Chemistry:Lanthanum hafnate
| 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
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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, La
2Hf
2O
7: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 → La
2Hf
2O
7 + 7 H
2O.
References
- ↑ 1.0 1.1 None Available (2020). Materials Data on La2Hf2O7 by Materials Project. Materials Project. doi:10.17188/1188964. https://materialsproject.org/materials/mp-12533/. Retrieved 30 April 2021.
- ↑ 2.0 2.1 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.
- ↑ 3.0 3.1 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. doi:10.1088/1742-6596/747/1/012043. Bibcode: 2016JPhCS.747a2043P.
- ↑ 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.
- ↑ 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. doi:10.1103/PhysRevB.77.214105. Bibcode: 2008PhRvB..77u4105G.
- ↑ Eagleman, Yetta; Weber, Marvin; Derenzo, Stephen (May 2013). "Luminescence study of oxygen vacancies in lanthanum hafnium oxide, La2Hf2O7". Journal of Luminescence 137: 93–97. doi:10.1016/j.jlumin.2012.10.034. Bibcode: 2013JLum..137...93E.
- ↑ 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. doi:10.1016/j.cej.2019.122314. https://scholarworks.utrgv.edu/chem_fac/137.
- ↑ Trojan-Piegza, Joanna; Zych, Eugeniusz (March 2021). "White persistent luminescence of La2Hf2O7:Ti,Pr". Optical Materials 113: 110896. doi:10.1016/j.optmat.2021.110896. Bibcode: 2021OptMa.11310896T.
- ↑ 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. doi:10.1016/j.jssc.2016.10.004. Bibcode: 2017JSSCh.245...89W.
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