Polyamorphism: Path to new high density glasses at ambient conditions

Polyamorphism is defined as the possibility for an amorphous material to exist with different structures. This has been demonstrated in solids for ice [O. Mishima, Y. Suzuki, Nature 419 (2002) 599], amorphous silicon [P.F. McMillan, M. Wilson, D. Daisenberger, D. Machon, Nature 4 (2005) 680], amorphous germanium and several oxide glasses [M. Grimsditch, Phys. Rev. 52 (1984) 2379, J.P. Itie, A. Polian, G. Calas, J. Petiau, A. Fontaine, H. Tolentino, Phys. Rev. 63 (1989) 398, C.H. Polsky, K.H. Smith, G.H. Wolf, J. Non-Cryst. Solids 248 (1999) 159, J. Nicholas, S Sinogeikin, J. Kieffer, J. Bass, Phys. Rev. Lett. 92 (2004) 215701, O. Majerus, L. Cormier, J.P. Itie, L Galoisy, D.R. Neuville, G. Calas, J. Non-Cryst. Solids 345&346 (2004) 34]: SiO2, GeO2, B2O3, SiO2-GeO2. Here we discuss the hysteresis curves corresponding to the evolution of the Raman bands as function of pressure for oxide glasses and compare it with ab-initio or molecular dynamics simulations [L. Huang, J. Kieffer, Phys. Rev. B 69 (2004) 224203, L. Huang, J. Kieffer, Phys. Rev. B 69 (2004) 244204, M. Durandurdu, Phys. Rev. B 73 (2006) 035209]. We show that these curves correspond for most of the glass studied to an irreversible change in the medium range order at ambient pressure. For a particular three component glass La2O3-B2O3-GeO2, (LBG) we demonstrate that this irreversibility occurs if the pressure is much higher than the in situ phase transformation pressure. It is predicted that this behaviour is general for glasses, leading to the possibility to recover new high density glass polymorphs in ambient conditions of temperature and pressure. (C) 2007 Elsevier B.V. All rights reserved.