Liquid GeO2 Research Articles

Correlation between structure and dynamics of liquid GeO2 under compression

Correlation between structure and dynamics of GeO2 system under compression is investigated by molecular dynamics and Monte-Carlo methods. Results show that structural phase transition occurs at the range of oxygen packing factor from 0.55 to 0.60. Self-diffusion coefficient of Ge and O exhibits anomalous and depends on percentage of GeOx polyhedrons (x = 4,5,6) and packing factor/ free volume of model. The self-diffusion coefficient can be determined via percentage of GeOx units and free volume fraction. The data mining technique is applied to clarify the polyamorphism, structure and dynamics heterogeneities. The cause of anomalous diffusion has been elucidated.

Structural transformation and anomalous diffusion in network forming liquid GeO2

In this study, we simulated the structural transformation and self-diffusion mechanism in liquid GeO2 oxide system. Under compression, structure of liquid GeO2 model tends to transform gradually from low-density phase to high-density phase. Concentration of basic structural units can be determined via density of material model. The average Ge–O bond distance in GeO4 tetrahedra is smaller than the ones in GeO5 pentahedra and GeO6 octahedra. Each GeOx polyhedron always exists a Ge–O bond with the longest length (the weakest bond). The diffusion mechanism in liquid GeO2 oxide system is via breaking the weakest bonds that accompany the change local coordination environment of Ge cations. The longest Ge–O bond in a GeO5 pentahedron is very weak in comparison to the one in other polyhedra. The diffusivity is significantly dependent on the number of GeO5 pentahedra. The increase of GeO5 under compression is the origin of anomalous diffusion in liquid GeO2 oxide. The increase of average Ge–O bond distance under compression is also clarified in this work.

MÔ PHỎNG ĐỘNG LỰC HỌC PHÂN TỬ ĐỐI VỚI CẤU TRÚC KHÔNG ĐỒNG NHẤT VÀ QUÁ TRÌNH KHUẾCH TÁN TRONG GeO2 LỎNG

In this paper, we perform a simulation about liquid GeO2. The structure and diffusion process are analyzed through the radial distribution function, the distribution of GeOx (x = 4, 5, 6) structural units, length distribution, angle distribution, and data visualization. Simulation results show that the structure of liquid GeO2 composes clusters of GeO4, GeO5, or GeO6. These clusters have sizes depending on pressure and are distributed heterogeneously in space. This result confirms the origin of dynamical heterogeneity in the liquid oxide systems. In addition, the diffusion coefficient of Ge and O decreases upon pressure. We show that the diffusion relates to the breaking bond Ge-O.

The structural phase-transition pathway under compression and dynamic properties in liquid GeO2

We perform a simulation of the structural phase-transition pathway under compression and dynamic properties in liquid germania (GeO2). The structure of liquid GeO2 is clarified through the pair radial distribution function (PRDF), distribution of GeO[Formula: see text] [Formula: see text] units, bond angle and length distribution, and three-dimensional (3D) visualization. The result shows that the structure of liquid GeO2 is built by GeO4, GeO5 and GeO[Formula: see text]units, which are linked to each other via common oxygen atoms. The GeO[Formula: see text] units lead to form into the separate GeO4-, GeO5- and GeO6-phases. The existence of separate phases is evidence of dynamical heterogeneity (DH) in liquid GeO2. The atoms in GeO5-phase are more mobile compared to other ones. The variation of the self-diffusions of Ge and O atoms under pressure is examined via the characteristics of separate GeO4-, GeO5- and GeO6-phases. We found that under compression, there is diffusion anomaly in liquid GeO2. This is suggested to be related to the very high mobility of Ge and O atoms in the GeO5-phase compared to GeO4- and GeO6-phase.

Structural dynamics and diffusion mechanism in glass-forming liquid under high pressure

Structural dynamics and diffusion mechanism in liquid GeO2 (a typical glass-forming liquid) have been studied by molecular dynamics simulation. Models consisting of 1998 atoms have been constructed under a wide pressure range (from 0 to 48 GPa) and at 3,200 K. The structural dynamics has been analyzed through the nearest-neighbor atomic exchange among coordination units, spatially heterogeneous dynamics (SHD), clustering and structural stability (lifetime of basic structural units). Investigation of structural dynamics has allowed us to gain insight into various important atomic (molecular) properties and to clarify the diffusion mechanism and origin of SHD phenomena in glass-forming liquids under high pressure.

Atomic diffusion in covalent liquids under pressure fromab initiomolecular dynamics

2 Research Fellow of the Japan Society for the Promotion of Science Abstract. The microscopic mechanisms of atomic diffusion in liquid GeO2 and SrGeO3 are investigated by ab initio molecular-dynamics simulations. We clarify the differences of diffusion mechanism between liquid GeO2 and SrGeO3. In both liquids, non-bridging oxygen double bonded to only one germanate plays a key role in the atomic diffusion mechanism. It is found that, in liquid SrGeO3 which has non-bridging oxygen in the equilibrium state at ambient pressure, atomic diffusion is possible without generating overcoordinated atoms at ambient pressure, while the over coordinated atoms are always needed for the formation of non-bridging oxygens in liquid GeO2. When the pressure increases, only liquid GeO2 has a diffusion maximum, which is given by, the atomic diffusion with concerted reaction gives the diffusion maximum.

First-principles molecular dynamics simulations of the structure of germanium dioxide under pressures

We have carried out first-principles molecular dynamics simulations of glass and liquid germanium dioxide (GeO2) over a wide range of pressure. Our results show that in the glass GeO2 system nearly all Ge–O coordination environments are fourfold at low compression, whereas at high compression five- and sixfold coordination types coexist. In the liquid GeO2 system although most Ge–O coordination environments are fourfold, some threefold coordination types exist at low compression. Pentahedral units also exist in the liquid state while less than that in the glass state. At high compression, pentahedral units disappear and GeO6 octahedron is dominant in the liquid state going with some sevenfold coordination.

A study of pressure-induced polymorphism in liquid GeO2

Pressure-induced polymorphism in liquid GeO2 has been investigated by a molecular dynamic model with 1998 atoms and Oeffner–Elliot potential. The simulation reveals that liquid GeO2 is made up of the species GeOx with fraction depending on density. Here x = 4, 5 and 6. This viewpoint is supported by the fact that the density, the oxygen-connectivity and the volume of void could be expressed as a linear function of the GeOx fractions. The structural change that occurs upon compression is analysed through both atom- and void-species and discussed here.

Reversed Monte Carlo simulation to XAFS spectra of liquid GeO2 polymorphs

X-ray absorption fine structure (XAFS) spectra of Ge-K edge of liquid GeO2 polymorphs (quartz-type and rutile-type GeO2) at temperature 1126 °C were collected at Beijing Synchrotron Radiation Facility (BSRF) and Spring-8. Reversed Monte Carlo (RMC) method was used to simulate the XAFS spectra with k2 weight. More than 200 independent configurations were used to do statistic analysis. There are 3.7 oxygen atoms surrounding Ge with Ge-O bond length of 1.74 Å for rutile-type GeO2 melt, and 3.6 oxygen atoms surrounding Ge with Ge-O bond length of 1.75 Å for quartz-type GeO2 melt. The long-range order was completely destroyed and partial short-range and intermediate-range order were kept in the two kinds of liquid GeO2 (at 1126 °C). Because partial Ge-O bonds were broken, the local atomic structures of liquid GeO2 were reconstructed. Besides the four-folded Ge-O coordination, three-folded and five-folded coordinations were also found. The liquid structures of the two GeO2 polymorphs are similar but not the same. The averaged Ge-O-Ge and O-Ge-O coordination triangles are larger in QGeO2 melt than in RGeO2 melt.

A volume temperature relationship for liquid GeO2 and some geophysically relevant derived parameters for network liquids

The thermal expansivity of liquid GeO2 at temperatures just above the glass transition has been obtained using a combination of scanning calorimetry and dilatometry. The calorimetric and dilatometric curves of c p and dV/dT are normalized to the temperature derivative of fictive temperature versus temperature using the method of Webb et al. (1992). This normalization, based on the equivalence of relaxation parameters for volume and enthalpy, allows the completion of the dilatometric trace across the glass transition to yield liquid expansivity and volume. The values of liquid volume and expansivity obtained in this study are combined with high temperature densitometry determinations of the liquid volume of GeO2 by Sekiya et al. (1980) to yield a temperature-volume relation for GeO2 melt from 660 to 1400 °C. Liquid GeO2 shows a strongly temperature-dependent liquid molar expansivity, decreasing from 20.27 × 10−4 cm3 mol−1°C−1 to 1.97 × 10−4cm3 mol−1 °C−1 with increasing temperature. The coefficient of volume thermal expansion (α v ) decreases from 76.33 × 10−6 °C−1 to 2.46 × 10−6 °C−1 with increasing temperature. A qualitatively similar volume-temperature relationship, with α v decreasing from 335 × 10−6 °C−1 to 33 × 10−6 °C−1 with increasing temperature, has been observed previously in liquid B2O3. The determination of the glass transition temperature, liquid volume, liquid and glassy expansivities and heat capacities in this study, combined with compressibility data for glassy and liquid GeO2 from the literature (Soga 1969; Kurkjian et al. 1972; Scarfe et al. 1987) allows the calculation of the Prigogine-Defay ratio (Π), c p -c v and the thermal Grüneisen parameter (γ th) for GeO2. From available data on liquid SiO2 it is concluded that liquid GeO2 is not a good analog for the low pressure properties of liquid SiO2.

Viscosity‐Temperature Relation for Network Liquids

The viscosity‐temperature relation for the network liquids is considered in the light of the results for associated liquids and polymers. A critical examination of all the data available indicates that for liquid B2O3, SiO2, and BeF2 the energy of activation for flow is temperature dependent. Liquid GeO2 is possibly an anomaly. Empirical equations which satisfactorily describe the viscosity of associated liquids are not applicable to liquid B2O3 and SiO2.

Structure of Glass Forming Halides. I. Liquid Beryllium Fluoride

Viscosity and electric conductivity measurements have been made on liquid beryllium fluoride over the temperature range 700–950°C. The high specific resistance and viscosity and the magnitude of the corresponding energies of activation indicate that the classical random network structure for glasses is applicable. Liquid BeF2, similar to liquid GeO2 and SiO2, is highly associated even at elevated temperatures. At a temperature 200° above the melting point, the energy of activation for viscous flow is greater than the heat of vaporization. The ease of glass formation is attributed to the network structure of the liquid.

Surface Tension of Some Liquid Oxides and Their Temperature Coefficients

Surface‐tension data are reported for liquid Al2 O3, B2 O3, GeO2, P2 O5, and SiO2. Abnormal positive temperature coefficients for B2 O3, GeO2, and SiO2 are shown to be due mainly to changes in the liquid structure (dissociation) with temperature.

Structure of Liquid Germanium Dioxide

Viscosity and electric conductivity measurements have been made on liquid germanium dioxide over the temperature range 1250–1550°C. The relationship between log viscosity and 1/T is not linear and the energy and entropy of activation for viscous flow decreases with increasing temperature. Electric conduction obeys the empirical Arrhenius relationship, the energy of activation for conduction being 46.5 kcal/mole. From electronegativity considerations the energy of the Ge–O bond is estimated to be 104±8 kcal. Liquid GeO2, similar to liquid SiO2 is highly associated, the classical network structure for solid glasses being applicable. A mechanism for viscous flow is postulated.