We have investigated the nanoscale switching properties of strain-engineered BiFeO 3 thin films deposited on LaAlO 3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically-driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material which is promising for a plethora of applications.

BiFeO3 thin films can be epitaxially stabilized in a nearly-tetragonal phase under a high biaxial compressive strain. Here we investigate the polarized Raman spectra of constrained BiFeO3 films with tetragonal-like (BFO-T) , rhombohedral-like (BFO-R) and multiphase (BFO-T+R) structure. Based on analysis of the number and symmetry of the Raman lines, we provide strong experimental evidence that the nearly-tetragonal films are monoclinic (Cc symmetry) and not tetragonal (P 4mm). Through the Raman mapping technique we show localized coexistence of BFO-T and BFO-R phases with the relative fraction dependent on the film thickness.PACS numbers: 63.20.Dj, 75.85.+t Constant demand for miniaturization in modern devices have provided a big stimulus for research into multi-functional materials. BiFeO 3 , or simply BFO, is a prototypical multiferroic material due to the simultaneous co-existence of ferroelectric, ferroelastic and antiferromagnetic order. It is also currently widely investigated as it offers room-temperature multi-functionality after very high polarization values were reported in 2003 for films grown on SrTiO 3 (STO) substrates.[1] However, it can be argued that the rhombohedral R3c structure of BFO-R possess significant difficulties and challenges. For example, the ferroelectric polarization of BFO-R is directed along the (111) direction giving rise to eight possible polarization orientations. As a result, ferroelectric switching is complicated and very hard to control for any meaningful multi-functionality. Therefore, BFO phase of different symmetry, which in principle could address these issues, is desired .This interest increased after recently it was predicted theoretically and confirmed experimentally that the structure and properties of BiFeO 3 films under a large, biaxial compressive strain could deviate significantly from the bulk material into a "super-tetragonal" structure with an extremely high c/a ratio. [2][3][4][5][6][7] This phase, in some sense, appears incommensurable to its rhombohedral counterpart and requires a thorough investigation much along the lines that bulk BFO has received. Apart from possibly higher ferroelectric polarization values and significantly simpler switching properties, this phase is especially suitable for ultra-thin film applications where the strain effect is maximum.Based on earlier theoretical predictions, it was anticipated that tetragonal BFO could belong to the P 4mm (#99) space group [2]. But careful X-ray diffraction analysis of BFO films deposited on LaAlO 3 (LAO) and YAlO 3 (YAO) substrates show evidence of monoclinic distortions [5,6], and very recently ab-initio calculations have also indicated [7] that the monoclinic Cc (#9) structure is indeed energetically more favorable than the tetragonal P 4mm structure, when the compressive strain is greater than 4%. The three structures that could be used to describe strained BFO thin films grown on LAO substrates are shown in Fig

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Structural, electrical, and magnetic properties of chemical solution deposited Bi ( Fe 0.95 Cr 0.05 ) O 3 thin films on platinized silicon substrates effects on the ferroelectric and magnetic properties of chemical solution deposited Bi Fe O 3 thin films Epitaxial BiFeO 3 thin films have been grown on ͑100͒-oriented SrTiO 3 and Nb-doped SrTiO 3 substrates using the pulsed laser deposition technique under identical thermodynamic and variable kinetic conditions. The variation of growth kinetics through laser fluence and pulse repetition rate had minimal effect on the structure and magnetic properties of films. However, large changes were observed in the microstructure, with initial island growth mode approaching toward step-flow type growth and roughness reducing from 12.5 to 1.8 nm for 50 nm thick film. Correspondingly, the leakage current density at room temperature dropped consistently by almost four orders of magnitude. The dominant mechanism in low leakage current films was space-charge-limited conduction. These findings suggest that the issue of leakage current can be dealt favorably by controlling kinetic growth parameters. The application of high electric field and observation of maximum polarization value up to 103 C / cm 2 could be possible in these samples. An appearance of saturated hysteresis behavior depending upon bottom electrode was also observed. This fact is qualitatively explained on the basis of recent concepts of switchability and polarity of thin film-electrode interface.

With the development of consumer electronic devices and electric vehicles, lithium-ion batteries (LIBs) are vital components for high energy storage with great impact on our modern life. However, LIBs still cannot meet all the essential demands of rapidly growing new industries. In pursuance of higher energy requirement, metal batteries (MBs) are the next-generation high-energy-density devices. Li/Na metals are considered as an ideal anode for high-energy batteries due to extremely high theoretical specific capacity (3860 and 1165 mAh g À 1 for Li and Na, respectively) and low electrochemical potential (À 3.04 V for Li and À 2.71 V for Na vs. standard hydrogen electrode). Unfortunately, uncontrolled dendrite growth, high reactivity, and infinite volume change induce severe safety concerns and poor cycle efficiency during their application. Consequently, MBs are far from commercialization stage. This Review represents a comprehensive overview of failure mechanism of lithium/sodium metal anode and its progress for rechargeable batteries through (i) electrolyte optimization, (ii) artificial solidelectrolyte interphase (SEI) layer formation, and (iii) nanoengineering at materials level in current collector, anode, and host. The challenges in current MBs research and potential applications of lithium/sodium metal anodes are also outlined and summarized.

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Lithium-Sulfur (Li-S) batteries have recently attracted considerable attention in the energy storage sector due to their high theoretical performance and low cost of active materials compared to the state-of-the-art Li-ion batteries. Despite the recent progress in both developments of electrode and electrolyte materials and fundamental understanding, practical use of conventional Li-S batteries is still hindered by their safety concerns and poor cycling performance. Solid state Li-S batteries (SSLSBs) have the great potential to conquer these challenges. This review describes the basic requirements of solid-state electrolytes (SSEs) and fundamental understanding of solid electrolytes by addressing the key issues in the areas of ion transport. We emphasize on recent advances in various solid state electrolytes used in SSLSBs. We also address the challenges and plausible solutions, involving improved designs and compositions of solid state electrolytes, electrode materials and electrode electrolyte interfaces. Even though several technological and fundamental issues still need to be solved to develop commercially viable technologies, SSLSBs offer a great opportunity to deal with the present limitations.

We report a detailed study on the electromagnetic interference (EMI) shielding effectiveness (SE) properties in La 0.7 Sr 0.3 MnO 3 (LSMO) nanomaterials. The samples were prepared by a solution chemistry (sol-gel) route at different sintering temperatures. The single-phase samples with grain sizes of 22 and 34 nm showed DC electrical conductivity variation from 0.65 to 13 S cm À1 at room temperature. The application of a high magnetic field resulted in higher conductivity values. The electrical conductivity variation with temperature could be fitted with a variable range hopping mechanism in a limited temperature range.The variation of frequency dependent electromagnetic parameters measured at room temperature within the X-band region is consistent with the electrical conductivity behavior. The complex permittivity and permeability parameters were determined in line with the Nicolson-Ross-Weir algorithm. The LSMO nanomaterial samples showed EMI shielding effectiveness values of up to 19 dB (96.3% attenuation) over the X-band frequency range, making them suitable for microwave radiation shielding in commercial and defense appliances.