Effects of Vacancies on Properties of Relaxor Ferroelectrics: a First-Principles Study (original) (raw)
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Effects of vacancies on the properties of disordered ferroelectrics: A first-principles study
Physical Review B, 2007
A first-principles-based model is developed to investigate the influence of lead vacancies on the properties of relaxor ferroelectric Pb(Sc 1/2 Nb 1/2)O 3 (PSN). Lead vacancies generate large, inhomogeneous, electric fields that reduce barriers between energy minima for different polarization directions. This naturally explains why relaxors with significant lead vacancy concentrations have broadened dielectric peaks at lower temperatures, and why lead vacancies smear properties in the neighborhood of the ferroelectric transition in PSN. We also reconsider the conventional wisdom that lead vacancies reduce the magnitude of dielectric response.
A Brief Review on Relaxor Ferroelectrics and Selected Issues in Lead-Free Relaxors
Relaxor ferroelectricity is one of the most widely investigated but the least understood material classes in the condensed matter physics. This is largely due to the lack of experimental tools that decisively confirm the existing theoretical models. In spite of the diversity in the models, they share the core idea that the observed features in relaxors are closely related to localized chemical heterogeneity. Given this, this review attempts to overview the existing models of importance chronologically, from the diffuse phase transition model to the random-field model and to show how the core idea has been reflected in them to better shape our insight into the nature of relaxor-related phenomena. Then, the discussion will be directed to how the models of a common consensus, developed with the so-called canonical relaxors such as Pb(Mg 1/3 Nb 2/3)O3 (PMN) and (Pb, La)(Zr, Ti)O3 (PLZT), are compatible with phenomenological explanations for the recently identified re-laxors such as (Bi 1/2 Na 1/2)TiO3 (BNT)-based lead-free ferroelectrics. This review will be finalized with a discussion on the theoretical aspects of recently introduced 0−3 and 2−2 ferroelectric/relaxor composites as a practical tool for strain engineering.
High-T m relaxor ferroelectrics: 0.3BiScO 3 – 0.6PbTiO 3 – 0.1Pb " Mn 1Õ3 Nb 2Õ3 …O 3
High-T m relaxor materials are being developed for high-temperature high-power density electrotransduction applications and high-temperature capacitors in automobile applications. A relaxor ferroelectric material of composition 0.3BiScO 3 -0.6PbTiO 3 -0.1Pb(Mn 1/3 Nb 2/3 )O 3 having a very high dielectric maximum of ϳ350°C is reported. The relaxor behavior is confirmed by studying polarization relaxation and frequency and temperature dependent dielectric behavior. The dielectric constant in the low-temperature region of 10°CϽTϽ150°C is found to be independent of the frequency with a temperature gradient of ץ/ץTϭ2.5/°C. The room-temperature magnitude of dielectric constant is ϳ600.
Journal of Alloys and Compounds, 2019
Studies of the dielectric relaxation and the electrical conductivity processes for Sr 0.15 Ba 0.85 Bi 2 Nb 2 O 9 relaxor ferroelectric ceramic are carried out to evaluate the influence of extrinsic and/or intrinsic defects on the a.c. response. The Cole-Cole model and the Universal Dielectric Response are used to determine the nature of these defects. The temperature dependence of both processes in the range 30 C approximately 210 C is associated to the response of polarons, in disordered surrounding, to the applied electric field. For higher temperatures, the main contribution to both dielectric relaxation and electrical conductivity processes is attributed to electrons that result from the ionization of oxygen vacancies. The study provides indirect evidence on the relaxor freezing temperature.
Relaxor Pb(Mg1/3Nb2/3)O3: A Ferroelectric with Multiple Inhomogeneities
Physical Review Letters, 2009
Despite intensive studies on PbðMg 1=3 Nb 2=3 ÞO 3 (PMN) relaxor, understanding the exact nature of its giant dielectric response and of its physical ground state is a fundamental issue that has remained unresolved for decades. Here, we report a comprehensive study of PMN relaxor crystal, and show that (i) its anomalous dielectric behavior in a broad temperature range results from the reorientation of polarization in the crystal, and (ii) the PMN relaxor is essentially a nanosized ferroelectric material with multiscale inhomogeneities of domain structure in addition to the well-known inhomogeneities of chemical composition and local symmetry. Such inhomogeneities are believed to play a crucial role in producing the huge and enigmatic physical effects in relaxor system, and may be used to design other new systems with giant effects such as a relaxor system.
2011
The complex structure of relaxor ferroelectrics comprises polar nanoregions (PNRs) which appear upon cooling below the Burns temperature and quenched compositional (chemical) disorder. The relation between the polar nanostructure and compositionally ordered regions (CORs) often observed in relaxors has been the subject of extensive theoretical investigations; however, the experimental data, especially concerning Pb(B0 1=3B00 2=3)O3-type complex perovskite relaxors, are rather
Ferroelectric relaxor behaviour in Pb(Fe0.5Ta0.5)O3
Indian Journal of Physics, 2009
The relaxor ferroelectric lead iron tantalate, Pb(Fe 0.5 Ta 0.5)O 3 (PFT) is synthesized by Coulombite precursor method. The X-ray diffraction pattern of the sample at room temperature shows a cubic phase. The field dependence of dielectric response is measured in a frequency range 0.1 kHz-1 MHz and in a temperature range from 173-373 K. The temperature dependence of permittivity (ε ′) shows broad maxima at various frequencies. The frequency dependence of the permittivity maximum temperature (T m) has been modelled using Vogel-Fulcher relation.
Journal of Applied Physics, 2012
In situ temperature-dependent Raman-scattering experiments under an external dc electric field E have been performed on PbSc 0:5 Ta 0:5 O 3 (PST) and Pb 0:78 Ba 0:22 Sc 0:5 Ta 0:5 O 3 (PST-Ba) in order to give further insights into the atomistic mechanism of polar coupling in perovskite-type (ABO 3) relaxor ferroelectrics near the intermediate characteristic temperature T ?. The polarized Raman spectra collected under an electric field E applied along the cubic [100], [110], or [111] crystallographic direction were analyzed in terms of hard-mode spectroscopy. The T ? ðEÞ dependence was derived from the behavior of the phonon mode near 230 cm À1 localized in off-centered B-site cations. In the case of stoichiometric PST, the increase of T ? with E is much stronger when the field is applied along [111] than when E is along [100] or [110]. This indicates that the actual polar B-cation shifts are along the cubic body diagonals, implying a rhombohedral structure of the polar nanoregions. The T ? ðEÞ-dependence reveals that the local structural distortions associated with locally coupled polar displacements of B-site cations reach saturation near 0.5 kV/cm. When Pb 2þ is partially replaced by Ba 2þ , the strong increase of T ? with E occurs if the electric field is applied along the [110] direction. This indicates that the substitution disorder on the A-site lowers the symmetry of the polar nanoregions to orthorhombic or monoclinic. The T ? ðEÞ dependence determined from the B-cation localized mode shows saturation near 2.0 kV/cm, indicating that the zero-field structural state of PST-Ba exhibits less coupled polar shifts of B-site cations as compared to that of PST. According to the E-dependence of the Raman scattering near 55 cm À1 , for both compounds the overall response of the Pb system to the external electric field in the vicinity of T ? ðEÞ resembles antiferroelectric behavior, which along with the fact that the coupling between the B-site cations is ferroelectric, suggests that the polar nanoregions in Pb-based relaxors are ferrielectric in nature. V
Dielectric behaviors of Pb(Fe2∕3W1∕3)-PbTiO3 relaxors: Models comparison and numerical calculations
Journal of Applied Physics, 2007
Regarding the dielectric characteristics of the diffusion phase transition (DPT) in ferroelectric relaxor materials, several researchers have provided similar but different laws to explain these phenomenon. These laws, presented by Burfoot et al. and Eiras et al., have been proven to provide a better explanation, especially the dielectric diffusion phenomenon, of the incomplete DPT materials if compared with the models presented by Smolensky, and Isupov. However, the differences in fitting adaptability and the physical and mathematical meanings between these two laws have never been discussed. In this paper, we analyze these two laws in the (1−x)Pb(Fe2∕3W1∕3)-xPbTiO3 [(1−x)PFW-xPT] relaxor system using the statistical regression theory. We find that the laws of both Burfoot and Eiras demonstrate the same adaptability and provide smaller estimation bias on the samples than the models of Smolensky and Isupov, despite the complete or incomplete DPT characteristics. When x is smaller, t...
A Transition From Relaxor To Normal Ferroelectric: An Overview
International journal of engineering research and technology, 2013
Relaxors like PMN and PMN based materials proved to be promising candidate for multilayer capacitors (MLCs) and electrostriction actuators , pyroelectric bolometers, piezoelectric sensors replacing normal ferroelectrics such as BaTiO 3 and PZT. The compositional heterogeneity resulting from scale of ordering at the B-site influences relaxor to normal ferroelectric behavior .The genesis and growth of PMR resulted in ferroelectric transition. The distribution of curie points in PMR leads to DPT behavior. The dielectric relaxation is attributed to the relaxation of domain walls. Strong charge effects developed as a result of 1:1 ordering at the B-site limits the ordering of domains hence the size growth. The difference between NFE and RFE along with mechanism influencing the transition from RFE to NFE have been discussed.