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The phase transition process of pure and 0.5 at% Fe-doped 0.95(Na1/2Bi1/2)TiO3–0.05BaTiO3 (NBBT5) single crystals under in-situ electric-field was investigated using the Raman spectroscopy. The pure NBBT5 exhibited R3c (a−a−a− octahedral tilting) symmetry when subjected to an external electric field (E) up to 70 kV/cm. While after the Fe-doping, the crystal underwent a transition from P4bm (a0a0c+ octahedral tilting) to P4mm (a0a0c0 octahedral tilting) phase under E of 30–40 kV/cm. The results indicated that the octahedral tilting in the Fe-NBBT5 was substantially suppressed by the electric field, which was suggested to contribute to the enhanced piezoelectric response compared to the pure one.

A nanolaminated structure that is predominated by nanoscale lamellar boundaries with misorientations

Single crystals of x at.% Nb + 0.94(Na0.5Bi0.5)TiO3–0.06BaTiO3 (x%-Nb:NBT-6BT, x = 0.12, 0.23, and 0.48) show improved ferroelectric and piezoelectric properties. In particular, the large piezoelectric constant (d33 = 532 pC/N) and high field-induced strains (Smax = 0.57%) in 0.23%-Nb:NBT-6BT single crystal demonstrate its promising application potential. The underlying mechanisms were investigated directively by atomistic scale simulations. We found that, Nb5+ cations prefer to substitute Ti4+ cations on B-site and will first fill up the oxygen vacancies generated due to the loss of Bi2O3 and/or Na2O. Higher concentration of Nb2O5, however, will be compensated by Ti and/or Bi vacancies. The ions positions surrounding the defect center(s) were identified.

A new relaxor-based ferroelectric ternary system Pb(Lu 1/2 Nb 1/2 )O 3 –Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PLN–PMN–PT), with a combination of a high-Curie temperature system Pb(Lu 1/2 Nb 1/2 )O 3 –PbTiO 3 (PLN–PT) and a high piezoelectricity system Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PMN–PT), was investigated in this paper. Single crystal PLN–PMN–PT with dimensions of Φ20×45 mm 3 was grown successfully by the modified Bridgman technique for the first time. The studies of structure and composition of the as-grown crystal showed structural consistency but compositional deviation along the growth direction. The 〈0 0 1〉-oriented wafers of the PLN–PMN–PT single crystal showed excellent electrical properties at room temperature: e 33 ~4500, tan δ ~0.5%, d 33 ~2300 pC/N. The crystal was found to exhibit high Curie temperature ( T C ~176°C), rhombohedral–tetragonal phase transition temperature ( T RT ~108 °C) and coercive field ( E C ~8.1 kV/cm), superior to those of PMN–0.3PT single crystal. Studies of temperature dependence ferroelectric properties showed that high values of k 33 and d 33 could be maintained up to the T RT . These results showed that PLN–PMN–PT piezoelectric single crystal has a higher Curie temperature and coercive field with excellent electrical properties, making the crystal a promising candidate for high-power transducer applications in a broad temperature range.

A series of (Na0.5Bi0.5)TiO3–PbTiO3 (NBT–PT) single crystals with compositions near the morphotropic phase boundary (MPB) region were grown by the modified Bridgman technique. The dependence of structure on composition was measured, and the MPB region of the NBT–PT system was confirmed. The dielectric properties of the NBT–PT single crystals were investigated, and the phase transition behaviour of the NBT–PT single crystals during heating was examined. With increasing addition of PT, the coercive field of the NBT–PT crystals decreased to levels much lower than that of the pure NBT system; such a change allowed easy poling of the NBT–PT crystals and the resultant piezoelectric properties were significantly enhanced. The electromechanical coupling factor of the crystals showed relatively constant thermal stability at the depolarization temperature (Td). Finally, studies of the domain evolution of NBT–0.09PT showed the disappearance of domains at the Td, which indicates that phase transition at the Td is related to changes in domain structures.

Dielectric, ferroelectric and piezoelectric properties of lead-free Na1/2Bi1/2TiO3–xK1/2Bi1/2TiO3 (NBT–xKBT) ferroelectric single crystals were characterized systematically. With increasing KBT concentration, the remanent polarization and coercive electric field decrease, while the piezoelectric constant and the electromechanical coupling coefficient increase. The evolution of average and local structures as a function of temperature and composition was investigated using in-situ X-ray diffraction and Raman spectroscopy. The structure/property relationship of NBT–xKBT single crystals was discussed in detail.

Peculiar L-shaped diffuse streaks along pc were observed in (Na 0.5 Bi 0.5 )TiO 3 (NBT) below the Burns temperature, revealing the existence of polar nanoregions (PNRs). The displacement of Bi 3+ cations is ∼0.26 A along pc in the PNRs, with a size of ∼13 A in NBT. The BaTiO 3 doping drives the diffuse scattering patterns to evolve from the L-shape into an ellipsoidal along pc in (Na 0.5 Bi 0.5 )TiO 3 –x BaTiO 3 . An abnormally large correlation length was observed in the morphotropic phase boundary composition with x = 0.05.

Giant bipolar and unipolar strains i.e. S max > 0.5%, e max / E max > 1000 pm V –1 have been observed in Mn-doped Na 0.5 Bi 0.5 TiO 3 –6BaTiO 3 single crystals after being annealed. Temperature-dependent impedance spectra were studied and activation energies of oxygen vacancies were calculated accordingly. The two different binding energies present in X-ray photoelectron spectra for Na and Bi were assigned to different coordinate environments. However, titanium exhibits only one oxidation state (e.g. Ti 4+ ). The site occupation and valence fluctuation of Mn were characterized by electric paramagnetic resonance spectra.

0.95Na 0.5 Bi 0.5 TiO 3 –0.05K 0.5 Bi 0.5 TiO 3 lead-free piezoelectric single crystal with rhombohedral structure was grown by the top-seeded solution growth method. The temperature dependence of dielectric constant and loss, polarization hysteresis loops, the optimum poling condition and the electromechanical coupling property were investigated for the 〈100〉-oriented as-grown crystal. The curves e ( T ) show two anomalies, which are related to the two phase transformations at the temperature range of 130–340 °C. The piezoelectric constant d 33 and electromechanical coupling coefficient k t for the 〈001〉-oriented crystal at room temperature reached 147 pC/N and 0.52, respectively. The value of k t demonstrated a relatively stable thermal electromechanical coupling property over the temperature range of 15–130 °C.

A pure Cu (99.995 wt%) has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy (TEM) assisted by convergent beam electron diffraction (CBED) analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries ( ) up to the maximum angle of 9 degrees. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.

The formation kinetics of e-Fe3–2N phase in a nanocrystalline α-Fe, which was processed by surface mechanical attrition treatment, is found to be obviously increased with respect to that in the coarse-grained form. This can be attributed to the much enhanced heterogeneous nucleation rate at numerous grain boundaries in the nanocrystalline α-Fe.