Synthesis of complex metal oxides using hydroxide, cyanide, and nitrate solid solution precursors

Precursor solid solutions provide convenient routes for preparing complex metal oxides. Hydroxide solid solutions of the general formula $Ln_{1-x}M_x(OH)_3$ (where Ln = La or Nd and M = Al, Cr, Fe, Co, or Ni) and $La_{1-x-y}M'_xM″_y(OH)_3$ (where M′ = Ni and M″ = Co or Cu) crystallize in the rare earth trihydroxide structure and can be decomposed at relatively low temperatures to yield complex metal oxides. Several oxides of the type $LaNiO_3$, $NdNiO_3$, $LaNi_{1-x}Co_xO_3$, and $LaNi_{1-x}Cu_xO_3$ have been prepared by the hydroxide precursor route. Thermal decomposition of cyanide precursors of the type $Ln[M_{1-x}M′_x(CN)_6]$· $5H_2O$ and $Ln_{1-x}Ln′_x[M(CN)_6]$· $5H_2$O yields the quaternary oxides which are not readily made by ceramic methods. Nitrate solid solution precursors of the type $Ba_{1-x}Pb_x(NO_3)_2$, $Sr_{1-x}Pb_x(NO_3)_2$, and $BaSrPb(NO_3)_6$ have been used for preparing several interesting oxides such as $BaPbO_3$, $Ba_2PbO_4$, and $BaSrPbO_4$.