Cation coordination and Fe{sup 3+} luminescence in LiAlO{sub 2} polymorphs prepared by a hydrothermal method

Journal Article · Fri Jan 15 04:00:00 EST 1999 · Materials Research Bulletin

DOI:https://doi.org/10.1016/S0025-5408(99)00014-8· OSTI ID:352419

Kutty, T R.N.; Nayak, M ^[1]

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1. Indian Inst. of Science, Bangalore (India). Materials Research Centre

The polymorphs {alpha}-, {beta}-, and {gamma}-LiAlO{sub 2} were synthesized by a hydrothermal method. The as-prepared product obtained at 240 C was {beta}-LiAlO{sub 2}, which converted completely to {gamma}-LiAlO{sub 2} above 1,000 C. {alpha}-LiAlO{sub 2} was obtained by the decomposition of LiAl(OH){sub 4}{center_dot}H{sub 2}O prepared by imbibition of LiOH into LiAl{sub 2}(OH){sub 7}{center_dot}2H{sub 2}O hydrothermally at 140 C. Solid state MAS NMR (magic-angle spinning nuclear magnetic resonance) studies indicate that Li{sup +} uniquely occupies octahedral sites in all the polymorphs. This observation indicates that the results of XRD and crystal structure studies on {beta}- and {gamma}-LiAlO{sub 2} reported in the literature that indicate the presence of Li{sup +} in the tetrahedral site are apparently in error with respect to Li{sup +} coordination. The other cation, Al{sup 3+}, occupied octahedral sites in {alpha}-LiAlO{sub 2} and tetrahedral sites in the {beta}- and {gamma}-LiAlO{sub 2}. The Fe{sup 3+} doped in the various polymorphic forms of this compound was found to uniquely occupy the octahedral Li{sup +} site. EPR spectrum of the Fe{sup 3+} doped in these polymorphs indicates that during the transformation this site is distorted. The Fe{sup 3+} photoluminescent emission maximum was different for each polymorph. The difference in the luminescence characteristics among the polymorphic forms is due to the change in the site symmetry because of the distortion of the octahedra occupied by Fe{sup 3+} across the phase transition. The infrared spectrum indicates that site symmetry is lowered during the phase transition.

• OSTI ID: 352419
• Journal Information: Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 2 Vol. 34; ISSN MRBUAC; ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CRYSTAL STRUCTURE
HYDROTHERMAL SYNTHESIS
INFRARED SPECTRA
IRON ADDITIONS
LITHIUM OXIDES
LUMINESCENCE
NUCLEAR MAGNETIC RESONANCE
X-RAY DIFFRACTION