Determination of uncombined barium oxide in barium titanate by the X-ray diffraction method

Studies on analysis of electroceramics and its raw materials. III

Abstract

The determination of uncombined barium oxide in barium titanate which is synthesized from barium carbonate and titanium dioxide at high temperatures can be a useful production test. Although the acetic acid technique is used as a chemical test, more rapid method is required. The authors have studied the X-ray diffraction method to satisfy the requirement.
The crystal structure of barium titanate is tetragonal at the room temperature and the lattice constants are a =3.994Å and c =4.038Å. The X-ray diffraction peaks of the 002 and 200 reflections of a perfect crystal of barium titanate are separate from each other. However, if the crystal lattice of barium titanate is disordered during the synthesis, these diffraction peaks overlap each other.
The “overlapping value” is defined in order to express quantitatively the degree of the overlapping of the 002 and 200 reflections (Fig. 1) and is used to estimate uncombined barium oxide. It is found that the “overlapping value” increases when the temperature of the synthesis decreases. There are many factors of the broadening of the diffraction peaks. It is supposed that in this experiment the main factor is the disorder of the crystal lattice of barium titanate. Because perfect crystals of barium titanate are insoluble in acetic acid, the amount of the titanium soluble in acetic acid in the specimen is determined in order to examine the supposition. The amount of the soluble titanium increases as the temperature of the synthesis decreases. Moreover, the disorder of the crystal lattice of barium titanate is examined by Hall's method of X-ray diffractometry. Both results show a similar tendency. Therefore, the content of barium atoms which are not in their normal position in the crystal frame can be identified as the content of uncombined barium oxide from the “overlapping value”.
A linear relationship is observed between the “overlapping value” and the logarithm of the content of uncombined barium oxide which is determined by the acetic acid technique, when this content is between 0.3 and 10%. As the results of the experiment with the specimens which are synthesized by using the different kinds of titanium dioxide, the particle size of which are 0.3 and 7.5 μm respectively, it becomes clear that the particle size affects the “overlapping value” very seriously. However, the above-mentioned linear relationship holds for specimens prepared from the same titanium dioxide. Therefore, the calibration curve should be prepared by using the same titanium dioxide as that is used for samples.
The results by the proposed method and the acetic acid technique agree well, and the proposed method is useful for the production test in the synthetic process. The detecting limit of this method is about 0.3%, which is not achieved by the ordinary X-ray diffraction method.