As part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO3 with Bi(M)O3, where M represents a net‐trivalent B‐site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to the stability of the dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R‐type BaTiO3‐based dielectrics. Although detailed understanding of the structure–processing–property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO3‐Bi(M)O3 dielectrics as well as the processing challenges and opportunities associated with these materials.

Domain wall motion in the tetragonal phase is also readily apparent and exhibits a degree of frequency dispersion similar to that measured in both the relative permittivity and piezoelectric coefficients at similar conditions.

High-resolution x-ray and neutron diffraction of (0.96)Na0.5Bi0.5TiO3–(0.04)BaTiO3 (NBT-4BT) reveal subtle structural distortions that evidence lower symmetry than allowed in the R3c space group. The combined refinement that best models the diffraction patterns is a two phase mixture of a monoclinic Cc phase and a minor fraction of a metrically cubic Pm3¯m phase (13 wt. %). The cubic phase is utilized to account for nanometer-scale regions whose local deviations from the long-range symmetry are not observed, such as polar nano-regions or tetragonal platelets. This suggests that the low symmetry found in the NBT-rich phases extends from 0 at. % to at least 4 at. % BT.

The complex crystallographic structures of (1−x)BaTiO3-xBi(Zn1/2Ti1/2)O3 (BT-xBZT) are examined using high resolution synchrotron X-ray diffraction, neutron diffraction, and neutron pair distribution function (PDF) analyses. The short-range structures are characterized from the PDFs, and a combined analysis of the X-ray and neutron diffraction patterns is used to determine the long-range structures. The results demonstrate that the structure appears different when averaged over different length scales. In all compositions, the local structures determined from the PDFs show local tetragonal distortions (i.e., c/a > 1). However, a box-car fitting analysis of the PDFs reveals variations at different length scales. For 0.80BT-0.20BZT and 0.90BT-0.10BZT, the tetragonal distortions decrease at longer atom-atom distances (e.g., 30 Å vs. 5 Å). When the longest distances are evaluated (r > 40 Å), the lattice parameters approach cubic. Neutron and X-ray diffraction yield further information about the long-range structure. Compositions 0.80BT-0.20BZT and 0.90BT-0.10BZT appear cubic by Bragg diffraction (no peak splitting), consistent with the PDFs at long distances. However, these patterns cannot be adequately fit using a cubic lattice model; modeling their structures with the P4mm space group allows for a better fit to the patterns because the space group allows for c-axis atomic displacements that occur at the local scale. For the compositions 0.92BT-0.08BZT and 0.94BT-0.06BZT, strong tetragonal distortions are observed at the local scale and a less-distorted tetragonal structure is observed at longer length scales. In Rietveld refinements, the latter is modeled using a tetragonal phase. Since the peak overlap in these two-phase compositions limits the ability to model the local-scale structures as tetragonal, it is approximated in the refinements as a cubic phase. Collectively, the results demonstrate that alloying BT with BZT results in increased disorder and disrupts the long-range ferroelectric symmetry present in BT, while the large tetragonal distortion present in BZT persists at the local scale.