LaMn_{1-x} Fe_xO_3晶内电不均匀性与静态介电常数的成分变化
Intragrain electrical inhomogenities and compositional variation of static dielectric constant in LaMn_{1-x}Fe_xO_3
摘要：
对Fe替代的LaMn_{1-x} Fe_xO_3（0 <= x <= 1.0）样品进行了体直流电阻率和介电常数随温度和频率的测量。不同频率下的介电常数实部的温度依赖性表明，当x >= 0.15时，在低温下，ε_0与频率和温度无关，其中ε_0随着x的增加而增加，在x = 0.5时达到最大值，然后在x = 0.70时急剧下降，表现出随着x的进一步增加而进一步增加的趋势。在x = 0.70时，δ_s的急剧下降与晶体结构由菱方晶转变为斜方晶有关。当x从0.15增加到0.50时，观察到Δ ε_s ~ 43%的显著增加。此外，由于x <= 0.50的氧退火，Δ ε_s显著增加（在x = 0.5时高达~ 17%）。当x <= 0.50时，满足变程跳跃模型的低温电导率与电导率随x的增加有关。在低温下的复阻抗和模量平面的分析表明，在化合物的晶粒内部的电不均匀性。
英文摘要：
Bulk dc resistivity and dielectric constant measurements with temperature and frequency have been performed in LaMn_{1-x}Fe_xO_3 (0 <= x <= 1.0) as a result of Fe substitution both for the as-synthesized and oxygen annealed samples. Temperature dependence of real part of dielectric constant at different frequencies show a frequency and temperature independent value (epsilon_s) at low temperature for x >= 0.15 where epsilon_0 rises with x reaching a maximum at x = 0.5 and then it decreases sharply at x = 0.70 showing a further increasing trend with the further increase in x. The sharp drop of epsilon_s at x = 0.70 is correlated with the structural change from rhombohedral to orthorhombic structure. A considerable increase of epsilon_s ~ 43% is observed for an increase of x from 0.15 to 0.50. Furthermore, epsilon_s is increased considerably (up to ~ 17% at x = 0.5) due to the oxygen annealing for x <= 0.50. The low temperature resistivities satisfying Variable Range Hopping model are found to be related with the increase of epsilon_s with x for x <= 0.50. The analysis of the complex impedance and modulus planes at low temperature indicates the electrical inhomogeneities in the grain interior of the compounds.
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