Spectroscopic Characterization of Precursors Used in the Pechini-Type Polymerizable Complex Processing of Barium Titanate

Abstract

Precursor solutions containing citric acid (CA), ethylene glycol (EG), and barium and titanium ions, previously used in the Pechini-type polymerizable complex (PC) processing of BaTiO 3, have been extensively characterized by Raman and 13 C NMR spectroscopy. The simultaneous presence of Ba and Ti ions has brought about the unusual dissociation of proton from the alcohol OH group of CA, thereby creating an alkoxide oxygen atom with a strong nucleophilic nature, which prompts rearrangement of CA to form a barium−titanium mixed-metal CA complex with a stoichiometry close to Ba/Ti/CA = 1:1:3. The solution spectroscopy data have been compared with those obtained for an isolated mixed-metal CA complex from a solution with a chemical formula of BaTi(C 6 H 6 O 7 ) 3 ·4H 2 O. The Raman spectrum of BaTi(C 6 H 6 O 7 ) 3 ·4H 2 O has shown that the two terminal COOH groups of each CA coordinate in a monodentate fashion either to Ba or to Ti, while the central COOH group is not coordinating. The solid-state 13 C NMR spectrum of the same complex has indicated that the alcohol OH in CA is fully deprotonated to form an alkoxide oxygen atom, in agreement with the solution 13 C NMR data. A proposed model for the coordination structure of BaTi(C 6 H 6 O 7 ) 3 species, inferred from all these spectroscopic data, has displayed the presence of three fused six-memberd chelate rings arising from the full alkoxylation of CA ligands.