Molecular Dynamics Analysis of Negative Poisson Ratios over the α-β Transition in Cristobalite, SiO2

Abstract

Cristobalite, a low-density polymorph of silicon dioxide (SiO2), shows an unusual elastic behavior of negative Poisson ratio, contracting laterally when compressed and expanding laterally when stretched. We have successfully evaluated the adiabatic second-order elastic stiffness constants in the temperature range of 300-1,800K, including a displacive phase transition region, with the equilibrium molecular dynamics method using the statistical fluctuation formula. We have found that the cristobalite exhibits a negative Poisson ratio over this temperature range, however, with different mechanisms between low-temperature (α) and high-temperature (β) phases.