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

Abstract

A series of (1 − x)(K0.48Na0.52)NbO3‐x(Bi0.5Na0.5)(Zr0.55Ni0.45)O3‐δ (KNN‐BNZN) ceramics are designed to achieve excellent piezoelectric response along with narrow bandgap. The ceramics with x = 0.04 exhibit unprecedented piezoelectric coefficient d33 ~ 318±10pC N−1 in comparison with all reported narrow bandgap ceramics. A rhombohedral‐orthorhombic‐tetragonal (R‐O‐T) phase boundary is observed, indicating the formation of defect dipoles (Ni2+‐Vo¨) at morphotropic phase boundary region is desirable for piezo‐/ferroelectric properties. In addition, a narrow bandgap ~2.5 eV along with gap states (~0.9 eV and ~1.6 eV) is obtained from the ceramics when x > 0.02, which can be persuasively explained by the schematic plot of bandgap splitting mechanism proposed in this work, where Ni 3d energy state plays a role as a scaffold in the process of electron transition. More importantly, largely enhanced photovoltaic performance of the ceramics is achieved under AM 1.5 irradiation. The NIR photoresponse property (maximum current density of ~100 nA cm−2) indicates such KNN‐based ceramics with sub bandgap ~ 0.9 eV may even have potential to be applied in NIR light‐activated devices. Our findings might pave way for the further development of piezoelectric/photoresponsive multifunctional devices.

Photoresponsive Piezoelectrics

“…The band gap of 0.96-0.04KNBNZNO could be undoubtedly determined as 2.5 eV (reduced from 3.1 eV of KNBNZ) (Zhong et al, 2019). Nevertheless, gap states at 0.9 and 1.6 eV were also found (Zhong et al, 2019).…”

“…Figure 1 compares the band gaps and d 33 values of different compositions discovered to date for both wide and narrow gap piezoelectrics. It can be noticed in the figure that, although the currently experimented band gap engineering methodologies are believed to degrade ferroelectricity to some extent (Bai et al, 2018a;Bai et al, 2019a (Bai et al, 2017b;Xiao et al, 2019a;Lou et al, 2019;Zhong et al, 2019). This fact gives the narrow band gap piezoelectrics an obvious advantage over their wide band gap counterparts, i.e., the narrow band gap piezoelectrics can effectively absorb the majority of visible lights while exhibiting an uncompromized piezoelectric response, which can clearly be seen in Figure 1.…”

“…The parental composition here, KNBNZ, constructed an MPB between two ferroelectric phases, inducing increased domain wall mobility and thus large piezoelectricity (Zheng et al, 2018). Meanwhile, it was claimed that the introduction of Ni 2+ -oxygen vacancy combinations may help to flatten the free-energy profile by inducing heterogeneous polar regions and additional interfacial energies especially at the MPB and thus enhancing piezoelectricity (Zhong et al, 2019). In addition, in KNBNZNO Ni 2+ was added individually without associated Ba 2+ , which might eliminate the negative effect of Ba 2+ on the ferroelectricity and thus piezoelectricity as presented above.…”

“…In addition, in KNBNZNO Ni 2+ was added individually without associated Ba 2+ , which might eliminate the negative effect of Ba 2+ on the ferroelectricity and thus piezoelectricity as presented above. (Yue and Yi-jian, 2003;Bavbande et al, 2012;Kumar and Kim, 2012;Mamoun et al, 2013;Bowen et al 2014;Paillard et al, 2016;Wu et al (2016); Bai et al, 2017a, Bai et al, 2018aDurruthy-Rodríguez et al, 2018;Xiao et al (2019a); Zhong et al 2019;Lou et al, 2019).…”

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).…”