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In the present work, the technique of Back Scattering Micro-Raman was employed at low and room temperatures in order to examine all the possible phonon vibration modes present in a crystal of BiFeO 3 (BFO). The observation & identification of all E (TO), E (LO), A1 (TO), and A1 (LO) normal modes was sucessfully accomplished. The low temperature Raman spectroscopy measurements showed two one-magnon branches, σ-magnon at 20.06 cm−1 and γ-magnon at 26.93 cm−1. The spectral characteristics of the three A1 (LO) modes were observed at roughly 176.63 cm−1, 225.93 cm−1 and 505.53 cm−1, exhibiting low intensity longitudinal optical modes. The observed peaks at 145.34 cm−1, 223.92 cm−1, 292.54 cm−1, and 552.18 cm−1 were identified and categorized as A1 (TO) modes. E (TO) peaks were observed at 73.30 cm-1, 131.94 cm-1, 239.35 cm-1, 265.04 cm-1, 278.45 cm-1, 349.95 cm-1, 374.69 cm-1, 441.04 cm-1, 522.99 cm-1. In addition, E(LO) peaks were observed at 80.76 cm-1, 175.03 cm-1, 241.59 cm-1, 275.42 cm-1, 346.92 cm-1, 371.34 cm-1, 419.38 cm-1, and 469.65 cm-1. • Micro-Raman Backscattering Technique was used. • E(TO), E(LO), A1(TO) and A1(LO) normal modes were assigned. • σ-magnon and ϒ-magnon were observed at 20.06 cm-1 and at 26.93 cm-1, respectively. • A1(LO) modes were observed at 176.63 cm-1, 225.93 cm-1 and 505.53 cm-1. • A1(TO) modes were observed at 145.34 cm-1, 223.92 cm-1, 292.54 cm-1 and 552.18 cm-1. [ABSTRACT FROM AUTHOR]

PZT and ZnO heterostructures were fabricated by using the sol-gel spin-coating method on two different substrates, viz., ITO-coated glass and Corning glass. UV–Vis spectroscopy of these heterostructures showed 80% transparency in the visible region of the electromagnetic spectrum, which is desirable for optical device applications. Tauc's relation was used to calculate the energy bandgap, which was found to be blue shifted to 3.96 eV in the case of the heterostructure on ITO-coated glass and 3.9 eV for that on Corning glass, indicating a difference of Δ E = 0.06 eV due to the change in substrate. The refractive index (n), extinction coefficient (k), and the real and imaginary parts of the dielectric constant (ε 1 and ε 2) of the heterostructures were estimated. The second order non-linear refractive index (n 2) and the third order non-linear optical susceptibility (χ (3)) were determined by generalized Miller's rule in the photon energy range of 0.5–6.5 eV by using the UV–Vis spectroscopic data. The respective values of χ (1) and χ (3) values were found to be in the range 0.10–0.45 and 3.88 × 10−13–6.0 × 10−12. The optical and structural studies established that the nanocrystalline PZT-ZnO heterostructure on ITO-coated glass was more optically transparent and had better non-linear properties as compared to that on the corning glass substrate. These properties are advantageous for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Films with designed surface morphologies are of great importance for high-performance devices and other applications such as gas sensors and catalysts. Na 2 WO 4 films with various surface morphologies have been fabricated via physical evaporation inside the chamber created by approaching mouth to mouth two alumina boats containing precursors and by covering alumina boat with aluminum foil, respectively. The temperature-dependence Raman investigation reveals red shifting of the Raman peaks with increasing temperature in all cases. The observed Raman shifts are relatively small confirming high stability of the Na 2 WO 4 films within the investigated temperature range. [ABSTRACT FROM AUTHOR]

Abstract: A novel multilevel resistive switching was observed in trilayer stacked geometry composed of graphene nano flakes sandwiched between polyvinylidene fluoride layers fabricated by spin coating method, which are expected to fulfill the need of high density data storage memories. External parameters such as current compliance and induced voltage pulse imposed on the devices provided an aid to tune the inherent resistance states. As fabricated devices exhibited multi level switching with stable resistance ratios between different resistance states having excellent data retention and endurance. Space charge limited conduction and Fowler–Nordheim (F–N) tunneling were found to be responsible for the switching mechanism. Graphene enriched with trapping sites provides the adequate environment for F–N tunneling process to occur, resulting in multi-bit resistance states. [Copyright &y& Elsevier]

Abstract: We here report the structural and optical studies of Zn1−x−y Be x Mg y O (0≤ x ≤0.15; 0≤ y ≤0.20) powders and thin films. From the Rietveld refinement of the powder X-ray diffraction (XRD) patterns it was revealed that the value of ‘a’ lattice parameter remains almost unchanged whereas ‘c’ parameter reduces with Be and Mg co-doping in ZnO. The Zn-O bond length also decreases in co-doped samples. Raman studies of the pure ZnO powder showed all the characteristic peaks of the wurtzite hexagonal structure and with (Be, Mg) co-doping new modes appeared which can be attributed to arise as a result of substitution. The XRD of the films prepared from the powders using pulsed laser deposition (PLD) technique exhibited the preferential orientation and with increase in co-doping the (0002) peak also shifts to higher 2θ values suggesting the incorporation of Be/Mg at the Zn-site. From the UV–visible optical transmittance measurement it was noticed that the band gap of the pristine ZnO film is 3.3eV which enhanced up to 4.51eV for Zn0.7Be0.1Mg0.2O film which lies in the solar blind region and is very useful in the realization of deep UV detectors. [ABSTRACT FROM AUTHOR]

MgxZn1−xO (MZO) thin films were deposited from MZO targets as well as sequential deposition of ZnO/MgO multilayers on c-plane Al2O3 substrates using pulsed laser deposition. The total thickness of the films used in this study was ∼300 nm. For multilayer deposition, the thickness of each single ZnO layer was varied in the range of 0.75–2.5 nm followed with the MgO layer thickness of 1 nm. The structural transition from the hexagonal to the cubic phase was observed with the increase in Mg concentration at/above 40% from the single targets. Similar structural change was also observed with the decrease in thickness of single ZnO layer from 2.5 to 0.75 nm in multilayer deposition. The bandgap was increased with increase of Mg contents from 3.3 to 6.2 eV as well as with the change of ZnO sublayer thickness. In both cases it has not been possible to fabricate single-phase stable MZO alloys with a bandgap between 4 and 6 eV. [Copyright &y& Elsevier]

The Fe-doped PZT, Pb (Zr, Ti) 1-x Fe x O 3 , ceramics have gathered plenty of attention because of the interplay of ferroelectric and ferromagnetic properties. In the present study, we report the properties of Pb(Zr 0.52 Ti 0.48) 1-x Fe x O 3 prepared by conventional solid-state reaction route with varying Fe3+ doping concentrations, x = 0, 0.05, 0.10, 0.15 and 0.20. Study of X-ray diffraction patterns confirmed the tetragonal crystal structure along with reduction in tetragonality and unit-cell size with doping. It also showed formation of secondary magneto-plumbite phase at higher doping concentrations. The SEM micrographs exhibited decrease in grain size with increase in doping concentration (for x > 0.05). The increase in oxygen vacancies and the formation of secondary magneto-plumbite phase and Fe3+–VO2−–Fe3+ defect dipole complexes introduced with the acceptor (Fe3+) doping, caused clamping of the domain walls and hence reduced the room temperature dielectric constant as the doping concentration was increased. The coexistence of electrical polarization and magnetic moment at room temperature in all PFZT compositions confirmed the multiferroic characteristic in the ceramic samples. Electric polarization (P r) and coercive fields (E c) decreased with increase in Fe3+ concentration in PFZT sample. However, magnetization (M) and magnetic coercive fields (E c) increased with the increasing Fe3+ concentration due to the dominant effect of F-center exchange mechanism in Fe3+–VO2−–Fe3+ and formation of ferromagnetic secondary magneto-plumbite phase. [ABSTRACT FROM AUTHOR]

Highlights • Engineered ferroelectric-ferromagnetic heterostructures showed good magnetic response. • Heterostructures are found to sustain a magnetocaloric effect for broad temperature. • These effects are attributed to epitaxial strains and magnetoelectric coupling. • These results may help in development of spintronics and solid state refrigerators. Abstract This study reports the magnetocaloric effect (MCE) and piezoresponse of integrated ferroelectric-ferromagnetic heterostructures of PbZr 0.52 Ti 0.48 O 3 (PZT) (5 nm)/Bi-Sr-Ca-Cu 2 -O X (BSCCO) (5 nm)/La 0.67 Sr 0.33 MnO 3 (LSMO) (40 nm)/MgO (0 0 1). Magnetic and pizoresponse behavior of the heterostructures are found to be governed by magneto-electric coupling and induced lattice strains. In addition, a maximum MCE is studied using Maxwell equations from both Field Cooled (FC) and Zero Field Cooled (ZFC) magnetization data. Maximum MCE entropy change (|Δ S |) of 42.6 mJkg−1K−1 (at 258 K) and 41.7 mJkg−1K−1 (at 269 K) are found corresponding to FC and ZFC data, respectively. The variation in maximum entropy change and corresponding temperatures for FC and ZFC data revealed that the application of a magnetic field can significantly contribute towards tuning of the MCE. Interestingly, these multilayered structures are found to sustain MCE over a broad temperature range, which makes them attractive for improved solid-state energy conversion devices. [ABSTRACT FROM AUTHOR]

Emerging interdisciplinary fields of multiferroics and spin-optronics demand for new oxide materials that unfolds significant coupling between electric and magnetic order at room temperature, preferably with controlled optical properties. Rare-earth orthoferrites (RFeO 3 ) have received much attention due to their coupled electric, magnetic and optic properties. Here we report structural, optical, temperature-dependent (83–800 K) Raman spectroscopy, electronic transition analysis and electric poling induced magnetic modulation in nanostructured SmFeO 3 (SFO). Rietveld refinement of SFO confirmed the orthorhombic phase (space group D 2 h 16 , Pbnm ) with expanded lattice parameters (a o = 5.3979 Å < b o = 5.5922 Å < c o = 7.7104 Å). Microstructural analysis revealed the formation of uniformly distributed spherical grains of 40 ± 2 nm size. First-order 18 Raman active vibrational phonon modes identified using damped harmonic oscillator model suggested the main activity in SFO lies between 100 and 650 cm −1 . Above 483 K, clear fading of high frequency mode (~ 632 cm −1 ) due to spin-reorientation and fusion in low frequency modes (~132 cm −1 ) around 673 K is considered as direct evidence of possible phase transition from antiferromagnetic to paramagnetic order. Optical response in studied spectral range from 200 to 800 nm is dominated by two ( p-d ) and ( d-d ) charge transfer transitions, which favors strong exchange interaction as well as high magnetic transition temperatures. Large observed bandgap E g of 5.21 eV, determined from diffuse reflectance Uv–visible spectroscopy in combination with the electric poling induced magnetic modulation establish SFO, a suitable oxide material for future power efficient microelectronic and spin-optoelectronic devices. [ABSTRACT FROM AUTHOR]

We report the room temperature thermal conductivity of polycrystalline twisted bilayer graphene (tBLG) as a function of grain size measured by employing a noncontact optical technique based on micro-Raman spectroscopy. Polycrystalline tBLG sheets of different grain sizes were synthesized on copper by hot filament chemical vapor deposition. The thermal conductivity values are 1305±122, 971±73, and 657±42 Wm-1K-1 for polycrystalline tBLG with average grain sizes of 54, 21, and 8 nm, respectively. Based on these thermal conductivity values, we also estimated the grain boundary conductance, 14.43±1.21 x 1010Wm-2K-1, and the thermal conductivity for single crystal tBLG, 1510±103Wm-1K-1 . Our results show that the relative degradation of thermal conductivity due to grain boundaries is smaller in bilayer than in monolayer graphene. Molecular dynamics simulations indicate that interlayer interactions play an important role in the heat conductivity of polycrystalline bilayer graphene. The quantitative study of the grain size dependent thermal conductivity of polycrystalline bilayer graphene is valuable in technological applications as well as for fundamental scientific understanding. [ABSTRACT FROM AUTHOR]

Core-shell like structured barium zirconium titanate-barium calcium titanate-poly(methyl methacrylate) [(Ba 0.94 Ca 0.06 )(Zr 0.16 Ti 0.84 )O 3 -PMMA] nanocomposites were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate (MMA) from the surface of BZT-BCT nanoparticles. X-ray diffraction patterns of pure polymer and BZT-BCT nanoparticles revealed their amorphous and polycrystalline natures respectively. Fourier transform infrared spectroscopy confirmed the grafting of the PMMA shell on the surface of the BZT-BCT nanoparticles cores. Transmission electron microscopy (TEM) results revealed that BZT-BCT nanoparticles were covered by a very thin layer of PMMA forming a core-shell like structure and thermogravimetric analysis results showed that the grafted BZT-BCT-PMMA nanoparticles consist of ∼80.1% PMMA by weight. Polymer grafted BZT-BCT nanocomposite thick films (∼10 μm) have shown an improved dielectric constant (ε∼56), a high breakdown field strength (∼3 MV/cm) and high-energy storage density ∼22.5 J/cm 3 . The improved electrical properties of core-shell like structured BZT-BCT-PMMA nanocomposites were attributed to improved nanoparticle dispersion and enhanced interfacial polarization due to the covalent linkage between polymer and nanoparticle interface. Mechanically stable and homogeneous composite films were obtained using the surface grafted BZT-BCT ceramic nanoparticles. [ABSTRACT FROM AUTHOR]

[Display omitted] • NaH 2 PO 4 ·2H 2 O and ZrO 2 samples have a monoclinic phase at room temperature. • The conductivity increases by 1 to 2 orders of magnitude due to addition of ZrO 2. • The highest conductivity value of composites electrolytes 80SDP·2H 2 O/20ZrO 2 was found to be 1.78 × 10-3 S cm-1 at 270 °C. • The time-stable protonic conductivity for SDP·2H 2 O and composites was observed for the first time under hermetically closed conditions. Composites of proton-conducting material based on sodium dihydrogen phosphate were prepared and doped with zirconium oxide. The structural, thermal, and transport properties of composite proton electrolytes were observed by different analyses. The performance of NaH 2 PO 4 ·2H 2 O was observed in terms of conductivity and stability because of the addition of ZrO 2 and exhibited conductivity in the higher and lower temperature range. The time-stable protonic conductivity for NaH 2 PO 4 ·2H 2 O and composites was observed for the first time under hermetically confined conditions which was found to be stable. Thermal characterization of composites showed that the dehydration behavior in DTA shifted to a lower. Arrhenius' plots confirmed the conductive nature of NaH 2 PO 4 ·2H 2 O. The electrodes were made by the vapor deposition technique. The improvement of mechanical and hydrophobic properties of the composites makes them more promising as compared to single salt NaH 2 PO 4 ·2H 2 O. [ABSTRACT FROM AUTHOR]

High quality (1 0 0) oriented thin films of (Y 0.9 Bi 0.1 )(Fe 0.5 Cr 0.5 )O 3 [YBFCO] were deposited on (1 0 0) LAO substrates with conducting LNO buffer layer as bottom electrode. YBFCO thin film was found to demonstrate interesting room temperature multiferroic properties where the origin of weak ferroelectricity could be mainly attributed to disordered transition metal ions of unlike spins, and magnetic behavior was ascribed to uncompensated weak ferromagnetism arises due to magnetic cluster state in disordered system. Dielectric anomaly near magnetization reversal temperature ( T irr ) revealed magnetodielectric effect in YBFCO film. In addition, leakage current behavior of the film was explained by trap-controlled space-charge-limited current conduction (SCLC) mechanism. [ABSTRACT FROM AUTHOR]

Rare-earth (Sm) and transition metal (Co) modified polycrystalline BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2/Si substrate successfully through pulsed laser deposition (PLD) technique. Piezoelectric, leakage current and temperature dependent dielectric and magnetic behaviour were investigated for the films. Typical "butterfly-shaped" loop were observed in BSFCO films with an effective piezoelectric constant (d33) ~94 pm/V at 0.6 MV/cm. High dielectric constant ~900 and low dielectric loss ~0.25 were observed at room temperature. M-H loops have shown relatively high saturation magnetization ~35 emu/cm³ at a maximum field of H ~20 kOe. Enhanced magnetoelectric coupling response is observed under applied magnetic field. The multiferroic, piezoelectric, leakage current behaviours were explored. Such studies should be helpful in designing multiferroic materials based on BSFCO films. [ABSTRACT FROM AUTHOR]

Highlights: [•] High quality thin film of multiferroic BiFeO3 on SrRuO3 is grown by RF Sputtering. [•] The Pt/BFO/SRO structure showed diode like behavior through I–V measurement. [•] Appreciable VOC and JSC were observed with illumination of white light. [•] The photoresponse at zero bias of BFO film showed rapid increase in photocurrent. [•] Application of BFO film for photosensitive capacitor is demonstrated. [ABSTRACT FROM AUTHOR]