The relaxational properties of compositionally disordered ABO₃perovskites

Abstract

Random lattice disorder produced by chemical substitution in ABO3 perovskites can lead to the formation of dipolar impurities and defects that have a profound influence on the static and dynamic properties of these materials that are the prototypical soft ferroelectric (FE) mode systems. In these highly polarizable host lattices, dipolar entities form polar nanodomains whose size is determined by the dipolar correlation length, rc, of the host and that exhibit dielectric relaxation in an applied ac field. In the very dilute limit (< 0.1at.%) each domain behaves as a non-interacting dipolar entity with a single relaxation time. At higher concentrations of disorder, however, the domains can interact leading to more complex relaxational behaviour. Among the manifestations of such behaviour is the formation of a glass-like relaxor (R) state, or even an ordered FE state for a sufficiently high concentration of overlapping domains. After a brief discussion of the physics of random-site electric dipoles in dielectrics, this review begins with the simplest cases, namely the relaxational properties of substitutional impurities (e.g., Mn, Fe and Ca) in the quantum paraelectrics KTaO3 and SrTiO3. This is followed by discussions of the relaxational properties of Li-and Nb-doped KTaO3 and of the strong relaxors in the PbMg1/3Nb2/3O3 and La-substituted PbZr1−xTixO3 families. Some emphasis will be on the roles of pressure and applied dc biasing electric fields in understanding the physics of these materials including the R-to-FE crossover.

Electrical Processes in Polycrystalline BiFeO3 Film

“…As reported, the activation energy for dipolar relaxation in ferroelectrics is about 100~400meV (Samara, 2003). Therefore, the relaxation process with the activation energy of 230 meV in our samples may be a kind of dipolar relaxation process related to oxygen vacancies.…”

“…The relationship between the logarithm of measuring frequency and the reciprocal of T m is nearly linear. It is suggested that the relationship between the measuring frequency and T m following the Arrehenius law, which can be expressed as (Samara, 2003) …”

Bias-field effect on the temperature anomalies of dielectric permittivity inPbMg1∕3Nb2∕3

“…We assume a close relationship to the dynamic behavior of PNR's, which are believed to be at the heart of the relaxor behavior. 1,28 We should notice that the nearly vertical line is close to the Vogel-Fulcher temperature T VF , where the PNR's size strongly changes 29 and above which the PNRs are dynamic ͑T VF is always close to the ZFHaFC line, which marks the disappearance of macroscopic metastable ferroelectric states͒. At low bias fields, the phase transition is diffuse due to coupling between Q and random fields.…”

Effect of cobalt doping on the dielectric response of Ba0.95Pb0.05TiO3 ceramics

“…Co 3+ acceptor ions are incorporated into the Ti 4+ -lattice site because of their similar ionic radii and oxygen vacancies are generated in order to compensate the valence. The resultant acceptor-oxygen vacancy dipoles in highly polarizable lattice can form either polar nanoregions (PNRs) like in ferroelectric relaxors [22][23][24] or can result in an internal bias which is formally equivalent to the energy difference of the dipolar defects between the accessible directions of the spontaneous polarization and affects the dielectric response [25][26][27]. Due to high polarizability of the ABO 3 lattice the dipolar defects polarize the neighboring part of the lattice forming the polar nanoregions the size of which is determined by temperature -dependent correlation length of the host.…”