Abstract
Charles Kittel has written a masterpiece book, “Introduction to Solid State Physics” (ISSP). He mentions in the chapter on ferroelectrics in detail that barium titanate is the typical displacive-type ferroelectric compound where the Ti4+ displacement develops a dipole moment, which has made a deep impression in our mind. The author’s group, however, has arrived at an alternative viewpoint on the unit cell structure of barium titanate based on their exhaustive experimental studies. Accordingly, the author sent his relevant papers in 2006 and 2007 to Kittel. He endorsed the results frankly with reminiscence. He mentioned revising the ferroelectric chapter of ISSP according the author’s suggestions. It appears to be admissible to publish details now after Kittel has passed away. A long time misunderstanding of the phase transition in barium titanate is due to the text book knowledge of ISSP.
Highlights
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More than seventy years ago, Megaw studied a powder sample of barium titanate, using a diffractometer [5]. She concluded that barium titanate has a tetragonal unit cell at room temperature
It is thought that barium titanate changes its structure from a cubic to a tetragonal at the phase transition temperature, but the tetragonal structure is unstable due to the comparatively large axial ratio, so that it immediately yields monoclinic domains interstitially inside of it, which causes the displacement current flow
Summary
Concerning the description of barium titanate BaTiO3 , he explains the Ti4+ displacement in the unit cell of the ferroelectrics phase, and mentions that this displacement develops a dipole moment. He does not reveal the structure figure in which the concrete distance of the Ti4+ displacement is expressed based on some reliable experimental measurement, but merely shows an illustration for the purpose of its explanation [3]. More than seventy years ago, Megaw studied a powder sample of barium titanate, using a diffractometer [5] She concluded that barium titanate has a tetragonal unit cell at room temperature. Could not clarify the essential structural nature of barium titanate
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