Electronic Properties and Defect Structure of Ti407: Correlation of Magnetic Susceptibility, Electrical Conductivity, and Structural Parameters via EPR Spectroscopy

Abstract

Variable temperature EPR studies of polycrystalline Ti₄O₇ and preliminary single crystal studies have been interpreted in relation to the static magnetic susceptibility, electrical conductivity and X‐ray diffraction data obtained on Ti₄O₇ samples from the same chemical run. This has facilitated the calculation of the mobility, the electrical conductivity, and the electronic effective mass in both the metallic and semiconducting regions of Ti₄O₇. Below ≈ 149 K a hopping mechanism dominates the conduction properties and at ≈ 120 K, μ_hop ≈ 4 × 10⁻⁶ cm²/Vs and σ_cal ≈ 1.49 × 10⁻³ (Ω cm)⁻¹. This latter value is in good agreement with σ_meas ≈ 3 × 10⁻³ (Ω cm)⁻¹ obtained experimentally. An electronic effective mass of 5.6 m_e has been obtained for the semiconducting region and is consistent with a value of ≈ 5 m_e determined from thermoelectric and Hall effect data for the low temperature phase of Ti₂O₃. Above 149 K optical mode phonon scattering and ionized defect scattering combine to yield a total mobility of μ_T ≈ 0.6 cm²/Vs and σ_cal ≈ 1.43 × 10³ (Ω cm)⁻¹ which is in excellent agreement with the electrical conductivity results at 295 K.