Nengneng Luo

Progress in lead-based ferroelectric and antiferroelectric single crystals: composition modification, crystal growth and properties

Ferroelectric and antiferroelectric materials, with complex perovskite structures, have experienced wide interest due to their peculiar structure and properties. In this highlight, recent advances of these two types of materials are reviewed, with particular emphasis on piezoelectrics/ferroelectric and antiferroelectric single crystals, owing to their ultra-high electric properties for practical application. Relaxor ferroelectric single crystals, represented by Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) at compositions near the morphotropic phase boundary (MPB), possess a high piezoelectric constant d33 (>2000 pC N−1) and electromechanical coupling factors k33 (90–92%). However, a low ferroelectric phase transition temperature Tr-t, far below the Curie temperature Tc restricts its further application in a broad temperature range. Some work on the design of a new pseudo-ternary system of Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 (PMN-PZ-PT) and Pb(Mg1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–PbTiO3 (PMN-PFN-PT) have been demonstrated with emphasis on the composition modification and crystal growth. Moreover, for relaxor antiferroelectrics represented by (Pb,La)(Zr,Sn,Ti)O3 (PLZST) it is very difficult to grow bulk and high quality single crystals because of its incongruent melting. Our recent investigations on the flux growth of PLZST single crystals, especially the flux selection, compositions optimization, and defect analysis of as-grown single crystals are also described in this highlight.

Crystallographic dependence of internal bias in domain engineered Mn-doped relaxor-PbTiO3 single crystals

The incorporation of acceptor dopants and the resulting internal bias in Pb(Zr,Ti)O3 (PZT) piezoelectric ceramics lead to reduced electrical and mechanical losses, but at the expense of decreased electromechanical properties. Analogous to PZTs, acceptor doped relaxor-PbTiO3 (relaxor-PT) single crystals show an improved mechanical quality factor (decreased mechanical loss), but with a minimal impact on the electromechanical properties. In this research, the internal bias and associated impacts on electromechanical properties were studied in Mn-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (Mn:PIN–PMN–PT) single crystals, showing strong crystallographic orientation dependent behaviors. By active control of defect dipoles through domain engineering, different defect dipole configurations were obtained (defect dipole engineering), leading to the unique characteristics of relaxor-PT single crystals when compared to the conventional polycrystalline ferroelectric ceramics.

New Pb(Mg1/3Nb2/3)O3–Pb(In1/2Nb1/2)O3–PbZrO3–PbTiO3 Quaternary Ceramics: Morphotropic Phase Boundary Design and Electrical Properties

Four series of Pb(Mg1/3Nb2/3)O3-Pb(In1/2Nb1/2)O3-PbZrO3-PbTiO3 (PMN-PIN-PZ-PT) quaternary ceramics with compositions located at the morphotropic phase boundary (MPB) regions were prepared. The MPBs of the multicomponent system were predicted using a linear combination rule and experimentally confirmed by X-ray powder diffraction and electrical measurement. The positions of MPBs in multicomponent systems were found in linear correlation with the tolerance factor and ionic radii of non-PT end-members. The phase structure, piezoelectric coefficient, electromechanical coupling coefficient, unipolar strains, and dielectric properties of as-prepared ceramics were systematically investigated. The largest d33s were obtained at S36.8, L37.4, M39.6, and N35.8, with the corresponding values of 580, 450, 420, and 530 pC/N, respectively, while the largest kps were found at S34.8, L37.4, M39.6, and N35.8, with the respective values of 0.54, 0.50, 0.47, and 0.53. The largest unipolar strain Smax and high-field piezoelectric strain coefficients d33* were also observed around the respective MPB regions. The rhombohedral-to-tetragonal phase transition temperature Trt increased with increasing PIN and PZ contents. Of particular importance is that high Trt of 140-197 °C was achieved in the M series with PZ and PIN contents being around 0.208 and 0.158, which will broaden the temperature usage range.

PMN-PT based quaternary piezoceramics with enhanced piezoelectricity and temperature stability

The phase structure, piezoelectric, dielectric, and ferroelectric properties of (0.80 − x)PMN-0.10PFN-0.10PZ-xPT were investigated systematically. The morphotropic phase boundary (MPB) was confirmed to be 0.30 < x < 0.34. Both MPB compositions of x = 0.32 and x = 0.33 exhibit high piezoelectric coefficients d33 = 640 pC/N and 580 pC/N, electromechanical couplings kp of 0.53 and 0.52, respectively. Of particular importance is that the composition with x = 0.33 was found to process high field-induced piezoelectric strain coefficient d33* of 680 pm/V, exhibiting a minimal temperature-dependent behavior, being less than 8% in the temperature range of 25–165 °C, which can be further confirmed by d31, with a variation of less than 9%. The temperature-insensitive d33* values can be explained by the counterbalance of the ascending dielectric permittivity and descending polarization with increasing temperature. These features make the PMN-PT based quaternary MPB compositions promising for actuator applications dem...

Temperature and electric field induced phase transition in [110]C-oriented 0.63Pb(Mg1/3Nb2/3)O3–0.37PbTiO3 single crystals

Temperature-dependent domain configurations were studied for both unpoled and poled [110]C-oriented 0.63Pb(Mg1/3Nb2/3)O3–0.37PbTiO3 (PMN–0.37PT) single crystals by polarized light microscopy (PLM). Combining the dielectric properties and the domain configurations upon heating, it was found that the temperature-induced phase transition in the unpoled [110]C-oriented PMN–0.37PT single crystal followed the tetragonal (T) → cubic (C) sequence. However, under an electric (E) field of 10 kV cm−1 along the [110]C direction, a single domain orthorhombic (O) phase was induced. The E field-dependent domain structures were observed in situ under PLM, which verified that the T phase turned to O phase when an E field of 10 kV cm−1 was applied along the [110]C direction. Upon subsequent heating, the phase transition followed the O → T → C sequence. The O–T discontinuous phase transition led to a remarkable change in the dielectric coefficient and strain with increasing temperature. The strain at 45 °C (0.148%) was 2.2 times larger than that at room temperature (0.068%), accompanied by a tremendous piezoelectric coefficient ( ~1645 pm V−1).

Composition and phase dependence of dielectric activity in [111]-oriented (1−x)Pb(Mg 1/3 Nb 2/3 )O 3 −xPbTiO 3 crystals as a function of DC bias

Dielectric permittivity of [111]-oriented Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) single crystals with various PT content and phase were investigated as a function of temperature and applied DC electric field. The temperature dependent dielectric permittivity with different PT content showed various dielectric anomalies, revealing different ferroelectric phase at room temperature. The dielectric permittivity-electric field (ε-E) measurement showed that the dielectric permittivity was strongly dependent on the applied electric field and phase structures, where different dielectric anomalies can be observed as a function of DC bias and phase, being inherently associated with the electric field induced domain switching and phase transition.