Generally speaking, tantalum and niobium have almost the same method in preparing the precursors of ferroelectric materials, because tantalum and niobium are both VA transition elements with similar atomic radii and very similar properties. However, the main disadvantages of the alkali-based process are that tantalum ethanol and niobium ethanol are expensive, extremely sensitive to moisture, and the preparation process requires a strictly dry environment, usually in a Glove box, and some chemical reactions need to be carried out on a Schlenk vacuum line. Storage of prepared precursor solution also requires waterproof gas and short service life. Although some improvement measures have been adopted, such as replacing alkoxy groups with ligands such as ethylene glycol methyl ether, which has partially improved the stability of the precursor, the problem cannot be fundamentally solved, and the commercial application of similar precursor systems has been greatly restricted. Tantalum pentachloride and niobium pentachloride have also been used as precursors to tantalum or niobium. Although it is less expensive and has improved stability compared to alcohols, it is inevitable that the small residual chlorine in the final material may deteriorate the photoelectrical properties associated with the material.
To provide a method for the preparation of stable water-soluble niobium and tantalum precursors and to apply the precursors to ferroelectric thin films and powders. The invention also aims to provide a method with low cost of raw materials, simple process, suitable for industrial application and quality assurance for ferroelectric film preparation.
The purpose of the invention is to use tantalum or niobium pentaoxide as raw material, mix niobium pentaoxide or tantalum pentaoxide with potassium hydroxide or sodium hydroxide in a certain ratio of molar ratio and grind them evenly, put them into a corundum crucible, and burn them at 400-550℃ for 2-4 hours to obtain melts of potassium niobate (sodium) or potassium tantalate (sodium). Dissolve the melt in deionized water, and add proper amount of acetic acid to the filtrated clear solution. White niobic acid precipitate (Nb2O5·nH2O) or tantalic acid precipitate (Ta2O5·nH2O) will be generated in the solution, and then adjust the PH value (PH < 4).
The preparation method of stable water-soluble niobium and tantalum precursor, using tantalum or niobium pentaoxide as raw material, niobium or tantalum pentaoxide and potassium hydroxide or sodium hydroxide according to the molar ratio of mixing and grinding evenly, at 400-550℃ burning reaction for 2-4 hours, to obtain potassium niobate (sodium) or potassium tantalum (sodium) melt; The melt was dissolved in deionized water, and the filtrated clear solution was strongly acidic (pH < 2). Niobium or tantalum in the solution was precipitated completely in the form of niobium or tantalum acid. The niobic acid precipitate was added to an aqueous solution of citric acid or tantalic acid precipitate was added to an aqueous solution of oxalic acid to obtain a water-soluble niobium precursor or tantalum oxalic acid solution. The invention is used to prepare ferroelectric precursor solution such as SBN, and obtain extremely stable water-soluble tantalum or niobium precursor through a simple and feasible synthesis path using cheap and stable raw materials.
