482 / 2019-03-18 14:18:53

Correlation between Structural Changes and Electrical Transport Properties of Spinel ZnFe2O4 Nanoparticles under high Pressure

spinel ferrite, phase transition, electrical transport properties, grain boundary

全体主题 > High Pressure Physics and Materials Science

Significant anomalies are observed in the properties of the grain boundary resistance (Rgb), the relaxation frequency (fmax), and the relative permittivity (Ɛr) in the ZnFe2O4 nanoparticles (ZFO NPs) under the pressures around 17.5-21.5 GPa. These anomalies are believed to be correlated with a cubic-to-orthorhombic phase transition of ZFO at the pressures at about 21.9 GPa, which is found to be partially reversible. Pressure-tuned dielectric properties are measured for the cubic and the orthorhombic phases of ZFO, respectively. Remarkably, Rgb decreases up to six orders of magnitude as a function of pressure in the cubic phase. Dielectric polarization is obviously strengthened with increased fmax and decreased Ɛr with pressure in the orthorhombic phase. Furthermore, it is confirmed that external pressure effectively improves the electrochemical stability of the sample based on the cycled measurements of impedance spectra at various pressures. The changes of the complex permittivity (Ɛ', Ɛ") and the dielectric loss tangent (tan δ) with frequency reveal the irreversible increase of the dielectric loss accompanied by the phase transition. Magnetoresistivity measurements indicate that ZFO NPs are superparamagnetic under high-pressure up to 40 GPa. TEM images reflect the decrease of grain boundary number and some local amorphization of grains after compression, which provides good explanations for the changes of the electrical transport properties as a function of pressure. Herein, structural and electrical properties of ZnFe2O4 NPs generated are preserved by quenching the high-pressure phase to ambient conditions, thus providing great choices of ferrites materials for a variety of applications.