Surface Exchange of Oxygen in La1−x Sr x FeO3−δ (x = 0, 0.1)

Wærnhus, Ivar; Grande, Tor; Wiik, Kjell

doi:10.1007/s11244-011-9712-z

Cited by 16 publications

(15 citation statements)

References 25 publications

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“…In the absence of systematic experimental data on BiFeO 3 it is useful to look at other Fe‐containing complex oxides. Interestingly, Sr‐doped LaFeO 3 was found experimentally to exhibit analogous behavior to that predicted for BiFeO 3 , with conductivity that is orders of magnitude lower at low oxygen partial pressures [σ(789°C) = 10 (Ohm m) −1 at p (O 2 ) = 10 −20 ] than at high partial pressures [σ(789°C) = 4000 (Ohm m) −1 at p (O 2 ) = 1] …”

Section: Dielectric Permittivity Electrical Conductivity and Defectsmentioning

confidence: 75%

BiFeO₃ Ceramics: Processing, Electrical, and Electromechanical Properties

et al. 2014

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Dedicated to Prof. Dr. Marija Kosec, our Mari cka, who left us after a long struggle in her tenacious spirit in December 2012.Bismuth ferrite (BiFeO 3 ), a perovskite material, rich in properties and with wide functionality, has had a marked impact on the field of multiferroics, as evidenced by the hundreds of articles published annually over the past 10 years. Studies from the very early stages and particularly those on polycrystalline BiFeO 3 ceramics have been faced with difficulties in the preparation of the perovskite free of secondary phases. In this review, we begin by summarizing the major processing issues and clarifying the thermodynamic and kinetic origins of the formation and stabilization of the frequently observed secondary, nonperovskite phases, such as Bi 25 FeO 39 and Bi 2 Fe 4 O 9 . The second part then focuses on the electrical and electromechanical properties of BiFeO 3 , including the electrical conductivity, dielectric permittivity, high-field polarization, and strain response, as well as the weak-field piezoelectric properties. We attempt to establish a link between these properties and address, in particular, the macroscopic response of the ceramics under an external field in terms of the dynamic interaction between the pinning centers (e.g., charged defects) and the ferroelectric/ferroelastic domain walls. J ournalFeature BiFeO 3 ceramics. Among the most interesting are the BiFe-O 3 -PbTiO 3 (BFPT) 14,16 and BiFeO 3 -BaTiO 3 (BFBT) 15,17,18 systems, which provide both enhanced piezoelectricity and a high T C at the MPB, the latter exceeding that of Pb(Zr,Ti)O 3 (PZT) (T C~6 50°C for BFPT, T C~6 00°C for BFBT and T C~3 50°C for PZT at the MPB). In addition, a number of other BiFeO 3 -based lead-free compositions are presently the subject of intensive studies, including BiFeO 3 -REFeO 3 (RE = La, Nd, Sm, Gd, Dy), 19-21 BiFeO 3 -AETiO 3 (AE = Mg, Ca, Sr), 22-26 BiFeO 3 -Bi 0.5 K 0.5 TiO 3 27 , and BiFe-O 3 -Bi(Zn 0.5 Ti 0.5 )O 3 . 28 The piezoelectric properties of many of these ceramic systems have not yet been characterized systematically.The processing of single-phase BiFeO 3 ceramics is difficult; however, significant progress has been made recently, particularly in relation to the identification of the origins of the frequently formed nonperovskite, secondary phases. In addition, the complex relationship between processing and defects, on one hand, and the high-and weak-field electrical and electromechanical properties, on the other, has been addressed to some extent. Up to now, a lot of these new findings, in particular those relating to processing and domain-switching behavior, have not been considered sufficiently or are even ignored in the literature. Along with the aim of presenting a detailed overview of the past and recent results on BiFeO 3 ceramics, this absence or poor coverage of some important topics was one of the motivations that led us to prepare a comprehensive article, which also includes new data.The review comprises two topics on BiFeO 3 that are the most controvers...

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Section: Dielectric Permittivity Electrical Conductivity and Defectsmentioning

confidence: 75%

BiFeO₃ Ceramics: Processing, Electrical, and Electromechanical Properties

et al. 2014

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“…Surface exchange and bulk diffusion coefficients obtained from ECR measurements have been shown to exhibit a discrepancy between steps performed from high to low (reduction) and low to high (oxidation) oxygen partial pressures in a number of reports [3,4,5,6,7]. The apparent difference in oxidation and reduction values is in general more pronounced at decreasing p O 2 .…”

Section: Motivation and Initial Resultsmentioning

confidence: 99%

“…By performing a step change in oxygen partial pressure, which will lead to a change in the oxygen non-stoichiometry, and monitoring the electronic conductivity response, the change in non-stoichiometry over time and thus the oxygen transport kinetics can be deduced. The validity of this technique, especially for materials exhibiting high oxygen exchange rates and/or at low partial pressures of oxygen, has however been questioned [3,4]. In this study we will investigate the validity of ECR in terms of transport coefficient assessment both from an experimental and a theoretical modelling approach.…”

Section: Introductionmentioning

confidence: 99%

The Significance of Gas-Phase Mass Transport in Assessment ofk_chemandD_chem

Lohne

Søgaard

Wiik

2013

J. Electrochem. Soc.

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In this work, the validity of electrical conductivity relaxation (ECR) as a method for the assessment of chemical surface exchange, k chem , and bulk diffusion, D chem , coefficients is investigated with respect to mass transport limitations in the gas phase. A model encompassing both the oxygen surface exchange, mass transport in the bulk sample and the gas phase was set up and solved under different conditions using finite element software. It is found that the transport of oxygen in the gas phase is insufficient at low oxygen partial pressures, causing a concentration boundary layer at the sample surface to develop. This significantly decreases the driving force for oxygen exchange. The effect of mass transport limitations on the computed apparent transport coefficients is shown to be pronounced and surface exchange coefficients are shown to deviate as much as one order of magnitude from the set values. When mass transport limitations are pronounced, a discrepancy between oxidation and reduction values of the apparent k chem and D chem is evident and modelled apparent activation energies for k chem are shown to decrease significantly. The validity of the apparent transport coefficients can be improved by changing the experimental parameters, however the surface exchange coefficient is extremely sensitive to insufficient transport of oxygen in the gas phase and improvements are in general marginal. A criteria for the validity of D chem is introduced while no such measure could be introduced for k chem . The effect of experimental parameters and material properties on mass transport limitations are presented and general recommendations concerning the assessment of k chem and D chem are given.

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“…Densities/porosities were determined by the Archimedes method using isopropanol as immersion liquid. Direct current (DC) conductivity measurements were performed by using a DC standard 4-point technique (in-house built setup [31]) at temperatures between RT and 900 º C in synthetic air at 100 º C temperature intervals and thermal equilibration at each temperature. Seebeck coefficient measurements were done in synthetic air at temperatures between RT and 900 º C using Omega software and a ProboStat TM sample holder (NORECS, Norway) inserted into a vertical tube furnace, utilizing the inherent temperature gradient along the furnace length.…”

Section: Materials Characterizationmentioning

confidence: 99%