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We investigate electrical and dielectric properties of cadmium titanate (CdTiO3) nanofiber mats prepared by electrospinning. The nanofibers were polycrystalline having diameter ∼50 nm-200 nm, average length ∼100 μm and crystallite size ∼25 nm. Alternating current impedance measurements were carried out from 318 K – 498 K. The frequency of ac signal was varied from 2 – 105 Hz. The complex impedance plots revealed two depressed semicircular arcs indicating the bulk and interface contribution to overall electrical behavior of nanofiber mats. The bulk resistance was found to increase with decrease in temperature exhibiting typical semiconductor like behavior. The modulus analysis shows the non-Debye type conductivity relaxation in nanofiber mats. The ac conductivity spectrum obeyed the Jonscher power law. Analysis of frequency dependent ac conductivity revealed presence of the correlated barrier hopping (CBH) in nanofiber mats over the entire temperature range

We have investigated the phase changes in CdTiO3 nanofibers as the annealing temperature of nanofibers was increased from 600 to 1200 °C. The nanofibers annealed at 600 °C were ilmenite with a very small amount of CdO. Upon annealing at 950 °C, CdO was completely removed. Annealing at 1000 °C yielded pure perovskite nanofibers, and at temperatures above 1100 °C rutile TiO2 nanofibers were obtained. Brunauer-Emmett-Teller (BET) analysis showed that with increase in annealing temperature the surface area of nanofibers was decreased. The nanofibers annealed at 600 °C have the higher surface area of ∼9.41 m(2)/g. Then oxygen sensors using CdTiO3 nanofibers annealed at 600 °C (ilmenite) and 1000 °C (perovskite) were fabricated. The sensitivity of the ilmenite nanofibers sensor was 2 times than that of the perovskite nanofibers sensor. The response and recovery times were 120 and 23 s, respectively, for the ilmenite nanofibers sensor, whereas response and recovery times were 156 and 50 s, respectively, for the perovskite nanofibers sensor. Better oxygen characteristics of ilmenite nanofibers are attributed to their large surface area and porosity. Therefore, we believe that ilmenite CdTiO3 nanofibers are potential candidates to develop practical oxygen sensors.

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Temperature and frequency dependent ac electrical measurements were used to explore density of states, conduction mechanisms and dielectric properties of nickel disulfide (NiS2) nanoparticles. The NiS2 nanoparticles were prepared by conventional one step solid state reaction method at 250 °C. X-ray diffraction (XRD) confirmed cubic phase of prepared nanoparticles. Scanning electron microscope (SEM) images revealed presence of irregular shaped nanoparticles as small as 50 nm. The ac electrical measurements were carried out from 300 K to 413 K. Two depressed semicircular arcs from 20 Hz to 2 MHz showed presence of bulk and grain boundary phases in NiS2 nanoparticles at all temperatures. Small polaron hopping conduction from 300 K to 393 K and correlated barrier hopping conduction mechanism at temperatures higher than 393 K was observed. High value of density of states (of the order of 1024 eV−1cm−3) was calculated from ac conductivity. At low frequencies high values (of the order of 104-107) of real part of dielectric constant (ε′) were observed at different temperatures. These observations suggest that NiS2 nanoparticles may find applications in electronic devices.

Relative humidity (RH) sensing properties of zinc oxide nanofibers (ZNF), synthesized using electrospinning technique, were studied by impedance spectroscopy. RH sensors were fabricated with two different electrodes (Au and Ni) using lithography on top of the nanofibers deposited on Si/SiO2 substrate. Compare with the Ni electrode sensor, Au electrode sensor exhibits larger sensitivity and quicker response/recovery. Capacitance, electrical conductivity and electrical modulus were studied at 40%-90% RH as a function of the frequency of the applied AC signal in the frequency range of 10−2-106 Hz. The corresponding response and recovery times are 3s and 5s for Au, and 6s and 10s for Ni electrode sensor, respectively. The sensors exhibited a reversible response with small hysteresis of less than 4% and 12% for Au and Ni electrodes respectively. Stability of the sensor device with Au electrode was confirmed by testing the device for 13 days. The excellent sensing characteristics and comparison of sensors with different electrode materials may offer an effective route for designing and optimizing RH sensors.