BaTiO_3-BaB_2O_4系状態図とその熔融物からのBaTiO_3結晶の育成 Phase Diagram of the BaTiO_3-BaB_2O_4 System and Growth of BaTiO_3 Crystals in the Melt

X線解析, 偏光顕微鏡による観察および示差熱分析により, BaTiO3-BaB2O4系平衡状態図を定めた. これによるとこの系の相図は単純共晶型であることが明らかになり, BaTiO3単結晶がBaB2O4をフラックスとして育成されうることがわかった. 具体的には45モル%BaTiO3の混合物を1150℃から950℃まで1-5℃/hrの速度で徐冷し, 数ミリの結晶を得ることが出来たが, 種結晶回転法がさらに適切であった. 得られた結晶は, 昇温過程で132.5°, 降温過程では130.3℃のキュリー点をもつことが示された.

(1) The phase diagram of the system BaTiO3-BaB2O4 has been determined by analyzing the quenched meterial by X-ray and polarizing microscope. Differential thermal analysis has been also used to determine the eutectic temperature in this system. The system makes a simple eutectic type diagram which has no intermediate compound. The eutectic point has been found at the composition of 32 mole% BaTiO3 and the temperature 942°C.(2) The diagram shows possibility of growing pure BaTiO3 by using BaB2O4 as flux material. Actually, pale lumpish crystals of about 5mm on edge were produced by simple cooling a mixture of 45 mole% BaTiO3 in platinum crucible from 1150° down to 955°C at the rate of 1°-5°C/hr. But a seed rotating technique seems to be more preferable to get good crystals, since the crystals grown by simple cooling method often encompass large flux inclusions.(3) Crystals thus obtained have Curie temperature at 132.5°C in heating process and 130.3°C in cooling process.The authors thank Dr. F. W. Perry for his valuable discussions in growing crystals by seed rotating technique.