The dynamic properties of elastic domain walls in BaTiO 3 were investigated using resonance ultrasonic spectroscopy (RUS). The sequence of phase transitions is characterized by minima in the temperature dependence of RUS resonance frequencies and changes in Q factors (resonance damping). Damping is related to the friction of mobile twin boundaries (90• ferroelectric walls) and distorted polar nanoregions (PNRs) in the cubic phase. Damping is largest in the tetragonal phase of ceramic materials but very low in single crystals. Damping is also small in the low-temperature phases of the ceramic sample and slightly increases with decreasing temperature in the single crystal. The phase angle between the real and imaginary part of the dynamic response function changes drastically in the cubic and tetragonal phases and remains constant in the orthorhombic phase. Other phases show a moderate dependence of the phase angle on temperature showing systematic changes of twin microstructures. Mobile twin boundaries (or sections of twin boundaries such as kinks inside twin walls) contribute strongly to the energy dissipation of the forced oscillation while the reduction in effective modulus due to relaxing twin domains is weak. Single crystals and ceramics show strong precursor softening in the cubic phase related to polar nanoregions (PNRs). The effective modulus decreases when the transition point of the cubic-tetragonal transformation is approached from above. The precursor softening follows temperature dependence very similar to recent results from Brillouin scattering. Between the Burns temperature (≈586 K) and T c at 405 K, we found a good fit of the squared RUS frequency [∼ (C 11 − C 12 )] to a Vogel-Fulcher process with an activation energy of ∼0.2 eV. Finally, some first-principles-based effective Hamiltonian computations were carried out in BaTiO 3 single domains to explain some of these observations in terms of the dynamics of the soft mode and central mode.

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Strain response of polycrystalline barium titanate (BaTiO3) was investigated under high unipolar electric field (0 to 4 kV/mm) and compressive stress (0 to 400 MPa) in the temperature range from 25 to 160 °C. In the vicinity of the Curie point (TC), nonlinear and hysteretic strain-electric field and strain-stress constitutive behaviors were observed, persisting above TC where they correspond to the well-known electric field induced double loop polarization behavior. Analogous to the electrical double loops, the mechanical (strain-stress) hysteretic behavior above TC is caused by a stress induced phase transition from the paraelectric/paraelastic to ferroelectric/ferroelastic phase; the electro-elastic (strain-electric field) hysteresis is similarly caused by an electric field induced phase transition. The stress and electric field at which transitions occur increase linearly with increasing temperature, exhibiting critical behavior typical for the first order phase transitions. The temperature limit for the induced phase transition extends up to 12 °C over TC. Results are discussed in relation to the Landau-Ginzburg-Devonshire free energy expansion.

The ferroelectric, ferroelastic, and dielectric properties as well as the crystal structure were investigated for polycrystalline donor doped lead zirconate titanate (PZT) with grain sizes ranging from 0.25 to 5 μm, which were prepared using a novel zirconium titanium hydrate precursor (ZTH) with a specific surface area of 310 m 2 /g. Piezoforce microscopy was used to investigate the change in the domain structure, revealing a change in the domain configuration from a complex 3D structure to a simple lamellar domain formation at a 1 μm grain size that corresponded to a rapidly increasing internal mechanical stress observed with in situ synchrotron x-ray experiments. The correlation between the change in domain configuration, increasing internal stresses, effects of poling on the crystal structure, and the macroscopic ferroelectric and ferroelastic properties are discussed in detail, allowing a deeper understanding of size effects in polycrystalline donor doped PZT ceramics.