Low amplitude, low frequency elastic measurements using Dynamic Mechanical Analyzer (DMA) spectroscopy

The applications of DMA methods for the investigation of the dynamical mechanical properties of materials are reviewed. Experimental details of this method are described including the combination of DMA with Xray rocking curve measurements to investigate the details of the domain patterns. Emphasis is given to the effect of phase transitions, in particular in ferroelastic and co-elastic systems where the 'easy' movement of domain boundaries, twin walls and other interfaces lead to super-elastic softening of the material. Thermodynamic constraints, such as in the adiabatic-isothermal crossover are discussed. Smooth, ballistic propagation of domain walls are contrasted with the jerky behaviour of interfaces when phase transitions of first order are investigated. It is shown that for the ballistic behaviour, momentum driven wall movements are common and that their representation in Cole-Cole plots leads to depressed semi-circles, similar to methods used in dielectric spectroscopy. In jerky elastic responses the energy dissipation follows power law dependences. Domain wall pinning and domain wall freezing is discussed in some detail.