Fig. 3.

Non-volatile strain property of PMN-PT (011). a P-E loops of PMN-PT with symmetric and asymmetric bipolar electric fields. b Non-volatile piezostrain ε_x and ε_y versus electric field curves along the [100] and [$01\overline{1}$] directions, respectively, with asymmetric bipolar electric fields. The arrows in a and b indicate the electric-field sweeping directions. c, d Illustration of the FE polarization structure of PMN-PT for E = ±0 kV cm⁻¹, respectively. The rhombohedral crystal structure of PMN-PT (011) has eight spontaneous ferroelectric polarization directions along the <111> directions (the body diagonals of the pseudocubic unit cell); that is, four possible polarization directions lie in the (011) plane, while two point upward and two downward, respectively. e Evolution of the PMN-PT (022) diffraction peaks with varying electric fields, in which the electric field swept following the procedure indicated by the arrow