Directional property tetragonal

Exists in five cryst modifications. The tetragonal form (obtained by the wet process) appears to have the most desirable electric properties and is described here d 6.08. mp 1625. Curie point 120". Has ferroelectric and piezoelectric properties. Becomes parmanently polarized when exposed to high voltage direct current, provided the temperature is never allowed to rise above Curie pt. Has high dielectric properties which can be influenced by temp, voltage, and frequency. 

In cubic crystals containing a small amount of a foreign ion such as Cu++ or Ni+ at low temperatures it is found (58) that each metal ion has a distorted environment, but that the tetragonal axis of this environment may have a number of equivalent orientations relative to the crystal as a whole. At higher temperatures the direction of the tetragonal axes changes so very rapidly that each ion experiences on the average a cubic crystal field. Thus impurity ions in a cubic crystal exhibit just the properties expected for isolated complexes, as indeed they should. 

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