Structural Properties and Phase Transitions of Bi_{4 −x}La_xTi₃O₁₂ Crystals

Abstract

The measurement of P-E loops, dielectric, thermo-mechanical and micro-structural properties was performed on ferroelectric Bi_{4 − x} La _x Ti₃O₁₂ (BLT) crystals in order to clarify their ferroelectricity and to provide an explanation for the phase transition with La incorporated. The grown c-axis Bi_4.3Ti₃O₁₂ and Bi_3.65La_0.47Ti₃O₁₂ crystals showed ferroelectricity but the P-E hysteresis loop of the c-axis Bi_2.76La_1.67Ti₃O₁₂ crystal was not fully saturated. BLT crystals tend to change from a monoclinic to an orthorhombic structure with increasing La concentration because they substitute La for Bi with a lone-pair electron. From the measurement of physical properties under varying temperatures, the ferroelectric phase transition of BLT crystals was showed to occur at temperature close to 500°C.

Keywords:

• Bi_{4 −x} La _x Ti₃O₁₂ crystals
• orthorhombic structure
• lone pair electron
• ferroelectric phase transition

ACKNOWLEDGEMENT

This work was supported by grant No. R01-2003-000-10027-0 from the Korea Science & Engineering Foundation.