Interactions between components of SrTi0.98Nb0.02O3−δ–YSZ and SrTi0.98Nb0.02O3−δ–CeO2 composites Related Investigation of sensing mechanism of Nasicon electrocatalytic sensors in nitrogen dioxide and ammonia Characterization of CaTi0.9Fe0.1O3 / La0.98Mg0.02NbO4 composite