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This paper is concerned with the temperature dependence of viscosity for sodium germanate glasses differing in sodium oxide content and discusses some aspects of the liquid–glass transition in them, including a kinetic glass transition criterion. Using parameters of the Williams–Landel–Ferry (WLF) equation, we have calculated the temperature range characterizing the glass transition region and the structure relaxation time at the glass transition temperature of the glassed studied. We propose generalization and substantiation of the Schmelzer kinetic glass transition criterion. [ABSTRACT FROM AUTHOR]

If there is no definite relationship between the elastic moduli B and G separately and the Grüneisen parameter γ, a measure of anharmonicity, the ratio B/G turns out to be an unambiguous function of γ. The nature of the linear correlation between (B/G) and γ is discussed. [ABSTRACT FROM AUTHOR]

It is found that in the Leont'ev and Belomestnykh–Tesleva formulas for the Grüneisen parameter, the righthand sides of the equalities depend on the anharmonicity through the dependence of the ratio of the squared acoustic wave velocities v L 2 / v S 2 on the Grüneisen parameter γ. The theoretical dependence of v L 2 / v S 2 on γ in general agrees with experimental data both for crystals and glassy solids. The quantity v L 2 / v S 2 turns out to be a single-valued function of the ratio of the tangential and normal stiffness of the interatomic bond. [ABSTRACT FROM AUTHOR]

We examine the notion that atom delocalization, thought of as the limiting atom displacement from the local equilibrium position, is a process that reduces to local excitation in an elastic continuous medium. The atom delocalization energy estimated for inorganic glasses using the elastic continuum theory is in satisfactory agreement with that calculated using other approaches. [ABSTRACT FROM AUTHOR]

This work is devoted to analysis and generalization of the kinetic criteria of vitrification using the model of delocalized atoms. The generalized criterion of a liquid–glass transition is proposed. Liquid transfers to the frozen vitreous state when its cooling rate q = dT/dt reaches a certain part of Cg of the characteristic cooling rate qg = Tg/τg closely connected with the relaxation time of the structure τg at the glass transition temperature Tg. [ABSTRACT FROM AUTHOR]

The dependence of the ratio of the squared velocities of longitudinal and transverse acoustic waves on Grüneisen parameter γ, which is the measure of anharmonicity, and that agrees with the experimental data has been obtained. The quantity turns out to be a single-valued function of the ratio of the tangential and normal stiffness of the interatomic bond. [ABSTRACT FROM AUTHOR]

The temperature dependence of the glass transition activation energy for amorphous organic polymers and inorganic glasses is calculated using the Williams–Landel–Ferry equation for the relaxation time (viscosity). The results obtained are in satisfactory agreement with the experiment. The nature of the dependence of the glass transition activation energy on the temperature is discussed. [ABSTRACT FROM AUTHOR]

A modification to a previously proposed glass transition criterion is analyzed and substantiated in terms of the delocalized atom model. The atom delocalization energy in sodium germanate, alkali silicate, and sodium borate glasses is shown to be a linear function of their glass transition temperature. [ABSTRACT FROM AUTHOR]

Using the pulsed molecular acoustics method, the velocity of longitudinal and lateral sound waves in amorphous organic polymers is measured. The elastic moduli and Poisson ratio, as well as the previously introduced effective elastic modulus, are determined. It is shown that for amorphous polymers the ratio of the bulk modulus to the effective elastic modulus is a single-valued function of the Poisson ratio. The effective elastic modulus is closely related to the Grüneisen parameter, a measure of anharmonism. The nature of the Poisson ratio of amorphous polymers is considered. [ABSTRACT FROM AUTHOR]

The appearance of an additional term in the glass transition criterion is substantiated. The concept is developed that glass transition occurs when the energy of thermal vibrations of the lattice per atom becomes less than the enthalpy of atomic delocalization—its ultimate displacement from the local equilibrium position. A linear relationship is ascertained between the energy of atomic delocalization and the glass transition temperature of a number of glasses. The nature of the liquid–glass transition of various classes of glassy systems is considered. [ABSTRACT FROM AUTHOR]

Abstract—We develop the notion that, near the glass transition temperature, amorphous substances undergo reversible configurational structural changes accompanied by local expansion and compression (atom delocalization). They are similar in nature to configurational changes in the structure of glasses in the case of reversible frozen deformation and its thermally stimulated relaxation. [ABSTRACT FROM AUTHOR]

The product of the density of a solid with the square of the root mean square velocity of deformation waves in it, which has features characteristic of elastic moduli, is named an effective modulus of elasticity. We demonstrate that the ratio of the bulk modulus to the effective modulus of elasticity of oxygen-free chalcogenide glasses is a single-valued function of Poisson's ratio, like in the case of oxide glasses. The effective modulus of elasticity is closely related to the Grüneisen parameter, which quantifies anharmonicity. Based on the single-valued relation between the Grüneisen parameter and Poisson's ratio, we discuss the nature of the interrelationship between harmonic (linear) and anharmonic (nonlinear) quantities. [ABSTRACT FROM AUTHOR]

New data on the effect of small concentrations of zirconium-oxide nanoparticles on the structural behavior of cold-pressed powder matrices based on aluminum (or aluminum with 1.5% copper added), which were sintered under forevacuum, are presented. It is demonstrated that even small concentrations of nanoadditives produce a marked positive effect: the ultimate tensile, bending, and compression strength and the yield strength increase. [ABSTRACT FROM AUTHOR]

In this communication, a condition based on the deactivation of the trigger mechanism of creep is proposed for the liquid–glass transition of an amorphous substance. This mechanism is confined to the atom delocalization process, which in silicate glasses represents the ultimate displacement of the bridging oxygen atom in the Si–O–Si bridge due to the local low-activation elastic strain of the silicon–oxygen network [1, 2]. [ABSTRACT FROM AUTHOR]

A viewpoint is developed that formation of a hole in amorphous substances corresponds to the atom delocalization process, i.e., its fluctuation limiting shift from the temporary equilibrium state. The molecular-kinetic processes proceeding in liquids and amorphous rigid solids do not depend on the classical van der Waals free volume, "void statistical space between atoms," but mainly depend on the fluctuation dynamic free volume, which coincides with the fluctuation free volume caused by the atom delocalization. The atom delocalization process (local configuration structural change) plays the key role in the viscous flow of glass-forming liquids. The softening of glasses (at Tg) and their frozen reversible deformation (at 20°C) are characterized by the same molecular mechanism, namely, the atom delocalization. From the same positions as noted above, the effect of plasticity of inorganic glasses and amorphous organic polymers was considered. [ABSTRACT FROM AUTHOR]

The basic concepts of the delocalized-atom model have been shown to be applicable to low-melting-point sulfophosphate glasses and parameters of the model have been calculated. The parameters have been used to gain insight into the "atom delocalization" process in the glasses and assess their properties (viscosity, microhardness, glass transition temperature, and internal pressure). The results demonstrate that there is a linear correlation between the atom delocalization energy and glass transition temperature. The melt–glass transition is accompanied by the freezing of the atom delocalization process. [ABSTRACT FROM AUTHOR]

Abstract: An extended interpretation of the Wolkenstein-Ptitsyn formula for temperature band δTg, characterizing a range of transition from liquid to glass, is considered using the Razumovskaya-Bartenev concept. The derivation of this formula proposed by the authors does not depend on the specific type of temperature dependence of relaxation time. For silicate glasses, calculation δTg by this formula agrees with the calculation by the Williams-Landel-Ferry relation and with the left side of glass transition equation qτg = δTg, where q is the cooling rate and τg is relaxation time. Based on the experimental data, the calculation of parameters of the Razumovskaya-Bartenev equation for silicate glasses and amorphous polymers is carried out for the first time. [ABSTRACT FROM AUTHOR]

A derivation of the Williams-Landel-Ferry equation for the temperature dependence of relaxation time τ(T) in the glass transition range is proposed. This derivation is of a general character and is not related to any particular form of the functional dependence τ(T), in contrast to the known approaches. The modification of the Williams-Landel-Ferry equation and examples of its practical applications are considered. [ABSTRACT FROM AUTHOR]

In Bartenev's well-known approach to determining the dependence of glass-transition temperature on melt cooling rate, it was proposed to take into account the temperature dependence of the activation energy of the liquid-to-glass transition. The physical meaning of parameters of the obtained equation is discussed. [ABSTRACT FROM AUTHOR]

A concept in accordance with which the formation of a hole in amorphous substance corresponds to delocalization of atom is developed. It is shown that the fractions of fluctuation volume calculated using the viscosity data and the dependence of the glass-transition temperature on the cooling rate of melt are identical at a conventional cooling rate of 3 K/min. The Bartenev equation is applied in the study of oxygen-free glasses. [ABSTRACT FROM AUTHOR]

The parameters of the model of delocalized atoms applied to metallic glasses have been calculated using the data on empirical constants of the Vogel-Fulcher-Tammann equation (for the temperature dependence of viscosity). It has been shown that these materials obey the same glass-formation criterion as amorphous organic polymers and inorganic glasses. This fact qualitatively confirms the universality of the main regularities of the liquid-glass transition process for all amorphous materials regardless of their origin. The energy of the delocalization of an atom in metallic glasses, Δε ≈ 20-25 kJ/mol, coincides with the results obtained for oxide inorganic glasses. It is substantially lower than the activation energies for a viscous flow and for ion diffusion. The delocalization of an atom (its displacement from the equilibrium position) for amorphous metallic alloys is a low-energy small-scale process similar to that for other glass-like systems. [ABSTRACT FROM AUTHOR]

Within the model of delocalized atoms, it is shown that the parameter δ T , which enters the glasstransition equation qτ = δ T and characterizes the temperature interval in which the structure of a liquid is frozen, is determined by the fluctuation volume fraction $${f_g} = {\left( {{{\Delta {V_e}} \mathord{\left/ {\vphantom {{\Delta {V_e}} V}} \right. \kern-\nulldelimiterspace} V}} \right)_{T = {T_g}}}$$ frozen at the glass-transition temperature T and the temperature T itself. The parameter δ T is estimated by data on f and T . The results obtained are in agreement with the values of δ T calculated by the Williams-Landel-Ferry (WLF) equation, as well as with the product qτ-the left-hand side of the glass-transition equation ( q is the cooling rate of the melt, and τ is the structural relaxation time at the glass-transition temperature). Glasses of the same class with f ≈ const exhibit a linear correlation between δ T and T . It is established that the currently used methods of Bartenev and Nemilov for calculating δ T yield overestimated values, which is associated with the assumption, made during deriving the calculation formulas, that the activation energy of the glass-transition process is constant. A generalized Bartenev equation is derived for the dependence of the glass-transition temperature on the cooling rate of the melt with regard to the temperature dependence of the activation energy of the glasstransition process. A modified version of the kinetic glass-transition criterion is proposed. A conception is developed that the fluctuation volume fraction f = Δ V / V can be interpreted as an internal structural parameter analogous to the parameter ξ in the Mandelstam-Leontovich theory, and a conjecture is put forward that the delocalization of an active atom-its critical displacement from the equilibrium position-can be considered as one of possible variants of excitation of a particle in the Vol'kenshtein-Ptitsyn theory. The experimental data used in the study refer to a constant cooling rate of q = 0.05 K/s (3 K/min). [ABSTRACT FROM AUTHOR]

Studies concerning the relationship between the value of μ and a number of mechanical and thermal properties of amorphous polymers and glasses are analyzed with the aim to gain information about the origin of Poisson ratio μ in these systems. It is shown that the Poisson ratio features a more pronounced structure-sensitive behavior than the elastic modulus, although the Poisson ratio varies in a narrow range. The relationship between the Poisson ratio and the Grüneisen parameter is substantiated. In this context, the issue of the correlation between harmonic and anharmonic quantities is highlighted. The Poisson ratio is sensitive to lattice dynamics and atomic-molecular structures of polymers and glasses. When light atoms, for example, hydrogen atoms in polyethylene, are replaced with larger and heavier atoms on pendant chains of the macromolecular backbone, anharmonicity increases; that is, lattice Grüneisen parameter γ increases. As a result, the Poisson ratio increases because these quantities are related unambiguously. Conditions of preparing an isotropic material with a negative Poisson ratio (μ < 0) are discussed. The relative ultimate strain of the interatomic bond in glassy systems is a function of the Poisson ratio solely. The frozen elastic strain of amorphous polymers and glasses is likewise a single-valued function of the Poisson ratio. The discussed phenomena are interpreted in terms of the Kuz'menko and Pineda theories and the Berlin-Rothenburg-Bathurst model. [ABSTRACT FROM AUTHOR]

For multicomponent sheet and lead glass, the delocalization energy of Δε atoms is calculated from the experimental data on viscosity. It is shown that the value of Δε remains constant in sufficiently broad temperature range in the glass transition region. The results are in good agreement with the calculation on the formula of the model of delocalized atoms, which includes the glass transition temperature and fraction of fluctuating volume frozen at this temperature. [ABSTRACT FROM AUTHOR]

Parameter C from the main glass-transition equation qτg = C according to Nemilov's theory has the meaning of temperature bandwidth δTg in which the freezing of the structure of the glass-forming liquid occurs (where q is the cooling rate of a melt and τg is the time of structural relaxation at the glass-transition temperature). The currently used method to estimate C results in inflated values, a circumstance that is due to the assumption of the constancy of the activation energy of the glass transition in the derivation of the calculation formula. Methods of estimation of C that are in agreement with the experimental data have been considered. A calculation of the time of structural relaxation, τg, on the basis of the values of the parameters of the Williams-Landel-Ferry equation has been proposed. [ABSTRACT FROM AUTHOR]

An equation which is able to describe the temperature dependence of the viscous flow of glassforming melts in a broad range, including the glass-transition range and elevated temperatures has been obtained. The equation contains three parameters; one of them is the preexponential multiplier, which is defined by the extension of the viscosity curve to elevated temperatures (using the Lagrange polynomial), and the other two, the delocalization energy of the atom and the transition potential of the particle, are adjustable parameters. The delocalization energy of the atom that is determined by adjustment is in sufficient accordance with the calculation according to the model of delocalized atoms. The nature of the viscous flow of glass and its melts is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Using the model of delocalized atoms, an explanation is offered for the linear dependence of the microhardness of inorganic glasses on their glass transition temperatures. In these systems, the elementary volume required for the delocalization of atoms is determined by the nature of the bridging atoms and bridging valence bonds. An estimate of the volume of atom delocalization is given, based on data for the glass transition temperature and microhardness. [ABSTRACT FROM AUTHOR]

Product of the hardness of a solid body and the squared RMS velocity of strain waves having the characteristics typical of the elastic modulus is referred to as the effective elastic modulus. The ratio of the bulk compression modulus to the effective elastic modulus of optical glasses is an unambiguous function of Poisson's coefficient. The nature of Poisson's coefficient of the glasses is discussed. [ABSTRACT FROM AUTHOR]

In the developed two-level model, the atom delocalization in silicate glass represents a shift of the bonded oxygen atom in the Si-O-Si bridge resulting in a local low-activation deformation of the siliconoxygen network. [ABSTRACT FROM AUTHOR]

The article presents a study on the transition of an amorphous substance from the liquid state to the glassy state based on a proposed model of delocalized atoms. The liquid-glass transition is explained by freezing of mobility of delocalized excited kinetic units. It discusses the concurrence of the glass transition temperature of amorphous polymers with the vibrational dynamics of molecules' temperature of quantum of freezing.

The nature of the parameter involved in the Bartenev equation qτ = C relating the cooling rate of a glass-forming melt to its structural relaxation time in the glass transition region is discussed on the basis of the Volkenshtein-Ptitsyn theory using a number of known relationships. It is established that parameter C for amorphous substances with the same fragility is linearly temperature dependent. This parameter is shown to equal the narrow temperature range δ T characterizing the liquid-glass transition region (by Nemilov); i.e., C = δ T. It is concluded that δ T for most glassy systems is only ∼0.7% of the glass transition temperature T. The narrowness of temperature range δ T is explained by the small fluctuation volume fraction f 'frozen' at the glass transition temperature. The concept of a close relationship between constant C and the structural order at T (i.e., the characteristic of the inner state of a nonequilibrium 'frozen' amorphous system) is developed. [ABSTRACT FROM AUTHOR]

Constancy of the ratio between the parameters of the Bartenev equation for the dependence of the glass-transition temperature on the cooling rate of a glass-forming melt is closely related to the liquid-glass transition criterion in the model of delocalized atoms. A linear correlation between the ratio of the parameters of the well-known Williams-Landel-Ferry equation and the glass-transition temperature for some amorphous substances has been found and made it possible to write this equation in a modified form in which two almost 'universal' dimensionless constants appear. A relationship between the parameters of the Bartenev and Williams-Landel-Ferry equations has been derived. In terms of the developed concepts, the transition of an amorphous material from the liquid (rubberlike) state to the glassy state is attributed to the freezing of the delocalization of kinetic units (such as the bridging oxygen atom in the Si-O-Si bridge in inorganic glass and groups of atoms in the linking unit of the macromolecule in amorphous polymers). [ABSTRACT FROM AUTHOR]

Results of experimental investigation of the low-frequency shear elasticity of liquids depending on the angle of shear strain are presented. A cluster model of the liquid structure is suggested to explain the low-frequency viscoelastic relaxation. [ABSTRACT FROM AUTHOR]

A refined model of delocalized atoms of amorphous solids is suggested. The critical displacement of an atom from its equilibrium position corresponding to bending of the potential curve is considered as its delocalization (local excitation). The application of the model to plastic deformation of glassy solids and to viscous flow in the region of transition to glass is discussed. [ABSTRACT FROM AUTHOR]

Based on the equation for the dependence of the glass-transition temperature vs. the cooling rate, the analogous dependence has been determined for the fraction of fluctuation volume, which is frozen at the glass-transition temperature. It has been shown that the constant ratio of empirical constants of the given equation is the consequence of the criterion of vitrification in the model of delocalized atoms. The nature of the free volume of amorphous substances has been discussed. [ABSTRACT FROM AUTHOR]

It is proposed to refer to the product of the density by the squared mean square velocity of deformation waves, which has characteristic features of elastic moduli, as an effective modulus of elasticity. The ratio of the bulk modulus to the effective modulus of elasticity is a single-value function of the Poisson coefficient not only for crystals but also for inorganic glass, as well as amorphous and partially crystalline polymers. The effective elastic modulus may be useful when considering the anharmonicity of vibrations of the lattice of deformable bodies. [ABSTRACT FROM AUTHOR]

The article discusses a study on a proposed approach for deformation activation, which states that a network of covalent bonds' low-activation deformation is needed in the viscous flow of glasses. It states that the explicit form of the dependence was determined using the quasi-lattice model of amorphous substances. It presents the obtained mathematical expression for the assumption of the atom delocalization energy.

The Gruneisen parameter of glassy polymers and inorganic glass is a linear function of the fraction of the fluctuation volume that is frozen at the glass transition temperature. The nature of an interrelation between linear and nonlinear properties of solids, in particular, between the Gruneisen parameter and Poisson's ratio is discussed. [ABSTRACT FROM AUTHOR]

The ratio of softening temperature (glass transition temperature) to elastic modulus ( T/ E) is mainly determined by the limiting elastic deformation of an interatomic bond, which characterizes the transition of a structural microregion from an elastic into a viscous-flow state. In silicate glasses, this transition is caused by the limiting deformation of directed ionic-covalent Si-O-Si bonds. In the case of amorphous hydrocarbons, it is related to the relatively weak intermolecular bonds between regions in chain macromolecules, and the T/ E ratio is significantly higher than in inorganic glasses. In glassy systems of one class, this ratio turns out to be constant ( T/ E ≈ const), and a linear correlation is detected between softening temperature and elastic modulus, which can be explained in terms of the delocalized atom model. The values of T/ E can be used to classify glasses similarly to the well-known Angell classification according to so-called fragility. [ABSTRACT FROM AUTHOR]

The Jenckel equation for the temperature dependence of the free activation energy of viscous flow of inorganic glasses has been satisfactorily interpreted within the hole-activation model of viscous flow. 'The formation of a fluctuation hole' (deformation of a region of the network) characterizes a preliminary local change in the structure that is necessary for the main elementary act of viscous flow of refractory glass-forming melts, i.e., the switching of bridge valence bonds according to the Muller-Nemilov mechanism. [ABSTRACT FROM AUTHOR]

A development of the model of delocalized atoms of liquids and glasses is proposed. It is shown that the basic equation of the model for the probability of delocalization (excitation) of an atom can be obtained not only from the Clausius relation but also by other methods of statistical physics. Techniques for calculating the parameters of the model are developed. The critical displacement of an atom from the equilibrium position, which corresponds to the maximum interatomic attraction force, can be considered as a delocalization (local excitation) of this atom in an elastic continuum. The energy of the critical displacement of an atom calculated as the work of the limit elastic deformation of the interatomic bond in an elastic continuum is in agreement with the results of calculation by the model of delocalized atoms. This energy can also be calculated from the data on surface tension and atomic volume. In silicate glasses, the process of delocalization of an atom represents the critical displacement of a bridging oxygen atom in the structural fragment of a silicon-oxygen (Si-O-Si) network before the switching of the valence bond, whereas, in amorphous organic polymers, the delocalization of an atom corresponds to the limit displacement of a fragment of the main chain of a macromolecule (a group of atoms in the connecting link). [ABSTRACT FROM AUTHOR]

The entropy of a glass-liquid quasiphase transition that depends weakly on the nature of vitreous systems is introduced in analogy with the Clausius-Clapeyron equation. We suggest a common nature for the elementary act of the softening process for glasses with different chemical compositions. The elementary act in question is reduced mainly to the ultimate strain (excitation) of an interatomic bond corresponding to the maximum attraction force between atoms. [ABSTRACT FROM AUTHOR]

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 Grüneisen parameter and Poisson's ratio is discussed. [ABSTRACT FROM AUTHOR]

The interrelation between the delocalization of atoms during melting of crystals and their excitation during softening of glasses is considered. The fraction of excited kinetic units (particles displaced through the critical distance) at the softening temperature is close in order of magnitude to the fraction of delocalized atoms at the melting point. The entropy of glass-liquid quasi-phase transition almost coincides with the entropy of melting of crystals with 'loose structures.' It is proposed that the elementary acts of crystal melting and glass softening are of the same origin. [ABSTRACT FROM AUTHOR]

Linear correlation is established in glasses between the Grüneisen parameter and the ratio of propagation velocities of the longitudinal and transverse acoustic waves. An interpretation is given within the Pineda-Kuz'menko model to the relation between the harmonic and anharmonic quantities. [ABSTRACT FROM AUTHOR]

Half-quantum interpretation is proposed for the liquid-glass transition as the freezing of characteristic acoustic frequencies (degrees of freedom) that are related to the molecular mobility of delocalized excited kinetic units, namely, linear quantum oscillators. There exists a correlation between the energy quantum of an elementary excitation (atom delocalization energy) and the glass transition temperature, which is proportional to the characteristic Einstein temperature. By analogy with the Einstein theory of the heat capacity of solids, the temperature range of the concentration of excited atoms in an amorphous medium is divided into the following two regions: a high-temperature region with a linear temperature dependence of this concentration and a low-temperature region, where the concentration of excited atoms decreases exponentially to the limiting minimum value (about 3%). At this value, the viscosity increases to a critical value (about 10 Pa s), which corresponds to the glass transition temperature, i.e., the temperature of freezing the mobility of excited kinetic units. The temperature dependence of the free activation energy of viscous flow in the glass transition range is specified by the temperature dependence of the relative number of excited atoms. [ABSTRACT FROM AUTHOR]

A new approach to interpreting the hole-activation model of a viscous flow of glass-forming liquids is proposed. This model underlies the development of the concept on the exponential temperature dependence of the free energy of activation of a flow within the range of the liquid-glass transition in complete agreement with available experimental data. The “formation of a fluctuation hole” in high-heat glass-forming melts is considered as a small-scale low-activation local deformation of a structural network, i.e., the quasi-lattice necessary for the switching of the valence bond, which is the main elementary event of viscous flow of glasses and their melts. In this sense, the hole formation is a conditioned process. A drastic increase in the activation free energy of viscous flow in the liquid-glass transition region is explained by a structural transformation that is reduced to a limiting local elastic deformation of the structural network, which, in turn, originates from the excitation (critical displacement) of a bridging atom like the oxygen atom in the Si-O-Si bridge. At elevated temperatures, as a rule, a necessary amount of excited bridging atoms (locally deformed regions of the structural network) always exists, and the activation free energy of viscous flow is almost independent of temperature. The hole-activation model is closely connected with a number of well-known models describing the viscous flow of glass-forming liquids (the Avramov-Milchev, Nemilov, Ojovan, and other models). [ABSTRACT FROM AUTHOR]

Atomic displacement energy Δε in multicomponent sheet and lead-silicate glasses is calculated from the free activation energy of a viscous flow. The value of Δε is shown to remain constant in a rather wide range of temperatures in the glass transition region. Satisfactory agreement with calculations of Δε using the current formula incorporating the glass transition temperature and the fluctuation volume fraction frozen at this temperature is obtained. The validity of the above formula not only at the glass transition temperature but also in the temperature region adjacent to it is confirmed. [ABSTRACT FROM AUTHOR]

A linear correlation between the Grüneisen parameter and ratio of the velocities of longitudinal ( νl)and transverse ( νt) acoustic waves in crystals is found. It is assumed that velocities νl and νt are severally harmonic parameters, while their ratio νl/ νt is an anharmonic quantity and depends on the ratio between the shear and flexural rigidities of interatomic bonds. [ABSTRACT FROM AUTHOR]