DETWINNING FERROELECTRIC CRYSTALS ^55 



the direction of their polarization. Such ceramics can be used iri piezo- 

 electric devices with high alternating fields without "depolarization" and 

 can therefore achieve electro-mechanical coupling at higher power levels 

 than ceramics that do not retain their polarization under the influence of 

 a reverse field. Only a small proportion of ceramic specimens could be poled 

 in this way and the factor common to these has not yet been ascertained. 



In the light of the single-crystal experiments reported in this paper, it 

 seems apparent that ceramics composed of inhomogeneously strained crys- 

 tals (excluding twin-boundary strain) could not be poled. Three ceramic 

 specimens whose poling history was known were available. Of these only 

 one could be poled. X-ray diffraction photographs of the two unpolable 

 ceramics showed streaked reflections from the individual grains, indicating 

 strain. The grain-size of the polable specimen was much smaller, so small 

 that reflections from individual grains could not be identified. 



It is anticipated that ceramics for different uses should be differently 

 fired and perhaps even differently composed as well as subjected to different 

 electrical treatment subsequent to their formation. 



