Deepak R. Patil

Multiple broadband magnetoelectric response in thickness-controlled Ni/[011] Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 single crystal/Ni laminates

We report the realization of a multiple, broadband, magnetoelectric (ME) response using Ni/[011]-Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMN-PZT) single crystal/Ni laminates that take advantage of the multiple mechanical resonances inherent to laminates with anisotropic piezoelectric properties. The ME voltage coefficient of the laminates showed three distinct resonance frequencies and large in-plane anisotropy in its sign and magnitude owing to the anisotropic planar piezoelectric coefficient of [011]-oriented PMN-PZT single crystals. Upon serially connecting three such laminates with different thickness ratios between the Ni and PMN-PZT layers, we observed two distinct frequency windows with bandwidths of ∼60 kHz showing flat, giant ME responses of over 16 V/cm Oe, which suggests that these ME laminates are good candidates for application in broadband field sensors or energy harvesters.

Anisotropic self-biased dual-phase low frequency magneto-mechano-electric energy harvesters with giant power densities

We report the physical behavior of self-biased multi-functional magneto-mechano-electric (MME) laminates simultaneously excited by magnetic and/or mechanical vibrations. The MME laminates composed of Ni and single crystal fiber composite exhibited strong ME coupling under Hdc = 0 Oe at both low frequency and at resonance frequency. Depending on the magnetic field direction with respect to the crystal orientation, the energy harvester showed strong in-plane anisotropy in the output voltage and was found to generate open circuit output voltage of 20 Vpp and power density of 59.78 mW/Oe2 g2 cm3 under weak magnetic field of 1 Oe and mechanical vibration of 30 mg, at frequency of 21 Hz across 1 MΩ resistance.

Enhancement of resonant and non-resonant magnetoelectric coupling in multiferroic laminates with anisotropic piezoelectric properties

Giant transverse magnetoelectric voltage coefficients |αE| = 751 and 305 V/cmOe at two electromechanical antiresonance frequencies are found in the symmetric metglas/[011]-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 crystal/metglas laminate. Unique torsional and diagonal vibration modes are identified to be responsible for those giant |αE| values. Moreover, αE is found to be anisotropic depending on the in-plane magnetic field directions, making the piezoelectrics with anisotropic planar piezoelectricity potentially useful base materials for multi-frequency, phase-sensitive magnetoelectric devices.

Observation of multiferroic properties in pyroxene NaFeGe2O6

We report the observation of multiferroicity in a clinopyroxene NaFeGe(2)O(6) polycrystal from the investigation of its electrical and magnetic properties. Following the previously known first magnetic transition at T(N1) = 13 K, a second magnetic transition appears at T(N2) = 11.8 K in the temperature dependence of the magnetization. A ferroelectric polarization starts to develop clearly at T(N2) rather than T(N1) and its magnitude increases up to ~13 μC m(-2) at 5 K, supporting the idea that the ferroelectric state in NaFeGe(2)O(6) stems from a helical spin order stabilized below T(N2). When a magnetic field of 90 kOe is applied, the electric polarization decreases to 9 μC m(-2) and T(N2) slightly increases by 0.5 K. At intermediate magnetic fields, around 28 and 78 kOe, anomalies in the magnetoelectric current, magnetoelectric susceptibility, and field derivative of magnetization curves are found, indicating field-induced spin-state transitions. Based on these electrical and magnetic properties, we provide a detailed low temperature phase diagram up to 90 kOe, and discuss the nature of each phase of NaFeGe(2)O(6).

Large Longitudinal Magnetoelectric Coupling in NiFe2O4–BaTiO3 Laminates

In contrast to the Pb-based magnetoelectric laminates (MELs), we find in the BaTiO3 and NiFe2O4 laminates (number of layers n=5–25) that the longitudinal magnetoelectric (ME) voltage coefficient αE33 becomes much larger than the transverse one due to preferential alignment of magnetic moments along the NiFe2O4 plane. Moreover, upon decreasing each layer thickness down to 15 µm, we realize enhanced αE33 up to 18 mV/(cmOe) and systematic increase of the ME sensitivity in proportion to n to achieve the largest in the Pb-free MELs (400×10-6 V/Oe), thereby providing pathways for tailoring ME coupling in mass-produced, environment friendly laminates.

Ag:BiVO4 dendritic hybrid-architecture for high energy density symmetric supercapacitors

We demonstrate the fabrication of Ag:BiVO4 with a dendritic architecture by a template free hydrothermal method. Then, symmetric cells based on Ag:BiVO4 electrodes were assembled which exhibit an extended voltage window of up to 1.6 V with an excellent energy density of 2.63 mW h cm−3 (38.43 W h kg−1) and a power density of 558 mW cm−3 (8.1 kW kg−1).

Colossal magnetoelectric response of PZT thick films on Ni substrates with a conductive LaNiO3 electrode

We have characterized the magnetoelectric (ME) properties of Pb(ZrTi)O3/LaNiO3/Ni (PZT/LNO/Ni) composites, which are fabricated using aerosol deposition. LNO acted as the bottom electrode for the PZT film and could effectively transfer the stress generated through the magnetostrictive effect of Ni into the piezoelectric PZT film. The PZT/LNO/Ni ME structure exhibits an ME coefficient αE31 = 1Vc m −1 Oe −1 at a very low bias magnetic field of 30 Oe and shows 8.5 V cm −1 Oe −1 at a magneto-mechanical resonance frequency of 204 kHz corresponding to the Ni substrate. These huge ME coefficients are attributed to the improved coupling between the magnetostrictive Ni layer and the piezoelectric PZT thick film via the LNO layer, which is possible due to similar mechanical impedances of Ni, LNO and PZT.

One-Pot in Situ Hydrothermal Growth of BiVO 4 /Ag/rGO Hybrid Architectures for Solar Water Splitting and Environmental Remediation

BiVO4 is ubiquitously known for its potential use as photoanode for PEC-WS due to its well-suited band structure; nevertheless, it suffers from the major drawback of a slow electron hole separation and transportation. We have demonstrated the one-pot synthesis of BiVO4/Ag/rGO hybrid photoanodes on a fluorine-doped tin oxide (FTO)-coated glass substrate using a facile and cost-effective hydrothermal method. The structural, morphological, and optical properties were extensively examined, confirming the formation of hybrid heterostructures. Ternary BiVO4/Ag/rGO hybrid photoanode electrode showed enhanced PEC performance with photocurrent densities (Jph) of ~2.25 and 5 mA/cm2 for the water and sulfate oxidation, respectively. In addition, the BiVO4/Ag/rGO hybrid photoanode can convert up to 3.5% of the illuminating light into photocurrent, and exhibits a 0.9% solar-to-hydrogen conversion efficiency. Similarly, the photocatalytic methylene blue (MB) degradation afforded the highest degradation rate constant value (k = 1.03 × 10−2 min−1) for the BiVO4/Ag/rGO hybrid sample. It is noteworthy that the PEC/photocatalytic performance of BiVO4/Ag/rGO hybrid architectures is markedly more significant than that of the pristine BiVO4 sample. The enhanced PEC/photocatalytic performance of the synthesized BiVO4/Ag/rGO hybrid sample can be attributed to the combined effects of strong visible light absorption, improved charge separation-transportation and excellent surface properties.

Quantitative Measurements of Size-Dependent Magnetoelectric Coupling in Fe3O4 Nanoparticles

Bulk magnetite (Fe3O4), the loadstone used in magnetic compasses, has been known to exhibit magnetoelectric (ME) properties below ∼10 K; however, corresponding ME effects in Fe3O4 nanoparticles have been enigmatic. We investigate quantitatively the ME coupling of spherical Fe3O4 nanoparticles with uniform diameters (d) from 3 to 15 nm embedded in an insulating host, using a sensitive ME susceptometer. The intrinsic ME susceptibility (MES) of the Fe3O4 nanoparticles is measured, exhibiting a maximum value of ∼0.6 ps/m at 5 K for d = 15 nm. We found that the MES is reduced with reduced d but remains finite until d = ∼5 nm, which is close to the critical thickness for observing the Verwey transition. Moreover, with reduced diameter the critical temperature below which the MES becomes conspicuous increased systematically from 9.8 K in the bulk to 19.7 K in the nanoparticles with d = 7 nm, reflecting the core-shell effect on the ME properties. These results point to a new pathway for investigating ME effect in various nanomaterials.

BiVO4 Fern Architectures: A Competitive Anode for Lithium-Ion Batteries

The development of high-performance anode materials for lithium-ion batteries (LIBs) is currently subject to much interest. In this study, BiVO4 fern architectures are introduced as a new anode material for LIBs. The BiVO4 fern shows an excellent reversible capacity of 769 mAh g-1 (ultrahigh volumetric capacity of 3984 mAh cm-3 ) at 0.12 A g-1 with large capacity retention. A LIB full cell is then assembled with a BiVO4 fern anode and LiFePO4 (LFP, commercial) as cathode material. The device can achieve a capacity of 140 mAh g-1 at 1C rate, that is, 81 % of the capacity of the cathode and maintained to 104 mAh g-1 at a high rate of 8C, which makes BiVO4 a promising candidate as a high-energy anode material for LIBs.