Lanthanum hafnate

Lanthanum hafnate

Identifiers
3D model (JSmol)	Interactive image
InChI InChI=1S/2Hf.2La.7O/q2*+4;2*+3;7*-2 Key: AUXGONVMFPDWKD-UHFFFAOYSA-N
SMILES [La+3].[La+3].[Hf+4].[Hf+4].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2].[O-2]
Properties
Chemical formula	La2Hf2O7
Molar mass	746.79 g/mol
Appearance	colorless solid
Density	7.86 g/cm^3[1]
Band gap	4.233 eV[1]
Structure
Crystal structure	Cubic
Space group	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). Infobox references

Lanthanum hafnate (La₂Hf₂O₇) or lanthanum hafnium oxide is a mixed oxide of lanthanum and hafnium.

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.

References

1. None Available (2020). "Materials Data on La2Hf2O7 by Materials Project". Materials Project. doi:10.17188/1188964. Retrieved 30 April 2021. {{cite journal}}: Cite journal requires |journal= (help)
2. Ji, Yaming; Jiang, Danyu; Fen, Tao; Shi, Jianlin (March 2005). "Fabrication of transparent La2Hf2O7 ceramics from combustion synthesized powders". Materials Research Bulletin. 40 (3): 553–559. doi:10.1016/j.materresbull.2004.10.010.
3. Popov, V V; Menushenkov, A P; Yastrebtsev, A A; Zubavichus, Ya V (September 2016). "La 2 Hf 2 O 7 crystal and local structure changes on the fluorite - pyrochlore phase transition". Journal of Physics: Conference Series. 747 (1): 012043. Bibcode:2016JPhCS.747a2043P. doi:10.1088/1742-6596/747/1/012043.
4. Blanchard, Peter E. R.; Liu, Sam; Kennedy, Brendan J.; Ling, Chris D.; Avdeev, Max; Aitken, Jade B.; Cowie, Bruce C. C.; Tadich, Anton (7 February 2013). "Investigating the Local Structure of Lanthanoid Hafnates Ln 2 Hf 2 O 7 via Diffraction and Spectroscopy". The Journal of Physical Chemistry C. 117 (5): 2266–2273. doi:10.1021/jp311329q.
5. Garg, Nandini; Pandey, K. K.; Murli, Chitra; Shanavas, K. V.; Mandal, Balaji P.; Tyagi, A. K.; Sharma, Surinder M. (13 June 2008). "Decomposition of lanthanum hafnate at high pressures". Physical Review B. 77 (21): 214105. Bibcode:2008PhRvB..77u4105G. doi:10.1103/PhysRevB.77.214105.
6. Eagleman, Yetta; Weber, Marvin; Derenzo, Stephen (May 2013). "Luminescence study of oxygen vacancies in lanthanum hafnium oxide, La2Hf2O7". Journal of Luminescence. 137: 93–97. Bibcode:2013JLum..137...93E. doi:10.1016/j.jlumin.2012.10.034.
7. Gupta, Santosh K.; Zuniga, Jose P.; Abdou, Maya; Thomas, Melonie P.; De Alwis Goonatilleke, Manisha; Guiton, Beth S.; Mao, Yuanbing (January 2020). "Lanthanide-doped lanthanum hafnate nanoparticles as multicolor phosphors for warm white lighting and scintillators". Chemical Engineering Journal. 379: 122314. Bibcode:2020ChEnJ.37922314G. doi:10.1016/j.cej.2019.122314. S2CID 199650816.
8. Trojan-Piegza, Joanna; Zych, Eugeniusz (March 2021). "White persistent luminescence of La2Hf2O7:Ti,Pr". Optical Materials. 113: 110896. Bibcode:2021OptMa.11310896T. doi:10.1016/j.optmat.2021.110896. S2CID 233842128.
9. Wahid, Kareem; Pokhrel, Madhab; Mao, Yuanbing (January 2017). "Structural, photoluminescence and radioluminescence properties of Eu3+ doped La2Hf2O7 nanoparticles". Journal of Solid State Chemistry. 245: 89–97. Bibcode:2017JSSCh.245...89W. doi:10.1016/j.jssc.2016.10.004.