Bandgap engineering of BZT-BCT by Mn doping and the emerging strong photo-pyroelectric effect

Developing narrow bandgap ferroelectrics with a sizable polarization presents great potential toward photoelectric applications. Unfortunately, most ferroelectrics exhibit wide bandgaps, while lowering their bandgaps constantly accompanies the serious deterioration of ferroelectricity. By utilizing the Jahn-Teller (J-T) effect of Mn ion, here we report an exception of lead-free ferroelectric 0.5Ba(Zr0.2-xTi0.8Mnx)-0.5(Ba0.7Ca0.3)TiO3 ceramics showing narrow bandgaps and large polarizations. Especially for the composition x = 0.12, a low bandgap of 1.2 eV with a high residual polarization 9.9 µC/cm2 is achieved. Further investigations indicate that it has negligible photovoltaic effect due to the high density of point defects, but a significant improvement in near-infrared (NIR) light induced pyroelectric response, driven by the simultaneously increased photothermal conversion ability and room temperature pyroelectric coefficient. The pyroelectric device as demonstrated shows excellent linear dependence on the NIR light intensity with current and voltage sensitivities of 0.169 nA/(mW/cm2) and 0.052 V/(mW/cm2), respectively. Furthermore, the device possesses substantial pyroelectric response to the infrared irradiation from human body and excellent anti-interference ability. This study not only find an excellent lead-free ferroelectric composition for human body recognition, but also provide a new strategy of materials design for light energy harvesting and photodetection.