KF添加のチタン酸バリウム単結晶（Ba1 －xKxTiO3 －xFx）において，x ＝0.1のとき，室温での圧電定数d33が300 pCN －1と大きな値を持つことを見出した。また，BaTiO3とは組成の異なるBaTi2O5単結晶において，誘電率が30000にも達する誘電異常がTC＝750 K 付近に存在し，室温で7 µCcm －2の自発分極が出現することを見出した。応用的にも興味深く思われるので，これら新規チタン酸バリウム系強誘電体単結晶の誘電的，熱的，構造的特徴を，BaTiO3の場合と比較しつつ紹介する。
Barium titanate single crystals doped with KF (Ba1－xKxTiO3－xFx with x＜－0.1) have been successfully grown; the ferroelectric Curie temperature TC decreases with increasing x. Moreover, the crystal with x＝0.1 has a large dielectric constant of e'＝1200 and has a large piezoelectric constant of d33＝300 pC N－1 at room temperature. On the other hand, in barium dititanate (BaTi2O5) single crystals, a spontaneous polarization of 7 mC cm－2 has been observed at room temperature. The e' measured at 1 MHz reaches very large value of approximately 30000 at the ferroelectric Curie temperature of TC＝750 K, while the dielectric loss tand remains small at values below 0.1 at around TC. These dielectric, thermal and structural properties of the single crystals are described in detail.
