NOVELTY - Producing particles having regions of at least one metal oxide having nano-sized grains, involves: (a) making a mixture of particles of material (P1) having an initial non-equiaxed shape and one or more precursors of at least one metal oxide; and (b) treating the mixture such that the precursors of the metal oxide react with particles (P1) to form regions of metal oxide on or within the particles, where atoms from (P1) form part of a matrix of metal oxide and the metal oxide has nano-sized grains and at least some of the regions of metal oxide have a non-equiaxed grain shape.    USE - For producing particles of material incorporating nano-sized metal oxides useful for producing nano-sized complex metal oxides (claimed), the particles of material may be in the form of metal or mixture of metals or metal alloys or metal compounds e.g. oxides, nitrates and/or hydroxides. The complex metal oxides are useful as e.g. catalysts for oil refining (cracking and reforming), as automotive exhaust catalysts, for manufacturing plastics, production of synthesis gas, in chemical synthesis or in the manufacture of fuel cells.    ADVANTAGE - The process provides complex metal oxide matrix incorporating the particles of material that exhibits uniform composition on the nanometer scale. The complex metal oxides formed have enhanced thermal stability compared to the complex metal oxides produced by the prior art methods. The initial morphology (e.g. nano-size) of the particles is retained in the metal oxide complex formed.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for producing complex metal oxide particles having nano-sized grains, involving: (1a) preparing a solution containing one or more metal cations; (1b) mixing the solution from step (1a) with surfactant such that surfactant micelles are formed within the solution to form a micellar liquid; and (1c) heating the micellar liquid from step (1b) to form metal oxide, the heating step is undertaken to remove the surfactant and to form metal oxide particles; the micellar liquid heated in step (1c) also contains particles of material of non-equiaxed particle shape, the particles containing one or more further metals in the form of metal(s) or metal compound(s) and the one or more metal cations react with the particles of material to form at least regions of metal oxide on or within the particles of material, where atoms from the particles of material form part of a matrix of at least one metal oxide and the metal oxide has nano-sized grains and at least some of the regions of metal oxide on or within the particles have a non-equiaxed grain shape.