Growth and thermal properties of CO2+:LaMgAl11O19 crystal

The 0.5 and 1 at% Co2+-doped lanthanum magnesium hexaluminates (LaMgAl11O19, LMA) polycrystalline material was synthesized with high-purity (99.99%) La2O3, MgO, Al2O3 and analytical purity Co(CH3COO)(2)center dot 4H(2)O by the solid-state reaction technique. The blue Co2+ : LMA single crystal up to (D 40 x 50 turn was successfully grown by the Czochralski method. X-ray powder diffraction (XRPD) results show that the as-grown Co:LMA crystal belongs to the hexagonal system and P6(3)/mmc space group. X-ray fluorescence (XRF) analysis indicates that the effective segregation coefficient of Co2+ ions in the Co:LMA crystal is k(eff)(Co) = 0.7487. The high crystalline quality of the as-grown Co:LMA crystals was confirmed by High-resolution X-ray diffraction (HRXRD), which showed the full-width half-maximum (FWHM) of the rocking curves to be less than 20 arcsec on the (008) and (200) diffraction planes of the 0.5 at% Co:LMA crystal. The average linear thermal expansion coefficients are alpha(1) = 9.9720 x 10(-6)/K, alpha(2) = 11.4451 X 10(-6)/K and alpha(3) = 16.4328 x 10(-6)/K for the 0.5 at% Co:LMA crystal and alpha(1) = 9.8753 x 10(-6) /K, alpha(2) = 10.7768 x 10(-6)/K and alpha(3) = 15.8901 x 10(-6)/K for the 1at% Co:LMA crystal in the temperature range from 300.15 to 1133.15K along the three respective crystallophysical axes. The specific heat of the as-grown Co:LMA crystal increases from 565.36 to 825.12J K-1 mol(-1) when the temperature increases from 323.15 to 1163.15K. The density of the as-grown Co:LMA crystals is measured by the buoyancy method at 22 degrees C and the results were 4.236 and 4.243g cm- 3 for 0.5 at% and 1 at% Co:LMA crystal, respectively. The thermal diffusion coefficient of the 0.5 at% Co:LMA crystal was measured in the temperature range of 298.15 to 563.15 K. The calculated thermal conductivity is 4.758 (3.238) W m(-1) K-1 along the X-2 (X-3) crystallophysical direction at 328.15 K. These thermal properties show Co: LMA crystal may be used in high-power laser system. (c) 2005 Elsevier B.V. All rights reserved.