DETWINNING FERROELECTRIC CRYSTALS 



947 



Single-crystal Experiments 



Parts A and B of Fig. 1 are photomicrographs of barium titanate crystals, 

 both grown from the same melt by B. T. Matthias. The composition of 

 the melt was 26 grams BaCOs , 6.5 grams Ti02 , 50 grams BaCl2 , and the 

 method followed was that described by Matthias in 1948^. Each of the 

 crystals shows several domains and some inhomogeneous strain as indicated 

 by birefringence evident between crossed nicols when the crystal is at the 

 extinction position, Fig. 2, A and B, i.e. when its edges are parallel to 

 the polarization directions in the polarizer and analyzer. An unstrained 

 crystal in this position appears black between crossed nicols. 



Fig 2 — A. Same as Fig. lA, but at extinction position. 

 B. Same as Fig. IB, but at extinction position. 



Optical Evidence of the Effect of a High Field 



However, crystal a can be made to assume essentially a single orientation 

 throughout by the application of a high field at elevated temperature as 

 shown in Fig. 3A, but the same treatment applied to crystal h results only 

 in the formation of a large number of domains, as shown in Fig. 3B. A 

 field of 16000 volts per cm. was applied across each crystal at 125°C. and 

 continued until the crystal had cooled to less than 50°C. Parts A and B of 

 Fig. 4 are the extinction-position photographs corresponding to Parts A 

 and B of Fig. 3. 



X-RAY Evidence of Inhomogeneous Strain 



The reason for the difference in behavior of the two crystals is suggested 

 by their back-reflection Laue photographs. Parts A and B of Fig. 5 are Laue 



• Matthias, B. T., Phys. Rev. 73, 808-9, 1948. 



