Netsu Sokutei, 33 (4), p. 160, (2006)



New Ferroelectrics in Barium Titanate System

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.