Lanthanum hafnate
Ceramic metal compound
From Wikipedia, the free encyclopedia
Lanthanum hafnate (La2Hf2O7) or lanthanum hafnium oxide is a mixed oxide of lanthanum and hafnium.
| Identifiers | |
|---|---|
3D model (JSmol) |
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| Properties | |
| La2Hf2O7 | |
| Molar mass | 746.79 g/mol |
| Appearance | colorless solid |
| Density | 7.86 g/cm3[1] |
| Band gap | 4.233 eV[1] |
| Structure | |
| Cubic | |
| Fm3m (< 1000 °C) Fd3m (> 1000 °C) | |
| Related compounds | |
Other cations |
Lanthanum zirconate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Properties
Lanthanum hafnate is a colorless ceramic material[2] 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).[3][4]
The compound decomposes into its constituent oxides at 18 GPa.[5]
Luminescence
Oxygen vacancies in the base material give luminescence spanning across the visible light spectrum, with a peak near 460 nm.[6] The luminescent properties can be fine-tuned by doping with various rare earth and group 4 metals;[7][8] for example, La2Hf2O7:Eu3+ nanoparticles exhibit a red photoluminescence or radioluminescence near 612 nm when exposed to ultraviolet or X-ray radiation.[9]
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:[2]
- 4 La + 4 Hf + 7 O2 → 2 La2Hf2O7
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:[3]
- 2 La(OH)3 + 2 Hf(OH)4 → La2Hf2O7 + 7 H2O.