We demonstrate a capacitor with high energy densities, low energy losses, fast discharge times, and high temperature stabilities, based on Pb(0.97)Y(0.02)[(Zr(0.6)Sn(0.4))(0.925)Ti(0.075)]O3 (PYZST) antiferroelectric thin-films. PYZST thin-films exhibited a high recoverable energy density of U(reco) = 21.0 J/cm(3) with a high energy-storage efficiency of η = 91.9% under an electric field of 1300 kV/cm, providing faster microsecond discharge times than those of commercial polypropylene capacitors. Moreover, PYZST thin-films exhibited high temperature stabilities with regard to their energy-storage properties over temperatures ranging from room temperature to 100 °C and also exhibited strong charge-discharge fatigue endurance up to 1 × 10(7) cycles.

Lead-free Mn-doped (K0.5, Na0.5)NbO3 (KNN) thin films were fabricated by the chemical solution deposition method. The addition of small concentration of Mn dopant effectively reduced the leakage current density and enhanced the piezoelectric properties of the films. The leakage current density of 0.5 mol. % Mn-doped KNN film showed the lowest value of ∼10-7 A/cm2 at 10 V compared to the films with other doping concentrations and the piezoelectric d33 and e31 coefficients of this film were ∼90 pm/V and −8.5 C/m2, respectively. The maximum power and power density of the lead-free thin film-based vibrational energy harvesting device were 3.62 μW and 1800 μW/cm3 at the resonance frequency of 132 Hz and the acceleration of 1.0 G. The results prove that the 0.5 mol. % Mn-doped KNN film is an attractive candidate transducer layer for the piezoelectric MEMS energy harvesting device applications with a small volume and a long-lasting power source.

No abstract

In spite of extremely high piezoelectric and pyroelectric coefficients, there are few reports on flexible ferroelectric perovskite film based nanogenerators (NGs). Here, we report the successful growth of a flexible Pb(Zr0.52Ti0.48)O3 (PZT) film and its application to hybrid piezoelectric-pyroelectric NG. A highly flexible Ni-Cr metal foil substrate with a conductive LaNiO3 bottom electrode enables the growth of flexible PZT film having high piezoelectric (140 pC/N) and pyroelectric (50 nC/cm(2)K) coefficients at room temperature. The flexible PZT-based NG effectively scavenges mechanical vibration and thermal fluctuation from sources ranging from the human body to the surroundings such as wind. Furthermore, it stably generates electric current even at elevated temperatures of 100 °C, relative humidity of 70%, and pH of 13 by virtue of its high Curie temperature and strong resistance for water and base. As proof of power generation under harsh environments, we demonstrate the generation of extremely high current at the exhaust pipe of a car, where hot CO and CO2 gases are rapidly expelled to air. This work expands the application of flexible PZT film-based NG for the scavenging mechanical vibration and thermal fluctuation energies even at extreme conditions.

Solution-derived poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) piezoelectric thin films on cellulose paper substrates were prepared as flexible power generators for wearable device applications. Optimization of appropriate annealing and cooling sequences of the co-polymer films resulted in the formation of dense and uniform microstructures exhibiting a well-developed β-phase. A maximum open-circuit voltage of 1.5 V was generated from the periodic bending and releasing of the paper power generator at approximately 1 Hz. To demonstrate the wearable applications, P(VDF-TrFE) piezoelectric film-based paper power generators were directly attached on the back of a human hand, and they generated a maximum output open-circuit voltage of 0.4 V at low bending frequencies of 0.25 Hz. Good open-circuit voltage performance at low frequencies makes P(VDF-TrFE) piezoelectric thin films on paper substrates a strong candidate for future self-powered wearable devices.

Environmentally benign lead-free ferroelectric (K0.5,Na0.5)(Mn0.005,Nb0.995)O3 (KNMN) thin film capacitors with a small concentration of a BiFeO3 (BF) dopant were prepared by a cost effective chemical solution deposition method for high energy density storage device applications. 6 mol. % BF-doped KNMN thin films showed very slim hysteresis loops with high maximum and near-zero remanent polarization values due to a phase transition from the orthorhombic structure to the pseudo-cubic structure. Increasing the electric field up to 2 MV/cm, the total energy storage density (Jtotal), the effective recoverable energy density (Jeff), and the energy conversion efficiency (η) of lead-free KNMN-BF thin film capacitors were 31.0 J/cm3, 28.0 J/cm3, and 90.3%, respectively. In addition, these thin film capacitors exhibited a fast discharge time of a few μs and a high temperature stability up to 200 °C, proving their strong potential for high energy density storage and conversion applications.

We deposited (K0.5Na0.5)(Mn0.005Nb0.995)O3 (KNMN) thin films on Pt(111)/TiO2/SiO2/Si(100) substrates with a top electrode of indium tin oxide and investigated photocurrent properties in the wavelength range of 300−400 nm. Before the photocurrent measurement, the KNMN film was poled by applying a DC voltage. The photocurrents strongly depend on the wavelength of the incident photon energy. The photocurrents of the first measurement with poling in the up (−5 V) and down (+5 V) states were 21 and 3.2 nA/cm2, respectively, at 344 nm. The difference in the photocurrents in both poling directions was explained by a space charge due to an asymmetric Schottky barrier height, which was caused by an internal electric field and polarization in the KNMN thin film.

Vertically aligned core–shell PbTiO3@TiO2 heterojunction nanotube arrays are fabricated on F:SnO2 (FTO) glass substrate via a unique three-step process: an electron beam vapor deposition of Ti thin film on FTO, anodic oxidation of the Ti film to TiO2 nanotubes, and finally formation of PbTiO3 perovskite layer at the inner wall of the TiO2 nanotubes. The PbTiO3@TiO2 nanotube array exhibits dramatically improved photoactivity relative to TiO2 nanotubes or PbTiO3/TiO2 composite powders in photoelectrochemical water splitting and photocatalytic isopropyl alcohol decomposition under visible light irradiation (>420 nm). In the core–shell heterojunction electrodes, PbTiO3 serves as a visible light responsive inorganic photosensitizer with its small band gap and forms a heterojunction with TiO2 for effective charge separation.