Voltage tunable dielectric properties of oxides at nanoscale: TiO2 and CeO2 as model systems

• Published in: Superlattices and microstructures Vol. 91; pp. 182 - 187
• Main Authors: Prakash, T., Tamil Selvan, A., Suraiya Begum, S.N.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-03-2016
• Subjects: Dielectric constant; Grain boundary double Schottky potential barrier height; Impedance spectroscopy; Dielectric constant; Grain boundary double Schottky potential barrier height; Impedance spectroscopy
• ISSN: 0749-6036; 1096-3677
• DOI: 10.1016/j.spmi.2016.01.006

Carrier transport through electrically active grain boundaries has been studied under biased condition using Solartron 1260 impedance/gain phase analyzer with an applied AC potential of 250 mV in the frequency range 1 Hz–1 MHz for nanocrystalline TiO2 and CeO2 as the model systems. Prior to the measurement both the materials were converted into cylindrical pellets with (8 mm diameter and 1 mm thick) by applying uni-axial pressure of 4 ton using a hydraulic press, then sintered at 300, 450 and 600 °C for 30 min for TiO2 sample and for the case of CeO2 it was done at 300, 600 and 900 °C for 30 min. Further, they were characterized using powder X-ray diffractometer (XRD) and transmission electron microscopy (TEM) to know the crystal structure, average crystallite size and morphology. The impedance measurements were performed at room temperature under applied DC bias voltages from 0 to 3 V in the periodic increment of 0.2 V. The observed applied bias voltage effect on dielectric constant of both the systems was analyzed with ‘grain boundary double Schottky potential barrier height model’ for different grain sizes. The percentage of voltage tunable dielectric constant (T%) as a function of frequency was estimated for all the grain sizes and it was found to be increase with reduction of grain size. Our experimental findings reveal the possibilities of utilizing these nanocrystals as a potential active material for phased array antenna since both the samples exhibits T% = 85% at 100 Hz frequency.
•Single phase TiO2 and CeO2 were prepared using wet-chemical methods, then as-prepared materials were converted into cylindrical pellets with (8 mm diameter and 1 mm thick) by applying uni-axial pressure of 4 ton using a hydraulic press, then sintered at 300, 450 and 600 ºC for 30 min for TiO2 sample and for the case of CeO2 it was done at 300, 600 and 900 ºC for 30 min.•Influence of grain boundary effect on the dielectric properties of nanocrystalline TiO2 and CeO2 as a function of applied bias voltages. Since nanocrystals have large number of grain boundary interfaces in which the local atomic arrangements are different from those of the crystal lattice. If the bias voltage is applied more and more, then the suppression of grain boundary potential barrier height can be realized with an apparent reduction in the permittivity values. It was experimentally observed in both the systems for all the crystallite sizes and the percentage of tunability at 100 Hz for 9 nm CeO2 and 6 nm TiO2 was found to be ~85%.•Percentage of voltage tunable dielectric constant, tunability (T%) is very high in both the systems, it explores the possibilities of applying these nanocrystals as a potential material for phased array antenna applications.