Preparation of Powders and thin Films of Complex Oxides From Metal Alkoxides
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ABSTRACT Preparation of complex oxides in the form of powders and thin films from metal alkoxides is discussed. Most attention is paid to terroelectric and related materials - complex titanates and zirconates. Techniques for preparation of high-purity morphologically homogeneous powders TiO2 , ZrO 2 , barium titanate and BaTiO 3 -based solid solutions, MgTiO 3 , Bi 2 WO 6, Bi2 MoO 6 are proposed and discussed with respect to their application in ceramics technology. The solutions prepared electrochemically in methoxyethanol were widely used for formation of thin films, e.g. Y_0 1 -stabilized ZrQ2 and PZT solid solutions on Pt-coated silicon substrates. INTRODUCTION The preparation of complex oxides in the forn of powders aid thin films is attracting increasing attention nowadays. However in many cases it remains impossible to give general recommendations for the choice of alkoxide substituents or hydrolysis conditions. Therefore in our work we try to optimize different stages of the preparation techniques (preparation of the initial alkoxide precursors, hydrolysis conditions and thermal treatment). In the case of powders, together with purity, chemical mid phase homogeneity, special attention was paid to the morphological characteristics of the powders. Working in cooperation with technologists we tried to make our techniques for preparation of powders and filn-fonning solutions suitable for tecinological applications. Most attention has been paid to ferroelectric and related materials - such as complex titanates and zirconates. Therefore, the preparation of TiO 2 and ZrO2 powders has been the focus of our studies. ZrO2 AND ZrO 2 -BASED SOLED SOLUTIONS ZrQ 2 -based materials were prepared by slow precipitation of the hydrated oxide from colloidal solution obtained by partial hydrolysis of metal alkoxides [1]: M(OR)n + H2 0 M(OR)n. 1(OH) + M(OR)n- 1 (OH)
-t
M(OR)n.I(OH) + ROH
(1)
--
(OR),. IM-O-M(OR)n . +H2 0
(2)
15 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
The morphology of the particles in this case is determined by the relative rates of nucleation anc growth on the one hand and their solubility in the solvent on the other hand. This method was first used for the preparation of high-quality silicon oxide powders by the process of hydrolysis ol Si(OR) 4 [2]. Recently however it was extended to the preparation of transition metal oxides suct as Tie 2 , ZrO2 , Ta2O5 [3]. We used different zirconium alkoxides Zr(OPr-i) 4 - i-PrOH, Zr(OBu) 4 , and "Zr(OC 2 H4 OMe) 4 " for preparation of ZrO2 -based powders. The general scheme of ZrO2 preparation comprised addition of a dilute solution of die Zr alkoxide component in EtOH to refluxing ethyl alcohol containing the necessary amount of water for hydrolysis. On cooling of the mixture, gradual precipitation occurred. Precipitates were isolated firom the mother liquor by centrifugation and precipitates separation was repeated several times (fractional sedimentation) at one-day intervals for several days. The precipitates were dried in air
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