Structure and properties of samarium-doped lanthanum hafnates annealed at the temperatures of 800 and 900 °C

Hydroxide precipitates composed of 33 mol.% lanthanum, 67–62 mol.% hafnium, and samarium ranging from 0 to 5 mol.% were synthesized using a chemical method in the presence of auxiliary substances. The precipitates were annealed at temperatures of 800 and 900°C. The resulting structures were analyzed using X-ray diffraction, Raman spectroscopy, thermogravimetry combined with mass spectroscopy, BET analysis, scanning electron microscopy, diffuse reflectance powder spectroscopy, and photoluminescence. It was determined that for lanthanum hafnate doped with samarium, the critical annealing temperature of 800–900°C is essential for the transition from the disordered fluorite phase to the ordered pyrochlore phase. The primary particle size is approximately 11–12 nm. The lanthanum hafnate powders exhibited strong agglomeration which resulted in a low specific surface area (5–8.6 m 2 /g). The band gap energy of the La 2 Hf 2 O 7 phase ranged from 5.3 to 5.55 eV. Additionally, the incorporation of Sm 3+ cations into the lanthanum hafnate structure induced photoluminescence when excited at 405 nm.