Lead-based relaxor ferroelectrics are characterized by outstanding piezoelectric and dielectric properties, making them useful in a wide range of applications. Despite the numerous models proposed to describe the relation between their nanoscale polar structure and the large properties, the multiple contributions to these properties are not yet revealed. Here, by combining atomistic and mesoscopic-scale structural analyses with macroscopic piezoelectric and dielectric measurements across the (100-x)Pb(Mg 1/3 Nb 2/3) O 3-xPbTiO 3 (PMN-xPT) phase diagram, a direct link is established between the multiscale structure and the large nonlinear macroscopic response observed in the monoclinic PMN-xPT compositions. The approach reveals a previously unrecognized softening effect, which is common to Pb-based relaxor ferroelectrics and arises from the displacements of low-angle nanodomain walls, facilitated by the nanoscale polar character and lattice strain disorder. This comprehensive comparative study points to the multiple, distinct mechanisms that are responsible for the large piezoelectric response in relaxor ferroelectrics.

The spatial distribution of different linkers within mixed-linker metal-organic frameworks crucially influences the properties of such materials. A simple and robust approach based on (1)H spin-diffusion magic-angle-spinning nuclear magnetic resonance measurements and modeling of spin-diffusion curves is presented; this approach facilitates the distinction between homogeneous and clustered distributions. The performance of the approach is demonstrated with an example of an aluminum-based metal-organic material DUT-5, which has framework consisting of biphenyl and bipyridyl dicarboxylic linkers. The distribution is shown to be homogeneous in this material. The approach could be applied to studying other spatially disordered crystalline materials.

The high Curie temperature (TC ∼ 825 °C) of BiFeO3 has made this material potentially attractive for the development of high-TC piezoelectric ceramics. Despite significant advances in the search of new BiFeO3-based compositions, the piezoelectric behavior of the parent BiFeO3 at elevated temperatures remains unexplored. We present here a systematic analysis of the converse, longitudinal piezoelectric response of BiFeO3 measured in situ as a function of temperature (25–260 °C), driving-field frequency, and amplitude. Earlier studies performed at room temperature revealed that the frequency and field dependence of the longitudinal response of BiFeO3 is dominated by linear and nonlinear piezoelectric Maxwell-Wagner mechanisms, originating from the presence of local conductive paths along domain walls and grain boundaries within the polycrystalline matrix. This study shows that the same mechanisms are responsible for the distinct temperature dependence of the piezoelectric coefficient and phase angle and thus identifies the local electrical conductivity as the key for controlling the temperature dependent piezoelectric response of BiFeO3 and possibly other, more complex BiFeO3-based compositions.

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