Criteria for bombardment-induced structural changes in non-metallic solids

Abstract

Structural transformations in non-metallic solids induced by energetic heavy ions at intermediate (∼10¹³−10¹⁶ ions/cm²) and high (∼ 10¹⁷ ions/cm²) doses normally take the form of amorphization, crystallization, or stoichiometry changes. Using the results of 72 substances both a temperature-ratio and a bond-type criterion are shown to be successful in predicting the occurrence of amorphization or crystallization. The former, based on a physical model involving thermal spikes, states that amorphization should occur whenever the ratio (crystallization temperature)/(melting point) exceeds 0.30. The latter, of more or less empirical origin, states that amorphization should occur whenever the ionicity is ≤0.47. Stoichiometry changes are basically different from amorphization and crystallization and this is reflected in the criterion. It is shown that whether or not a substance (such as AgBr or TiO₂) loses a component (such as Br or O) during bombardment correlates with the heat of atomization showing a minimum for a particular degree of loss. One of the intended applications of the present work lies in predicting which minerals ought to contain fission-fragment tracks and therefore be useful for geological dating. It is argued that minerals consisting wholly or in part of the following maybe interesting: Nb₂O₅, Ta₂O₅, V₂O₅ and WO₃.