Structure and Electrical-Transport Relations in Ba(Zr,Pr)O3-δ Perovskites.
Inorg Chem
; 56(15): 9120-9131, 2017 Aug 07.
Article
em En
| MEDLINE
| ID: mdl-28742340
ABSTRACT
Members of the perovskite solid solution BaZr1-xPrxO3-δ (0.2 ≤ x ≤ 0.8) with potential high-temperature electrochemical applications were synthesized via mechanical activation and high-temperature annealing at 1250 °C. Structural properties were examined by Rietveld analysis of neutron powder diffraction and Raman spectroscopy at room temperature, indicating rhombohedral symmetry (space group R3Ì
c) for members x = 0.2 and 0.4 and orthorhombic symmetry (Imma) for x = 0.6 and 0.8. The sequence of phase transitions for the complete solid solution from BaZrO3 to BaPrO3 is Pm3Ì
m â R3Ì
c â Imma â Pnma. The structural data indicate that Pr principally exists as Pr4+ on the B site and that oxygen content increases with higher Pr content. Electrical-conductivity measurements in the temperature range of 250-900 °C in dry and humidified (pH2O ≈ 0.03 atm) N2 and O2 atmospheres revealed an increase of total conductivity by over 2 orders of magnitude in dry conditions from x = 0.2 to x = 0.8 (σ ≈ 0.08 S cm-1 at 920 °C in dry O2 for x = 0.8). The conductivity for Pr contents x > 0.2 is attributable to positively charged electronic carriers, whereas for x = 0.2 transport in dry conditions is n-type. The change in conduction mechanism with composition is proposed to arise from the compensation regime for minor amounts of BaO loss changing from predominantly partitioning of Pr on the A site to vacancy formation with increasing Pr content. Conductivity is lower in wet conditions for x > 0.2 indicating that the positive defects are, to a large extent, charge compensated by less mobile protonic species. In contrast, the transport mechanism of the Zr-rich composition (x = 0.2), with much lower electronic conductivity, is essentially independent of moisture content.
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MEDLINE
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En
Ano de publicação:
2017
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Article