engleski

FINGERPRINT OF GLASSES IN LOW TEMPERATURE THERMODYNAMICS

The Debye model predicts a T3 dependence of the specific heat Cp at sufficiently low temperatures (T) in insulators and it reproduces a wealth of data in isotropic crystals. Amorphous compounds also show universal low‐T thermal properties which are, however, anomalous with respect to those of the corresponding crystalline phases. The best known fingerprints of glasses appear in specific heat and thermal conductivity. There are two anomalies that show up as an excess to the constant Cp(T)/T3 in glasses and amorphous systems: the upturn below 1 K and a broad bump at T∼10 K. As little was known about the second feature other than its bosonic character, so it became known as the “boson peak” (BP). Since then, the origin of the BP has remained a puzzle and the main topics in a very wide field of glasses from both experimental and theoretical point of view. There are even some expectations that the clarification of the BP origin may also help to solve an even older problem, namely to explain the peculiarities of the glass transition itself. In this short overview two limiting cases will be presented for long (L) and short (S) range (R) order (O): „superstructural glass” (LRO) and metallic glass (SRO). On general grounds we show that the Cp of incommensurate (IC) modulated systems bears many similarities with that of amorphous systems and that IC systems could provide a model approach to low‐T behavior of glasses. On the other side, the possible correlation between glass forming ability (GFA) and BP in metallic glasses might shed new light to this puzzle.

metallic glasses; glass forming ability; boson peak; heat capacity

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