Lanthanum hafnate

Lanthanum hafnate 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 1000 C, above which it transitions to a pyrochlore phase; an amorphous phase also exists below 800 C.

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:Eu(3+) 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 1850 C for 6 hours:
 * 4 La + 4 Hf + 7 → 2.

It may also be made by precipitating hafnium and lanthanum hydroxides from solution and then calcinating in air at 600–1400 C for 3 hours:
 * 2 La(OH)3 + 2 Hf(OH)4 → La2Hf2O7 + 7 H2O.