Crystal Characterization

High-strain relaxor-based ferroelectric (FE) single crystals Pb(Mg_1/3Nb_2/3)_1-xTi_xO₃ (PMNTx) and Pb(Zn_1/3Nb_2/3)_1-xTi_xO₃ (PZNTx) exhibit extremely large electromechanical coupling factor k₃₃ (>94%), ultrahigh piezoelectric coefficient d₃₃ (>2500 pC/N), a large strain level (up to ~1.7%), and low hysteresis. Such high piezoelectric performance, which converts mechanical and electric energies, gives extremely promising applications in medical imaging, actuators, sonar, and accelerometers. The exceptional piezoelectric properties have been related to the existence of M_A-, M_B-, and M_C-type monoclinic (M) and orthorhombic (O) phases in the morphotropic phase boundary (MPB) region between rhombohedral (R) and tetragonal (T) phases. The intermediate phases (M and O) have been found in both PMNTx and PZNTx, and strongly depend on titanium content, temperature, history, strength of external E field, and crystallographic orientation. However, thermal instability (variation with temperature) caused by overheating still remains a challenging issue in use of these materials. Physical properties of PMNT and PZNT are sensitive to Ti content, poling process, electric (E)-field strength, crystallographic orientation, and history. To find high-strain piezoelectric crystals with high T_C (Curie or depolarization temperatures) is also a goal in our research, so that thermal instability can be minimized. Among high-T_C piezoelectric crystals, Pb(In_1/2Nb_1/2)_x(Mg_1/3Nb_2/3)_yTi_zO₃ (PIMNTx/y/z) crystals and ceramics have drawn attention in recent years.

We characterize their E-field-, temperature-, and orientation-dependent domain structures and phases using:

• Dielectric permittivity measurements
• Polarizing microscopy
• Ferroelectric hysteresis-loop analysis
• Strain measurement
• Brillouin light scattering
• X-ray diffraction (XRD)
• Scanning electron microscopy (SEM)

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Last updated: 05/24/06.