Ho-Yong Lee

Solid-state conversion of (Na1/2Bi1/2)TiO3-BaTiO3-(K1/2Na1/2)NbO3 single crystals and their piezoelectric properties

Piezoelectric ceramic with a composition of (94 − x)(Na1/2Bi1/2)TiO3-6BaTiO3−x(K1/2Na1/2)NbO3 (NBT-BT-xKNN) is a promising lead-free piezoelectric material for actuator applications because of its giant electric-field-induced strains, which are comparable with that of soft Pb(ZrxTi1−x)O3 (PZT) ceramics. Using the solid-state single crystal growth method, we succeeded in fabricating usable single crystals of NBT-BT-3KNN (6 mm × 6 mm × 8 mm size) with a uniform chemical composition. The room temperature piezoelectric properties of ⟨001⟩, ⟨110⟩, and ⟨111⟩ oriented single crystals were measured. Single crystals showed strong anisotropic strain characteristics. In particular, ⟨001⟩ oriented single crystals had excellent piezoelectric properties with small hysteresis and a high strain of 0.57% at 7 kV/mm. In addition, the fabricated single crystals exhibited a high converse piezoelectric constant, Smax/Emax, of over 1000 pm/V at 4 kV/mm. These values are greater than those reported for any lead-containing and l...

High transition temperature lead magnesium niobate–lead zirconate titanate single crystals

Recently developed relaxor lead magnesium niobate–ferroelectric lead zirconate titanate single crystals exhibit large length extensional k33 coupling, improved thermal stability, and a higher coercive field compared to morphotropic lead magnesium niobate–lead titanate single crystals. Experimental results and implications for sound projectors are presented and discussed in terms of the morphotropic phase boundary slope and width. Spontaneous polarizations derived from the calculated atom shifts in both crystals compared favorably with experimental values.

Piezoelectric Loss Performance in Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystals

Lead magnesium niobate–lead titanate (PMN–PT) single crystals are a suitable replacement over conventional PZT-based ceramics in transducer applications because of their large electromechanical coupling factors (k > 0.90) and piezoelectric constants (d > 1000 pC/N). For single crystals, it is possible to modify the performance by suitable selection of the orientation, and appropriate composition changes or doping can be utilized to improve the mechanical quality factor Qm. In this research, we report the piezoelectric loss performance in PMN–PT single crystals as a function of orientation, doping and vibration mode. The loss characteristics are based on mechanical quality factor Qm as well as the Q values at resonance (QA) and anti-resonance (QB). The Mn-doping resulted in almost twice the enhancement of the mechanical quality factor Qm and the maximum vibration velocity in comparison with the undoped samples.

Evolution of a nonspontaneous, high piezoelectric coupling symmetry axis in relaxor-ferroelectric single crystals

A nonspontaneous, high permittivity, “dielectrically soft” symmetry axis possessing large piezoelectric activity was found to exist for predominantly ferroelectric tetragonal FT compositions in the relaxor lead magnesium niobate–ferroelectric lead titanate, (1−x)Pb(Mg1∕3Nb2∕3)O3–(x)PbTiO3, single crystal system. The symmetry axis is not unique. It is a function of the lead titanate concentration x. It becomes the [011] for tetragonal compositions with x>0.35 and the [001] for rhombohedral compositions with 0.30⩽x⩽0.34. The two axial systems are degenerate for x∼0.35 and likely to converge at x∼0.29. Domain engineering for maximum piezoelectric response is easily accomplished for electric fields applied along this axis. The observations were confirmed by (1) isothermal resonance-antiresonance experiments on length extensional bars fabricated from multidomain (1−x)Pb(Mg1∕3Nb2∕3)O3–(x)PTiO3 single crystals and (2) numerical computation using Devonshire’s theory. The results are discussed in terms of recent f...