Dielectric relaxation in Ba-based layered perovskites

Abstract

Ferroelectric materials with Bi-layered structure such as SrBi2Ta2O9 and SrBi2Nb2O9 are now intensively investigated in view of their applications in nonvolatile computer memories and high-temperature piezoelectric transducers. When Sr2+ is substituted with Ba2+, a significant disorder is induced and the material exhibits broadening of the phase transition. Such broadening is essential for applications since it allows achieving smooth temperature characteristics while maintaining high dielectric and piezoelectric properties. In this work, stoichiometric dense BaBi2Nb2O9 (BBN) ceramics are sintered using a mixed oxide route. Dielectric and ferroelectric properties are investigated in a broad range of temperatures and frequencies. Strong dispersion of the complex relative dielectric permittivity is observed including typical relaxor features such as shift of the permittivity maximum with frequency and broadening of the relaxation time spectrum with decreasing temperature. The dielectric relaxation obeys the Vögel–Fulcher relationship with anomalously low freezing temperature (Tf≈100 K), which is much lower than the permittivity maximum in the radio-frequency range. Polarization hysteresis loops testify linear properties of BBN at all temperatures above Tf. The properties of BBN ceramics are compared to conventional relaxor systems such as Pb(Mg, Nb)O3 and (Pb, La)(Zr, Ti)O3.

Dielectric Relaxation Phenomenon in Ferroelectric Perovskite-related Structures

“…On the other hand, for the layered ferroelectric perovskites (Aurivillius family, [Bi 2 O 2 ] 2+ [A n−1 B n O 3n+1 ] 2− ), the oxygen vacancies prefer to stay in the Bi 2 O 2 layers, where their effect upon the polarization is considered to be small, instead of the octahedral site, which controls the polarization. The origin of the dielectric behavior for these materials have been associated to a positional disorder of cations on A-or B-sites of the perovskite layers that delay the evolution of long-range polar ordering (Blake et al, 1997;Ismunandar & Kennedy, 1999;Kholkin et al, 2001;Haluska & Misture, 2004;Huang et al, 2006). For at least several decades, the dielectric response of ferroelectric materials (polycrystals, single crystals, liquids, polymers and composites) has been of much interest to both experimentalists and theorists.…”

“…i) marked frequency dispersion in the vicinity of temperature (T m ) where the real part of the dielectric permittivity (ε') shows its maximum value, ii) the temperature of the corresponding maximum for ε' and the imaginary part of the dielectric permittivity (ε'') appears at different values, showing a frequency dependent behavior, iii-the Curie-Weiss law is not fulfilled for temperatures around T m . The materials have attracted considerable attention due to their large remanent polarization, lead-free nature, relatively low processing temperatures and other characteristics (Miranda et al, 2001;Kholkin et al, 2001;Lee et al, 2002;Nelis et al, 2005;Huang et al, 2006;Watanabe et al, 2006). The origin of the relaxor behavior for these materials has been associated to a positional disorder of cations on A or B sites of the perovskite blocks that delay the evolution of long-rage polar ordering (Miranda et al, 2001).…”

“…However, the substitution of Ca 2+ for Bi 3+ in the bismuth layers increases the electrical conductivity. The Aurivillius family exhibit a dielectric behavior characteristic for ferroelectric relaxors (Miranda et al, 2001;Kholkin et al, 2001), e.g. i) marked frequency dispersion in the vicinity of temperature (T m ) where the real part of the dielectric permittivity (ε') shows its maximum value, ii) the temperature of the corresponding maximum for ε' and the imaginary part of the dielectric permittivity (ε'') appears at different values, showing a frequency dependent behavior, iii-the Curie-Weiss law is not fulfilled for temperatures around T m .…”

Microstructure and electrical properties of Aurivillius phase (CaBi2Nb2O9)1−x(BaBi2Nb2O9)x solid solution

“…The number of octahedra along the c-axis between two neighboring ͑Bi 2 O 2 ͒ 2+ layers is indicated by m. 2 Aurivillius phase materials have generated increasing attention due to their potential use in nonvolatile ferroelectric random-access memory 3,4 and high-temperature piezoelectric applications 5 because of their fatigue-free properties and high Curie point, respectively. Some Aurivillius phase compounds show interesting relaxor and multiferroic properties when Ba/lanthanides 6,7 and Fe ͑Ref. 8͒ are on the A-and B-site in the general formula, respectively.…”

High temperature lead-free relaxor ferroelectric: Intergrowth Aurivillius phase BaBi2Nb2O9–Bi4Ti3O12 ceramics

“…Compared to the normal ferroelectric behavior of BIT, both BBN and BBTN show much stronger frequency dependence of dielectric constant and loss, as is the case for a typical relaxor. 50 The dielectric constants of BBN and BBTN decrease dramatically as the frequency increases. On the contrary, the dielectric constant of BIT just shows a slight decrease.…”