Lanthanum hafnate

Lanthanum hafnate (La
₂Hf
₂O
₇) or lanthanum hafnium oxide is a mixed oxide of lanthanum and hafnium.

Properties

Lanthanum hafnate is a colorless ceramic material with the La and Hf atoms arranged in a cubic lattice. The arrangement is a disordered fluorite-like structure below 1,000 °C (1,270 K; 1,830 °F), above which it transitions to a pyrochlore phase; an amorphous phase also exists below 800 °C (1,070 K; 1,470 °F).

The compound decomposes into its constituent oxides at 18 GPa.

Luminescence

Oxygen vacancies in the base material give luminescence spanning across the visible light spectrum, with a peak near 460 nm. The luminescent properties can be fine-tuned by doping with various rare earth and group 4 metals; for example, La₂Hf₂O₇:Eu³⁺ nanoparticles exhibit a red photoluminescence or radioluminescence near 612 nm when exposed to ultraviolet or X-ray radiation.

Synthesis

Bulk ceramics can obtained by combusting the elements in powder form, and then pressing and sintering the powder at 180 MPa and 1,850 °C (2,120 K; 3,360 °F) for 6 hours:

4 La + 4 Hf + 7 O
₂ → 2 La
₂Hf
₂O
₇.

It may also be made by precipitating hafnium and lanthanum hydroxides from solution and then calcinating in air at 600–1,400 °C (873–1,673 K; 1,112–2,552 °F) for 3 hours:

2 La(OH)₃ + 2 Hf(OH)₄ → La₂Hf₂O₇ + 7 H₂O.

References