Electron-irradiation-induced nucleation and growth in amorphous LaPO{sub 4}, ScPO{sub 4}, and zircon

Journal Article · Tue Jul 01 04:00:00 EDT 1997 · Journal of Materials Research

DOI:https://doi.org/10.1557/JMR.1997.0250· OSTI ID:548792

Meldrum, A ^[1]; Boatner, L A ^[2]; Ewing, R C ^[1]

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1. Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131-1116 (United States)
2. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6056 (United States)

Synthetic LaPO{sub 4}, ScPO{sub 4}, and crystalline natural zircon (ZrSiO{sub 4}) from Mud Tanks, Australia were irradiated by 1.5 MeV Kr{sup +} ions until complete amorphization occurred. The resulting amorphous materials were subsequently irradiated by an 80 to 300 keV electron beam in the transmission electron microscope at temperatures between 130 and 800 K, and the resulting microstructural changes were monitored {ital in situ}. Thermal anneals in the range of 500 to 600 K were also conducted to compare the thermally-induced microstructural development with that produced by the electron-irradiations. Amorphous LaPO{sub 4} and ScPO{sub 4} annealed to form a randomly oriented polycrystalline assemblage of the same composition as the original material, but zircon recrystallized to ZrO{sub 2} (zirconia)+amorphous SiO{sub 2} for all beam energies and temperatures investigated. The rate of crystallization increased in the order: zircon, ScPO{sub 4}, LaPO{sub 4}. Submicrometer tracks of crystallites having a width equal to that of the electron beam could be drawn on the amorphous substrate. In contrast, thermal annealing resulted in epitaxial recrystallization from the thick edges of the TEM samples. Electron-irradiation-induced nucleation and growth in these materials can be explained by a combination of radiation-enhanced diffusion as a result of ionization processes and a strong thermodynamic driving force for crystallization. The structure of the amorphous orthophosphates may be less rigid than that of their silicate analogues because of the lower coordination across the PO{sub 4} tetrahedron, and thus a lower energy is required for reorientation and recrystallization. The more highly constrained monazite structure-type recovers at a lower electron dose than the zircon structure-type, consistent with recent models used to predict the crystalline-to-amorphous transition as a result of ion irradiation. {copyright} {ital 1997 Materials Research Society.}

• OSTI ID: 548792
• Journal Information: Journal of Materials Research, Journal Name: Journal of Materials Research Journal Issue: 7 Vol. 12; ISSN JMREEE; ISSN 0884-2914
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AMORPHOUS STATE
ELECTRON BEAMS
ION BEAMS
LANTHANUM OXIDES
MICROSTRUCTURE
NUCLEATION
PHASE TRANSFORMATIONS
PHOSPHORUS OXIDES
PHYSICAL RADIATION EFFECTS
SCANDIUM OXIDES
SILICON OXIDES
TEMPERATURE DEPENDENCE
ZIRCONIUM OXIDES