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.