Pressure-induced structural transitions and phase decomposition in the Cd{sub 2}Nb{sub 2}O{sub 7} pyrochlore

Journal Article · Wed Nov 01 04:00:00 EST 2006 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.74.174116· OSTI ID:20853855

Zhang, F X; Lian, J; Becker, U; Ewing, R C; Wang, L M; Boatner, L A; Hu, Jingzhu; Saxena, S K ^[1]

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1. Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States)

The structural transitions of the pyrochlore, Cd{sub 2}Nb{sub 2}O{sub 7}, at pressures up to 32.5 GPa have been investigated by in situ Raman scattering and angle-dispersive x-ray diffraction (ADXRD) methods. The x-ray diffraction results reveal that small amounts ({approx}7%) of metallic cadmium form by chemical decomposition at pressures greater than 4 GPa. Both Raman and XRD results indicate that a pressure-induced structural distortion from pyrochlore to defect fluorite occurs in pyrochlore Cd{sub 2}Nb{sub 2}O{sub 7} at pressures of 12-14 GPa. Subsequently, a new high-pressure phase formed and the phase transition was complete at {approx}27 GPa. The high-pressure phase is either monoclinic or orthorhombic and transforms to either the pyrochlore (or defect fluorite) structure or the amorphous state when quenched to ambient conditions. Energy dispersive spectroscopy (EDS) analysis and high-resolution transmission electron microscopy (HRTEM) observation of the quenched sample confirmed the Cd loss and resulting mixture of ordered pyrochlore, defect fluorite, high-pressure phase, as well as amorphous domains.

• OSTI ID: 20853855
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 17 Vol. 74; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
AMORPHOUS STATE
CADMIUM COMPOUNDS
CHEMICAL ANALYSIS
DECOMPOSITION
FERROELECTRIC MATERIALS
FLUORITE
MIXTURES
MONOCLINIC LATTICES
NIOBATES
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
PRESSURE DEPENDENCE
PRESSURE RANGE GIGA PA
PYROCHLORE
RAMAN EFFECT
RAMAN SPECTRA
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION