Abstract
Niobate perovskites like the (K,Na)NbO3 (KNN) family are among the most important lead-free ferroelectrics. Ba and Ni have been co-doped into KNN to induce Ni2+-oxygen vacancy defect dipoles to sig...
Highlights
Most ferroelectrics are considered as insulators or semiconductors with wide optical band gaps beyond the majority of photon energy of visible light (e.g., >2.7 eV), their band gaps can be engineered as small as 1.1 eV.[3]
Ferroelectrics may exhibit a photovoltaic effect, and given proper conditions, they are able to deliver above band gap, ultra-high photovoltages and a photovoltaic energy conversion efficiency that breaks the physical (Shockley−Queisser) limit predicted for conventional semiconductor solar cells.[4−6]
The residual NiO did not diffuse into the unit cells as expected, reflecting observations in the literature.[8,10]
Summary
Ferroelectrics, among polar dielectrics with switchable spontaneous polarizations (namely, ferroelectricity) in unit cells and domains, are widely used in electro-mechanothermal coupling components like memories, detectors, and transducers.[1,2] most ferroelectrics are considered as insulators or semiconductors with wide optical band gaps beyond the majority of photon energy of visible light (e.g., >2.7 eV), their band gaps can be engineered as small as 1.1 eV (same as that of Si).[3]. Most high-performance ferroelectrics have ABO3 perovskite structures. The d0 transition metals on the B-sites possess necessary electronic structures for the second-order Jahn− Teller distortion, driving the B-site cations to displace from the center positions in the O-octahedra and giving rise to ferroelectricity.[7] the large electronegativity difference between the two ends of the B−O bonds leads to a high charge transfer energy from O 2p states to the B-site metal d states, resulting in a large band gap.[7] Pioneer studies suggested that by properly introducing non-d0 metal states into the B-sites as well as pairing them with O vacancies (VO), the large band gap in ABO3 ferroelectric perovskites could be effectively reduced. Polarizations were suppressed to a negligible level at room temperature in the KNbO3-BNNO, a follow-up work has proven that by precisely controlling and limiting the BNNO dopant to 2 mol % and by introducing Na+ on the A-site to help increase unit cell distortion, the doped (K0.5Na0.5)NbO3 reduced the band gap by up to 2.4 eV (from 4 to 1.6 eV) and simultaneously retained the remanent polarization at 11 μC cm−2 (55% of that of the undoped (K0.5Na0.5)NbO3).[8]
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