Identification of the Charge Carriers in Cerium Phosphate Ceramics Page: 1 of 7
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Identification of the Charge Carriers in Cerium Phosphate Ceramics
Hannah L. Ray a,b, L. C. De Jonghe a,b
a Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley,
California, 94720, USA
b Department of Materials Science and Engineering, University of California, Berkeley,
Berkeley, California, 94720, USA
The total conductivity of Sr-doped cerium orthophosphate changes
by nearly two orders of magnitude depending on the oxygen and
hydrogen content of the atmosphere. The defect model for the
system suggests that this is because the identity of the dominant
charge carrier can change from electron holes to protons when the
sample is in equilibrium with air vs. humidified hydrogen. In this
work are presented some preliminary measurements that can help
to clarify this exchange between carriers. The conduction behavior
of a 2% Sr-doped CePO4 sample under symmetric atmospheric
conditions is investigated using several techniques, including AC
impedance, H/D isotope effects, and chronoamperometry.
Introduction
In a material that can conduct two different types of carriers, it is important to
quantify the relative concentrations of the carriers when it is in equilibrium with a series
of different atmospheres. If the variation of the carrier concentration with atmospheric
content is known, the interaction between the carriers, or the effect one can have on the
other's mobility, can be elucidated from conductivity measurements. In this study are
presented the results of some preliminary experiments for identifying and determining the
interactions between charge carriers in the 2% Sr-doped cerium orthophosphate (CePO4)
material system.
In past studies of the proton-conducting properties of Sr-doped CePO4, it has been
observed that the material's conductivity changes by two orders of magnitude in
oxidizing vs. reducing conditions [1, 2]. This large change in conductivity is caused by
the dominance of different charge carriers in different atmospheres. Defect models
propose that electron holes are the dominant carrier in oxidizing conditions, whereas in
reducing conditions, protons dominate. In phosphate materials, oxygen vacancies are
manifested as pyrophosphate links [3].
V o+ 2 PO4XPo4 - P207 (2PO4) []
Where V o is an oxygen vacancy, PG4 P04 is a phosphate tetrahedron on its proper
site, and P207 (2PO4) represents two phosphate tetrahedra sharing an oxygen corner.
Oxygen vacancies are generally created either by acceptor doping or native Schottky
disorder induced during the high temperature synthesis. These oxygen vacancies can be
compensated by incorporation of either a proton or an electron hole.
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Ray, Hannah L. & Jonghe, Lutgard C. De. Identification of the Charge Carriers in Cerium Phosphate Ceramics, article, June 2, 2010; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1012950/m1/1/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.