ABSTRACT
Relaxor ferroelectrics show substantial responses to electric fields. The key difference from normal ferroelectrics is a temperature-dependent inhomogeneous structure and its dynamics. The lead-based complex perovskite Pb(In1/2Nb1/2)O3 is an intriguing system in which the inhomogeneous structure can be controlled by thermal treatment. Herein, we report investigations of the phase transitions in single crystals of Pb(In1/2Nb1/2)O3 via changing the degree of randomness in which In and Nb occupy the B site of the ABO3 perovskite structure. We studied the dynamic properties of the structure using inelastic light scattering and the static properties using diffuse X-ray scattering. These properties depend on the degree of randomness with which the B site is occupied. When the distribution of occupied In/Nb sites is regular, the antiferroelectric phase is stabilised by a change in the collective transverse-acoustic wave, which suppresses long-range ferroelectric order and the growth of the inhomogeneous structure. However, when the B site is occupied randomly, a fractal structure grows as the temperature decreases below T *~475 K, and nanosized ferroelectric domains are produced by the percolation of self-similar and static polar nanoregions.
ABSTRACT
The domain structures of poled and depoled lead-based relaxor ferroelectric solid-solution single-crystal 24Pb(In(1/2)Nb(1/2))O(3)-46Pb (Mg(1/3)Nb(2/3))O(3)-30PbTio(3) are studied by polarized light microscopy, piezoresponse force microscopy (PFM), scanning electron microscopy (SEM), and dielectric spectroscopy. The domain structures in the nonergodic relaxor state are found by PFM to consist of tweed structures resulting from random fields from the competition between ferroelectric and antiferroelectric distortion, and planar defects found by SEM are treated as dislocations associated with strain accommodation, resulting in superior piezoelectric properties. This domain structure is found to be connected with hierarchical domain structures.
ABSTRACT
The piezoelectric properties of a Pb[(Mg(1/3)Nb(2/3))(0.68)]Ti(0.32)O(3) binary system single crystal poled along the [001] direction in the rhombohedral phase were investigated under pressures up to 400 MPa at 25 °C. For the transverse electromechanical property, the difference Δf between the resonance f(r) and antiresonance frequencies f(a), the Δf/f(r) and the electromechanical coupling coefficient k(31) value in the k(31) mode with hydrostatic pressure (p) became smaller because of the increase in f(r) and the almost constant f(a) with p. The k(31) value decreased by 16% at 400 MPa. On the other hand, for the longitudinal electromechanical property, the Δf, the Δf/f(r) and the k(33) value in the k(33) mode with p remained almost constant because of the almost constant f(r) and f(a) with p. The changes in the values of the elastic compliances s(11)(E) and s(33)(E) with p were found to be large from the changes in f(r) and f(a) with p. s(11)(E) and s(33)(E) at 400 MPa were estimated to be 35.4 and 75.1 × 10(-12) m(2) N(-1), respectively. A mechanical quality factor Q almost constant with p in the k(33) mode in contrast to the large decrease in Q in the k(31) mode with p in the pressure range up to 200 MPa was observed. A k(33) value almost constant with p is considered, on the basis of the engineered domain concept, to be due to the stable domain configuration responsible for the longitudinal k(33) mode. Furthermore, the superior piezoelectric properties of the rhombohedral [001] single crystal in the vicinity of the morphotropic phase boundary composition were recently pointed out to come from the large shear piezoelectric constant d(15) of their single domain property. The hydrostatic pressure cannot influence the piezoelectric properties from the viewpoint of the contribution of the large shear mode d(15), since the uniform pressure introduces no shearing stresses. Consequently, the k(33) value measured for the k(33) mode remained almost constant with p in the measured pressure range.
