Synthesis of a 12R-type hexagonal perovskite solid solution Sr 3 NdNb 3−x Ti x O 12−δ and the influence of acceptor doping on electrical properties

• Published in: Dalton transactions : an international journal of inorganic chemistry 2015, Vol.44 (16), p.7643-7653
• Main Authors: Chinelatto, Adilson L., Boulahya, Khalid, Pérez-Coll, Domingo, Amador, Ulises, Tabacaru, Corina, Nicholls, Simon, Hoelzel, Markus, Sinclair, Derek C., Mather, Glenn C.
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/C5DT00170F

A solid solution forms for Sr 3 NdNb 3−x Ti x O 12−δ with approximate limits 0 ≤ x ≤ 0.06. The system crystallizes with a 12R-type hexagonal perovskite structure in the space group R 3̄, as determined by neutron diffraction and selected area electron diffraction. The electrical properties of the end members have been investigated by impedance spectroscopy in the temperature range 550–800 °C under various gas atmospheres and as a function of oxygen and water-vapour partial pressure. Proton transport dominates under wet oxidising conditions in the temperature range 550–700 °C, as confirmed by the H + /D + isotope effect. Acceptor doping considerably enhances proton conductivity with a value of 3.3 × 10 −6 S cm −1 for the bulk response of x = 0.06 at 700 °C in moistened air. The presence of a −¼ slope for both doped and undoped samples in the range 10 −19 ≤ p O 2 ≤ 10 −8 atm at 900 °C indicates n-type transport under reducing conditions following the extrinsic model attributable to acceptor centres. The conductivity is essentially independent of p O 2 at 600 °C under dry oxidising conditions, consistent with oxide-ion transport; a positive power-law dependence at higher temperature indicates extrinsic behaviour and a significant electron–hole contribution. The dielectric constant at RT of nominally stoichiometric Sr 3 NdNb 3 O 12 is ε r ∼ 37, with a moderately high quality factor of Q × f ∼ 16 400 GHz at f r ∼ 6.4 GHz. The temperature coefficient of resonant frequency of x = 0 is τ f ∼ 12 ppm °C −1 , which lowers to −3 ppm °C −1 for the Ti-doped phase x = 0.06.