Abstract
Impedance spectroscopy technique has been used to study the effect of grains and grain boundaries in a heterostructure constituted with ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 (BST) layers grown by pulsed laser deposition technique on (1 0 0) oriented MgO substrate. Frequency and temperature dependence of the complex impedance and complex electric modulus were measured in (BST20u.c,/LSMO10u.c)25 over a temperature range of 360–500 K. Non-Debye relaxation was observed in the investigated system. An equivalent circuit and the modified constant phase element circuit were used to describe the impedance spectroscopy, and excellent agreement between the calculated and measured curves was obtained from each model. The activation energy (∼0.25 eV–0.48 eV) has been obtained from Arrhenius fitting of different relaxation processes present in the material, and its characteristic values support a model of Maxwell–Wagner relaxation in the heterostructured film at elevated temperatures and in the low frequency range. The electrical ac and dc conductivity studies showed that the heterostructure possesses negative temperature coefficient of resistance properties. It was found that the resistance of grain boundaries was larger than the resistance of intra-grains.
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