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Domain structures in polar materials provide an additional degree of freedom to tune ferroelectric photovoltaic (PV) effects. One of the approaches to control domain structures is to form a solid solution with analogs in different symmetries. In this study, we investigate the influence of domain structures on the PV properties of ferroelectric thin films in the xBaTiO3–(1−x)BiFeO3 (BT–BFO) solid-solution system (x = 0.1 and 0.2). We found that a substitution of BT for BFO substantially decreases the domain size down to several tens of nanometers, leading to an enhanced PV response owing to a marked contribution of the domain-wall PV effect.

We investigate ferroelectric BaTiO3 capacitors with SrRuO3-based electrodes employing a (BaxSr1−x)TiO3 (BST) buffer layer on (100) SrTiO3 substrates prepared by pulsed laser deposition. Structural analysis by high-resolution X-ray diffraction reciprocal space mapping shows that the BST (x = 0.5 and 0.7) layers are relaxed and have their bulk in-plane lattices in the upper part owing to strain relief. The bottom electrodes on the buffer layers grow heteroepitaxially but cannot withstand a tensile stress and then show a diminution of the in-plane lattice. On the BST (x = 0.7) layer, compared with the capacitor with an SrRuO3 electrode, that with a Ba0.1Sr0.9RuO3 one has a reduced in-plane lattice relaxation of the BaTiO3 film and then exhibits a larger remanent polarization (Pr) of 34 μC/cm2 associated with a smaller shift of the hysteresis loop. The polarization hysteresis shift is attributed to a flexoelectric effect stemming from the coupling between out-of-plane polarization and a strain gradient in the BaTiO3 film. We conclude that a reduced misfit strain relaxation in the ferroelectric film achieved with the Ba0.1Sr0.9RuO3 electrode on the thicker BST (x = 0.7) buffer layer is the origin of an enhanced Pr with a smaller hysteresis shift.

Photovoltaic (PV) properties of ferroelectric SrRuO3/BiFeO3/SrRuO3 (SRO/BFO/SRO) epitaxial thin-film capacitors are investigated. The experimental results of the markedly reduced PV response caused by the doping of Mn provide evidence that the PV properties originate not from the bulk-derived PV effect but from an interfacial band bending. We show that the capacitors having a defective layer composed of oxygen vacancies at the SRO/BFO interface exhibit a markedly large photocurrent. Our study demonstrates that a cooperative effect between the interface charges arising from ferroelectric polarization and the oxygen-vacancy-rich layer enhances the PV response in capacitor form in the BFO system.