arXiv 2407.075272024-07-10cond-mat.mtrl-sci

BaFe$_{0.5}$Nb$_{0.5}$O$_3$双钙钛矿结构陶瓷的低温电导率

Low temperature conductivity of BaFe$_{0.5}$Nb$_{0.5}$O$_3$ double perovskite structure ceramics

Vijay Khopkar, Balaram Sahoo

AI总结：

本研究探究20-300K下多晶BFN陶瓷的载流子输运机制，明确电子与离子电导的来源及活化能，验证其电导符合OLP、VRH等模型并测得缺陷密度，为理解其低温电导机制提供依据。

摘要：

本研究探究了20K至300K低温区间内，多晶铌铁酸钡（BFN，BaFe$_{0.5}$Nb$_{0.5}$O$_3$）陶瓷中载流子的起源、类型及其输运机制。晶粒内的观测点缺陷与晶界区域的表面缺陷是电子电导的来源，而晶界区域的偶极子是离子电导的来源，这两种相互独立的电子电导与离子电导共同构成了BFN样品的总电导率。经计算，晶界区域电子传导与晶粒区域离子传导所需的活化能分别为317 meV和17 meV。晶粒区域的电子电导符合Jonscher幂律。对随温度变化的频率指数的分析表明，晶粒的电子电导遵循重叠大极化子隧穿（OLP）模型。电导率的温度依赖性符合Mott变程跳跃模型（VRH），显示跳跃范围随温度降低而增大。测得的晶粒缺陷密度为$3.17 \ imes 10^{17}$ eV/cm$^3$。通过Schankenberg模型理解了声子对电导率的贡献：110 meV的活化能对应多声子（光学声子与声学声子）过程，1.6 meV的活化能仅对应声学声子过程。本系统研究为深入理解多晶BFN陶瓷的低温电导机制提供了依据。

英文摘要：

In this work, we explore the origin and type of charge carriers, and their transport mechanism in polycrystalline barium-iron-niobate (BFN, BaFe$_{0.5}$Nb$_{0.5}$O$_3$) ceramics, at lower temperatures between 20K and 300K. The observed point defects at grain andsurface defects at grain boundary region are responsible for the electronic conductivity, whereas dipoles at grain boundary region are responsible for the ionic conductivity, these independent electronic and ionic conductivity were responsible for the total conductivity of our BFN sample. The required activation energy for conduction of electrons in grain boundary region and ions in grain region were calculated to be 317 meV and 17 meV respectively. The electronic conductivity of grain region obey Jonscher's power law. Analysis of the temperature dependent frequency exponent suggest that the electronic conductivity of grain follows the overlapping large polaron tunneling (OLP) model. The temperature dependent conductivity follows the Mott variable range hopping model(VRH), showing hopping range increases with decreasing temeprature. The defect density of the grain obtained to be $3.17 \times 10^{17}$ eV/cm$^3$. The contribution of phonon to the conductivity understood by considering Schankenberg model, activation energy of 110 meV corresponds to the multiphonon (both optical and acoustic) and 1.6 meV corresponds to acoustic phonon only. Our systematic study provides in-depth understanding of the low temperature conductivity mechanism of polycrystalline BFN ceramics.

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