Pyroelectric properties of bismuth ferrite in the low-temperature range

The pyroelectric effect in bismuth ferrite single crystals is studied in the temperature range from 4.2 to 200 K (limited from above only by the high conductivity of the sample). A nonmonotonous character of the temperature dependence of the pyroelectric coefficient is revealed in the range 120-160 K: at T = 140 K, the pyroelectric coefficient reaches the maximum value equal to 1.2 x 10(-4) C/(m(2) K). The crystallophysical analysis of the BiFeO3 structure based on the structural data confirms that the octupole moment of the structure makes the main contribution to the spontaneous polarization. This circumstance leads to a small (in comparison with isostructural compounds) spontaneous polarization of bismuth ferrite and anomalous behavior of the pyroelectric coefficient caused by the contribution of local vibrations of strongly distorted TiO6 octahedra.