Investigation of Ternary System PbHfO ₃ – PbTiO ₃ – Pb ( Mg 1/3 Nb 2/3 ) O ₃ with Morphotropic Phase Boundary Compositions

Ternary system, (1− x ) Pb ( Hf 1− y Ti y ) O 3 – x Pb ( Mg 1/3 Nb 2/3 ) O 3 ( x = 0–0.5, y = 0.45–0.70) was prepared using two‐step precursor method. The phase structure, dielectric, piezoelectric, and ferroelectric properties of the ceramics near morphotropic phase boundary ( MPB ) have been investigated systematically. On the basis of the results of X ‐ray powder diffraction and dielectric‐temperature measurement, the MPB region and isothermal map of Curie temperature ( T C ) for the ternary system were obtained. The optimum piezoelectric and electromechanical properties were achieved in the MPB composition 0.8 Pb ( Hf 0.445 Ti 0.555 ) O 3 –0.2 Pb ( Mg 1/3 Nb 2/3 ) O 3 , with piezoelectric d 33 being on the order of 680 pC/N, while the maximum high‐field piezoelectric d 33 * of 780 pm/V was observed for 0.82 Pb ( Hf 0.445 Ti 0.555 ) O 3 –0.18 Pb ( Mg 1/3 Nb 2/3 ) O 3 with tetragonal composition, due to the high extrinsic contribution induced by domain wall motion. In addition, the fracture toughness K I C and flexural strength σ f were measured and found to be 1.2 MPa · m 1/2 and 71.4 MPa, respectively, comparable to PZT ‐based ceramics.