Local polar structure and multiferroic properties of (1- x)Bi _0.9Dy_0.1FeO₃- x PbTiO₃ solid solution

The multiferroic (1-x)[0.9BiFeO₃-0.1DyFeO₃]- xPbTiO₃ (BDF-xPT) solid solution with compositions around the morphotropic phase boundary (x = 0.25, 0.28, 0.31, 0.34, and 0.37) has been synthesized in the form of ceramics. The phase symmetry, microstructure, ferroelectricity, piezoresponse, and ferromagnetic properties have been characterized by various techniques. It is found that, with increasing content of lead titanate from x = 0.25 to x = 0.37, the grain size increases and the ferroelectric property is improved. The ferroelectric performance is further enhanced by the introduction of an excess amount (2%) of TiO₂ or by sintering in oxygen atmosphere, which reduces the leakage. The local polar structure is imaged by piezoresponse force microscopy. Both the out-of-plane and in-plane images reveal distinct ferroelectric domain structures, with the amplitude and the average domain size decreasing with the increase of lead titanate amount. Compared with the (1-x)BiFeO₃-xPbTiO₃ binary solid solution of about the same concentration of PT, the magnetic properties are enhanced in BDF-xPT due to the presence of dysprosium, as demonstrated by the ferromagnetic hysteresis loops displayed at room temperature and at 10 K, but the remnant magnetization decreases with increasing PT content. The simultaneous presence of ferroelectricity and ferromagnetism entitles the BDF-xPT solid solution a room-temperature multiferroic material.