Synthesis, Sintering and Dielectric Properties of Nano Structured High Purity Titanium Dioxide

High purity nanosized titanium dioxide (TiO2) powders were synthesized by precipitation method using Ti(IV)-isopropoxide as starting material. Well-crystallized and phase pure anatase TiO2 powders with a particle size about 10nm can be obtained by calcination of freeze-dried precipitates at 400 o C. The sinterability of powders calcined at 400 o C and 700 o C were compared with commercial TiO2 powders with similar particle size. The electrical and dielectric properties of the TiO2 bulk samples sintered at various temperatures were measured and correlated with the microstructural development. INTRODUCTION Due to its wide applications such as photocatalysts, 1 solar cells, 2 gas sensors 3 and dielectric materials 4 , TiO2 has attracted great scientific and technological interest. TiO2 powders are commonly prepared by means of the sulphate process, the chloride process, 5 or sol-gel process. 6 In this study, high purity and nanosized TiO2 powders were prepared to obtain nanostructured dielectric materials with low loss factor and leakage current. EXPERIMENTAL High purity nanosized TiO2 powders were prepared by precipitation of Ti(IV)-isopropoxide followed by freeze-drying of the precipitates. 50ml Ti(IV)-isopropoxide (Ti[OCH(CH3)2]4 99.995%, Alfa-Aesar) was added into 1L deionized water under constant stirring. The precipitate was mixed with 1L of 2-Propanol (99.5% Alfa-Aesar) and ultrasonicated (SONICS, Vibra-Cell, Newtown, CT, USA) for 1 minute to deflocculate the hydroxides. Gel-like precipitates were freeze-dried (Genesis SQ Freeze Dryers, Winchester, Hampshire,UK) at -25 o C under vacuum for 72hrs. Fluffy precursor powders were calcined at various temperatures (400 o C, 500 o C, 600 o C and 700 o C) for 1h with a heating and cooling rate of 2 o C/min and 5 o C/min, respectively. The crystallinity and phase composition of the calcined powders were determined by X-ray diffraction (XRD, Philips X’Pert, Holland). The size and morphology of powder were observed by Scanning Electron Microscopy (SEM, Hitachi S-4700, Japan). Pellets were prepared by uniaxial pressing at 50MPa followed by iso-static pressing at 300MPa using powders calcined at 400 o C and 700 o C. Commercially available TiO2 powders (99.9%, Sigma Aldrich) were also pressed into pellets following the same procedure. Sintering was performed at 900 o C, 950 o C and 1000 o C for 2hrs in oxygen atmosphere with a heating rate of 4 o C/min. Samples about 10mm in diameter and 0.8mm in thickness were used for electrical property Page 1 of 8