Crystal structure of a strontium-tantalum and a magnesium-niobium heterometal alkoxide: precursors for the MOCVD of ferroelectric oxides

The heterometal alkoxides Sr[Ta(OPri)(6)](2). 2Pr(i)OH 1 and Mg[Nb(OEt)(6)] (2). 2EtOH 2 have been structurally characterised by X-ray diffraction. Com pound 1 is a precursor for the deposition of strontium bismuth tantalate (S rBi2Ta2O9) by metalorganic chemical vapour deposition (MOCVD), whilst 2 is a potential precursor for the MOCVD of lead magnesium niobate [Pb(Mg0.33Nb0 .66)O-3]. In this paper it is shown how the presence of Pb(thd)(2) (thd = 2 ,2,6,6-tetramethylheptane-3,5-dionate) significantly influences the deposit ion chemistry of 2. In the absence of Pb(thd)(2) and at low substrate tempe ratures (ca. 425 degreesC) the Mg:Nb ratio in the oxide film grown from 2 i s close to 1:2, whereas at higher substrate temperatures (600 degreesC) the films are magnesium deficient, indicating partial decomposition of 2. Howe ver, in the presence of Pb(thd)(2) films grown from 2 at low temperature (4 25-500 degreesC) contain no detectable Mg whilst the 1:2 Mg:Nb ratio, requi red in Pb(Mg0.33Nb0.66)O-3, is now obtained at higher substrate temperature s (600 degreesC). This is attributed to the formation of a thermally stable Mg beta -diketonate species via a gas-phase ligand exchange reaction betwe en Pb(thd)(2) and 2.