Structural transformation and dynamical heterogeneity in Germania melt under compression: molecular dynamic simulation

The structural transformation and dynamical heterogeneity in Germania (GeO2) are investigated via molecular dynamics (MD) simulation. The MD model with 5499 atoms was constructed under pressure up to 150 GPa and at a temperature of 3500 K. The structural transformation mechanism has been studied by observing domain structures and boundary oxygen atoms. The simulation result reveals that GeO2 consists of separate domains and boundaries in its melt structure. Under compression, the structure of GeO2 changes gradually and represents many types of structures. The melt structure exhibits many structural domains Dx, and polymorphism appears at pressures of 12 and 20 GPa. The change of tetrahedral structure to octahedral structure in germanium coordination occurred in parallel with the process of merging and splitting of domain structure. Moreover, the existence of high- and low-density phases in GeO2 melt is indicated. The high-density phase is D6 domain and boundary oxygen while the low-density phase is D4 and D5 domain. The compression mechanism in GeO2 melt mainly is a reduction of average Voronoi volume of oxygen and Voronoi volume of D6, boundary atoms oxygen. Furthermore, we find the dynamical heterogeneity at ambient pressure. The separate “fast” regions and “slow” regions in GeO2 are detected via link-cluster function.

Anomalous Temperature Dependences of Kinematic Viscosity in a Multicomponent Metal Melts

The temperature dependence of the kinematic viscosity was determined in the Fe84.5Cu0.6Nb0.5Si1.5B8.6P4C0.3 melt, which has an anomaly in the temperature range 1700–1900 K. The cluster sizes participating in the viscous flow were calculated using the transition state theory. It is shown that the activation energy Ea is directly proportional to the natural logarithm of the cluster size d, and the melt viscosity decreases with increasing cluster size. In the anomalous region at heating, the activation energy first decreases and then increases. This behavior was associated with the cluster dissolution and the subsequent formation of new clusters with a different size and chemical composition. Upon cooling, the viscosity corresponds to the melt structure formed at the maximum heating temperature.

VISCOSITY OF CuPb, CuPbSn, CuPbSnGa AND CuPbSnGaBi MELTS OF EQUIATOMIC COMPOSITIONS

We investigated the viscosity of CuPb, CuPbSn, CuPbSnGa and CuPbSnGaBi melts of equiatomic compositions by the method of damped torsion vibrations of a crucible. We saw the melts of equiatomic composition as the melts high-entropy. All the investigated melts demonstrated the different temperature dependences of viscosity for heating and cooling. There is an anomalous reduction in viscosity resulted when the melt is heated to a specific temperature. The anomalous behaviour for viscosity we interpreted in terms of melt structure. This structural changes in the melt resulted when the melt is heated to a specific temperature. The microstructure of CuPbSnGaBi ingot of equiatomic composition we investigated using optical microscopy and measurement of microhardness. Collations data of the microstructures with of the microhardness gave three structural components: CuGa2 dendrites, (Sn) + (Bi) + Bi3Pb7 ternary eutectic and rounded Pb inclusions having dimensions of 5 m.