Laser and phosphor host La/sub 1-//sub x/MgAl/sub 11+//sub x/O/sub 19/ (x = 0. 050): Crystal structure at 295 K

Journal Article · Wed Apr 01 00:00:00 EST 1987 · J. Chem. Phys.; (United States)

OSTI ID:6651709

Abrahams, S C; Marsh, P; Brandle, C D

The laser and phosphor host material with nominal composition LaMgAl/sub 11/O/sub 19/ is shown to be nonstoichiometric. Czochralski grown crystals are hexagonal, with space group P6/sub 3//mmc, and a = 5.589 82(5), c = 21.9738(12) A at 295 K. The thermal expansivity has been determined over the range 295 to 860 K: at 295 K, ..cap alpha../sub 1/ = 4.97(2) x 10/sup -6/ K/sup -1/ and ..cap alpha../sub 3/ = 8.14(3) x 10/sup -6/ K/sup -1/and at 775 K, ..cap alpha../sub 1/ = 7.01(1) x 10/sup -6/ K/sup -1/ and ..cap alpha../sub 3/ = 10.1(2) x 10/sup -6/ K/sup -1/. The integrated intensities of 20 487 reflections within a reciprocal lattice sphere of radius (sin theta)/lambda = 1.0 A/sup -1/ were measured on a CAD-4 diffractometer with MoK..cap alpha.. radiation, resulting in 18 232 reflections above background. Correction and averaging gave 864 independent structure factors with an internal agreement factor of 0.0145. The crystal structure was solved from the Patterson function and Fourier series and refined by the method of least squares. The final agreement factor R = 0.013 98. The composition corresponds to La/sub 1-//sub x/MgAl/sub 11+//sub x/O/sub 19/, with x = 0.0502(8): the La deficiency is exactly compensated by excess Al. The principal La site is not fully occupied, but contains 4.76 at. % Al and 5.2 at. % Schottky defects. The remaining 4.94 at. % La and 0.26 at. % Al are distributed over two threefold satellite sites 0.583(3) A distant from the principal La sites. The Mg atoms share a tetrahedral site equally with Al, while the Al atoms in the trigonal bipyramidal site undergo anharmonic motion.

• Research Organization: AT and T Bell Laboratories, Murray Hill, New Jersey 07974
• OSTI ID: 6651709
• Journal Information: J. Chem. Phys.; (United States), Vol. 86:7
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
LANTHANUM COMPOUNDS
CRYSTAL STRUCTURE
LASER MATERIALS
MAGNESIUM COMPOUNDS
ALUMINATES
STOICHIOMETRY
THERMAL EXPANSION
X-RAY DIFFRACTION
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
COHERENT SCATTERING
DIFFRACTION
EXPANSION
MATERIALS
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
SCATTERING
420300* - Engineering- Lasers- (-1989)