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)2·4H2O by the solid-state reaction technique. The blue Co2+:LMA single crystal up to Φ 40×50 mm 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 P63/mmc space group. X-ray fluorescence (XRF) analysis indicates that the effective segregation coefficient of Co2+ ions in the Co:LMA crystal is keff(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 (0 0 8) and (2 0 0) diffraction planes of the 0.5 at% Co:LMA crystal. The average linear thermal expansion coefficients are α1=9.9720×10-6/K, α2=11.4451×10-6/K and α3=16.4328×10-6/K for the 0.5 at% Co:LMA crystal and α1=9.8753×10-6/K, α2=10.7768×10-6/K and α3=15.8901×10-6/K for the 1 at% Co:LMA crystal in the temperature range from 300.15 to 1133.15 K along the three respective crystallophysical axes. The specific heat of the as-grown Co:LMA crystal increases from 565.36 to 825.12 J K−1 mol−1 when the temperature increases from 323.15 to 1163.15 K. The density of the as-grown Co:LMA crystals is measured by the buoyancy method at 22 °C and the results were 4.236 and 4.243 g 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 X2 (X3) crystallophysical direction at 328.15 K. These thermal properties show Co:LMA crystal may be used in high-power laser system.