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TY - THES AU - Siemons, Maike TI - High throughput methods for synthesis and impedance characterisation of ABO3 gas sensing materials CY - Aachen PB - Publikationsserver der RWTH Aachen University M1 - RWTH-CONV-114568 SP - 201 S. : Ill., graph. Darst. PY - 2007 N1 - Aachen, Techn. Hochsch., Diss., 2006 AB - This PhD thesis deals with the preparation and characterisation of resistive thick-film gas sensors by use of high throughput impedance spectroscopy. Since the 1960s semiconducting resistive gas sensors are used in a wide range of applications. However, commercial systems show disadavantages which might be overcome by the use of new materials. The sensitivity and selectivity of new sensing materials cannot be predicted resulting from the complex interplay of different parameters. In sensor research materials are typically discovered by a “one at a time” strategy that is both time consuming and costly. A possible way to overcome these problems is the use of high throughput research which enables the screening of a multitude of different materials in short time. The polyol method enabled the preparation of a wide range of different ABO3 compounds. The fast and simple reaction method allowed mixing on the molecular level and bulk doping of the materials during the preparation. Nanoscaled compounds that crystallised after temperature treatment were achieved. The prepared ABO3 materials offered various properties and possibilities for gas sensing materials, especially for high temperature use. The prepared materials were used to fabricate active layers on electrode structures to form gas sensors. Substrate plates of diverse metal-doped oxides were rapidly synthesised and screened with the high throughput impedance spectroscopy setup. 64 different materials could be screened on one multi electrode substrate. The measurements were performed between 200 and 500°C and the test gases were hydrogen, carbon monoxide, nitrogen oxides, ethanol, and propylene in synthetic air. Two different material systems, CoTiO3 and LnMO3 (Ln=lanthanide, M=Cr, Fe), were presented in detail. All prepared materials showed typical p-type semiconduncting behaviour. Incorporation of various volume dopants into CoTiO3 changed the resistance and improved the sensing properties of the base material. Lanthanum doping was found to be most effective. By introducing to CoTiO3:La a number of surface and solid surface dopants in different concentrations, the sensitivity was influenced. Secondly, the preparation and characterisation of 25 lanthanide orthochromites LnCrO3 and orthoferrites LnFeO3 was described. They all showed hydrocarbon and NO2 sensitivity. One of the outstanding materials, SmFeO3, was investigated further towards volume and surface doping influences. From the measurements on LnMO3 materials, a trend in sensing performance as a function of composition was found. The sensitivity of these materials was inversely connected to the binding energy of the compounds. Changes of the M-site cation had more influence on the sensitivity than changes in the Ln-site. The materials shown here have high potential for gas sensing applications. With the use of high throughput impedance spectroscopy, a great number of different compounds were screened in a short amount of time. Only the great number of measuring data achieved under comparable conditions allowed to find structure-property relations. LB - PUB:(DE-HGF)11 UR - https://publications.rwth-aachen.de/record/52336 ER -