Vapour deposition method for preparing amorphous lithium-containing compounds

A vapour deposition method for preparing an amorphous lithium-containing oxide or oxynitride compound not containing phosphorous, the method comprising:

• providing a vapour source of each component element of the compound, wherein the vapour sources comprise at least a source of lithium, a source of molecular oxygen, and source or sources of one or more glass-forming elements;
• providing a substrate at a temperature below 100° C.;
• and
• co-depositing the component elements from the vapour sources onto the substrate, wherein the component elements react on the substrate to form the amorphous compound,
• in which the source or sources of one or more glass-forming elements comprises:
• a. a source of boron and a source of silicon, and the amorphous compound is lithium borosilicate;
• or
• b. a source of boron, a source of silicon and a source of nitrogen, and the amorphous compound is nitrogen-doped lithium borosilicate.