The invention relates to a multilayer material deposited by ALD. A multi-layer structure of a high refractive index material is deposited on a substrate using ALD at a temperature below about 450° C. Advantageous results are obtained when a high refractive index material A is coated with another material B after a certain thickness of material A has been achieved. Thus, the B barrier layer stops the tendency for material A to crystallize. The amorphous structure gives rise to less optical loss. Further, the different stress nature of materials A and B may be utilized to achieve a final optical material with minimal stress. The thickness of each material B layer is less than that of the adjacent A layer(s). The total effective refractive index of the high refractive index material A+B being shall be greater than 2.20 at a wavelength of 600 nm. Titanium oxide and aluminium oxide are preferred A and B materials. The structure is useful for optical coatings.