engleski

Structure of zirconium titanate ceramics for humidity sensors

It has been reported recently that the ZrTiO4 (ZT) ceramic can possess humidity sensing ability [1]. The sensitivity and stability of sensing are related to the porous structure of the ceramics. In this work porous ZT ceramics was prepared by sintering ball milled powder precursor. The preparation of ceramics from ball milled precursor decreases the sintering temperature without additives and thus reduces the energy necessary for solid state synthesis of pure ceramics. The variation of ceramics porosity from highly porous ceramics to almost completely dense ceramics was tailored by changing the sintering temperature. Powder precursor produced by high-energy ball milling of TiO2 and ZrO2, facilitates the solid state reaction toward ZrTiO4 even before heat treatment [2]. Prior to sintering the ball milled powder precursor was compacted at 180 MPa. The ceramics were prepared by sintering for 8 h at 1100, 1200, 1300 and 1400 °C. The structure of the ceramics was obtained by combining the results of Raman spectroscopy (RS), rietveld refinement of X-ray powder diffraction (XRD) patterns, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). A multiphase character of the ceramics sintered at 1100 °C is evident by RS, XRD and HRTEM measurements ; while a comparison of SEM, HRTEM and XRD corroborate that the formed sintered grains are polycrystalline with small crystalline sizes. The observations obtained by RS, XRD and HRTEM undoubtedly identified the samples sintered at 1200, 1300 and 1400 °C as single phase ZrTiO4, although the morphology, sintered grains, pores and crystallites are different in sizes and shapes and dependent on the sintering temperature. The pores in ZT-1200 ceramics are open as observed by SEM and TEM measurements and of similar sizes as in ZT-1100 ceramics. By further increase of sintering temperature to 1300 °C some pores become closed, while in ZT-1400 ceramic only small number of closed pores was observed. The SEM images show regular growth of sintered grains with increase of temperature from 1100 to 1400 °C. On the contrary, the Rietveld refinement of XRD patterns indicated anomaly for the ceramics sintered at 1300 °C in both crystallite size and microstrain i.e. their values are lower in comparison with the ceramics sintered at 1200 °C. A higher order in the ZT-1300 ceramics structure is supported by RS measurements, where some Raman bands are better resolved, and HRTEM observations of well defined grain boundaries.

zirconium titanate ceramics; structure

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