Abstract
Spinel vanadates possess rich physics arising from the interaction among spin, orbital and lattice degrees of freedom. We report the dielectric properties of polycrystalline Fe1.8V1.2O4. A thermally activated dielectric relaxation appeared in low temperature due to the inhomogeneous conductivity between grains and grain boundaries. We found an artificial ferroelecticity in this sample. An abnormal frequency-independent dielectric peak appeared at room temperature when the samples were measured during warming in ambient air. However, this peak disappeared in the following cooling process. By dielectric frequency spectrum and equivalent circuit analysis in detail, we found the sample had a surface layer in warming but not in cooling process. We also confirmed that this surface layer was induced by the adsorption of water, which is responsible for the dielectric peak.
Highlights
Spinel vanadates possess rich physics arising from the interaction among spin, orbital and lattice degrees of freedom
The phenomenological constant phase element (CPE), which is a capacitive element with non-Debye behavior, is used to replace the ideal capacitor with Debye behavior due to the imperfect blocking characteristics of GBs and EIs [12,13,14]
Our equivalent circuit (EC) is composed of a set of parallel ideal resistor (Rg) and ideal capacitor (Cg) circuit (RC-circuit) for grains and a set of parallel ideal resistor (Rgb) and non-ideal CPE circuit (R-CPE) for grain boundaries as schematically shown in the upper right inset of Figure 1(c)
Summary
Spinel vanadates possess rich physics arising from the interaction among spin, orbital and lattice degrees of freedom. An abnormal frequency-independent dielectric peak appeared at room temperature when the samples were measured during warming in ambient air. This peak disappeared in the following cooling process. With partial replacement of V by Fe ions, the spinel Fe1+xV2 xO4 (0 x 2) family has a cation distribution of Fe2+(Fex3+V2 x3+)O4 for 0 x 0.35 and Fe3+(Fe2+Fex 13+V2 x3+)O4 for 1 x 2 [2], where the bracket indicates the B site Both cation ions are magnetic and have orbital degrees of freedom. Due to the complex interactions among charge, lattice, spin, and orbital degrees of freedom, the spinel vanadates show a variety of interesting electric and magnetic properties. We observed a dielectric relaxation in a low temperature range and a frequency independent dielectric peak in a high temperature range
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