Simultaneous measurements of oxygen pressure,composition, and electrical conductivity in praseodymium oxides: II. Pr10O18 and PrO2−x phases

Simultaneous measurements of oxygen pressure, composition, and electrical conductivity have been conducted in Pr₁₀O_18±x (epsilon) and PrO_2?x (alpha) phases, between Pr₉O_16±x (zeta) and Pr₁₀O_18±x phases, and between Pr₇O_12±x (iota) and PrO_2?x phases. In Pr₁₀O_18±x phase, the predominant defects are assigned to be neutral oxygen interstitials and neutral or doubly charged oxygen vacancies, and electrical conduction is thought to be governed mainly by the concentration of 7-coordinated praseodymium ions, which are the easiest sites for hopping electrons between Pr³⁺ and Pr⁴⁺ ions. In PrO_2?x phase, the electrical conductivity increases with oxygen pressure and the $\text{O}\text{Pr}$ ratio and the predominant defects are assigned to be neutral oxygen interstitials, indicating that oxygen vacancies are ordered in a short range and this phase is expressed by PrO_1.78+x rather than PrO_2?x in the region measured. The electrical conductivity-composition measurement, as well as the oxygen pressure-composition measurement, shows a reproducible hysteresis loop between Pr₉O_16±x and Pr₁₀O_18±x and it is discussed in terms of a domain model.