Praseodymium Orthoniobate and Praseodymium Substituted Lanthanum Orthoniobate: Electrical and Structural Properties

In this paper, the structural properties and the electrical conductivity of La(1−x)Pr(x)NbO(4+δ) (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) and PrNbO(4+δ) are presented and discussed. All synthesized samples crystallized in a monoclinic structure with similar thermal expansion coefficients. The phase transition temperature between the monoclinic and tetragonal structure increases with increasing praseodymium content from 500 °C for undoped LaNbO(4+δ) to 700 °C for PrNbO(4+δ). Thermogravimetry, along with X-ray photoelectron spectroscopy, confirmed a mixed 3(+)/4(+) oxidation state of praseodymium. All studied materials, in humid air, exhibited mixed protonic, oxygen ionic and hole conductivity. The highest total conductivity was measured in dry air at 700 °C for PrNbO(4+δ), and its value was 1.4 × 10(−3) S/cm.