Electrical properties of zinc ferrites ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{O}}_4$ with 0≤x<0.3

Resistivity and Seebeck coefficients are reported in the range 50 K<T<300 K for zinc ferrite single crystals ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$ ${\mathrm{Zn}}_{\mathit{x}}$ ${\mathrm{O}}_4$ in the composition range 0≤x<0.3. Samples with 0<x≲0.012 exhibited first-order phase transformations at the Verwey transition; in the range 0.012<x≲0.036 second- or higher-order continuous phase changes were observed. No transitions were encountered for x≳0.036. The electrical properties of the zinc ferrites are analyzed in terms of hopping charge-carrier transport involving valence fluctuations on cations located on octahedral sites. The electrical properties and Verwey transitions of ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$ ${\mathrm{Zn}}_{\mathit{x}}$ ${\mathrm{O}}_4$ and ${\mathrm{Fe}}_{3\left(1\mathrm{-}\mathrm{\delta }\right)}$ ${\mathrm{O}}_4$ match very well with the compositional correspondence x⇄3δ. Various implications of the above findings are discussed.