SELECTIVITY AND COMPOSITION DEPENDENCE OF RESPONSE OF GAS-SENSITIVE RESISTORS .2. HYDROGEN-SULFIDE RESPONSE OF CR-2-XTIXO3+Y

Titanium-substituted chromium oxides, Cr2-xTixO3+y, form solid solutio ns in the range 0 less than or equal to x less than or equal to 0.4, w ith surface enrichment of Ti, The electrical behaviour of these compou nds was consistent with charge compensation by chromium vacancies, The conductance of porous, small-grain-size specimens could be interprete d as surface trap-limited, with O-ads(-) as the surface species, Both molecular and dissociative chemisorption of H2S was observed, Exposure to H2S at low concentration in air resulted in the formation of sulfa te groups at the surface as well as surface hydroxylation, There was a range of binding energy of the surface sulfate: strongly bound sulfat e caused a permanent, temperature-dependent conditioning of the surfac e characterized by a permanent change in the air baseline resistance a fter an initial dose of H2S. The origin of the gas response of the ele ctrical resistance was attributed to the surface reaction of H2S with O-ads(-) to form adsorbed sulfate, which desorbs as sulfur dioxide, Th e electrical response was repeatable and stable.