MECHANICAL INSTABILITY IN ICE IH - A MECHANISM FOR PRESSURE-INDUCED AMORPHIZATION

The phenomenon of pressure-induced crystalline --> amorphous phase tra nsformation in ice I(h) has been studied with constant-pressure molecu lar dynamics calculations. It was found that although the temperature dependency of the transformation pressure resembles that of the extrap olated melting curve, the actual mechanism is due to a mechanical inst ability in the water framework. The elastic moduli calculated at the t ransition show a violation of Born criteria for mechanical stability.