Microstructure barium titanate

This kind of microstructure also influences other kinds of conductors, especially those with positive (PTC) or negative (NTC) temperature coefficients of resistivity. For instance, PTC materials (Kulwicki 1981) have to be impurity-doped polycrystalline ferroelectrics, usually barium titanate (single crystals do not work) and depend on a ferroelectric-to-paraelectric transition in the dopant-rich grain boundaries, which lead to enormous increases in resistivity. Such a ceramic can be used to prevent temperature excursions (surges) in electronic devices. 

Barium titanate, the first ceramic material in which ferroelectric behaviour was observed, is the ideal model for a discussion of the phenomenon from the point of view of crystal structure and microstructure see also [10] and [11]. 

Processing, Microstructure and Properties of Nanograin Barium Titanate Ceramics by Spark Piasma Sintering... 

The quality of the barium titanate starting powders used in ceramic fabrication is a key factor in determining the microstructure and properties of the final ceramic. 

Hosokura, T., Sakabe, Y., and Kuwabara, M. (2005) Preparation of barium titanate with patterned microstructure by a novel electrophoretic deposition method. /. Sol-Gel Sci. TechnoL, 33, 221-228. 

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). 

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