Role of domain walls in the abnormal photovoltaic effect in BiFeO3

Recently, the anomalous photovoltaic (PV) effect in BiFeO3 (BFO) thin films, which resulted in open circuit voltages (V-oc) considerably larger than the band gap of the material, has generated a revival of the entire field of photoferroelectrics. Here, via temperature-dependent PV studies, we prove that the bulk photovoltaic (BPV) effect, which has been studied in the past for many non-centrosymmetric materials, is at the origin of the anomalous PV effect in BFO films. Moreover, we show that irrespective of the measurement geometry, V-oc as high as 50V can be achieved by controlling the conductivity of domain walls (DW). We also show that photoconductivity of the DW is markedly higher than in the bulk of BFO

Characterisation of Pyroelectric Materials

Pyroelectrics form a very broad class of materials. Any material which has a crystal structure possessing a polar point symmetry—i.e. one which both lacks a centre of symmetry and has a unique axis of symmetry—will possess an intrinsic, or spontaneous, polarisation and show the pyroelectric effect. The pyroelectric effect is a change in that spontaneous polarisation caused by a change in temperature. It is manifested as the appearance of free charge at the surfaces of the material, or a flow of current in an external circuit connected to it. The effect is a simple one, but it has been used in a range of sensing devices, most notably uncooled pyroelectric infra-red (PIR) sensors, and has thus come to be of some engineering and economic significance, enabling a wide range of sensing systems, ranging from burglar alarms through FTIR spectroscopic instruments to thermal imagers