Electrical Transport in Terbium-iron-transition Metal Mixed Oxides

Abstract

This paper presents the results of electrical conductivity (σ) and seebeck coefficient (S) measurements on the pressed pellets of TbFeTO₄ (where T = Fe, Cr, Mn and Co) in the temperature range 400-1200 K. It has been found that these compounds are essentially electronic semiconductor with σ values lying in the range 10^-7 to 10^-3Ω^-1 m^-1 around 408 K. The maximum value of σ has been observed for TbFeMnO₄ and lowest for TbFe₂O₄. The log σT vs. T^-1 as well as S vs. T^-1 plots for the studied compounds have three linear regions separated by break temperatures T₁ and T₂ which are same in both the plots. The sign of S indicates that charge carriers are electrons in the studied temperature range. The electrical conduction in first range (T < T₁) is extrinsic and occurs due to donor type centers. In the second (T₁ < T < T₂) and third (T > T₂) ranges, electrical conduction is hopping type and occurs due to hopping of electrons from Fe²⁺ to Fe³⁺ in TbFe₂O₄, Co²⁺ to Fe³⁺ in TbFeCoO₄ and Fe²⁺ to Cr³⁺ in TbFeCrO₄. In TbFeMnO₄, electrical conduction occurs due to hopping of electrons from Mn³⁺ to Mn⁴⁺ centers in the temperature range T₁ < T < T₂ and from Fe²⁺ to Mn³⁺ centers in the range T > T₂.