Changes in macroscopic behaviour through segregation in niobium doped strontium titanate
Bäurer, M; Zagonel, LF; Barrett, N; Hoffmann, MJ
JOURNAL OF PHYSICS, 2008, Conference Series 94
The electrical properties of electroceramics are largely governed by their complex microstructure which must be precisely controlled for applications (as, for example, sensors, actuators and capacitors). In this study, the dependence of niobium segregation in strontium titanate on different sintering parameters is shown. 1.2 mol% Nb doped SrTiO3 was sintered at 1420°C in air for different times and with different post sintering cooling rates. Scanning electron microscopy images provided evidence of morphological differences among the prepared samples. X-ray diffraction revealed a decrease in lattice parameter due to niobium leaving titanium substitutional sites and going to grain boundary zones. X-ray photoemission spectroscopy has shown substitutional or segregated niobium has a 5+ chemical state. Impedance spectra analysis permitted estimation of changes in grain boundary thickness in agreement with other results. The analysis establishes that niobium segregation happens during cooling and is diffusion controlled, depending on grain size.