Structural and crystal chemical properties of alkali rare-earth double phosphates

J. Matt Farmer, L. A. Boatner, Bryan C. Chakoumakos, Claudia J. Rawn, Jim Richardson

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

When appropriately activated, alkali rare-earth double phosphates of the form: M3RE(PO4)2 (where M denotes an alkali metal and RE represents either a rare-earth element or Y or Sc) are of interest for use as inorganic scintillators for radiation detection at relatively long optical emission wavelengths. These compounds exhibit layered crystal structures whose symmetry properties depend on the relative sizes of the rare earth and alkali-metal cations. Single-crystal X-ray and powder neutron diffraction methods were used here to refine the structures of the series of rare-earth double phosphate compounds: K3RE(PO4)2 with RE = Lu, Yb, Er, Ho, Dy, Gd, Nd, Ce, plus Y and Sc - as well as the compounds: A3Lu(PO4)2, with A = Rb, and Cs. The double phosphate K3Lu(PO4)2 was reported and structurally refined previously, and it exhibited two lower-temperature phases. The compound K3Yb(PO4)2 reported here also exhibits a new second phase that occurs at T = 120 °C with a transformation to hexagonal P-3 space group symmetry and a Yb-ion coordination number reduction from seven to six. This latter result was confirmed using EXAFS. Comprehensive structural data and structural systematics are reported here for a number of alkali rare-earth double phosphates. Additionally, single-crystal growth methods for the preparation of large single crystals of these compounds are described, and the thermal expansion properties of the present series of alkali rare-earth double phosphates, as determined by both X-ray and neutron diffraction methods, are presented. These data represent a structural and thermal characteristics basis for continuing research on the use of alkali rare-earth double phosphates as scintillators for radiation detection - as well as for future studies of the fundamental phase properties of these compounds at elevated pressures.

Original languageEnglish
Pages (from-to)253-265
Number of pages13
JournalJournal of Alloys and Compounds
Volume655
DOIs
StatePublished - Jan 15 2016

Funding

Research at the Oak Ridge National Laboratory was sponsored in part by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division and in part by the Office of Nonproliferation Research and Engineering in the Office of Defense Nuclear Nonproliferation in the National Nuclear Security Administration (NNSA) . LAB was supported by the NNSA , and JMF and CJR were supported by the U.S. DOE/BES . BCC was supported by the U.S. DOE Scientific User Facilities Division . The authors acknowledge with thanks the contributions of Sandra Salmen to the manuscript and graphic arts preparation.

Keywords

  • Compounds
  • Rare earth alloys

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