Shukri, Khalid; (1999) Microstructure and response studies of chromium titanium oxide gas-sensitive resistors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of this project was to investigate the effects of microstructure and composition on the response of gas sensitive resistors fabricated from chromium titanium oxide powders. The methods of preparation were varied in order to vary the microstructure in the resulting devices. The chromium oxide starting material was obtained both by decomposition of ammonium dichromate, and by colloidal precipitation. Titanium dioxide was obtained by colloidal precipitation. Mixing both with and without the addition of surfactants was explored. Several compositions were prepared in each method and sintered at various firing temperatures. Changing the composition by varying the titanium content had a small effect on the response, which increased slightly as the titanium content was increased. Changing the microstructure by altering the preparation method or increasing the sintering time had a more prominent effect on the response, the response decreasing as the structure became more agglomerated and increasing to some of the test gases when the small grains were grown through prolonged sintering times. Agglomeration and grain-growth in the printed layers dominated the behaviour of the devices prepared from the powders. It was discovered that certain bonding agents used in printing the gold electrodes migrated into the oxide layer during the process of firing the oxide onto the substrate. The concentration of these fluxes was dependent on the preparation temperature of the sensors, and as this increased both the response of the sensor and its variation with depth within the porous oxide layer were affected.

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