Crystal structure and oxygen nonstoichiometry of the Ho x Sr1−x CoO3−δ

Samples with overall composition Ho x Sr 1− x CoO 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 x Sr 1− x CoO 3−δ oxides were obtained within the range 0.05 ≤ x ≤ 0.30. Solid solutions of Ho 0.05 Sr 0.95 CoO 3−δ and Ho 0.1 Sr 0.9 CoO 3−δ were indexed in the cubic structure ( Pm3m sp. gr.) with the unit cell parameters a = 3.846 A and a = 3.842 A, respectively. Further introduction of holmium leads to a change of crystal structure from cubic to a tetragonal 2 a p × 2a p × 4a p superstructure. All samples with x > 0.3 were multiphase, containing a saturated solid solution with approximate composition Ho 0.3 Sr 0.7 CoO 3−δ with Ho 2 O 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− x Sr x CoO 3−δ were measured by dilatometry within the temperature range 25 ≤ T (°C) ≤ 1100 in air.