Caesium monoxide

Caesium monoxide, (Cs2O), often simply Caesium oxide, is the simplest and most common oxide of the caesium. It forms yellow-orange hexagonal crystals.[1]

Caesium oxide[1][2]
Caesium oxide
IUPAC name
Caesium oxide
Other names
Cesium oxide (US)
  • 20281-00-9 checkY
3D model (JSmol)
ECHA InfoCard 100.039.693 Edit this at Wikidata
EC Number
  • 243-679-0
  • InChI=1S/2Cs.O/q2*+1;-2 checkY
  • InChI=1/2Cs.O/q2*+1;-2
  • [Cs+].[Cs+].[O-2]
Molar mass 281.81 g/mol
Appearance yellow-orange solid
Density 4.65 g/cm3, solid
Melting point 490 °C (914 °F; 763 K) (under N2)
reacts violently to form CsOH
+1534.0·10−6 cm3/mol
anti-CdCl2 (hexagonal)
76.0 J K−1 mol−1
146.9 J K−1 mol−1
-345.8 kJ/mol
Main hazards Corrosive
GHS pictograms GHS05: CorrosiveGHS08: Health hazard
NFPA 704 (fire diamond)
Flash point non-flammable
Related compounds
Other anions
Caesium sulfide
Caesium selenide
Caesium telluride
Caesium polonide
Other cations
Lithium oxide
Sodium oxide
Potassium oxide
Rubidium oxide
Related caesium oxides
Caesium suboxide
Caesium peroxide
Caesium sesquioxide
Caesium superoxide
Caesium ozonide
Related compounds
Caesium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references


Caesium oxide is used in photocathodes to detect infrared signals in devices such as image intensifiers, vacuum photodiodes, photomultipliers, and TV camera tubes[3] L. R. Koller described the first modern photoemissive surface in 1929–30 as a layer of caesium on a layer of caesium oxide on a layer of silver.[4] It is a good electron emitter; however, its high vapor pressure limits its usefulness.[5]


Elemental magnesium reduces caesium oxide to elemental caesium, forming magnesium oxide as a side-product:[6][7]

Cs2O + Mg → 2Cs + MgO

Cs2O is hygroscopic, forming the corrosive CsOH on contact with water.


  1. ^ a b Lide, David R., ed. (2006). CRC Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. pp. 451, 514. ISBN 0-8493-0487-3..
  2. ^ Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 97–100. ISBN 978-0-08-022057-4..
  3. ^ Capper, Peter; Elliott, C. T. (2000), Infrared Detectors and Emitters, Springer, p. 14, ISBN 978-0-7923-7206-6
  4. ^ Busch, Kenneth W.; Busch, Marianna A. (1990), Multielement Detection Systems for Spectrochemical Analysis, Wiley-Interscience, p. 12, ISBN 978-0-471-81974-5
  5. ^ Boolchand, Punit, ed. (2000), Insulating and Semiconducting Glasses, World Scientific, p. 855,, ISBN 978-981-02-3673-1
  6. ^ Turner Jr., Francis M., ed. (1920), The Condensed Chemical Dictionary, New York: Chemical Catalog Co., p. 121
  7. ^ Arora, M.G. (1997), S-Block Elements, New Delhi: Anmol Publications, p. 13, ISBN 978-81-7488-562-3