Temperature-dependent structural behavior of mixed-metal hydroxides in air

• Temperature-dependent structural behavior in air was investigated.
• The overall reaction of the mixed-metal hydroxide was proposed.
• The lattice parameters were refined for the variable temperature data.
• The various mixed-metal phases maintained homogeneity.

A co-precipitation process using transition metal hydrates was used to prepare a mixture of M(OH)2 and MO(OH) (M=Ni0.5Co0.2Mn0.3). This powder consisted of dense, quasi-spherical particles each composed of plate-like particles of ca. 250 nm across. By increasing the temperature, M(OH)2 was made to transform into MO(OH) at ca. 220 °C, then into M3O4 at ca. 330 °C. Moreover, the M3O4 phase persisted without further reaction until 700 °C. During these phase transitions, the mixed-metal (M) in M(OH)2, MO(OH) and M3O4 retained disordered cation distributions at the same crystallographic sites of their host lattices without appearance of any phases related to Ni, Co and Mn. The MO(OH) phase appeared owing to exposure to air. M(OH)2 at room temerature had the lattice parameters (a=b=2.9991(2) Å and c=8.5892(2) Å) with space group (P63/mmc).