Synthesis and characterization of pyrochlore lanthanide (Pr, Sm) zirconate ceramics

Three different lanthanide zirconate powders: Pr2Zr2O7, Sm2Zr2O7 and PrSmZr2O7 were prepared by combustion synthesis. The synthesis initially yielded amorphous powders, which crystallized after subsequent thermal treatment. Well-crystallized compounds were formed after calcination at temperature as low as 950 degrees C. Effect of the thermal treatment on the phase evolution was studied by X-ray powder diffraction (XRD). The powders calcined at the highest temperature (1550 degrees C) showed that all compositions possess the pyrochlore structure with the space group No. 227. The obtained powders were compacted and pressureless sintered without additive at 1600 degrees C for 4 h in the air. Microstructure development was examined by field emission scanning electron microscopy, as well as by transmission electron microscopy. It was found that the lowest value for thermal conductivity, 1.2 W/m K, was obtained for mixed lanthanide composition with pyrochlore structure (PrSmZr2O7). The effect of chemical composition on micro-hardness and thermal conductivity of the obtained zirconates was studied.