The Internal Bias Field of Ferroelectric (CH₃NH₃)₅Bi₂Br₁₁

Abstract

Spontaneous polarization of (CΗ3ΝΗ3)5Βi2Brιι crystals has been measured and the ferroelectric hysteresis loop has been studied. The observed time changes in the polarization have been ascribed to the change in the internal bias field of the crystal. Measurement results have also been discussed for the lower phase transition (ΤII = 77 K).

Polarization relaxation in (CH3NH3)5Bi2Br11 ferroelectric crystals

“…In these crystals there are regions which are strongly disposed towards a definite orientation of the polarization. Although the MAPBB crystals were not defected intentionally, they were grown in the ferroelectric phase with an excess of HBr and Br 2 molecules may form defect complexes, which stabilize the domain structure [18]. The results presented here refer to a single sample of MAPBB crystal, but they are typical of a fairly large number of specimens which reveal initial static unipolarity not removed during the annealing of the crystal above the T C .…”

Effect of internal bias field on domain switching in (CH3NH3)5Bi2Br11 crystal

“…Although the MAPBB crystals have not been defected intentionally, they were grown in the ferroelectric phase with an excess of HBr and Br 2 molecules may form defect complexes which stabilize the domain structure. 12 In some crystal samples the unipolar state observed in an as-grown crystal can be removed by the annealing of the crystal above the Curie temperature; thus it may be connected with the aging process. The selected sample exhibits a natural unipolarity not removed during the annealing process; thus it may be due to characteristic features of the growth of the crystal.…”

Phase Transitions in (CH3NH3)5Bi2X11(X=Cl, Br) Crystals

“…Hysteresis phenomena and temporary changes of the spontaneous polarization below Τ' . [9] show non-typical behaviour of the (CH3ΝΗ3)5Bi2Br11 crystals. In the low temperature region both analogues display the second-order phase transition with dielectric anomaly seen along the c-axis [10,11].…”

“…In the low temperature region both analogues display the second-order phase transition with dielectric anomaly seen along the c-axis [10,11]. The nontypical behaviour of spontaneous polarization [9] prompted us to examine electric properties along the b-axis in these crystals. Preliminary measurement results showed the existence of the spontaneous polarization along the b-axis at room temperature.…”