Dynamic mechanical analysis—a powerful tool for the study of phase transitions

Abstract

Dynamic Mechanical Analysis (DMA-7, PERKIN ELMER) is a very useful device for determining the thermal expansion and the low-frequency elastic compliances of crystals. The complex compliances can be measured in a frequency range from 10mHz to 50Hz and for temperatures between 6 and 1300K. A great advantage is that also very small samples (a 0.1 mm thick) can be measured.

Here we give an overview of our recent DMA-measurements in different systems and discuss the main results:

– In KSCN Entropy fluctuations were found for the first time at low frequencies.

– In Cm a glass transition was detected and the freezing process was studied in detail. Moreover, a very unusual elastic hardening was observed.

– In ALHS ferroelastic domain freezing was found for the first time.

From these examples one can see, that a variety of phenomena, i.e. low-frequency dynamics, due to entropy fluctuations, glass freezing, domain freezing, etc. can be well studied by Dynamic Mechanical Analysis.

Key Words:

• Elastic constants
• Phase transitions
• Fullerenes