Effect of Ti-substitution on the Electrical Properties of MnNb2O6- δ

• Published in: Chemistry of materials 2007-05, Vol.19 (9), p.2310-2315
• Main Authors: Orera, A, García-Alvarado, F, Irvine, J. T. S
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm062856u

Ti-substituted MnNb2O6 samples have been prepared to enhance conductivity via introduction of oxygen vacancies or hole formation. The single phase MnNb2- x Ti x O6- δ columbite existence range is narrow (0 < x < 0.2). The effect of the substitution on electrical properties has been evaluated and compared to both nominal MnNb2O6 as prepared in air and reduced MnNb2O6- δ (δ ∼ 0.02). Compared to the former, the effect of the dopant on both the sintering process and the electrical conductivity is beneficial. A homogeneous brick layer microstructure is obtained for a low extent of niobium substitution and short time of sintering. Conductivity of the Ti-substituted material is several orders of magnitude higher than that of the unsubstituted. On the other hand reduced MnNb2O6- δ (δ ∼ 0.02) exhibits a higher conductivity at high temperatures. Ti-substituted MnNb2O6 behaves as a hole/electron electronic conductor, yielding quite similar conductivities in air and 5% H2 at 900 °C but with differing dominant charge carriers. A small contribution to conductivity independent of the p O 2 suggests a possible ionic conductivity of approximately 6.0 × 10-5 ohm-1 cm-1. Magnetic properties are also affected by the substitution. Although the antiferromagnetic transition at low temperature due to Mn2+ ions still persists, a decrease in Neel temperature is observed as titanium content increases.