Linear bulk photovoltaic effect and phenomenological study in multi-phase co-existing ferroelectric system.

Ferroelectric systems with multi-phase co-existence are found to exhibit anomalous photovoltaic response. In this work, detailed photovoltaic studies are carried out under 405 nm light illumination on Ba1-x(Bi0.5Li0.5)xTiO3ferroelectric oxides having the coexistence of tetragonal and orthorhombic phases. The linear and sinusoidal photocurrent-dependence as a function of light intensity and polarization-direction, respectively elucidate the experimental evidence for linear bulk-photovoltaic effect. Importantly, the temperature-dependent photovoltaic studies display 2-fold enhancement in photovoltage near the ferroelectric transition temperature (TC). The observed features in photovoltage follow inverse temperature-dependence of the photoconductivity. The linear relationship between the calculated bulk-photovoltaic tensor component and the photocurrent established from the proposed phenomenological model is verified through their composition-dependent studies. These studies provide the desired design parameters to engineer the ferroelectric system for better photovoltaic characteristics suitable for device applications.

Electric field and mechanical stress driven structural inhomogeneity and compositionally induced relaxor phase transformation in modified BaTiO3 based lead-free ferroelectrics.

The compositionally induced ferroelectric to relaxor transformation via diffuse phase transition and structural disorder by external stimuli is explored in lead-free Ba1-x (Bi0.5Li0.5) x TiO3 (x = 0, 0.05, 0.1, 0.15, and 0.20) ferroelectric system. X-ray diffraction studies reveal the coexistence of the monoclinic phase along with the orthorhombic and tetragonal phases in BaTiO3, which could be the reason for its superior dielectric properties. The dielectric studies reveal that the x = 0.15 sample shows intrinsic dielectric relaxation due to the quenched-in random field caused by the atomic displacement. The ferroelectric to relaxor phase transformation is analysed by modified Curie-Weiss law. Furthermore, the driving forces for the relaxor behaviour in the system are attributed to the compositionally induced charge disorder, quenched-in random field, and oxygen vacancy related defects in the BBLT system. The detailed structural analysis on the relaxor ferroelectric samples displays direct evidence for the electric field and mechanical stress driven structural inhomogeneity. Notably, mechanically stressed and electrically poled x = 0.15 sample exhibits a remarkable 50% and 37% increase in orthorhombic phase fraction, respectively. Overall, the comprehensive studies on the lead-free modified BaTiO3 samples give further insight into understanding the relaxor system.

Giant photovoltaic response in band engineered ferroelectric perovskite.

Recently the solar energy, an inevitable part of green energy source, has become a mandatory topics in frontier research areas. In this respect, non-centrosymmetric ferroelectric perovskites with open circuit voltage (VOC) higher than the bandgap, gain tremendous importance as next generation photovoltaic materials. Here a non-toxic co-doped Ba1-x(Bi0.5Li0.5) x TiO3 ferroelectric system is designed where the dopants influence the band topology in order to enhance the photovoltaic effect. In particular, at the optimal doping concentration (x opt ~ 0.125) the sample reveals a remarkably high photogenerated field EOC = 320 V/cm (VOC = 16 V), highest ever reported in any bulk polycrystalline non-centrosymmetric systems. The band structure, examined through DFT calculations, suggests that the shift current mechanism is key to explain the large enhancement in photovoltaic effect in this family.