New compounds are described of general form [(ML3)xA]y where M is a rare earth metal or yttrium; L is a beta-diketone ligand; A is a linear polyether or polyamine; x and y are 1 or 2 depending on the identity of A and M. These compounds are precursors for chemical vapour deposition (CVD) of oxide layers in applications such as superconductors, piezoelectrics, microwaves, fuel cells, radiation detectors, optoelectronics and catalysts. They are an advance on previously reported materials because they are air and moisture stable, low melting, vacuum volatile at low temperatures leaving minimal residue and give good quality oxide deposits uncontaminated by fluorine. The diketone is preferably 2,2,6,6-tetramethyl-3,5-heptanedione. The polyether is selected from diglyme, triglyme or tetraglyme and the polyamine is selected from tetramethyl-ethylenediamine (tmeda), pentamethyl-diethylenetriamine (pmdeta), or hexamethyl-triethylenetetramine (hmteta).
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