Perovskite materials for high temperature and high performance actuators and transducers

#1. Field of the Invention

#The present invention relates to a body of perovskite material engineered by combining crystallographic engineering with tolerance property relationships for enhancement of piezoelectric properties. The material exhibits a morphotropic phase boundary (MPB) between the rhombohedral and tetragonal phases. More specifically, the present invention relates to the production of a perovskite solid solution having the general formula (1−x)BiMeO3-xPbTiO3, where Me is any suitably sized cation or combination of cations and x is a molar fraction.

#2. Description of Related Art

#FIG. 1 illustrates the rhombohedral to tetragonal phase transformation and E-field induced strain as pertains to c/a ratio for the perovskite according to the present invention;

#FIG. 2 is a graphical representation of Curie temperature of the MPB end member with PbTiO3 as a function of tolerance factor for both prior art perovskite materials and perovskites according to the present invention;

#FIG. 3 is a phase diagram for the perovskite having the formula (1−x)BiScO3-xPT, according to the present invention;

#By combining crystallographic engineering and tolerance property relationships, a new family of (1−x)BiMeO3-xPbTiO3 piezoelectric materials exhibiting a MPB between the rhombohedral and tetragonal phases, has been developed. The Me of the perovskite formula may be any suitably sized cation or combination of cations. Suitably sized cations may include, for example, scandium, indium, yttrium, ytterbium, and other rare earths. Other suitably sized cations that may be used in combination include, for example, iron, gallium, magnesium, zirconium, nickel (B-site), strontium, sodium, or potassium (A-site). Perovskite systems with these cations have demonstrated Curie temperatures greater than 400° C. and high piezoelectric coefficients (d33) of over 450 pC/N, and subsequently large strain levels and c/a ratios, even before application of further dopant strategy for property optimization.

#Property optimization may be achieved by doping the perovskite with at least one element that may or may not significantly shift TC. Suitable dopants include, for example, lanthanum, iron, manganese, niobium, tin, barium, and combinations thereof, and may be referred to as ‘donor’ and ‘acceptor’ additives.

#In one embodiment of the present invention, the perovskite system is represented by the formula (1−x)BiScO3-xPbTiO3. BiScO3 by itself exhibits poor perovskite phase stability as suspected from its low tolerance factor. However, the system (1−x)BiScO3-xPbTiO3 with x>0.50 molar fraction was found to form a phase pure perovskite solid solution, due to the addition of PbTiO3, with a substantially larger tolerance factor. Specifically, this system exhibits a MPB between a rhombohedral structure on the bismuth-rich side and a tetragonal structure on the lead-rich side, in the region 0.62<x<0.66, as illustrated in FIG. 3. The enhanced polarizability associated with an MPB is represented by increased polarization, shown in FIG. 4. As illustrated in FIG. 4, the polarization is greater than about 30 μC/cm2.