Amorphous indium oxide is insoluble in water but soluble in acids, whereas crystalline indium oxide is insoluble in both water and acids. The crystalline form exists in two phases, the cubic (bixbyite type)[1] and rhombohedral (corundum type). Both phases have a band gap of about 3 eV.[3][4] The parameters of the cubic phase are listed in the infobox.
The rhombohedral phase is produced at high temperatures and pressures or when using non-equilibrium growth methods.[5] It has a space group R3c No. 167, Pearson symbol hR30, a = 0.5487 nm, b = 0.5487 nm, c = 1.4510 nm, Z = 6 and calculated density 7.31 g/cm3.[6]
Thin polycrystalline films of indium oxide doped with Zn2+ are highly conductive (conductivity ~105 S/m) and even superconductive at liquid helium temperatures. The superconducting transition temperature Tc depends on the doping and film structure and is below 3.3 K.[8]
When heated to 700 °C, indium(III) oxide forms In2O, (called indium(I) oxide or indium suboxide), at 2000 °C it decomposes.[9]
It is soluble in acids but not in alkali.[9]
With ammonia at high temperature indium nitride is formed:[14]
In2O3 + 2 NH3 → 2 InN + 3 H2O
With K2O and indium metal the compound K5InO4 containing tetrahedral InO45− ions was prepared.[15]
Reacting with a range of metal trioxides produces perovskites[16] for example:
^Prewitt, Charles T.; Shannon, Robert D.; Rogers, Donald Burl; Sleight, Arthur W. (1969). "C rare earth oxide-corundum transition and crystal chemistry of oxides having the corundum structure". Inorganic Chemistry. 8 (9): 1985–1993. doi:10.1021/ic50079a033.
^Feng, Tom and Ghosh, Amal K. (1984) "Method for forming indium oxide/n-silicon heterojunction solar cells" U.S. patent 4,436,765
^Wiberg, Egon and Holleman, Arnold Frederick (2001) Inorganic Chemistry, Elsevier ISBN0123526515
^Lulei, M.; Hoppe, R. (1994). "Über "Orthoindate" der Alkalimetalle: Zur Kenntnis von K5[InO4]". Zeitschrift für anorganische und allgemeine Chemie. 620 (2): 210–224. doi:10.1002/zaac.19946200205.
^Shannon, Robert D. (1967). "Synthesis of some new perovskites containing indium and thallium". Inorganic Chemistry. 6 (8): 1474–1478. doi:10.1021/ic50054a009. ISSN0020-1669.