In this paper we report semiconductor to metal transition and polaron conduction in nanostructured cobalt ferrite. The material was prepared by the coprecipitation technique. Average particle size was determined to be ∼10 nm by x-ray diffraction and transmission electron microscope analysis. A detailed electrical characterization was performed in the frequency range 20 Hz–2 MHz and temperature range between 300 and 400 K. Nanostructured cobalt ferrite exhibits semiconductor behaviour from 300 to 330 K. From 330 to 400 K it has metallic behaviour. The change at ∼330 K is attributed to a change in cation distribution as obtained from Mössbauer spectroscopy. The ac conductivity of cobalt ferrite followed σac ∝ ω s dependence. The observed variation of the exponent ‘s’ with temperature suggests that overlapping large polaron tunnelling is the dominant conduction mechanism from 300 to 400 K and in the frequency range 20 Hz–2 MHz.

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Thermally induced semiconductor to metal transition has been investigated for tin doped cobalt ferrite nanoparticles using impedance spectroscopy in a wide frequency range (100 Hz-2 MHz) from 300 K to 400 K. In addition dc measurements are carried out in temperature range from 285 K to 410 K. Temperature dependence of impedance spectroscopy and dc resistivity reveal semiconductor to metal transition around 360 K. Metallic nature of the system above 360 K has been attributed to dominancy of delocalized charge carriers Fe3+–Fe2+/Co3+–Co2+ interactions over localized charge carriers Fe3–O2−–Fe3+/Co2+–O2−–Co2+ interactions. Interesting temperature dependent electrical behavior of the grain boundaries is reported and has been discussed in term of depletion space-charge layer in the vicinity of grain boundaries.

A porous core photonic crystal fiber (PCF) for transmitting terahertz waves is reported and characterized using finite element method. It is shown that by enveloping an octagonal core consisting of only circular air holes in a hexagonal cladding, it is possible to attain low effective material loss that is 73.8% lower than the bulk material absorption loss at 1.0 THz operating frequency. Moreover, a low confinement loss of 7.53×10–5 cm−1 and dispersion profile of 1.0823±0.06 ps/THz/cm within 0.7–1 THz are obtained using carefully selected geometrical design parameters. Other guiding properties such as single-mode operation, bending loss, and effective area are also investigated. The structural design of this porous core PCF is comparatively simple since it contains noncomplex lattices and circular shaped air holes; and therefore, may be implemented using existing fabrication techniques. Due to its auspicious guiding properties, the proposed fiber may be used in single mode terahertz imaging and other short distance terahertz applications.