Holmium carbonate is an inorganic compound of holmium and carbonate with the chemical formula Ho2(CO3)3. Hydrated forms are also known.
Preparation Holmium carbonate can be prepared by precipitation from aqueous Ho3+ solutions using ammonium bicarbonate.Li Xianbai; Yu Qinghua. "Preparation of crystalline dysprosium, holmium, erbium and yttrium carbonates". Rare Metals. 1994.
Rare-earth carbonate synthesis is strongly dependent on the precipitating reagent. Normal carbonates can also be obtained using soluble carbonate salts under suitable conditions.
Structure and properties Holmium carbonate is poorly soluble in water but dissolves in acids with release of carbon dioxide:
Ho2(CO3)3 + 6 H+ → 2 Ho3+ + 3 H2O + 3 CO2↑
Hydrated holmium carbonate phases are known. A hydrothermally synthesized hydrate with composition close to Ho2(CO3)3·3H2O adopts a structure related to the rare-earth carbonate mineral tengerite. Another reported hydrate, Ho2(CO3)3·2.25H2O, has a monoclinic structure.
Thermal decomposition On heating, holmium carbonate first loses water if hydrated and then decomposes to holmium(III) oxide. Rare-earth carbonates generally decompose through partial decarbonation, often involving an oxycarbonate intermediate.
For holmium carbonate, thermal studies have also reported decomposition without a clearly stable intermediate carbonate phase, with Ho2O3 as the final product.
The overall decomposition can be represented as:
Ho2(CO3)3 → Ho2O3 + 3 CO2↑
References