Molecular-dynamics study of the high-temperature elasticity of quartz above the α-β phase transition

Abstract

We have presented the molecular-dynamics ͑MD͒ results for the temperature dependence of the adiabatic elastic constants C i j of ␣ and ␤ quartz, using a statistical fluctuation formula. It is noteworthy that the calculated C i j values are in a good agreement with the experimental values in the entire temperature range of 300-1100 K, including the ␣-␤ phase-transition region. We have confirmed that the net increase of bulk C i j 's in the ␤ phase can be attributed to the internal relaxations, which arise from the cooperative motions of corner-linked SiO 4 tetrahedra. Our MD simulations have revealed the existence of dynamical disorder in ␤ quartz at high temperatures, and its influence on the macroscopic elastic properties, in contrast to the ordered ␤-quartz structure model.

Molecular dynamics study of the high‐temperature elasticity of SiO2 polymorphs: Structural phase transition and elastic anomaly

“…We have recently reported the molecular dynamics results concerning the elastic properties of b -cristobalite and b -quartz observed above the transition temperature [12,13]. Here we report the full methodology employed in the simulations and, for completeness, reproduce the calculations describing the auxetic behavior in the two SiO 2 polymorphs at a finite temperature.…”

“…Despite the simplicity, their force-field parameters are reasonably successful in describing the structural and dynamical properties of SiO 2 systems (see, for example, Refs. [13,[16][17][18][19]). …”

Auxetic behaviour from rotating rigid units

“…This was followed by some other isolated reports of this unusual behaviour, such as the report of negative Poisson's ratio in metallic alloys [4]. However, in the late 1980's, the study of materials exhibiting negative Poisson's ratios became more established and since then, negative Poisson's ratios have been predicted, discovered or deliberately introduced in several classes of naturally occurring and man-made materials including foams [5 -9], polymers [1,[10][11][12][13][14], composites [15,16], gels [17,18], laminates [19], metals [20], silicates [21][22][23][24][25] and zeolites [26,27].…”

Untitled

“…Therefore auxetic materials can be single molecules or a particular structure of macroscopic to micro level [11][12][13][14][15][16][17]. The known naturally and manmade auxetic materials include metals, silicates, zeolites, laminates, gels, composites foams and polymers [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. These materials are incorporated as core materials to produce sandwich panels, to reduce creep buckling failure, drug release systems, vibration damping and energy absorbance textiles [36][37][38][39][40].…”