Internal Friction Associated with the Domain Walls and the Second-Order Ferroelastic Transition in LNPP

An internal friction peak (P1) is measured at 5 and 50 kHz without thermal hysteresis near the ferroelastic transition temperature Tc of LNPP single crystal. The mechanism of internal friction due to a second-order transition is suggested. Experimental results show that the density of domain walls, N, in the ferroic phase is proportional approximately to (Tc - T)−1 with a remarkable hysteresis during heating and cooling. The peak P2, which appears at N = (50 ± 10) mm−1 obtained by in situ observation, is attributed to the static hysteresis loss due to the motion of newly appearing domain walls. Applying a small stress during cooling below Tc can freeze domains down to room temperature; as a result, P2 is suppressed and another broad peak (P3) appears at a lower temperature without thermal hysteresis. The peak is ascribed to the “frozen” domain walls.