Date of Graduation
2013
Document Type
Thesis
Degree Type
MS
Committee Chair
Torsten Granzow
Abstract
Magnetic and electric properties of a nano-sized particulate composite thin film consisting of non-percolating 11 nm superparamagnetic CoF e2O4 (CFO, Cobalt Ferrite) particles dispersed in a pure perovskite P b[Zr0.52T i0.48]O3 (PZT, Lead Zirconate Titanate) matrix have been studied. The main objective of the study was to fabricate a composite with high particle loading conserving good dielectric breakdown strength (DBS) and leakage currents, which are commonly decreased at high loadings levels due to percolation. In this work, a composite with 38 vol% particulate loading showing no sign of percolation was prepared and characterized by DBS, leakage and polarization measurements. This improvement is explained with an analytical model proposed by Kusy, where percolation is increased when the diameter of the particulates is larger than the diameter of the matrix precursor. As a result of this, the leakage currents measurements, at 667 kV/cm, indicated an increase from 3 ∗ 10−6 to 6 ∗ 10−5 A/cm2 ( 5 ∗ 10−10 and 9 ∗ 10−9 S/m ) for the samples with 1 and 38 vol% particulate loading, respectively, that remains lower than the leakage current of the PZT thin film, 6∗10−3A/cm2 (9 ∗ 10−7 S/m), due to the reduction in crystallite size and grain orientation. No percolation
was observed by the DBS characterization either, the increase of conductive CFO particles from 1 to 38 vol% decreased the DBS from 1800 kV/cm to 1200 kV/cm, respectively, which is still considerably higher than the DBS of the PZT thin film, 700 kV/cm, due to same reasons. Moreover, the behavior of the DBS for different particulate loadings is explained by an non-percolative analytical model consisting in the grain size effect and reduction of the effective film thickness given by the conductive phase, showing a good fit to the experimental data. This is in contrast to previously reported particulate composites, with magnetic and electric properties, that show percolation for low amounts of particulate loadings destroying the electric properties of the ferroelectric phase. The design proposed in this work is of great interest for the fabrication of films with high magnetic particulate loadings without degrading the electric properties for magnetoelectric applications.
Recommended Citation
Muchenik Cena, Tomas Ignacio, "Improvement of the dielectric breakdown strength and leakage currents of nano-sized CFO PZT particulate composite thin film with high particle loadings by controlled percolation for magnetoelectric applications." (2013). Graduate Theses, Dissertations, and Problem Reports (ETD). 11148.
https://researchrepository.wvu.edu/etd/11148