Influence of Lanthanum Concentration on Microstructure of (Ho1-xLax)(2)O-3 Magneto-Optical Ceramics

Transparent cubic-phase solid solution (Ho1-xLax)(2)O-3 (where x = 0, 0.03, 0.05, 0.07, and 0.1) ceramics are sintered in a vacuum at 1780 degrees C for 3 h from nanopowders made by self-propagating high-temperature synthesis. The lanthana is proved to significantly influence the microstructure of the ceramics. The average crystallite sizes of the (Ho1-xLax)(2)O-3 ceramics decrease with an increase in the concentration of lanthana. After vacuum sintering and low-temperature annealing in air, the ceramics have second-phase grains at the crystallite boundaries and the triple points. The volume fraction of the second phase is found to be in direct proportion to the lanthana content in the ceramics. This second phase is believed to be (Ho1-xLax)(2)O-3 solid solutions with a higher lanthanum content in comparison with the surrounding crystallites. Annealing of the ceramics at 1500 degrees C for 2 h leads to the elimination of the second phase.