning of DOD and electrical conductivity in AMC films by varying growth temperatures. Specifically, the pyrolysis threshold temperature is the key to growing variable-range-hopping conductive AMC with medium-range order (MRO), whereas increasing the temperature by 25 °C results in AMC losing MRO and becoming electrically insulating, with an increase in sheet resistance of 109 times. Beyond visualizing highly distorted nanocrystallites embedded in a continuous random network, atomic-resolution electron microscopy shows the absence/presence of MRO and temperature-dependent densities of nanocrystallites, two order parameters proposed to fully describe DOD. Numerical calculations establish the conductivity diagram as a function of these two parameters, directly linking microstructures to electrical properties. Our work represents an important step towards understanding the structure-property relationship of amorphous materials at the fundamental level and paves the way to electronic devices using 2D amorphous materials.

Fired hollow clay bricks manufactured from black cotton soils and natural pozzolans in Kenya

The fired hollow clay bricks (FHCBs) have been manufactured by firing a type of highly expansive soils, the black cotton soil (BCS), and natural volcanic ashes (VA), which were both collected from Kenya. Characterizations including the X-ray diffraction, thermogravimetric analyses and electron microscopy have been performed to derive mineralogical transformations in the firing process. Various feedings and firing temperatures have been tried to examine impacts on the physical-mechanical properties (compressive strength, bulk density, linear shrinkage and apparent porosity). Results indicated that the mass ratio of BCS:VA 7:3–8:2 can readily diminish the shrinkage of the FHCB, and the firing temperature (1000–1100°C) affords the best physical-mechanical performance. The products meet requirements of the first-class FHCBs MU10.0 referring to GB/T 13545-2014. The mineralogical study indicates that clay minerals in BCS undergo decomposition at about 900°C, and the reaction as well as the phase transformation was proposed as: phyllosilicates+volcanic glass→feldspar→pyroxene→melted substances→vitreous solids, which was a reverse geology evolution of volcanic lava. This research provides a strategy in making use of vast resources BCS in Kenya obtained from municipal constructions.

Analog of the Lindemann melting criterion for softening of vitreous solids

A condition for the glass-liquid transition that is similar to the Lindemann melting criterion is suggested.

Grüneisen parameter and propagation velocities of acoustic waves in vitreous solids

A linear correlation has been found between the Gruneisen parameter and the ratio of the propagation velocities of longitudinal and transverse acoustic waves in vitreous solids. The relation between these quantities has been interpreted in terms of the Pineda model.

Structural investigations of V2O5–P2O5–CaO glass system by FT-IR and EPR spectroscopies

xV2O5·(100 − x)[0.7P2O5·0.3CaO] glass system was obtained for 0 ≤ x ≤ 35 mol% V2O5. In order to obtain information regarding their structure, several techniques such as X-Ray diffraction, FT-IR, and EPR spectroscopies were used. X-Ray diffraction patterns of investigated samples are characteristic of vitreous solids. FT-IR spectra of 0.7P2O5·0.3CaO glass matrix and its deconvolution show the presence in the glass structure of all structural units characteristic to P2O5. Their number are increasing for x ≤ 3 mol% V2O5 then, for higher content of vanadium ions, the number of phosphate structural units are decreasing leading to a depolymerization of the structure. The structural units characteristic to V2O5 were not evidenced but their contribution to the glass structure can be clearly observed. EPR revealed a well resolved hyperfine structure (hfs) typical for vanadyl ions in a C4v symmetry for x ≤ 3 mol% V2O5. For 5 5 mol% V2O5.

Relation between the parameters of the elasticity theory and averaged bulk modulus of solids

A relation between the elastic moduli and Poisson’s ratio of crystalline and vitreous solids is considered. The feasibility of introducing the averaged bulk modulus, which has the same attributes as other elastic moduli, is substantiated. A relationship between the Gruneisen parameter and Poisson’s ratio is discussed.

Simulation of melt crystallization kinetics

Mathematical model of non-isothermal crystallization process, taking into account changes in the system composition is presented as a differential equation system. Application of the proposed model enables calculation of both general process kinetics and parameters, characterizing the forming structure (graininess) and texture of three-space systems and films. In general the presented mathematical model can be applied for the simulation of phase transition processes, such as crystallisation of melts, glasses and other vitreous solids, polymers, epitaxial growth of films, decomposition of solid solution etc.

Anharmonicity of lattice vibrations and transverse deformation of crystalline and vitreous solids

This paper reports on the additional data confirming the interrelation between the Gruneisen parameter and Poisson’s ratio in crystalline and vitreous solids. The assumption is made that the ratio between the velocities of longitudinal and transverse acoustic waves can depend on the anharmonicity of lattice vibrations.

Anomalous transport and diffusion versus extreme value theory

In the present work we match the biased hierarchical continuous-time random flight (HCTRF) on a regular lattice (based on hierarchical waiting-time distribution) and the extreme event theory (EVT). This approach extends the understanding of the anomalous transport and diffusion (for example, found in some amorphous, vitreous solids as well as in conducting and light-emitting organic polymers). Both independent approaches were developed in terms of random-trap or valley model where the disorder of energy landscape is exponentially distributed while the corresponding mean residence times in traps obey the power-law. This type of disorder characterizes several amorphous (even used commercially) materials which makes it possible to apply the HCTRF formalism. By using the EVT we additionally show that the rare (stochastic) events are indeed responsible for the transport and diffusion in these materials.

The hole-cluster model of vitreous solids and their melts

The paper discusses the basic principles of the free volume theory. The review and analysis of one of the phenomenological approaches, namely, the hole-cluster model of glasses and their melts, are presented.

Quantitative IR spectroscopy: Applications to studying glass structure and properties

Abstract A review of data obtainable with various methods of quantitative treatment of the IR spectra of glasses is given. The version of the dispersion analysis method using a specific analytical model for the complex dielectric constant of glasses is shown to be the most appropriate tool for calculating the IR band parameters for glasses. Applications of data on band parameters are illustrated by examples for binary silicate, borate, and germanate glasses. Band parameter versus glass composition plots are discussed and the opportunity to calculate the ‘static’ dielectric constant corresponding to that characteristic of the ultra high frequency range is shown. The above model uses the convolution of the Lorentzian and Gaussian functions, where the parameters of the Gaussian function characterize the random frequency distributions of the near-zero-wavevector phonon intensities. The idea of such a distribution can be a basis for the semi-empirical calculation of the IR spectra of vitreous solids.

Hydrolysis and initial polycondensation of phenyltrimethoxysilane and diphenyldimethoxysilane

The sol–gel process opens the possibility of producing vitreous solids containing the main structural groups of oxide glasses and polymers by introducing compounds of the type RnSi(OR′)4–n into the starting mixture. The Si–C bond is normally stable towards hydrolysis and therefore the ligand R acts as a network modifier in the resulting structure. Two organoalkoxysilanes were studied: phenyltrimethoxysilane (PTMOS) and diphenyldimethoxysilane (DPMOS). The compositional regions in PTMOS and DPMOS systems where the solution is homogeneous and the gelation takes place were investigated. The hydrolysis and initial polycondensation of PTMOS and DPMOS were studied by highresolution 29Si nuclear magnetic resonance. Signals due to the following monomers and oligomers have been identified: PhSi(OMe)2(OH); PhSi(OMe)(OH)2; PhSi(OH)3; Ph2Si(OMe)(OH); Ph2Si(OH)2(where Ph=C6H6). Concerning the difunctional alkoxysilane, it was shown that the substitution of the hydroxy group for the methoxy group resulted in an upfield shift of the signal which is opposite to the case for tetrafunctional alkoxides. For the PTMOS, the same substitution induces the conventional downfield shift. 29Si NMR quantitative analysis was performed on both alkoxide solutions during the following of the hydrolysis-condensation reactions and on the final gels. This provided information on the formation of the gels molecular structure.

Latent track structure in polymers as observed by a highly sensitive electrolytical conductivity measurement

First results of a new electrolytical conductivity cell are reported concerning the initial stage of the pore opening process during track etching in vitreous solids. On the basis of the soft mode (low-energy excitation) model for track etching, a distribution function for the number of perforated micropores as function of time is calculated by accounting for the radial etch rate as function of the effective pore radius.

Latent track structure in polymers as observed by a highly sensitive electrolytical conductivity measurement

First results of a new electrolytical conductivity cell are reported concerning the initial stage of the pore opening process during track etching in vitreous solids. On the basis of the soft mode (low energy excitation) model for track etching, a distribution function for the number of performed micropores as function of time is calculated. The results account for the radial etch rate as function of the effective pore radius.

Time Dependence Calculation of the Breakdown Rate for Electrical Breakdowns in Vitreous Solids

The anomalous behaviour of different physical quantities in vitreous solids contrary to the behaviour in crystalline solids, mainly the dielectric behaviour, can be described by the effect of a system of additional low-energy excitations in these solids. This also applies to the amorphous SiO2-layers in MOS structures. Therefore, a model of breakdown behaviour is developed basing on the assumption that there are fluctuations of the correlated local electrical fields and low-energy excitations present in these layers. On this basis, the time dependence of breakdown rate is determined. By these calculations, a good correspondence of the experimentally and theoretically determined characteristics is obtained. In these calculations, it should be paid attention to the fact, that the properties of the vitreous solids and the character of the internal interaction change by breakdowns already occured. Das anomale Verhalten verschiedenster physikalischer Größen in glasartigen Festkörpern gegenüber deren Verhalten bei kristallinen Festkörpern, insbesondere das dielektrische Verhalten, kann durch die Wirkung eines Systems zusätzlicher niederenergetischer Anregungen in diesen Festkörpern beschrieben werden. Das trifft auch auf die amorphen SiO2-Schichten in MOS-Strukturen zu. Deshalb wird ein Modell des Durchschlagverhaltens auf der Grundlage der Annahme über die Existenz von Fluktuationen der korrelierten lokalen elektrischen Felder und von niederenergetischen Anregungen in dieser Schicht erarbeitet. Darauf aufbauend wird die Zeitabhängigkeit der Durchschlagsrate berechnet. Diese Berechnungen führten zu einer guten Übereinstimmung der experimentell ermittelten und der theoretisch erhaltenen Charakteristika. Bei derartigen Berechnungen ist zu beachten, daß sich die Eigenschaften der glasartigen Festkörper und der Charakter der inneren Wechselwirkungsprozesse durch bereits erfolgte Durchschläge verändern.

A New Model Variant for Describing Dielectric Response on the Basis of the Impact of Low‐Energy Excitations

AbstractThe anomalous behaviour of very different physical characteristics in vitreous solids, particularly their dielectric behaviour, can be described by a system of additional low‐energy excitations. This holds also for the amorphous SiO2 layers in MOS structures. Therefore, an available model of time‐dependent dielectric response is completed. This model represents the basis for further research, especially of the dielectric behaviour of vitreous solids.

A model for describing dielectric breakdown in vitreous solids based on the concept of low‐energy excitations

AbstractThe anomalous behaviour of different physical characteristics in vitreous solids compared to the behaviour in the crystalline phase, in particular their dielectric behaviour, can be described by the concept of a system of low‐energy excitations in these solids. This concept is also applicable for amorphous SiO2 layers in MOS structures. Thus, a model of breakdown behaviour based on the assumption of the existence of fluctuations of correlated local internal electrical fields and low‐energy excitations within these layers is elaborated.

Description of the universal vitreous behaviour of solids with low-energy excitations and its application to the processes in polymer materials irradiated with heavy ions

Due to the fact, that anomalous behaviour of most different physical characteristics in vitreous solids compared with crystalline solids can be described by the action of a system of additional low-energy excitations, the application of this model to processes in polymer films irradiated with heavy ions, was studied. The irradiated polymer films were etched with simultaneous electrical conductivity measurements. It was shown, that the dependence of the radial etching rate on the distance from the trajectory of the heavy ion up to a determined radius can be described by the response function developed from the model of low-energy excitations.

Quasi-punctual defects in vitreous solids and liquid-glass transition

A new theory for the glass-liquid transition is proposed by assuming the existence of micro-density fluctuations or quasi-punctual defects in the supercooled liquid. Those defects are frozen in at T< T g. Hierarchical correlation effects are supposed to occur during atomic movements resulting in a molecular mobility linked to the concentration defects. This theory is focussed on kinetics and structure relaxation effects generally observed in the temperature range near T g.

Vapour pressure, solubility and affinity of undercooled melts and glasses

The temperature course of the vapour pressure and the solubility of glassforming systems is constructed, vitrification being considered as a freezing-in phenomenon. Generalized expressions for the vapour pressure of the crystal, the undercooled melt and the glass are obtained. The equilibrium constant and the affinity of heterogenous reactions with the participation of vitreous solids is determined and the kinetics of dissolution and precipitation of glasses are examined. A thorough investigation on the kinetics of dissolution of a simple glassforming model (phenolphthalein) gives for the first time an unambiguous solubility-temperature diagram of a glassforming system. Critical examination of experimental evidence on vapour pressure and the solubility of glasses is shown to be in agreement with therthermodynamic deductions given in the theoretical paragraphs of the paper. The problem of crystal growth at constant temperature with vitreous solids used as a constant source of supersaturation is reexamined and the possibility of the crystallization of a glass via a third phase (solution) below T g is investigated.