Abstract:

Two Kind of low frequency measurements, internal friction (IF) and dynamic shear modulus (G), were made in a single crystalline (TaSe₄)₂I sample, using a subresonant forced pendulum: 1) temperature dependence of IF and G, at 1Hz and strain amplitude (εᵖᵖ ~ 6 x 10ˉ⁴) during thermal cycles from 290 K to 190, 170, 150, 130 and 110 K, in cooling and heating rates of 0.4 K/min. 2) frequency dependence of IF and G from 10 Hz to 0.005 Hz during isothermals fromo 170 K to 270 K, at the same strain amplitude as before. Mainly remarks are the following: A dip in G vs. temperature is always observable in each one of the passages through the transition to the Peierls state, around 250 K in our sample. While an effect in IF is only clearly detected after cycling at 110 K, indicating that metaestable states are being freezing corresponding with matrix stresses and defect creation. A similar IF effect is observed doubling the strain amplitude, also associated with matriz defect creation. These results are discussed in the base of A. Virozstek-K. Maki model, which explains other authors results assuming that the lower sensibility of G (compared with Young modulus) for detecting the Peierls transition id due to the quasi-particles relaxation and its dependence with diffusion constant and measurement frequency. As in all the frequency range and all the thermal cycles the G defect is present, our conclusion is that this compound do no behave as the Virozsteck-Maki model or that the (TaSe₄)₂I diffusion constant is very far from the NbSe, and TaS, ones.