Effects of Sm3+ and Gd3+ Co-doping on Thermo-Physical Properties of LaMgAl11O19

The influence of partial substitution of La3+ by Sm3+ and Gd3+ in the LaMgAl11O19 magnetoplumbite system is studied by evaluating the coefficient of thermal expansion and the thermal conductivity of the compounds up to T = 1273 K. The X-ray diffraction patterns of the La1-2x(SmGd)(x)MgAl11O19 (LSGMAO, x = 0.0, 0.1, 0.2, 0.3) compositions are comprised of pure magnetoplumbite LaMgAl11O19 phase. The samples exhibit platelet-like and randomly arranged hexagonal grains. The thermal conductivities have been found to agree with point-defect phonon scattering mechanism by strain and mass fluctuations at the La3+ site. The low thermal conductivity can also be assigned to an enhanced phonon scattering on platelet-like grain boundaries. The coefficients of thermal expansion (CTE) of bulk La1-2x(SmGd)(x)MgAl11O19 have been recorded by high temperature dilatometer. As a result of the increased electronegativity difference between ions at La site and O site, a negative influence on CTE elevation with the increasing Gd3+ and Sm3+ fraction is found in the LSGMAO system. These results imply that Sm3+ and Gd3+ co-doped LaMgAl11O19 can be explored as the candidate material for the top ceramic layer in thermal barrier coatings system.