Structure-property relationships in ferroelectrics extend over several length scales from the individual unit cell to the macroscopic device, and with dynamics spanning a broad temporal domain. Characterizing the multi-scale structural origin of electric field-induced polarization reversal and strain in ferroelectrics is an ongoing challenge that so far has obscured its fundamental behaviour. By utilizing small intensity differences between Friedel pairs due to resonant scattering, we demonstrate a time-resolved X-ray diffraction technique for directly and simultaneously measuring both lattice strain and, for the first time, polarization reversal during in-situ electrical perturbation. This technique is demonstrated for BaTiO3-BiZn0.5Ti0.5O3 (BT-BZT) polycrystalline ferroelectrics, a prototypical lead-free piezoelectric with an ambiguous switching mechanism. This combines the benefits of spectroscopic and diffraction-based measurements into a single and robust technique with time resolution down to the ns scale, opening a new door to in-situ structure-property characterization that probes the full extent of the ferroelectric behaviour.

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Lead free 0.94(Bi 0:5 Na 0:5 ÞTiO 3 -0.06BaTiO 3 ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping (through Bi-excess) and acceptor-doping (through Na-excess). Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry. A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions. Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms. Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by $3-4 orders of magnitude and an associated activation energy of 1.57 eV which was close to half of the optical bandgap. In contrast, an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions. In addition, the Na-excess compositions exhibited low resistivities ( $ 10 3 -cm) with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in (Bi 0:5 Na 0:5 ÞTiO 3 . Long term annealing studies were also conducted at 800 C to identify changes in crystal structure and electrical properties. The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi 0:5 Na 0:5 ÞTiO 3 -0.06BaTiO 3 ceramics are very sensitive to Bi/Na stoichiometry.

The time and frequency dependence of the electric field-induced phase transition in BaTiO3-BiZn1/2Ti1/2O3 was studied using in situ X-ray diffraction. The kinetics of the field-induced phase transition between cubic and tetragonal phases was described using a modified Kolmogorov-Avrami-Ishibashi (KAI) equation. Unlike previous works, for which some assumptions (e.g., unimodal and Gaussian) on the distribution of transition rates are needed, the present work utilized Bayesian inference and a Markov chain Monte Carlo algorithm to obtain the distribution of transition rates empirically without a priori assumption on the distribution. The results show that the transition rate coefficient increases as the frequency of applied field increases. The mean value of exponent n in the modified-KAI equation was close to 1, implying that the field-induced phase transition is site saturated and the growth of the induced phase occurred primarily from the surface.

Ceramics based on the perovskite solid solution (1-x) NaNbO 3 -xBi (Zn 0.5 Ti 0.5 ) O 3 were prepared using conventional solid state synthesis. The crystal structure, electrical, and optical properties were examined. According to diffraction data, a single perovskite phase could be identified up to the composition x=0.09. As the Bi (Zn 0.5 Ti 0.5 ) O 3 content increased the crystal structure transitioned from orthorhombic to pseudocubic symmetry. Furthermore, dielectric data showed that the dielectric maximum shifted to lower temperatures with the addition of Bi (Zn 0.5 Ti 0.5 ) O 3 . Polarization hysteresis data revealed a slim linear loop across the whole range of solid solutions. Optical data also showed a decrease in the optical band gap from 3.4 eV for pure NaNbO3 to 2.9 eV for the x=0.09 composition. Using impedance spectroscopy, an electrically inhomogeneous microstructure was observed for compositions with increased Bi (Zn 0.5 Ti 0.5 ) O 3 content. Finally, the substitution of Ta on the B-site was shown to shift the dielectric maximum to temperatures as low as 100 K.