Structure evolution in the PbO-ZrO₂-TiO₂ sol-gel system: Part I - Characterization of prehydrolyzed precursors

In this investigation, several spectroscopic and analytical techniques were used to determine the chemical compositions and structures of the lead, zirconium, titanium, and Pb-(Zr, Ti) alkoxides involved in the sol-gel synthesis of PZT thin films. These techniques included ¹H, ¹³C, and ²⁰⁷Pb NMR; FT-IR; gas chromatography; Karl Fischer titration; and number-average molecular weights (M_n) determined by cryoscopy. It was found that the titanium precursor had a M_nof 548 and a formula of [Ti(OCH₂CH₂OCH₃)₄]_1.6; the zirconium precursor had a M_nof 1015 and a formula of [Zr(OCH₂CH₂OCH₃)₄]_2.6; and the lead precursor had a formula Pb₆(OOCCH₃)₅(OCH₂CH₂OCH₃)₇. 4 H₂O and a molecular weight of 2131 (M_n=2113). It was observed that residual water from the incomplete dehydration of lead acetate trihydrate coupled with released water due to the esterification of acetic acid caused M-O-M (M=Pb, Zr, Ti) bonds in the Pb-(Zr, Ti) alkoxide. Two possible isomeric structures of the Pb-(Zr, Ti) alkoxide have been proposed. They are both cyclic and have a formula of Pb₂M′M″O₂(OR)₈(ROH)₂, (M′M″=Zr and/or Ti) and a molecular weight of 1336 (M_n=1386).