title: Contamination in the Rare-Earth Element Orthophosphate Reference Samples.
abstract: Several of the fourteen rare-earth element (plus Sc and Y) orthophosphate standards grown at Oak Ridge National Laboratory in the 1980s and widely distributed by the Smithsonian Institution's Department of Mineral Sciences, are significantly contaminated by Pb. The origin of this impurity is the Pb2P2O7 flux that is derived from the thermal decomposition of PbHPO4. The lead pyrophosphate flux is used to dissolve the oxide starting materials at elevated temperatures (≈1360 °C) prior to the crystal synthesis. Because these rare-earth element standards are extremely stable under the electron beam and considered homogenous, they have been of enormous value to electron probe micro-analysis (EPMA). The monoclinic, monazite structure, orthophosphates show a higher degree of Pb incorporation than the tetragonal xenotime structure, orthophosphates. This paper will attempt to describe and rationalize the extent of the Pb contamination in these otherwise excellent materials.
authors.affiliation: Department of Geological Sciences, The University of Oregon, Eugene, OR 97403-1272.
authors.forename: John J
authors.initials: JJ
authors.lastname: Donovan
authors.affiliation: Department of Earth and Environmental Sciences, The George Washington University, Washington, DC 20006.
authors.forename: John M
authors.initials: JM
authors.lastname: Hanchar
authors.affiliation: Department of Geology, The University of Maryland, College Park, MD 20742.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Picolli
authors.affiliation: Department of Chemistry, The University of California, Berkeley, CA 94720.
authors.forename: Marc D
authors.initials: MD
authors.lastname: Schrier
authors.affiliation: Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831.
authors.forename: Lynn A
authors.initials: LA
authors.lastname: Boatner
authors.affiliation: Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560.
authors.forename: Eugene
authors.initials: E
authors.lastname: Jarosewich
keywords: EPMA; REE; microanalysis; orthophosphates; quantitative analysis; rare earth elements; rare earth phosphates; standards