Optical Control of Ferroelectric Domains: Nanoscale Insight into Macroscopic Observations

Abstract

has been investigated for the optical reading of ferroelectric random-access memories, [14,15] photodiodes, [16] and photovoltaic [4,[17][18][19][20][21][22][23] applications. Current research is focused on developing band-gap tuned ferroelectric materials as their performance is restricted by low mobility of charge carriers and short diffusion lengths. [24][25][26] Band-gap tuned ferroelectric materials are capable of hosting multiple functionalities (due to ferroelectricity and semiconducting features), which suggest the possibilities of multiple energy conversions (piezoelectric, pyroelectric, and photovoltaic) simultaneously. In this context, Bai et al. synthesized a novel band-gap (1.6 eV down from >4 eV) engineered lead-free ferroelectric composition, i.e. (K 0.5 Na 0.5 )NbO 3 -2 mol% Ba(Ni 0.5 Nb 0.5 )O 3−δ (KNBNNO or KNN-BNNO), and demonstrated multiple functionalities (piezoelectric, pyroelectric, and photovoltaic effects) and their cumulative effect using this single material. [27][28][29] (K 0.5 Na 0.5 )NbO 3 supports off-center distortion and is responsible for ferroelectric nature of KNN-BNNO while Ba(Ni 0.5 Nb 0.5 ) O 3−δ controls the electronic states in the gap of parent (K 0.5 Na 0.5 ) NbO 3 using oxygen vacancies and Ni +2 ions. [24] Simultaneous presence of ferroelectric and semiconducting features makes this composition alluring for photovoltaic applications. In addition, it also provides an opportunity to understand how ferroelectric properties in semiconductors could help in improving the photovoltaic response and vice versa. In this context, the present study aims to provide an insight into light-induced changes in the ferroelectric behavior of KNN-BNNO. Recent demonstration of light-driven switching of nanodomains in (K 0.5 Na 0.5 )NbO 3 also makes it interesting to further explore KNN-BNNO. [30] Light-induced changes in ferroelectrics could persist due to a number of reasons such as (i) localized heating assisted diffusion of alkali element (as in LiNbO 3 ) and oxygen vacancies, [31] (ii) change in oxidation state of the central atom (e.g., in BaTiO 3 ), [32] and (iii) Jahn-Teller distortions due to light-induced pyroelectric current or charge injection in the conduction band (as in SbSI). [7,13] Warren et al. suggested that similar to electrical and thermal fluctuations, an exposure to light involves "locking domains by electronic charge trapping at domain boundaries." [1] Any change in the macroscopic behavior could be attributed to nanoscale changes in the ferroelectric domains. Moreover, Domain wall nanoelectronics constitutes a potential paradigm shift for nextgeneration energy conversion and von-Neumann devices. In this context, attempts have been made to achieve energy-efficient control over ferromagnetic, ferroelectric, and ferroelastic domain walls through electric and magnetic fields or applied stress. However, optical control of ferroic domains offers an additional degree of freedom and significant advantages of reduced hysteresis and Joule heating losses, creating novel opport...

A Single‐Material Multi‐Source Energy Harvester, Multifunctional Sensor, and Integrated Harvester–Sensor System—Demonstration of Concept

“…However, in this work, the light source was a 405 nm laser, which only induced a local temperature change of 0.5 C in the KNBNNO. [37,62] Such a change is negligible compared with the nearly 45 C shown in Figure 7b. Therefore, the photovoltaic effect observed in this work was true and was not induced by the pyroelectric effect.…”

“…It has been reported that illumination could change the permittivity and thus capacitance, as well as resistivity and thus resistance, of the KNBNNO. [62] The changed capacitance and resistance could alter the resonant frequency of the KNBNNO element, leading to a reduced output current density (in the same way as shown earlier). [63] This is the reason that the add-on effect of the piezoelectric current density (35 nA cm À2 -positive maximum) and photovoltaic current density (20 nA cm À2 ) did not fulfill the linear superposition (45 nA cm À2 in reality instead of 55 nA cm À2 in theory).…”

“…This could be attributed to the interaction between incident light and domain wall motion, which has been comprehensively studied in previous works. [37,62] It has been reported that incident light is able to stimulate the ferroelectric domain wall motion of KNBNNO. [37] It has also been suggested that domain walls may play an important role in photo-ferroelectric materials-i.e., ferroelectrics showing a photovoltaic effect.…”

“…[68] C p and R p are the capacitance and parallel resistance of the KNBNNO, which may be affected by illumination and temperature. [37,62] The series resistance (R s ) accounts for all the voltage drops from the current sources (i photo and i pyro ) to the connection with the external resistive load (R load ). [68,69] Similarly, potential applications can be simultaneous double-source harvesting and sensing of solar (visible light) and thermal (temperature fluctuation) energy sources/stimuli, and harvesting using the photovoltaic effect for DC signals and sensing using the pyroelectric effect with distinguished AC signals (or vice versa).…”

Coalition of Thermo–Opto–Electric Effects in Ferroelectrics for Enhanced Cyclic Multienergy Conversion

“…In this context, two novel energy-conversion cycles are proposed in this article by exploring a novel monolithic multifunctional material KNBNNO ((K 0.5 Na 0.5 )NbO 3 -2 mol% Ba(Ni 0.5 Nb 0.5 )O 3Àδ )). [4,5,31] KNBNNO being a bandgap-engineered (1.6 eV) ferroelectric with good piezoelectric and pyroelectric responses is capable of simultaneously utilizing inputs from an external electric field, stress, thermal fluctuation, and light. [4,5,31] Recent work has shown the optical control of ferroelectric domains [31] and DOI: 10.1002/ente.202000500…”