The Role of the Grain Boundary on the Resistivity of Pb(Fe 1/2 Nb 1/2 )O 3 at Room Temperature
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`The Role of the Grain Boundary on the Resistivity of Pb(Fe1/2Nb1/2)O3 at Room Temperature Sang-Bop Lee, Kwang-Ho Lee and Hwan Kim School of Materials Science and Engineering, Seoul National University, Seoul, 151-744, Korea ABSTRACT The effect of changing sintering temperature on the grain boundary properties and the room temperature resistivity (ρRT) of Pb(Fe1/2Nb1/2)O3 (PFN) was investigated. Monitering the temperature dependence of resistivity showed that the ρRT’s of 1050oC and 1150oC-sintered specimen were 1011Ω·cm and 104Ω·cm respectively, but the resistivity above 300oC became nearly identical. The previous model, that the low resistivity of PFN is due to the electron hopping between Fe2+ and Fe3+ driven by the reduction of PFN, couldn’t explain this phenomenon, and the reconsideration of the Fe reduction revealed that the difference of electron concentration between the 1050oC and 1150oC-sintered specimen couldn’t exceed one order of magnitude. The role of the grain boundary was introduced in order to account for this phenomenon. INTRODUCTION PFN, a member of the Pb-based ferroelectric materials, also has the large dielectric constant and low sintering temperature, and in addition its intermediate characteristics between normal and relaxor ferroelectrics have been reported as the key to clarifying the relaxor mechanism [1,2]. In spite of these advantages, there is one critical problem preventing the usage of all the systems containing PFN, which is the high dielectric loss originated from its low resistivity. Many reports have explained the origin of low resistivity as being the result of PFN reduction as follows [3-5]: 1 2Fe ×Fe + O×O → 2Fe Fe ' + VO•• + O 2 (g) (1) 2 Fe Fe ' ↔ Fe ×Fe + e'
(2)
According to this model, the formation of oxygen vacancies results in Fe reduction, and the electrons hop from the Fe2+ to Fe3+ sites. And Wang et. al. verified the coexistence of Fe2+ and Fe3+ in PFN and PFT with Mössbauer spectroscopy, and supported this theory [6,7]. This theory explains the relatively lower resistivity of PFN than other Pb-based complex perovskites. But monitoring the temperature dependence of resistivity in this study raises some questions, which couldn’t be explained by Fe reduction. In this study, the effect of changing sintering temperature on the grain boundary properties and the room temperature resistivity (ρR.T.) of PFN was investigated. The role of the grain boundary on the room temperature D10.15.1 Downloaded from https://www.cambridge.org/core. Gothenburg University Library, on 03 Feb 2020 at 08:28:05, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-718-D10.15
resistivity of PFN was investigated, and the previous theory was reconsidered based on the typical oxidation-reduction mechanism. EXPERIMENTAL DETAILS Reagent grade oxide powders of PbO (99.9%, High Purity Chem. co., Japan), Nb2O5 (99.9%, High Purity Chem. co., Japan) and Fe2O3 (99.9%, High Purity Chem. Co., Japan) were used to prepare the Pb(Fe1/2Nb1
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