Ti precursor characteristics

Barium titanate powders were produced using either an amorphous hydrous Ti gel or anatase precursor in a barium hydroxide (Ba(OH)2) solution via a hydrothermal technique in order to discern the nucleation and formation mechanisms of BaTi03 as a function of Ti precursor characteristics. Isothermal reaction of the amorphous Ti hydrous gel and Ba(OH)2 suspension is believed to be limited by a phase boundary chemicd interaction. In contrast, the proposed BaTi03 formation mechanism from the anatase and Ba(OH>2 mixture entails a dissolution and recrystallization process. BaTi03 crystallite nucleation, studied using high resolution transmission electron microscopy, was observed at relatively low temperatures (38°C) in the amorphous hydrous Ti gel and Ba(OH)2 mixture. Additional solution conditions required to form phase pure crystallites include a C02-free environment, temperature >70°C and solution pH >13.4. Analysis of reaction kinetics at 75°C was performed using Hancock and Sharp s modification of the Johnson-Mehl-Avrami approach to compare observed microstructural evolution by transmission electron microscopy (7). 

Ti Precursor Characteristics. The phase of the as-received hydrous Ti gel was both XRD and TEM amorphous. Heat treatment of the as-received gel at 130°C produced a mixture of an amorphous phase with anatase. Increase in the reaction temperature to the 150°C hydrothermal treatment produced anatase crystallites, whereas calcination at 600°C produced a rutile phase. Further investigation proceeded with only the as-received gel and hydrothermally treated precursor, hereafter referred to as the anatase precursor. Observation of the precursor morphology by TEM indicated a fine gel structure and a lOnm granular nature for the as-received hydrous gel and anatase precursor, respectively. 

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