Preparation and characterization of uniform submicrometer metal niobate particles. I. Lead niobate
- PDF / 1,854,268 Bytes
- 11 Pages / 576 x 792 pts Page_size
- 68 Downloads / 180 Views
Colloidal amorphous lead niobate particles of different composition and morphologies were obtained by a metal-chelate decomposition method. The nature of the dispersions depended on the conditions of the preparation of the complexes, pH, aging time, and temperature. The structural and chemical changes of the so prepared powders on calcination were investigated by thermal and x-ray diffraction analyses. Chemical mechanisms of the formation and transformation of the particles are suggested.
I. INTRODUCTION
II. EXPERIMENTAL
Owing to their optical and electric properties, metal niobates have become important ceramic materials. For example, lithium niobate (LiNbO3) has excellent electrooptical, acoustooptical, and piezoelectrical characteristics,1 while lead based niobates, such as lead magnesium niobate, Pb(Mgi/3Nb2/3)O3, are promising dielectric materials for capacitors.2 Pure powders consisting of uniform particles of these compounds are desirable for good sinterability, dense packing, and fine-grained microstructures, which can lead to high quality products.3 Recent efforts in the preparation of such materials have been focused on the liquid phase techniques, since solid state reactions could not yield small and pure particles. Thus, Feng and Schulze obtained lead scandium niobate, Pb(Sc1/2Nbi/2)O3, by first precipitating niobium oxide (Nb2O5) by hydrolysis of alkoxide, then coating it with lead and scandium carbonates.4 Chaput et al.s synthesized lead magnesium niobate by hydrolysis of mixed alkoxides. Despite much research on binary niobates, pure phase and uniform size powders have not been achieved. Specifically, conflicting results are reported on the reaction between PbO and Nb2O5.6 There are six different lead niobate compounds with even more crystal structures, some of which are of quite similar symmetry,7'8 explaining the difficulties in understanding the reactions and in synthesizing pure phase products. Recently, uniform submicrometer particles of barium titanate9 and lead titanate10 were prepared by a metal-chelate decomposition method. A modification of this novel procedure was employed in this work to precipitate uniform finely dispersed lead niobates, which has helped to develop some mechanisms of chemical reactions yielding such materials.
A. Particle preparation
a)
Part of a Ph.D. Thesis by M. J. Kim.
840 http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 4, Apr 1991 Downloaded: 02 Apr 2015
All chemicals were of reagent-grade quality. Niobium pentachloride (SPEX), lead nitrate (Fisher), disodium salt of nitrilotriacetic acid (NTA, Aldrich), hydrogen peroxide (30%, Mallinckrodt), hydrochloric acid (37%, J.T. Baker), and ammonium hydroxide (VWR) were used as received. The solutions were filtered on 0.2 fim pore size Nuclepore membranes to remove any possible solid contaminants. The following stock solutions were prepared: Solution A: 0.1 mol dm 3 NbCl5; 0.1 mol dnT3 HC1; 5.0 moldm 3 H 2 O 2 Solution B: 0.1 moldm"3 Pb(NO3)2 Solution C: 0.1 moldm 3 disodium salt nitrilotriacetic acid (Na
Data Loading...
