DETERMINATION OF THE C A RATIO OF A SUBMICROMETER-SIZED CRYSTAL OF TETRAGONAL BARIUM-TITANATE BY THE SYNCHROTRON-RADIATION/

The tetragonality of submicrometer-sized crystals of barium titanate, BaTiO3, has been investigated by the ultramicro single-crystal X-ray d iffraction technique using synchrotron radiation. The c/a ratios have been determined using the splitting of Laue spots due to twinning to b e 1.0072(2) and 1.0106(6) for crystals with conversion diameters of 0. 56 mum and 10 mum, respectively. The c/a ratio of the 10 mum crystal i s approximately the same as that of the bulk crystal, while it is sign ificantly small for the 0.56 mum crystal, indicating that the size eff ect on the tetragonal-to-cubic phase transition is remarkable in the s ubmicrometer region. No clear splitting due to tetragonal twinning was observed for the crystal with a conversion diameter of 0.25 mum, sugg esting that the critical size for the transition is close to this size .