Transport and Gas Sensing Properties of Cadmium Titanate Nanofibers

Abstract

In this work AC & DC transport and sensing properties of cadmium titanate (CdTiO3) nanofibers have been investigated. Study of AC transport properties were explored using temperature dependent impedance spectroscopy. DC transport measurements were carried out using temperature dependent current-voltage (I-V) characterization. Cadmium titanate/polyvinyl-pyrrolidone composite nanofibers were prepared using an electrospinning technique. When temperature increased from 600 C to 1200 C the phase changes in CdTiO3 nanofibers were observed. The nanofibers annealed at 600 C had ilmenite phase with a very small amount of CdO. Pure ilmenite phase was obtained at 950 C. Annealing at 1000 C yielded pure perovskite phase. Further increase in annealing temperature resulted in rutile TiO2 phase. The average diameters of nanofibers annealed at 600 °C and 1000 °C were found to be ~150 nm and ~600 nm, respectively. The length of nanofibers was ~100 μm. Analysis of frequency dependent AC conductivity in ilmenite phase revealed correlated barrier hoping (CBH) conduction from 318 K – 498 K. In perovskite phase, thermally activated small polaron hopping (SPH) conduction played dominant role from 320 K – 420 K. In DC transport, Ohmic behavior was observed at low voltages followed by space charge limited current (SCLC) with traps at higher voltages at all temperatures (200 K – 420 K). Humidity sensing characteristics of ilmenite phase were investigated. Fast response time and recovery time of 4 seconds and 6 seconds was observed, respectively. The sensor was highly sensitive and showed a reversible response with small hysteresis of less than 7%. Long term stability of the sensor was confirmed during 30 days test. Oxygen sensing using ilmenite and perovskite phase CdTiO3 nanofibers was also performed. The gas response of the ilmenite nanofibers sensor to oxygen gas was twice as high as that of the perovskite phase. The response and recovery times were 120 seconds and 23 seconds, respectively for ilmenite phase, whereas response and recovery times were 156 seconds and 50 seconds, respectively for the perovskite phase. Better oxygen sensing characteristics of ilmenite phase were attributed to large surface area ~9.41 m2/g and porosity.