Structural, dielectric, and conduction behaviour of A-site deficient SrNaNbO ceramics

The crystallographic and electrical properties of A-site deficient Sr x Na 1−2 x NbO 3 ( x = 0.00, 0.05, 0.10, 0.15, 0.20, and 0.25) perovskites have been studied by X-ray diffraction, scanning electron microscopy, dielectric spectroscopy, impedance spectroscopy and polarisation against electric field loops. Despite complexities in the microstructural evolution due to the formation of a NaNb 3 O 8 liquid phase, the crystallographic and dielectric properties show much clearer trends. The introduction of A-site vacancies shows an almost linear expansion of the pseudo-cubic unit cell volume of ∼0.05 Å 3 per at%, stabilising the ferroelectric P 2 1 ma Q-phase. Compositions x > 0.10 show increasingly relaxor-like behaviour in the dielectric properties and impedance spectroscopy shows increasing conductivity and tan δ values associated with predominantly electronic conduction from x = 0.05 to 0.25. Measurements in N 2 at 600 °C show progressively n-type behaviour with increasing levels of A-site vacancies due to the increased tendency to lose under-bonded O 2− ions and therefore partially reduce some Nb 5+ to Nb 4+ ions. Although it is not possible to fully establish the electrical properties of our undoped NaNbO 3 ceramics, we propose they contain mixed ionic-electronic behaviour with the clear presence of a weak n-type dependent grain boundary contribution to the total conductivity. The structural and electrical properties of A-site deficient Sr x Na 1−2 x NbO 3 (0 ≤ x ≤ 0.25) ceramics have been studied by X-ray diffraction, electron microscopy, dielectric spectroscopy, impedance spectroscopy and polarisation against electric field.