Praseodymium(III)-substituted bismuth titanate thin-film generation using metallo-organic precursors with an M-O-C skeleton and sol-gel technique and employing 4f-4f transition spectra as a probe to explore kinetic performance

Abstract

A hetero-trimetallic lanthanide-substituted bismuth titanate (BLT, where lanthanide is praseodymium) with stoichiometry Pr0.75Bi3.25 Ti3O12 has been obtained as both highly homogenized crystalline and amorphous thin films using three different BLT precursors: (i) precursor A - (Pr(OC3H7i)3,Bi(OOCCH 3)3,Ti(OC3H7i) 4); (ii) precursor B - (Pr(OC3H7i)2(acac),Bi(OOCCH 3)3,Ti(OC3H7i) 3(acac)); and (iii) precursor C - (Pr(OC3H7i)2(acac),Bi(OOCCH 3)3,Ti(OC3H7i) 2(acac))2. These three BLT precursors (A, B, C) are prepared by reacting constituent monometallic precursors in the desired stoichiometry and by employing controlled acidic hydrolysis via the sol-gel method. Paramagnetic Pr(III), being a f2 ion, gives characteristic 4f-4f transition bands (3H4→3P2, 3H4→3P1, 3H4→3P0, and 3H4→1D2) in the visible region, the intensities of which have been found to be highly sensitive to even minor changes in the immediate coordination around Pr(III), occurring as a result of the progress of polycondensation reactions of three multicomponent BLT sols. We have used the changes with time in the intensities (represented by oscillator strengths of these four 4f-4f bands) and the magnitude and variation of the spectral parameters evaluated from the observed spectra with a view toward monitoring the sol-gel reactions of BLT precursors A, B, and C. 4f-4f transition spectra of the aliquots, withdrawn from the hydrolyzing A, B, and C sols at different time intervals, represent the changes occurring in the Pr(III) environment with the progress of sol-gel hydrolysis of BLT, and are used to investigate the kinetic performance in hydrolysis of the three precursors. Kinetics of hydrolysis of precursors A, B, and C indicate that all four f-f transition bands of Pr are almost equally sensitive to precursor hydrolysis in the order A>B>C. © 2003 Elsevier Science (USA). All rights reserved.