Design for Highly Piezoelectric and Visible/Near‐Infrared Photoresponsive Perovskite Oxides

Abstract

efficient/controllable photoexcited charge separation. [1,2] So far, the most commonly investigated SFPO is based on BiFeO 3 , [1,3] but its bandgap of ≈2.7 eV is not low enough to absorb the full spectrum of the visible light. The real potential of SFPO in photovoltaic applications significantly drives the exploring of new perovskite oxides with efficient visible light absorption. Recently, the realization of defect-driven-ferroelectricity and low bandgap states (even down to ≈1.1 eV) in perovskites (KNbO 3 ) 1−x (BaNi 1/2 Nb 1/2 O 3−δ ) x (KN-BNN) suggests that ferroelectricity and low bandgap can be simultaneously achieved by compositional modification. With two different transition-metal cations at the B-site in highly oxygen-vacancytolerable perovskite oxides, one cation (Nb 5+ ) provides off-center distortion and polarization, and the other (Ni 2+ ) decreases the difference in electronegativity within the perovskite BO bonds to create electronic states in the gap. The leaky conductivity associated with accommodation of Ni 2+ -oxygen vacancy combinations results in the loss of piezoelectricity especially at room temperature, which is generally the case for simple perovskite oxides. [4] Efforts have been taken to improve the tolerance of oxygen vacancies in order to keep the ferroelectricity, such as modifying the amount of BaNi 1/2 Nb 1/2 O 3−d (BNN) in the solid solution in order to decrease the concentration of oxygen vacancies, i.e., 0.98KN-0.02BNN, and 0.65PbTiO [5,6] or using more complex perovskite oxides with layered structure LaCoO 3 -mediated BiTiO 3 (E g = 2.65 eV). [7] However, an effective strategy to achieve an appropriate balance between the defect-induced low bandgap and defect-induced electrically leaky ferroelectricity is still currently lacking. Following the defect-engineered strategy, we present an efficient route to change the generally negative role of oxygen vacancies to be piezoelectrically/ferroelectrically friendly. Guided by the point-defect mediated large piezoelectricity in ferroelectric crystals, [8] defect-dipoles formed by dopant-oxygen vacancy pairs are preferentially coupled with the strong spontaneous polarization from host according to general symmetry-conforming property of point defects. [9][10][11] Moreover, both experiments and theoretical calculations provide strong evidence that the dopant-oxygen obtain low bandgap (i.e., 1.1-3.8 eV), the electrically leaky perovskite oxides generally lose piezoelectricity mainly due to oxygen vacancies. Therefore, the development of highly piezoelectric ferroelectric semiconductor remains challenging. Here, inspired by point-defect-mediated large piezoelectricity in ferroelectrics especially at the morphotropic phase boundary (MPB) region, an efficient strategy is proposed by judiciously introducing the gap states at the MPB where defect-induced local polar heterogeneities are thermodynamically coupled with the host polarization to simultaneously achieve high piezoelectricity and low bandgap. A concrete example, Ni 2+ -mediated (1...

Boosting piezoelectric response of KNN‐based ceramics with strong visible‐light absorption

“…Noting that the addition of Ni to KNN ceramics can induce the formation of defect dipoles (Ni 2+ ‐) . Besides, both experiments and theoretical calculations have illustrated that such combination can cause heterogeneous polar regions and additional interfacial energies which can flat the free‐energy profile of the whole system especially at the MPB, thus significantly enhancing the ferroelectricity and piezoelectricity . Hence, the elevation of d 3 3 in 0.96KNN‐0.04BNZN ceramics may be attributed to the effect induced by defect dipoles.…”

“…Yu et al prepared Pb(Zr 0.53 Ti 0.47 )O 3 ceramics mediated with Pb(Fe 0.5 Nb 0.5 )O 3 or Pb(Fe 0.5 Ta 0.5 )O 3 , which reduced the bandgap from 3.32 to 2.51 eV . In our previous study, we designed visible/near‐infrared photoresponsive perovskite oxides‐(1– x )Na 0.5 Bi 0.5 TiO 3 ‐ x Ba(Ti 0.5 Ni 0.5 )O 3–δ with narrow bandgap by introducing gap states through Ni doping. Besides, the power level and stability provided by a single‐source energy harvester are often insufficient for practical application, which inspires researchers to design perovskite oxides as hybrid energy harvester.…”

“…Besides, the power level and stability provided by a single‐source energy harvester are often insufficient for practical application, which inspires researchers to design perovskite oxides as hybrid energy harvester. However, it is still quite a challenge to realize narrow bandgap and high piezoelectricity in lead‐free ceramics simultaneously, for the highest d 33 value reported now is just 150 pC N −1 . Therefore, it is of great interests to design lead‐free materials with both excellent photovoltaic property and giant piezoelectricity.…”

Simultaneously Enhancing Thermal Stable Dielectric Property and Piezoelectric Response in Lead-Free LiNbO3-Modified (K0.5Na0.5)NbO3- (BaNi0.5Nb0.5O3) System

“…Very recently, various types of ferroelectric systems have been used for these promising applications. For example, Pb(Zr 0.53 Ti 0.47 )O 3 ceramics mediated with Pb(Fe 0.5 Ta 0.5 )O 3 or PbTiO 3 -0.35Bi(Ni 2/3+x Nb 1/3−x )O 3−δ ceramics (Evans et al, 2013;Liu et al, 2015), (1-x)KNbO 3 -xBaNi 1/2 Nb 1/2 O 3−δ (KBNNO) ceramics (Bai et al, 2019), (1-x) Na 0.5 Bi 0.5 TiO 3 -xBa(Ti 0.5 Ni 0.5 )O 3−δ ceramics (Xiao et al, 2019), and (K 0.5 Na 0.5 )NbO 3 doped with 2 mol% Ba(Ni 0.5 Nb 0.5 )O 3−δ ceramics (KNBNNO ceramics) (Bai et al, 2017;Zhong et al, 2019).…”

Room‐Temperature Magnetoelectric Response in Molecular–Ionic Ferroelectric‐Based Magnetoelectric Composites

“…Because 1 is a multiaxial ferroelectric and its P r is larger than that of [N(CH 3 ) 4 ][GaCl 4 ], we expected that the piezoelectric coefficient of 1 would be larger than that of [N(CH 3 ) 4 ][GaCl 4 ] [6a,b,9]. The thin film of 1 was fabricated on indium tin oxide (ITO)‐coated glass using a solution‐based method (Supporting Information) [6b].…”