Simultaneous measurements of oxygen pressure, composition, and electrical conductivity in praseodymium oxides: II. Pr 10O 18 and PrO 2− x phases

Abstract

Simultaneous measurements of oxygen pressure, composition, and electrical conductivity have been conducted in Pr 10O 18± x (epsilon) and PrO 2− x (alpha) phases, between Pr 9O 16± x (zeta) and Pr 10O 18± x phases, and between Pr 7O 12± x (iota) and PrO 2− x phases. In Pr 10O 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 Pr 3+ and Pr 4+ ions. In PrO 2− x phase, the electrical conductivity increases with oxygen pressure and the O 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 Pr 9O 16± x and Pr 10O 18± x and it is discussed in terms of a domain model.