Cerium(IV) oxide

{{for|the other compound also known as cerium oxide|Cerium(III) oxide}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 476998113 | Name = Cerium(IV) oxide | ImageFile = Cerium(IV) oxide.jpg | ImageName = Cerium(IV) oxide | ImageFile1 = Ceria-3D-ionic.png | ImageClass1 = bg-transparent | ImageName1 = | IUPACName = Cerium(IV) oxide | OtherNames = Ceric oxide, Ceria, Cerium dioxide |Section1={{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 8395107 | PubChem = 73963 | ChEBI_Ref = {{ebicite|changed|EBI}} | ChEBI = 79089 | UNII_Ref = {{fdacite|changed|FDA}} | UNII = 619G5K328Y | UNII1_Ref = {{fdacite|correct|FDA}} | UNII1 = 20GT4M7CWG | UNII1_Comment = (hydrate) | InChI = 1/Ce.2O/q+4;2*-2 | SMILES = [O-2]=[Ce+4]=[O-2] | InChIKey = OFJATJUUUCAKMK-UHFFFAOYAX | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/Ce.2O/q+4;2*-2 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = OFJATJUUUCAKMK-UHFFFAOYSA-N | CASNo = 1306-38-3 | CASNo_Ref = {{cascite|correct|CAS}} | CASNo2_Ref = {{cascite|correct|CAS}} | CASNo2 = 23322-64-7 | CASNo2_Comment = (hydrate) }} |Section2={{Chembox Properties | Formula = CeO2 | MolarMass = 172.115 g/mol | Appearance = white or pale yellow solid, slightly [[Hygroscopy|hygroscopic]] | Density = 7.215 g/cm3 | Solubility = insoluble | MeltingPtC = 2400 | BoilingPtC = 3500 | pKa = | pKb = | MagSus = +26.0·10−6 cm3/mol }} |Section3={{Chembox Structure | MolShape = | CrystalStruct = [[cubic crystal system]], [[pearson symbol|''cF12'']] ([[Fluorite structure|fluorite]])<ref>Pradyot Patnaik. ''Handbook of Inorganic Chemicals''. McGraw-Hill, 2002, {{ISBN|0-07-049439-8}}</ref> | SpaceGroup = Fm3m, #225 | Coordination = Ce, 8, cubic O, 4, tetrahedral | LattConst_a = 5.41 Å <ref>E. A. Kümmerle and G. Heger, “The Structures of C-Ce2O3+δ, Ce7O12, and Ce11O20,” Journal of Solid State Chemistry, vol. 147, no. 2, pp. 485–500, 1999.</ref> | LattConst_b = 5.41 Å | LattConst_c = 5.41 Å | LattConst_alpha = 90 | LattConst_beta = | LattConst_gamma = | Dipole = }} |Section7={{Chembox Hazards | ExternalSDS = | MainHazards = | NFPA-H = 1 | NFPA-F = 0 | NFPA-R = 0 | NFPA-S = }} |Section8={{Chembox Related | OtherAnions = | OtherCations = | OtherCompounds = [[Cerium(III) oxide]] }} }}

'''Cerium(IV) oxide''', also known as '''ceric oxide''', '''ceric dioxide''', '''ceria''', '''cerium oxide''' or '''cerium dioxide''', is an [[oxide]] of the [[rare-earth metal]] [[cerium]]. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial product and an intermediate in the purification of the element from the ores.<ref name="Ullmann"/> The distinctive property of this material is its reversible conversion to a [[Non-stoichiometric compound|non-stoichiometric oxide]].

==Production== [[Cerium]] occurs naturally as oxides, always as a mixture with other rare-earth elements. Its principal ores are [[bastnaesite]] and [[monazite]]. After extraction of the metal ions into aqueous base, Ce is separated from that mixture by addition of an oxidant followed by adjustment of the pH. This step exploits the low solubility of CeO2 and the fact that other rare-earth elements resist oxidation.<ref name="Ullmann">{{Ullmann|first1=Klaus|last1= Reinhardt|first2=Herwig|last2= Winkler|title=Cerium Mischmetal, Cerium Alloys, and Cerium Compounds|year=2000|doi=10.1002/14356007.a06_139}}.</ref>

Cerium(IV) oxide is formed by the [[calcination]] of [[cerium oxalate]] or [[cerium hydroxide]].

Cerium also forms [[cerium(III) oxide]], {{chem|Ce|2|O|3}}, which oxidizes in air to cerium(IV) oxide.<ref name="Ullmann"/><ref>{{cite web |url=http://courses.chem.indiana.edu/c360/documents/thermodynamicdata.pdf |url-status=dead |archive-url=https://web.archive.org/web/20131029204441/http://courses.chem.indiana.edu/c360/documents/thermodynamicdata.pdf |archive-date=October 29, 2013 |title=Standard Thermodynamic Properties of Chemical Substances }}</ref>

== Structure and defect behavior== Cerium oxide adopts the [[fluorite structure]], space group Fm3m, #225 containing 8-coordinate Ce4+ and 4-coordinate O2−. At high temperatures it releases oxygen to give a [[nonstoichiometric compound|non-stoichiometric, anion deficient form]] that retains the fluorite lattice.<ref>[https://arxiv.org/abs/1902.02662 DFT study of Cerium Oxide Surfaces] Applied surface science 2019 vol 478</ref> This material has the formula CeO(2−''x''), where 0 < ''x'' < 0.28.<ref name = "Hayes">Defects and Defect Processes in Nonmetallic Solids By William Hayes, A. M. Stoneham Courier Dover Publications, 2004.</ref> The value of ''x'' depends on both the temperature, surface termination and the oxygen partial pressure. The equation :<math>\frac{x}{0.35 - x} = \left(\frac{106\,000\text{ Pa}}{P_{\mathrm{O}_2}}\right)^{0.217} \exp\left( \frac{-195.6\text{ kJ/mol}}{RT} \right)</math> has been shown to predict the equilibrium non-stoichiometry ''x'' over a wide range of oxygen partial pressures (103–10−4 Pa) and temperatures (1000–1900 °C).<ref name="Bulfin2013">{{Cite journal | doi = 10.1021/jp406578z| title = Analytical Model of CeO2 Oxidation and Reduction| journal = The Journal of Physical Chemistry C| volume = 117| issue = 46| pages = 24129–24137| year = 2013| last1 = Bulfin | first1 = B.| last2 = Lowe | first2 = A. J.| last3 = Keogh | first3 = K. A.| last4 = Murphy | first4 = B. E.| last5 = Lübben | first5 = O.| last6 = Krasnikov | first6 = S. A.| last7 = Shvets | first7 = I. V.| hdl = 2262/76279| hdl-access = free}}</ref>

The non-stoichiometric form, which has a blue to black appearance, exhibits both ionic and electronic conduction with ionic being the most significant at temperatures > 500 °C.<ref>{{cite book | first1=K. | last1=Ghillanyova | first2=D. | last2=Galusek | editor1-first=Ralf |editor1-last=Riedel|editor2-first=I-Wie|editor2-last=Chen|title=Ceramics Science and Technology, Materials and Properties, vol 2|publisher=[[John Wiley & Sons]] |year=2011 |chapter=Chapter 1: Ceramic Oxides|isbn=978-3-527-31156-9|editor-link=Ralf Riedel}}</ref>

The number of oxygen vacancies is frequently measured by using [[X-ray photoelectron spectroscopy]] to compare the ratio of {{chem|Ce|3+}}to {{chem|Ce|4+}}.

The loss of oxygen continues into the molten liquid state where the local Ce-O coordination number drops to predominantly 6-fold, compared to 8-fold in the stoichiometric fluorite structure. This has been shown to be directly analogous to plutonium oxides, once differences in oxygen potential are accounted for.<ref>{{cite journal |last1=Wilke |first1=Stephen |last2=Benmore |first2=Chris |last3=Alderman |first3=Oliver |last4=Sivaraman |first4=Ganesh |last5=Ruehl |first5=Matthew |last6=Hawthorne |first6=Krista |last7=Tamalonis |first7=Anthony |last8=Andersson |first8=David |last9=Williamson |first9=Mark |last10=Weber |first10=Richard |title=Plutonium oxide melt structure and covalency |journal=Nature Materials |date=2024 |volume=23 |issue=7 |pages=884–889 |doi=10.1038/s41563-024-01883-3 |pmid=38671164 |bibcode=2024NatMa..23..884W |osti=2472836 |url=https://www.nature.com/articles/s41563-024-01883-3|url-access=subscription }}</ref>

===Defect chemistry=== In the most stable [[Fluorite structure|fluorite]] phase of ceria, it exhibits several defects depending on partial pressure of oxygen or stress state of the material.<ref>{{cite journal |last1=Munnings |first1=C. |first2=S.P.S. |last2=Badwal |first3=D. |last3=Fini |journal=Ionics |year=2014 |doi=10.1007/s11581-014-1079-2 |title=Spontaneous stress-induced oxidation of Ce ions in Gd-doped ceria at room temperature|volume=20 |issue=8 |pages=1117–1126 |s2cid=95469920 }}</ref><ref>{{cite journal |last=Badwal |first=S.P.S. |author2=Daniel Fini |author3=Fabio Ciacchi |author4=Christopher Munnings |author5=Justin Kimpton |author6=John Drennan |title=Structural and microstructural stability of ceria – gadolinia electrolyte exposed to reducing environments of high temperature fuel cells |journal=J. Mater. Chem. A |volume=1 |issue=36 |doi=10.1039/C3TA11752A |date=2013 |pages=10768–10782}}</ref><ref>{{Cite journal|last1=Anandkumar|first1=Mariappan|last2=Bhattacharya|first2=Saswata|last3=Deshpande|first3=Atul Suresh|date=2019-08-23|title=Low temperature synthesis and characterization of single phase multi-component fluorite oxide nanoparticle sols|journal=RSC Advances|language=en|volume=9|issue=46|pages=26825–26830|doi=10.1039/C9RA04636D|pmid=35528557 |pmc=9070433 |bibcode=2019RSCAd...926825A|issn=2046-2069|doi-access=free}}</ref><ref>{{cite journal |last1=Pinto |first1=Felipe M |title=Oxygen Defects and Surface Chemistry of Reducible Oxides |journal=Frontiers in Materials |date=2019 |volume=6 |page=260 |doi=10.3389/fmats.2019.00260 |bibcode=2019FrMat...6..260P |s2cid=204754299 |ref=Pinto, Felipe M., et al. "Oxygen Defects and Surface Chemistry of Reducible Oxides." Frontiers in Materials 6 (2019): 260.|doi-access=free }}</ref>

The primary defects of concern are oxygen vacancies and small [[polaron]]s (electrons localized on cerium cations). Increasing the concentration of oxygen defects increases the diffusion rate of oxide anions in the lattice as reflected in an increase in [[Ionic conductivity (solid state)|ionic conductivity]]. These factors give ceria favorable performance in applications as a solid electrolyte in [[solid-oxide fuel cell]]s. Undoped and doped ceria also exhibit high electronic conductivity at low partial pressures of oxygen due to reduction of the cerium ion leading to the formation of small [[polaron]]s. Since the oxygen atoms in a ceria crystal occur in planes, diffusion of these anions is facile. The diffusion rate increases as the defect concentration increases.{{cn|date=December 2025}}

==Natural occurrence== Cerium(IV) oxide occurs naturally as the mineral [[cerianite-(Ce)]].<ref name="mindat929">{{Cite web|title=Cerianite-(Ce)|url=https://www.mindat.org/min-929.html|access-date=2020-11-12|website=www.mindat.org}}</ref><ref name="minlist">{{Cite web|date=2011-03-21|title=List of Minerals|url=https://www.ima-mineralogy.org/Minlist.htm|access-date=2020-11-12|website=www.ima-mineralogy.org|language=en}}</ref> It is a rare example of tetravalent cerium mineral, the other examples being [[stetindite-(Ce)]] and [[dyrnaesite-(La)]]. The "-(Ce)" suffix is known as Levinson modifier and is used to show which element dominates in a particular site in the structure.<ref>{{Cite journal|last1=Burke|first1=Ernst|date=2008|title=The use of suffixes in mineral names|url=http://elementsmagazine.org/archives/e4_2/e4_2_dep_mineralmatters.pdf|journal=Elements|language=en|volume=4|issue=2|pages=96}}</ref> It is often found in names of minerals bearing [[rare earth elements]] (REEs). Occurrence of cerianite-(Ce) is related to some examples of [[cerium anomaly]], where Ce - which is oxidized easily - is separated from other REEs that remain trivalent and thus fit to structures of other minerals than cerianite-(Ce).<ref>{{Cite journal|last1=Pan|first1=Yuanming|last2=Stauffer|first2=Mel R.|date=2000|title=Cerium anomaly and Th/U fractionation in the 1.85 Ga Flin Flon Paleosol: Clues from REE- and U-rich accessory minerals and implications for paleoatmospheric reconstruction|journal=American Mineralogist|language=en|volume=85|issue=7|pages=898–911|doi=10.2138/am-2000-0703|bibcode=2000AmMin..85..898P|s2cid=41920305}}</ref><ref name="mindat929" /><ref name="minlist" />

==Applications== The principal industrial application of ceria is for polishing, especially [[Chemical-mechanical polishing|chemical-mechanical planarization]] (CMP).<ref name="Ullmann" /> For this purpose, it has displaced many other oxides that were previously used, such as [[iron oxide]] and [[zirconia]]. For hobbyists, it is also known as "opticians' rouge".<ref>{{Cite web|url=http://cameo.mfa.org/images/3/39/Download_file_187.pdf|title=Properties of Common Abrasives (Boston Museum of Fine Arts)}}</ref><ref>{{Cite web|url=https://cameo.mfa.org/wiki/Ceric_oxide|title=Ceric oxide - CAMEO|website=cameo.mfa.org}}</ref>

In its other main application, CeO2 is used to decolorize glass. It functions by converting green-tinted ferrous impurities to nearly colorless ferric oxides.<ref name="Ullmann"/>

===Other niche and emerging applications===

====Catalysis==== CeO2 has attracted attention in the area of [[heterogeneous catalysis]]. It catalyses the [[water-gas shift reaction]]. It oxidizes [[carbon monoxide]]. Its reduced derivative Ce2O3 reduces water, with release of hydrogen.<ref>{{cite journal |last1=Ruosi Peng |last2=et a.| title=Size effect of Pt nanoparticles on the catalytic oxidation of toluene over Pt/CeO2 catalysts | journal= Applied Catalysis B: Environmental | volume= 220 |year=2018|page=462 |doi=10.1016/j.apcatb.2017.07.048 |bibcode=2018AppCB.220..462P }}</ref><ref>{{cite journal|title=Fundamentals and Catalytic Applications of CeO2-Based Materials |last1=Montini|first1=Tiziano|last2=Melchionna|first2=Michele|last3=Monai|first3=Matteo|last4=Fornasiero|first4= Paolo |journal= Chemical Reviews|year=2016|volume=116|issue=10 |pages=5987–6041|doi=10.1021/acs.chemrev.5b00603|pmid=27120134 |hdl=11368/2890051 |hdl-access=free}}</ref><ref>{{cite journal|title=Oxygen Defects and Surface Chemistry of Ceria: Quantum Chemical Studies Compared to Experiment|last1= Paier|first1= Joachim|last2=Penschke|first2=Christopher|last3= Sauer|first3= Joachim|journal=Chemical Reviews|year=2013|volume=113|issue=6|pages=3949–3985|doi=10.1021/cr3004949|pmid=23651311}}</ref><ref>{{cite journal |doi=10.1002/aic.12234|title=Ceria in catalysis: From automotive applications to the water-gas shift reaction |year=2010 |last1=Gorte |first1=Raymond J. |journal=AIChE Journal |volume=56 |issue=5 |pages=1126–1135 |bibcode=2010AIChE..56.1126G }}</ref>

The interconvertibility of CeO''x'' materials is the basis of the use of ceria for an oxidation catalyst. One small but illustrative use is its use in the walls of [[self-cleaning ovens]] as a hydrocarbon oxidation catalyst during the high-temperature cleaning process. Another small scale but famous example is its role in oxidation of natural gas in [[gas mantle]]s.<ref>{{Greenwood&Earnshaw2nd}}</ref> [[File:Glowing gas mantle.jpg|thumb|right|A glowing [[Coleman Company|Coleman]] [[white gas]] lantern mantle. The glowing element is mainly [[thorium dioxide|ThO2]] doped with CeO2, heated by the Ce-catalyzed oxidation of the natural gas with air.]]

Building on its distinct surface interactions, ceria finds further use as a sensor in [[catalytic converter]]s in automotive applications, controlling the air-exhaust ratio to reduce [[Nitrogen oxide|NO''x'']] and [[carbon monoxide]] emissions.<ref>{{cite journal|title=Catalytic control of emissions from cars|author=Twigg, Martyn V.|journal=Catalysis Today|year=2011|volume=163|pages=33–41|doi=10.1016/j.cattod.2010.12.044 }}</ref>

==== Energy & fuels ==== Due to the significant [[Ionic compound|ionic]] and [[electron]]ic [[Electrical conductor|conduction]] of cerium oxide, it is well suited to be used as a [[mixed conductor]].<ref name="MPG2">{{cite web |title=Mixed conductors |url=http://www.fkf.mpg.de/2698712/MixedConductors |access-date=16 September 2016 |publisher=Max Planck institute for solid state research}}</ref> As such, cerium oxide is a material of interest for [[solid oxide fuel cell]]s (SOFCs) in comparison to [[Zirconium dioxide|zirconium oxide]].<ref>{{cite journal |last1=Arachi |first1=Y. |date=June 1999 |title=Electrical conductivity of the ZrO2–Ln2O3 (Ln=lanthanides) system |journal=Solid State Ionics |volume=121 |issue=1–4 |pages=133–139 |doi=10.1016/S0167-2738(98)00540-2}}</ref>

Thermochemically, the [[cerium(IV) oxide–cerium(III) oxide cycle]] or CeO2/Ce2O3 cycle is a two-step [[water splitting]] process that has been used for [[hydrogen production]].<ref>{{cite web |title=Hydrogen production from solar thermochemical water splitting cycles |url=http://www.solarpaces.org/Tasks/Task2/HPST.HTM |url-status=dead |archive-url=https://web.archive.org/web/20090830011704/http://www.solarpaces.org/Tasks/Task2/HPST.HTM |archive-date=August 30, 2009 |website=SolarPACES}}</ref><ref>{{cite web |title=CSIRO demonstrates new "beam-down" solar reactor to accelerate green hydrogen production |url=https://reneweconomy.com.au/csiro-demonstrates-new-beam-down-solar-reactor-to-accelerate-green-hydrogen-production/ |website=RenewEconomy |language=en-AU |date=16 June 2025}}</ref> Because it leverages the oxygen vacancies between systems, this allows ceria in water to form hydroxyl (OH) groups.<ref>{{Cite web |date=2018-07-01 |title=New discoveries made on the role of Cerium Oxide in Hydrogen production |url=https://www.ceric-eric.eu/2018/07/01/new-discoveries-made-on-the-role-of-cerium-oxide-in-hydrogen-production/ |access-date=2022-09-22 |website=Ceric |language=en-US}}</ref> The hydroxyl groups can then be released as oxygen oxidizes, thus providing a source of clean energy.

====Optics==== Cerium oxide is highly valued in the optics industry for its exceptional polishing capabilities.<ref>{{cite web |url=https://www.stanfordmaterials.com/blog/cerium-oxide-in-removing-scratches-from-phone-screens.html |title=Cerium Oxide in Removing Scratches from Phone Screens |website=Stanford Advanced Materials |access-date=July 1, 2024}}</ref> It effectively removes minor scratches and imperfections from glass surfaces through both mechanical [[Abrasion (mechanical)|abrasion]] and chemical interaction, producing a smooth, high-gloss finish.<ref>{{cite journal |last1=Janos |first1=Pavel |last2=Ederer |first2=Jakub |date=2016 |title=Chemical mechanical glass polishing with cerium oxide: Effect of selected physico-chemical characteristics on polishing efficiency |journal=Wear |volume=362-363 |pages=114–120 |doi=10.1016/j.wear.2016.05.020}}</ref> Cerium oxide can also enhance the [[durability]] of optical surfaces by forming a protective layer that increases resistance to scratches and environmental wear.<ref>{{cite book |date=1979 |title=The science of ceramic machining and surface finishing II: Proceedings of a symposium held at the National Bureau of Standards, Gaithersburg, Maryland, November 13-15, 1978 |editor-last1=Hockey |editor-first1=B.J. |editor-last2=Roy |editor-first2=Rice |publisher=University of Michigan Library |page=425 |asin=B0030T20RY}}</ref>

Cerium oxide has also found use in [[Infrared|infrared filters]] and as a replacement for [[thorium dioxide]] in [[Gas mantle|incandescent mantles]]<ref>{{cite web |title=Cerium dioxide |url=http://www.nanopartikel.info/cms/lang/en/Wissensbasis/Cerdioxid |url-status=dead |archive-url=https://web.archive.org/web/20130302081012/http://www.nanopartikel.info/cms/lang/en/Wissensbasis/Cerdioxid |archive-date=2013-03-02 |website=DaNa}}</ref>

====Welding==== Cerium oxide is used as an addition to tungsten electrodes for Gas Tungsten Arc Welding. It provides advantages over pure Tungsten electrodes such as reducing electrode consumption rate and easier arc starting & stability. Ceria electrodes were first introduced in the US market in 1987, and are useful in AC, DC Electrode Positive, and DC Electrode Negative.

==Safety aspects == Cerium oxide nanoparticles (nanoceria) have been investigated for their antibacterial and antioxidant activity.<ref name="RajeshkumarNaik20182">{{cite journal |last1=Rajeshkumar |first1=S. |last2=Naik |first2=Poonam |year=2018 |title=Synthesis and biomedical applications of Cerium oxide nanoparticles – A Review |journal=Biotechnology Reports |volume=17 |pages=1–5 |doi=10.1016/j.btre.2017.11.008 |issn=2215-017X |pmc=5723353 |pmid=29234605}}</ref><ref>{{cite journal |last1=Karakoti|first1= A. S.|last2= Monteiro-Riviere|first2= N. A.|last3= Aggarwal|first3=R.|last4=Davis|first4=J. P.|last5=Narayan|first5=R. J.|last6=Self|first6=W. T.|last7= McGinnis|first7=J.|last8=Seal|first8=S. |year=2008 |title=Nanoceria as antioxidant: synthesis and biomedical applications |journal=JOM |volume=60 |issue=3 |pages=33–37 |bibcode=2008JOM....60c..33K |doi=10.1007/s11837-008-0029-8 |pmc=2898180 |pmid=20617106}}</ref><ref>{{cite journal |vauthors=Hussain S, Al-Nsour F, Rice AB, Marshburn J, Yingling B, Ji Z, Zink JI, Walker NJ, Garantziotis S |year=2012 |title=Cerium dioxide nanoparticles induce apoptosis and autophagy in human peripheral blood monocytes |journal=ACS Nano |volume=6 |issue=7 |pages=5820–9 |doi=10.1021/nn302235u |pmc=4582414 |pmid=22717232}}</ref>

Nanoceria is a prospective replacement of [[zinc oxide]] and [[titanium dioxide]] in [[sunscreen]]s, as it has lower [[Photocatalysis|photocatalytic]] activity.<ref>{{cite journal |last1=Zholobak |first1=N.M. |last2=Ivanov |first2=V.K. |last3=Shcherbakov |first3=A.B. |last4=Shaporev |first4=A.S. |last5=Polezhaeva |first5=O.S. |last6=Baranchikov |first6=A.Ye. |last7=Spivak |first7=N.Ya. |last8=Tretyakov |first8=Yu.D. |year=2011 |title=UV-shielding property, photocatalytic activity and photocytotoxicity of ceria colloid solutions |journal=Journal of Photochemistry and Photobiology B: Biology |volume=102 |issue=1 |pages=32–38 |doi=10.1016/j.jphotobiol.2010.09.002 |pmid=20926307|bibcode=2011JPPB..102...32Z }}</ref>

== See also == * [[Cerium]] * [[Cerium anomaly]] * [[Zircon]]

==References== {{reflist|30em}} {{refbegin}} {{refend}}

==External links== {{Commons category|Cerium(IV) oxide}} *[http://www.webelements.com/compounds/cerium/ Webelements at University of Sheffield] *[https://web.archive.org/web/20100523171310/http://ceria.ru/ Synthesis and properties of ceria (in English/Russian)]

[[Category:Oxides]] [[Category:Cerium(IV) compounds]] [[Category:Catalysts]] [[Category:Sunscreening agents]] [[Category:Fluorite crystal structure]]