Phase transition-enabled MnFe2O4 nanoparticles modulated by high-pressure with enhanced electrical transport properties

Pressure tuned structure-function relationship of MnFe2O4 nanoparticles is established for the first time by the mean of XRD, Raman and impedance spectra measurements. The application of external pressure results in a continuous lattice contraction of MnFe2O4. In the pressure range of 17.1-26.3 GPa, MnFe2O4 undergoes a cubicto-orthorhombic structural phase transition. Meanwhile, increasing pressure from ambient state to 37.1 GPa leads to the continued improvement of conductivity of the sample. Further analysis shows that the hybridized enhancement between Fe-3d and O-2p orbits and the decrease in band gap upon compression are the major factors to affect the conductivity of MnFe2O4. With the release of pressure, the sample recovers to the cubic spinel structure, but the grain boundary resistance and dielectric constant are still decreased by nearly 3 orders of magnitude compared with the counterpart before compression. By analysis of Hall-effect and electron microscope on the recovered sample, the increased interfaces density and accordingly the enlarged carrier concentration account for the obvious improvement of electrical properties in MnFe2O4 nanoparticles. In this work, such a high enhancement in conductivity due to the annealing of pressure-cycle provides a newly feasible pathway to design ferrite materials with excellent electrical and electrochemical properties, and expands their application prospects in electronic devices and microwave industries, etc.