Dielectric and electrical characterization of hematite (α-Fe 2 O 3 ) nanomaterials synthesized by thermal decomposition of iron(III)citrate

Hematite nanomaterials were obtained on thermal decomposition of (i) iron (III) citrate, (ii) 3:1 mixture of iron (III) citrate and malonic acid, and (iii) 3:1 mixture of iron (III) citrate and glucose. The average particle size (22–55 nm) of the nanomaterials was significantly affected by the co-precursor. Frequency and temperature dependence of the dielectric constant, dielectric loss and ac conductivity of these hematite nanomaterials were studied. High values of the real part of dielectric constant ( ε^' ) were observed in the low-frequency region which eventually reached a frequency independent constant value above 10 kHz. A decrease in the value of ε^' with increase in temperature and an increase in the ε^' value with increase in the particle size were noticed. For the entire set of nanomaterials, the dielectric loss was found to have a decreasing tendency with increase in frequency with small humps at higher frequencies owing to the existence of relaxing dipoles. These nanomaterials were found to be non-Debye type and poly-dispersive. For all hematite nanomaterials, the ac conductivity followed Jonscher’s power law, and the particle-size-dependent conduction mechanisms (correlated-barrier-hopping for D = 22.5 nm and non-overlapping small polaron tunneling for D > 22.5 nm) in these nanomaterials were established. The dc conductivity values were measured as a function of temperature to confirm the semiconducting nature of these nanomaterials. The activation energy values derived from the dc conductivity studies decreased with increasing size of the nanoparticles. Analysis of the electric modulus study showed that the relaxation peaks shifted towards lower frequency with increasing temperature and found that the electrical conduction and dielectric polarization follow the same mechanism in these nanomaterials. The thermally synthesized hematite nanomaterials exhibited particle-size-dependent high dielectric constant and lower dielectric loss which highlight the synthetic method adopted as well as the synthesized materials’ suitability for applications.