Crystal structure and oxygen nonstoichiometry of the Ho xSr 1-xCoO 3-δ

Abstract

Samples with overall composition Ho xSr 1-xCoO 3-δ within the range 0.05 ≤ x ≤ 0.9 were prepared by a solid-state technique at 1100 °C in air. Single-phase Ho xSr 1-xCoO 3-δ oxides were obtained within the range 0.05 ≤ x ≤ 0.30. Solid solutions of Ho0.05Sr0.95CoO3-δ and Ho 0.1Sr 0.9CoO 3-δ were indexed in the cubic structure (Pm3m sp. gr.) with the unit cell parameters a = 3.846 Å and a = 3.842 Å, respectively. Further introduction of holmium leads to a change of crystal structure from cubic to a tetragonal 2a p × 2a p × 4a p superstructure. All samples with x > 0.3 were multiphase, containing a saturated solid solution with approximate composition Ho 0.3Sr 0.7CoO 3-δ with Ho 2O 3 and CoO. The change of oxygen nonstoichiometry was measured by thermogravimetric analysis within the temperature range 25 ≤ T (°C) ≤ 1100. The absolute value of oxygen nonstoichiometry was calculated from the results of chromatometric titration. Thermal expansion coefficients of Ho 1-xSr xCoO 3-δ were measured by dilatometry within the temperature range 25 ≤ T (°C) ≤ 1100 in air. © 2012 Materials Research Society.