Anomalies in the elastic and inelastic properties of ferromagnet–ferroelectric composites

We have studied the elastic and inelastic properties of composite materials of the Co$_x$(PZT)$_{1-x}$ system ($x$ = 0.23–0.79) possessing a nonequilibrium nanogranular structure with an average grain size of $\sim$3 nm. The results of mechanical tests performed in a temperature range of 300–900 K revealed a significant increase in the level of mechanical losses (Q$^{-1}$) above 750 K, which is caused by the thermoactivated migration of point defects. An additional heat treatment leads to grain coarsening and the appearance of a ferroelectric state in the dielectric matrix. The temperature dependences of Q$^{-1}$ in annealed samples exhibit two maxima, one of which is due to the interaction of domain boundaries with lattice defects and the other is related to the motion of interfaces in the region of the ferroelectric phase transition.