Current Understanding of Structure–Processing–Property Relationships in BaTiO₃–Bi(M)O₃ Dielectrics

Abstract

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.

Designing pseudocubic perovskites with enhanced nanoscale polarization

“…The archetype system of this type is lead zirconium titanate [1], the properties in which are amplified at the rhombohedral-tetragonal morphotropic phase boundary (MPB). For decades, the search for commercially viable formulations has focused on such MPB compositions but, recently, a different class of perovskite oxides has emerged that also exhibits technologically attractive functional properties [e.g., [2][3][4][5][6][7][8][9][10][11]. These materials are multicomponent metal components) solid solutions of distorted end-members but which by powder diffraction appear to have the cubic (pseudocubic) symmetry of an ideal ABO3 perovskite structure (space group Pm3m, lattice parameter a Å .…”

“…In some of the known pseudocubic perovskite solid solutions, the distortions are coherent over a scale of only a few nanometers (or less), whereas in others their coherence extends over a longer range but remains weak and, therefore, unresolvable even with high-resolution diffractometers. Examples of the first type of structures can be found in BaTiO3-BiMO3 (M=Sc, Mg½Ti½, Zn½Ti½) systems [11], which yield dielectric properties of interest for high-energy capacitor applications; and in Bi½K½TiO3-(Bi,Nd)FeO3 ceramics that generate strong, temperature-stable electromechanical responses [8]. An example of the second type is (K,Bi)(Nb,Fe)O3, which displays a widely tunable band gap in a long-range but weakly correlated ferroelectric structure [9].…”

Defect mechanisms in BaTiO3‐BiMO3 ceramics

“…Several Bi M O 3 compounds, for example, (Bi 1/2 Li 1/2 )TiO 3 , Bi(Mg 2/3 Nb 1/3 )O 3 , Bi(Mg 1/2 Ti 1/2 )O 3 , Bi(Zn 2/3 Nb 1/3 )O 3 , Bi(Zn,Sc,Ti)O 3 have been shown to exhibit the same effect on the electrical properties when added to BaTiO 3 . Studies to determine the type of charge carrier in these solid solutions are scarce, however, some of them have been shown to exhibit a simultaneous p‐type to n‐type transition of majority charge carriers, along with resistivity enhancement .…”

“…In the last two decades, bismuth has found special attention in following two fields of research. (i) The solid solutions of Bi‐perovskite with BaTiO 3 (BT) help improve their properties for energy storage applications across various length scales . Several BT‐Bi M O 3 ( M = metal) ceramics have promising properties as compared with traditional BT‐based ceramics in terms of temperature‐stability of permittivity, energy density values, insulation properties and others .…”

“…The study of structural changes that govern macroscopic properties in BT‐Bi M O 3 ceramics is often complicated by differences in local and average displacements . For relaxor BT‐Bi M O 3 ceramics, the macroscopic structure appears nearly cubic, while there are still significant distortions present at local level . Using the Pair Distribution Function (PDF) approach, it was found that the local tetragonal distortion in BT‐BZT is disrupted over a length scale of ~10 unit cells, leading to a pseudo‐cubic appearance .…”