Pressure-induced Transitions of Synthetic BiFeO3 Powders

• Main Authors: Zan-wun Chen, 陳贊文
• Other Authors: Jiann-Shing Lee
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/84831184533833994351

碩士 === 國立屏東教育大學 === 應用物理系 === 100 === There are several high-pressure modifications of BiFeO3 (Bismuth ferrite, BFO) whose symmetry and structures are still a matter of debate in the literature. In order to evaluate the effect of impurity substitution on phase transition of BFO, a hydrothermal synthesis route as well as flux-grown technique was utilized to fabricate pure BFO and doped BFO samples. In order to reveal the affecting factor of impurity on the BFO structure, the comparative high-pressure X-ray diffraction on these powders have been be performed through DAC device. The experimental results indicate that the pure BFO as well as doped BFO powder has been successively synthesized through those two synthetic routes. In addition, we obtain a small decrease in BFO particle size with an increase of the Ba-, Pb- and Ca-ion doping concentration in the flux-grown method. X-ray diffraction experiments on pure and doped BiFeO3 powders in diamond-anvil cells show that phase transitions take place in a similar way for pure and doped BFO. As a result, modifications in phase transition behavior due to minor ion incorporation highlight the low sensitivity of BFO to variations of chemical composition. The similar procedures (R3c → C2/m+OIII → Pnma) of reconstructive phas transition are observed in pure, Ca-doped and Pb-doped BFO samples. However, it is shown that the intermediate phase OIII is not detected in Ba-doped sample. Therefore, the present study suggests that a significant structural distortion induced by big Ba ion incorporation inhibits the crystallization of OIII phase. The bulk moduli of R3c were obtained by fitting cell-volume data with a second-order Birch-Murnaghan equation-of-state with K′ (= ∂K/∂P) fixed at 4, and were found to be K=155.8(0.3) GPa, 159.4(0.4) GPa, 205.5(1.0) GPa, 105.8(0.3) GPa for pure, Ca-, Pb-, and Ba-doped BFO, respectively. It is suggested that the remarkable difference in bulk modulus of R3c could be attributed to the size-induced effect.