Uranium oxide is an oxide of the element uranium

Uranium

Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

.

The metal uranium forms several oxides:

• Uranium dioxide
  Uranium dioxide
  Uranium dioxide or uranium oxide , also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used...
  
   or uranium(IV) oxide (UO₂, the mineral Uraninite
  Uraninite
  Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements...
  
   or pitchblende)
• Uranium trioxide
  Uranium trioxide
  Uranium trioxide , also called uranyl oxide, uranium oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph, γ-UO3, is a yellow-orange powder.-Production and use:There are three methods...
  
   or uranium(VI) oxide (UO₃)
• Triuranium octoxide (U₃O₈, the most stable uranium oxide, yellowcake
  Yellowcake
  Yellowcake is a kind of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores...
  
   typically contains 70 to 90 percent triuranium octoxide)
• Uranyl peroxide
  Uranyl peroxide
  Uranyl peroxide or uranium peroxide hydrate is a pale-yellow, soluble peroxide of uranium. It is found present at one stage of the enriched uranium fuel cycle and in yellowcake prepared via the in situ leaching and resin ion exchange system. This compound, also expressed as:UO3··, is very similar...
  
   (UO₂O₂ or UO₄)

Uranium dioxide is oxidized in contact with oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

to form triuranium octoxide.

3 UO₂ + 4 O₂ → U₃O₈; at 700 °C (970 K)

Uranium Oxide is one of the few compounds which bonds in Fibonacci numbers of atoms, e.g. 3 Uraniums and 8 Oxygens etc.
Uranium Oxide compounds pair up in Fibonacci numbers skipping one out in the middle, for example, Triuranium Octoxide, with 3 Uranium atoms and 8 Oxygen atoms.

Preparation 38

During World War II "Preparation 38" was the codename for uranium oxide used by the German scientists.