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Motivated by the industrial processing of chocolate, we study experimentally the fluidisation of a sessile drop of yield-stress fluid on a pre-existing layer of the same fluid under vertical sinusoidal oscillations. We compare the behaviours of molten chocolate and Carbopol which are both shear-thinning with a similar yield stress but exhibit very different elastic properties. We find that these materials spread when the forcing acceleration exceeds a threshold which is determined by the initial deposition process. However, they exhibit very different spreading behaviours: whereas chocolate exhibits slow long-term spreading, the Carbopol drop rapidly relaxes its stress by spreading to a new equilibrium shape with an enlarged footprint. This spreading is insensitive to the history of the forcing. In addition, the Carbopol drop performs large-amplitude oscillations with the forcing frequency, both above and below the threshold. We investigate these viscoelastic oscillations and provide evidence of complex nonlinear viscoelastic behaviour in the vicinity of the spreading threshold. In fact, for forcing accelerations greater than the spreading threshold, our drop automatically adjusts its shape to remain at the yield stress. We discuss how our vibrated-drop experiment offers a new and powerful approach to probing the yield transition in elastoviscoplastic fluids., Comment: 38 pages, 22 figures

In this paper, room temperature multiferroic behaviour in Ni (Nickel)-doped NBT (Na0.5Bi0.5TiO3) ceramics synthesized using solid state reaction technique have been investigated. Structural, dielectric, ferroelectric, magnetic and magneto-dielectric properties were consistently probed with the increment in transition metal doping. XRD peaks were indexed for the monoclinic Cc phase. SEM micrographs clearly depicted the reduction of grain size with addition of Ni content. Ferroelectric polarization (P) vs applied electric field (E) hysteresis curves shows an increase in lossy behaviour with an increase in Ni content. The room temperature magnetization (M) vs applied magnetic field (H) curves depict the weak ferromagnetic ordering on increasing the Ni doping. Enhanced magneto-dielectric change of 1.26% was observed in 25% Ni-doped NBT ceramic, which may be useful in the development of novel non-volatile lead-free multiferroic memory devices.

Here, we report on the temperature and frequency dependent electrical conduction and dielectric behaviour of YCrO3 ceramics. Dielectric studies reveal a peak in the dielectric constant ∼230 K, suggesting presence of spin-charge coupling. Also, an additional broad peak found at ∼450 K is reminiscent of a relaxor like behaviour for YCrO3, attributed to a diffused phase transition. The nature of dc conductivity is of Arrhenius type and shows an abrupt change in the activation energy at ∼230 K and ∼450 K. The activation energy suggests that the polaronic hopping mechanism stabilizes at low temperature while, at higher temperatures, the process is associated with the diffusion of double ionized oxygen vacancies. However, ac conductivity suggests that the overlapping large polaron tunnelling conduction mechanism drives the ac conduction below 300 K and above 300 K, the conduction behaviour is consistent with the correlated barrier hopping conduction mechanism.

We demonstrate the improved device performances by using the structure of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film coated onto the indium tin oxide (ITO) anodic electrode annealed at 400 °C under the normal ambient. The ITO thin films show the improved film quality with decreased dislocation density and lattice strain as annealing temperature increases. The spin-coated PEDOT:PSS film smoothens the wrinkle kind of surface morphology of the ITO film annealed at 400 °C. The annealed ITO (400 °C) with PEDOT:PSS interlayer improves the hole-current density in the hole-only devices (HODs) having the device structure of ITO/PEDOT:PSS/N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine as hole-transporting layer/Al. It enhances the efficiency of organic photovoltaic devices [ITO (annealed) /PEDOT:PSS/P3HT:PCBM (active layer)/LiF/Al] by three times higher (1.69 %) when compared to that (0.48 %) of pristine ITO based OPV device. These results show that the annealing of ITO film at the high temperature of 400 °C under the normal ambient improves the film quality and lowers the potential energy barrier at ITO/PEDOT:PSS interface for effective hole injection/extraction process, resulting in the enhanced device electrical performances.

Exceptional progress in the performance of perovskite solar cells in a very short time has made it a potential photovoltaic technology for future deployment. The compositional engineering in perovskite materials and other buffer layers makes it a feasible candidate for commercial applications in the near future. However, there are certain challenges associated with these devices which need to be addressed such as device stability, process dependent device efficiency, hole transport layer (HTL) etc. The device performance is highly dependent on the processing parameters of the precursors. Understanding the origin of this challenge is very crucial for reproducible device performance. In this work, we have focused on utilizing NiO as a HTL in planar perovskite solar cells and studied the ageing effect of NiO precursor solution on the perovskite film quality in terms of crystallinity, grain growth, surface morphology, and overall device performance. It is observed that the ageing of NiO precursor promotes the formation of NiO films with increased roughness which improves the perovskite film quality. Structural and morphological studies revealed that the perovskite films formed on aged NiO films were highly crystalline in nature, uniform and with larger grain size. Current– voltage characteristics under illumination show that the films casted from NiO aged solution are better for perovskite solar cell applications and result in reduced parasitic resistances and enhanced charge transport.

In this manuscript, we demonstrate screen printing, a low cost printing method, of PEDPOT:PSS as top transparent electrode which was integrated with organic solar cell devices fabricated on opaque steel substrates with device structure being Steel/Insulator/Al/ZnO/P3HT:PC61BM/PEDOT:PSS. To print PEDOT:PSS on the surface of hydrophobic active layer of P3HT:PC61BM, PEDOT:PSS is modified with isopropyl alcohol (IPA) and Fluorosurfactant Zonyl FS-300. Further, two-step annealing of screen printed PEDOT:PSS films, 50 °C for 5 min and then at 130 °C for 3 min, is found to be crucial in rendering low surface roughness. Adoption of these strategies together yielded PEDOT:PSS films of thickness in the range of 500–700 nm consistently with a roughness of ca. 55 nm. These PEDOT:PSS films were coupled with silver (Ag) grids in organic solar cell devices which yielded power conversion efficiency of ca. 0.7%.

The development of novel fluorescent polymers has attracted significant attention owing to their potential applications in energy and environmental sciences. This study reports novel oligomer (TRZBT) synthesis via Wittig-Horner reaction using bithiophene aldehyde and triazine triethyl phosphite. The resulting oligomer possesses large porous morphology, which was confirmed using SEM analysis. Further, the chemical structure of TRZBT was confirmed by FT-IR, NMR, and GPC studies. The triazine acceptor (A) unit linked with bithiophene donor (D) unit through olefin π-conjugation resulted in a Donor-π-Acceptor (D-π-A) type oligomer. Detailed studies of the solvent-dependent photophysical properties of TRZBT were performed. Due to the alternate d -A structure of oligomer, enhanced intramolecular charge transfer (ICT) properties between D and A moiety was observed. Further, TRZBT in THF and THF: H2O (10:90) system effectively detected nitro-explosives in aqueous media, which exhibited high sensitivity, selectivity, and quick response via fluorescence quenching. TRZBT showed a higher quenching constant (Ksv) value of 4.91 × 105 M−1 towards picric acid as compared with other nitroaromatics. Significantly, the detection limit of 1.58 nM in a 100 % aqueous medium confirms that the synthesized material can detect even trace levels of the analyte.

The effects of 10 MeV Al4+ ions irradiation on structural, surface morphological, optical and electrical properties of fluorine-doped tin oxide (FTO) substrates are presented for solar cell applications. The ions irradiation changes the surface morphology, average roughness, interface width, roughness exponent, and several other fractal parameters of the FTO surfaces. The UV–visible transmittance measurement shows an enhancement of transmittance in the ions irradiated substrates up to 95%. The electrical properties such as mobility, work-function, sheet resistance, and resistivity are also modified due to ions irradiation. In order to have functional applications of these ions irradiated substrates, we fabricated organic solar cells on these ions irradiated and pristine FTO substrates. The device performances are significantly improved for the case of ions irradiated FTO substrate in comparison to the pristine one. Thus, better device performance due to effective changes in physical properties suggests that the ions irradiated FTO substrates can be used as better electrodes for organic and hybrid photovoltaic device applications.

We have synthesized (010) textured polycrystalline thin films of gallium ferrite (GaFeO 3 or GFO) on n-Si(100) and Pt/Si(111) substrates using sol-gel assisted spin coating technique. Structural characterization using x-ray diffraction and Raman spectroscopy confirms formation of single phase with crystallite size ∼37–47 nm. Magnetic characterization demonstrates saturated magnetic hysteresis loop at room temperature and indicates that due to reduced crystallite size, ferri to paramagnetic transition temperature, T C ∼300 K is higher compared to bulk GFO, reported earlier. Room temperature piezo-response force microscopic analysis reveals local ∼180° phase switching of ferroelectric domains at very high coercive field, ∼700 kV/cm, consistent with recent experimental and first-principles studies. Our study opens up the possibility of integrating polycrystalline GFO in novel room temperature multiferroic devices.

Buffer layers play crucial role in increasing the power conversion efficiencies (η) in organic solar cells (OSCs) and hence it is important to understand the underlying microscopic mechanisms behind the improvements aiding the existing qualitative understanding. In this manuscript, we have investigated the role of zinc oxide (ZnO) and molybdenum oxide (MoO3) buffer layers on the current density - voltage (J-V) characteristics of inverted organic solar cell (IOSC) devices combining experimental results with drift-diffusion based transport modeling, on the active layer (ActL) blend of P3HT:PCBM (Poly 3-hexylthiophene (P3HT): (6, 6) phenyl C61 butyric acid methyl ester (PC61BM)), a workhorse system with well-established device data. The results show that while ZnO alone improves the open circuit voltage (VOC) significantly, use of both the ZnO and MoO3 layers help in improving the short-circuit current density (JSC), aided by contributions to exciton dissociation by both layers at the electrode ActL interface. Absence of ZnO, in particular, causes S-shaped J-V curve which is attributed to reduced surface recombination velocity of majority carriers due to hindered charge extraction and non-selectivity of carrier flow towards cathode. On the other hand, presence of MoO3film between ActL and the anode assists in making an energetically favourable contact with ActL and improves the extraction of photo generated charge carriers. Further in conjunction with dark J-V characteristics, impedance spectroscopy (IS) carried out under dark and illuminated conditions establishes the role of buffer layers in modifying the barrier heights at the contacts and the interfacial structure.

Ink-jet printing is a potentially attractive technique for printing of components for organic electronic devices primarily due to its ability to print patterned layers and reduced ink wastage. However, the mechanism of film formation is quite complex and needs an understanding of various printing parameters on the film growth. In this manuscript, we successfully demonstrate ink-jet printing of smooth zinc oxide (ZnO) thin films with controlled thickness as electron transport layers for inverted organic solar cell devices fabricated on indium tin oxide coated glass substrates. The parameters that strongly affect the formation of a continuous ZnO thin film with controlled thickness are ink concentration and viscosity, substrate surface treatment, drop spacing, substrate temperature during printing and the annealing temperature, affected by a combination of surface energetics, surface tension of the ink and the rate of solvent evaporation. The results suggest that one can achieve a transmittance of >85% for a 45 nm thin ZnO film possessing uniform structure and morphology, fabricated using a drop spacing of 40–50 μm at an ink viscosity of 4.70 cP with substrate held at room temperature. The P3HT:PC 61 BM inverted organic solar cell devices fabricated using printed ZnO films as electron transporting layers exhibit an efficiency of ∼3.4–3.5%, comparable to that shown by the devices fabricated on spin coated ZnO films. Finally, the device with printed P3HT:PC 61 BM active layer on printed ZnO layer showed a device efficiency of ca . 3.2% suggesting that nearly completely printed devices can deliver a comparable performance to the spin coated devices.

A polycrystalline ceramic sample of Y0.5Ho0.5CrO3 was studied using powder X-ray diffraction, Raman spectroscopic and dc magnetometry measurement to understand the structural and magnetic properties. The Rietveld refinement of X-ray data suggests sample crystallized in Pnma orthorhombic structure without formation of any secondary phases confirming their phase-pure nature. However, Raman study shows a prominent effect of Ho doping in low wavenumber Raman active phonon modes. Further, M-T measurement shows magnetic phase transition (TN) at 141 K and a negative value of Curie-Weiss temperature suggesting an antiferromagnetic system. Subsequent, the appearance of the clear opening in the M-H loop below TN is an evidence of the appearance of a weak ferromagnetic component in the low- temperature regime while the magnetization increases linearly in the high magnetic field regime suggest antiferromagnetic component.A polycrystalline ceramic sample of Y0.5Ho0.5CrO3 was studied using powder X-ray diffraction, Raman spectroscopic and dc magnetometry measurement to understand the structural and magnetic properties. The Rietveld refinement of X-ray data suggests sample crystallized in Pnma orthorhombic structure without formation of any secondary phases confirming their phase-pure nature. However, Raman study shows a prominent effect of Ho doping in low wavenumber Raman active phonon modes. Further, M-T measurement shows magnetic phase transition (TN) at 141 K and a negative value of Curie-Weiss temperature suggesting an antiferromagnetic system. Subsequent, the appearance of the clear opening in the M-H loop below TN is an evidence of the appearance of a weak ferromagnetic component in the low- temperature regime while the magnetization increases linearly in the high magnetic field regime suggest antiferromagnetic component.

Here, we present a time and temperature dependent magnetization study to understand the spin dynamics in flux grown single crystals of gallium ferrite (GaFeO 3 ), a known magnetoelectric, ferroelectric and ferrimagnet. Results of the magnetic measurements conducted in the field-cooled (FC) and zero-field-cooled (ZFC) protocols in the heating and cooling cycles were reminiscent of a “memory” effect. Subsequent time dependent magnetic relaxation measurements carried out in ZFC mode at 30 K with an intermittent cooling to 20 K in the presence of a small field show that the magnetization in the final wait period tends to follow its initial state which was present before the cooling break taken at 20 K. These observations provide an unambiguous evidence of single crystal gallium ferrite having a spin glass like phase.

In this manuscript, we report the effect of co-doping of La and Ni in controlling the electrical leakage and enhancing the ferroelectric polarization in chemical solution processed BiFeO3 (BFO) thin films grown on Pt/Si substrates. Structural analysis of the films using X-ray diffraction shows that all the films are phase pure with perovskite structure and a R3c space group. The films are polycrystalline without evidence of any preferred orientation. Compared to the undoped BFO thin films, the leakage current in co-doped thin films is minimum at a La doping of 5 at% and Ni doping of 2.5 at% beyond which the leakage increases. While ferroelectric polarization does decrease marginally on co-doping, the shape of ferroelectric hysteresis loop improves in comparison to the undoped or singly doped films. The samples with La doping of 5 at% and Ni doping of 2.5 at% (Bi0.95La0.05Fe0.975Ni0.025O3) show a remnant polarization (Pr) of ∼66 μC/cm2 and a coercive field of 0.3 MV/cm at room temperature.

Here, we review the advances in understanding the structure and properties of magnetoelectric gallium ferrite (GaFeO3 or GFO). Special significance of GFO lies in its compositional tunability over a large range of Ga:Fe ratio without forming a second phase which also renders prospective room temperature magnetoelectricity in the material. Detailed structural studies show noncentrosymmetric orthorhombic Pc21n symmetry without any structural phase transition between 4 K and 700 K. The material shows a ferrimagnetic behavior driven by cation site disorder, corroborated both experimentally as well as theoretically, with transition temperature dependent upon Ga:Fe ratio. GFO exhibits magnetostructural and magnetoelectric coupling indicating coupling among the structural, magnetic and electrical degrees of freedom which could possibly be utilized to strain engineer electrical and magnetic properties in the thin film structures. However, the biggest challenge remains to reduce the leakage in the material in both...

In this manuscript, we report on the role of interfacial morphology between poly(methyl methacrylate) or PMMA and poly(vinylidenedifluoride–trifluoroethylene) or P(VDF–TrFE) thin films upon improvement in the ferroelectric and leakage characteristics of the P(VDF–TrFE)–PMMA devices. Whilst keeping the overall thickness of 200 nm, PMMA is incorporated in different proportions along with P(VDF–TrFE) in three different configurations: in the form of blend, and two bilayer structures, one with PMMA films below P(VDF–TrFE) films and another with PMMA films on top of P(VDF–TrFE) films. In the blend form, addition of PMMA decreases the crystallinity of P(VDF–TrFE) resulting in deterioration of the ferroelectric properties of the blend before complete disappearance at 30% PMMA when the blend becomes amorphous. In the bilayer structures, whilst overall polarization of the bilayer structure decreased in comparison to a 200 nm P(VDF–TrFE) only device, ferroelectric polarization of P(VDF–TrFE) in the bilayer was larger than P(VDF–TrFE) only device for the similar voltage drop. This is attributed to the development of morphology in the bilayer structure. Importantly, PMMA incorporation leads to nearly two orders of magnitude reduction in the electrical leakage rendering bilayer devices more suitable for device applications than P(VDF–TrFE) only device.

We demonstrate that small but finite ferroelectric polarization ($\sim$0.01 $\mu$C/cm$^2$) emerges in orthorhombic LuFeO$_3$ ($Pnma$) at $T_N$ ($\sim$600 K) because of commensurate (k = 0) and collinear magnetic structure. The synchrotron x-ray and neutron diffraction data suggest that the polarization could originate from enhanced bond covalency together with subtle contribution from lattice. The theoretical calculations indicate enhancement of bond covalency as well as the possibility of structural transition to the polar $Pna2_1$ phase below $T_N$. The $Pna2_1$ phase, in fact, is found to be energetically favorable below $T_N$ in orthorhombic LuFeO$_3$ ($albeit$ with very small energy difference) than in isostructural and nonferroelectric LaFeO$_3$ or NdFeO$_3$. Application of electric field induces finite piezostriction in LuFeO$_3$ via electrostriction resulting in clear domain contrast images in piezoresponse force microscopy., Comment: 12 pages, 8 figures

We report on the use and stability of solution-processed molybdenum oxide (sMoOx) thin films as anode-modifying layers to replace conventionally used poly(3,4-ethyldioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) layers in poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT/PC61BM) bulk heterojunction organic solar cells. Our results show that while as prepared devices using the two anode-modifying layers possess similar performances, the sMoOx devices exhibit a staggering 20-fold stability improvement in its performance half-life compared with PEDOT/PSS devices, ~3400 h versus ~150 h, respectively. A further comparison of the stability between encapsulated and unencapsulated devices demonstrates the necessity for protection from atmospheric moisture and oxygen but again highlights the lucrative nature of sMoOx as a protective anode-modifying layer compared with PEDOT/PSS even under ambient conditions. Copyright © 2014 John Wiley & Sons, Ltd.

We report unusually high ferroelectric polarization in chemical solution processed thin films of BiFeO3–PbTiO3 (BF–xPT) of compositions near the morphotropic phase boundary (MPB). Saturated hysteresis loops were obtained showing a large remnant polarization of 80 μC/cm2 in thin films of composition BF–0.25PT with polarization decreasing for BF–0.30PT and BF–0.35PT. Structural analysis revealed single phase region with monoclinic Cm space group for composition x=0.25 while a two phase region of monoclinic (Cm) and tetragonal (P4mm) phase exists at x=0.30–0.35. The large polarization in BF–0.25PT films is attributed to superior polarizability of the monoclinic Cm phase.

We report on the tunability of ferroelectric properties of Poly(vinylidenedifluoride–trifluoroethylene) P(VDF–TrFE) thin films by controlling the cooling rate during transformation from high temperature paraelectric α-phase to low temperature ferroelectric β-phase. A faster cooling rate of P(VDF–TrFE) thin films leads to an increased polarization by 30% and much decreased coercivity by 60%. The origin of these improvements in the ferroelectric characteristics is attributed to evolution of a favorable microstructure and crystallographic alignment leading to (1 1 0) oriented films that are cooled faster. The microstructure of the films changes from a fine fibrous structure at fast cooling rate to a flatter ripple containing structure in the slow cooled samples. This dramatic change in the microstructure is attributed to the combination of incorporation of large stresses arising from almost 50% change in the molar volume of P(VDF–TrFE) upon α → β transformation and the cooling rate assisted stress relaxation, nucleation and growth. Infrared spectroscopy further showed that the substantial improvement in the device performance of the fast cooled samples arises from a favorable alignment of C–F dipoles due to short and ordered fibers lying on the substrate plane whose orientation becomes more random as the cooling rate is decreased.

Here, we review the advances in understanding the structure and properties of magnetoelectric gallium ferrite (GaFeO3 or GFO). Special significance of GFO lies in its compositional tunability over a large range of Ga:Fe ratio without forming a second phase which also renders prospective room temperature magnetoelectricity in the material. Detailed structural studies show noncentrosymmetric orthorhombic Pc21n symmetry without any structural phase transition between 4 K and 700 K. The material shows a ferrimagnetic behavior driven by cation site disorder, corroborated both experimentally as well as theoretically, with transition temperature dependent upon Ga:Fe ratio. GFO exhibits magnetostructural and magnetoelectric coupling indicating coupling among the structural, magnetic and electrical degrees of freedom which could possibly be utilized to strain engineer electrical and magnetic properties in the thin film structures. However, the biggest challenge remains to reduce the leakage in the material in both...

Orthorhombic GaFeO3 (o-GFO) with the polar Pna21 space group is a prominent ferrite owing to its piezoelectricity and ferrimagnetism, coupled with magnetoelectric effects. Herein, we demonstrate large ferroelectric remanent polarization in undoped o-GFO thin films by adopting either a hexagonal strontium titanate (STO) or a cubic yttrium-stabilized zirconia (YSZ) substrate. The polarization-electric-field hysteresis curves of the polar c-axis-grown o-GFO film on a SrRuO3/STO substrate show the net switching polarization of ~35 μC cm−2 with an unusually high coercive field (Ec) of ±1400 kV cm−1 at room temperature. The positive-up and negative-down measurement also demonstrates the switching polarization of ~26 μC cm−2. The activation energy for the polarization switching, as obtained by density-functional theory calculations, is remarkably high, 1.05 eV per formula unit. We have theoretically shown that this high value accounts for the extraordinary high Ec and the stability of the polar Pna21 phase over a wide range of temperatures up to 1368 K. Researchers have clarified why the measured remanent polarization of orthorhombic GaFeO3 is about 50 times smaller than its predicted value. Multiferroics are rare materials that simultaneously show ferroelectricity and ferromagnetism, making them potentially useful for sensors and electrically controllable magnetic memories. Now, by growing thin films of the multiferroic material orthorhombic GaFeO3 on cubic and hexagonal substrates, Hyun Myung Jang of Pohang University of Science and Technology in Korea and co-workers have observed ferroelectric polarization switching that has an extraordinarily high coercive field at room temperature. Numerical calculations revealed that this switching has a remarkably high activation energy. This finding both explains the unusually high coercive field and clarifies the puzzling discrepancy between observed values for the remanent polarization of orthorhombic GaFeO3 and those calculated in previous studies. The polarization-electric-field hysteresis curves of the polar c-axis-grown orthorhombic GaFeO3 (o-GFO) film on a SrRuO3/STO substrate show the net switching polarization of ~35 μC cm−2 with an unusually high coercive field (Ec) of ±1400 kV cm−1 at room temperature. The positive-up and negative-down measurement also demonstrates the switching polarization of ~26 μC cm−2. The activation energy for the polarization switching, as obtained by density-functional theory calculations, is remarkably high, 1.05 eV per formula unit. We have theoretically shown that this high value accounts for the extraordinary high Ec and the stability of the polar Pna21 phase over a wide range of temperature up to 1368 K.

A study on wear behavior of two medium carbon microalloyed steels has been carried out. Isothermal annealing has been performed on these steels in order to make pearlitic and bainitic morphologies and wear behavior of both the morphologies has been studied. The isothermal transformation temperatures for producing both the phases are chosen to produce finer to finest length scales in the pearlitic and bainitic microstructures. Further, the specimens are tested under dry sliding wear condition with varying normal load from 20 to 50 N and frequency from 5 to 11 Hz. Wear volume and wear rate of bainitic microstructure have been observed one order of magnitude less than that of the pearlitic steel. This is attributed to the higher hardness, higher dislocation density and much finer distribution of austenite–cementite aggregate phase throughout the bainite microstructure.

A first-principles study of structure property correlation and the origin of ferrimagnetism is presented based on LSDA+U method. In particular, the results for the ground state structure, electronic band structure, density of states, Born effective charges, spontaneous polarization and cationic disorder are discussed. The calculations were done using Vienna ab-initio simulation package (VASP) with projector augmented wave method. We find that the ground state structure is orthorhombic and insulating having A-type antiferromagnetic spin configuration. The cationic disorder is found to play an important role. Although the cationic site disorder is not spontaneous in the ground state, interchange of octahedrally coordinated Ga2 and Fe2 sites is most favored. We find that ferrimagnetism in gallium ferrite is primarily due to this exchange between Ga-Fe sites such that Fe spins at Ga1 and Ga2 sites are antiferromagnetically aligned while maintaining ferromagnetic coupling between Fe spins at Ga1 and Fe1 sites as well as between Fe spins at Ga2 and Fe2 sites. Further, the partial density of states shows noticeable hybridization of Fe 3d, Ga 4s, Ga 4p and O 2p states indicating some covalent character of Ga/Fe-O bonds. However, the charge density and electron localization functions show largely the ionic character of these bonds. Our calculation predicts spontaneous polarization of ~59 μC/cm2 along b-axis.

We report temperature dependent electron paramagnetic resonance (EPR) studies on polycrystalline YCrO3 samples at X-band (9.46 GHz) in the temperature range of 120 K-298 K. The EPR spectra exhibit a single broad line across the whole temperature range, attributed to Cr3+ ions. The variation of EPR spectra parameters (line width, integrated intensity, and g-factor) as a function of temperature was analyzed to understand the nature of spin-dynamics in the paramagnetic region of YCrO3. A peak in the g-factor suggests the presence of a new phase within the paramagnetic state at an intermediate point of temperature T IP ~ 230 K, attributed to the onset of short range canted antiferromagnetic correlations in the material much above 140 K, Neel temperature (T N) of YCrO3. The EPR intensity increases with a decrease in temperature up to T N due to the renormalization of the magnetic moments arising from the appearance of canted antiferromagnetic correlations. Further, temperature dependent dielectric measurements also exhibit an anomaly at ~230 K suggesting the presence of magnetodielectric coupling in YCrO3, with a possibility towards a relatively high temperature magnetodielectric system.

Here we report on the subtle changes in structure of BiFeO 3 thin films induced by lanthanum (La) doping and subsequent impact on the film's properties. Bi 1―x La x FeO 3 (BLFO) thin films (x = 0.0 to 0.30) were deposited by the chemical solution deposition method on indium tin oxide coated glass substrates. X-ray diffraction analyses ofthe films indicate the gradual structural changes in the films from a rhombohedral type towards a cubic like structure as the La content increases, also evident from changes in the lattice parameters and disappearance of peak splitting upon increasing doping. This was also accompanied by an increase in the remanent polarization, dielectric constant, magnetization and a marginal decrease in the leakage current density up to x = 0.20 followed by a reverse trend at higher doping levels.

In recent years, there has been considerable effort in designing improved delivery systems by including site-directed surface ligands to further enhance their selective targeting. The goal of this study is to engineer alpha5beta1-targeted stealth liposomes (nanoparticles covered with poly(ethylene glycol) (PEG)) that will bind to alpha5beta1-expressing LNCaP human prostate cancer cells and efficiently release the encapsulated load intracellularly. For this purpose, liposomes (with and without PEG2000) were functionalized with a fibronectin-mimetic peptide (PR_b) and delivered to LNCaPs. The amount of PEG2000 and other liposomal components were characterized by 1H NMR, and the amount of peptide by the bicinchoninic acid protein assay. Fibronectin is the natural ligand for alpha5beta1, and a promising design for a fibronectinmimetic peptide includes both the primary binding site (RGD) and the synergy site (PHSRN) connected by a linker and extended off a surface by a spacer. We have previously designed a peptide-amphiphile, PRb, that employed a hydrophobic tail, connected to the N-terminus of a peptide headgroup composed of a spacer, the synergy site sequence, a linker mimicking both the distance and hydrophobicity/hydrophilicity present in the native protein fibronectin (thus presenting an overall "neutral" linker), and finally the primary binding sequence. We have examined different liposomal formulations, functionalized only with PR_b or with PR_b and PEG2000. For PR_b-targeted PEGylated liposomes, efficient cell binding was observed for peptide concentrations of 2 mol % and higher. When compared to GRGDSP-targeted stealth liposomes, PR_b functionalization was superior to that of GRGDSP as shown by increased LNCaP binding, internalization efficiency, as well as cytotoxicity after incubation of LNCaPs with tumor necrosis factor-alpha (TNFalpha)-encapsulated liposomes. More importantly, PR_b is alpha5beta1-specific, whereas many integrins bind to small RGD peptides. Thus, the proposed PR_b-targeted delivery system has the potential to deliver a therapeutic payload to prostate cancer cells in an efficient and specific manner.

An attempt to synthesize multiferroic BiFeO3 by mechanical milling Bi2O3 and Fe2O3 powders showed very interesting results. 100 h milled powder was calcined at different temperatures and it was found that the BiFeO3 phase forms at 700°C followed by slow cooling. The magnetic behaviour and phase formation crucially depended on the cooling conditions. The samples were cooled from the calcinations temperature of 700°C in four different ways and Mossbauer measurements revealed different kinds of phases formed in these conditions. It was found that slow cooling favours BiFeO3 formation while rapid cooling leads to retention of Fe2O3. This was corroborated by differences in the magnetic ordering of phases as revealed by Mossbauer spectroscopy.

In this paper, we report the structural, dielectric and ferroelectric properties of zirconium (Zr)-modified barium strontium titanate (Ba 0.9 Sr 0.1 Zr x Ti 1− x O 3 ) ceramics with varying Zr content as x =0, 0.20, 0.25 and 0.30 synthesized by the sol–gel method. Stable polycrystalline perovskite phase is obtained at a processing temperature of 1150 °C, which is lower than the processing temperature of conventional solid-state reaction method. X-ray diffraction (XRD) shows a systematic peak shift with increasing Zr content, indicating incorporation of Zr in BST lattice. Scanning electron microscope (SEM) is done to investigate microstructure of the pellets. The diffusivity parameter ( γ ) and the standard deviation from the Curie–Weiss law have also been investigated as a function of Zr. The polarization vs electric field shows a decrease in remnant polarization with increasing Zr content.

Problems in the synthesis of phase-pure BiFeO 3 , a multiferroic material, are well known and presence of other phases often leads to inferior properties. Work reported here was carried out to obtain pure phase BiFeO 3 via a solid-state-reaction method in both pure and Sm-doped form. X-ray diffraction (XRD) of the calcined undoped samples showed that maximum amount of pure BiFeO 3 phase was obtained at a calcination temperature of 825 °C while a deviation in calcination temperature led to the increased amount of secondary phases such as Bi 25 FeO 40 . On the other hand, XRD patterns of Sm doped calcined samples of composition Bi 0.9 Sm 0.1 FeO 3 revealed that secondary phases do not appear on calcination at and above 800 °C for 1 h in air. Vibrating sample magnetometry (VSM) measurements showed that Bi 0.9 Sm 0.1 FeO 3 samples possess higher room temperature remnant magnetization than undoped samples. Temperature dependent measurements suggested antiferromagnetic behavior of Sm doped samples with Neel temperature of ∼ 370 °C. Ferroelectric measurements showed that Sm doping improves the polarization but enhances the leakage current.

This paper reports tribological characterization of titanium based coatings ion bonded on steel balls for automotive applications using exhaust gas recirculation (EGR). It is well known that lubricating oil drawn from EGR operated engine is contaminated with soot and higher amounts of wear debris compared to non-EGR operated engine. In this study, steel balls coated with TiN, TiAlN and TiCN are investigated in both fresh lubricating oil and EGR stressed oil for a comparative assessment of their wear characteristics in two mediums. Normal load was applied on the samples, tested against a rotating cast iron disk, simulating ring-liner interaction. In each experiment, about one quarter of disk was dipped in the oil (a) to ensure the presence of a thin oil film on the disk-ball interface during the experiment, and (b) to avoid exposure of the worn surface to atmospheric air. The results reveal that the wear rates of the coatings based on the change in the scar diameters of the samples, tested in EGR oil was 2–4 times higher than that of fresh lubricating oil. It was found that despite lowest hardness, TiN coated samples showed smaller scar diameters than TiAlN and TiCN coated samples in both lubricating oil environments. A simple geometric model was used to calculate the thickness of the coating removed as a function of the test duration. Results show that TiN coatings last for 120 min in fresh oil as compared to 30 min in the EGR oil under normal loading, whereas TiAlN and TiCN coating last for 60 and 30 min respectively in fresh oil and wear out in 15 min in EGR oil.

Here, we report results of electrical and magnetic characterization studies on polycrystalline (1-x) BiFeO3-xPbTiO3 (BF-xPT) thin films of compositions x = 0.25.0.30 and 0.35 near the morphotropic phase boundary. All films show saturated ferroelectric hysteresis loops at room temperature. DC leakage current studies reveal that different mechanisms affect the leakage behavior in these films. Low leakage current density observed results in saturated ferroelectricity at room temperature. Magnetic measurements show saturated hysteresis loops with remnant magnetization upto 0.1 µB/ formula unit. Micro Raman studies reveal that the films have monoclinic structure for x=0.25 which coexists with tetragonal phase in x=0.30 and x=0.35 compositions.

Polycrystalline fatigue-free Sm-substituted bismuth titanate thin films have been prepared on platinized silicon substrates by pulsed laser deposition (PLD) and chemical solution deposition (CSD), using similar annealing temperatures (∼700°C). X-ray diffraction and Raman spectroscopy results showed similar crystallographic orientations and structures for films fabricated using these different deposition methods. Atomic force microscopy showed that the surface roughness values were comparable, although PLD-grown films showed a more uniform and slightly larger surface feature size. Cross-sectional images obtained by scanning electron microscopy revealed dense, columnar grains for PLD-grown films compared to a more porous structure with isotropic grains for CSD-derived films. The piezoelectric response of both film types was studied using piezoresponse force microscopy, clearly showing domain switching and a strong correlation between grain structure and domain structure. The PLD-grown films showed ...

The interaction of the alpha5beta1 integrin with its ligand, fibronectin, supports numerous adhesive functions and has an important role in health and disease. In recent years, there has been a considerable effort in designing fibronectin-mimetic peptides to target the integrin. However, to date, the therapeutic use of these peptides has been limited, as they cannot accurately mimic fibronectin's binding affinity for alpha5beta1. A peptide-amphiphile (PR_b) was synthesized with a peptide headgroup composed of four building blocks: a spacer; RGDSP, the primary recognition site for alpha5beta1; PHSRN, the synergy binding site; and a linker. The linker was designed to mimic two important criteria: the distance and the hydrophobicity/hydrophilicity between PHSRN and RGD in fibronectin. Human umbilical vein endothelial cells were seeded on different substrates and evaluated in terms of adhesion, spreading, specificity, cytoskeleton organization, focal adhesions, and secretion of extracellular fibronectin. This peptide was shown to perform comparably to fibronectin, indicating that a biomimetic approach can result in the design of novel peptides with therapeutic potential for biomaterial functionalization.

Since the discovery of fatigue free La doped Bi4Ti3O12 films, considerable interest has been shown in studying the effects of various other rare earth dopants (e.g. Nd, Sm) on the ferroelectric properties of this material for applications in non-volatile ferroelectric random access memories. We have grown Nd-doped films from a ceramic target of composition Bi3.15Nd0.85Ti3O12 by pulsed laser ablation. Epitaxial films (c-axis and non-c-axis oriented) have been grown on strontium titanate substrates of different crystallographic orientations to study the effect of film orientation on ferroelectric properties. Films have been characterized using X-ray diffraction. Ferroelectric measurements have been performed to investigate the dependence of film properties on crystallographic orientation. †Paper originally presented at 10th European Meeting on Ferroelectricity, Cambridge, U.K., August 3–8, 2003.

W-doped SrBi2Ta2O9 (SBTW) thin films were deposited on Pt/Ti/SiO2/Si substrates by off-axis magnetron sputtering of SrBi2Ta1.8W0.2O9. Annealing at 750°C in air led to a predominant (115) orientation, coupled with a dense surface morphology. The films demonstrated well-defined hysteresis loops, with a remanent polarization (2P r ) of 12.6 μC/cm2 and coercive field (2E c ) of 137.5 kV/cm. A dielectric constant of 382 and a dielectric loss of 8% were measured for the SBTW thin films at 1.0 MHz. These ferroelectric and dielectric properties are much improved on those of SBT, by considering the fact that substitution of Ta5 + by W6 + can suppress oxygen vacancies in the layered perovskite lattice.

The dynamics of the ferroelectric phase transition in a SrBi2Ta 2O9 film of 5.5 µ mt hickness deposited on sapphire was studied by means of timedomain terahertz transmission spectroscopy (30–300 K) and Fourier transform far-infrared transmission spectroscopy (300–950 K). The optical soft mode near 28 cm −1 (at 300 K) exhibits a weak monotonic softening down to 20 cm −1 at 950 K with no significant anomaly near either the ferroelectric or ferroelastic phase transition. An additional relaxation process below the phonon frequencies was resolved in the terahertz transmission spectra. The critical slowing down of its relaxation frequency could be responsible for the dielectric anomaly near the ferroelectric transition temperature. This indicates that the ferroelectric transition is predominantly of order–disorder type.

Optical emission spectroscopy (OES) has been used for detailed characterization of the magnetron discharge during magnetron sputter deposition. In particular, we have studied the ionization of the sputtered flux as it travels from the target, and have observed the influence of the deposition parameters upon the ionization level. The addition of a secondary, radio frequency plasma between target and substrate during film growth leads to a significant increase in ionization of the depositing flux at the substrate. Using this technique we have assessed the influence of ionization of the depositing flux upon film growth through the measurement of film structure and properties, observing large variations as a function of total ion flux, ion energy and ionization fraction (the proportion of the depositing flux which is ionized). This illustrates the increase in control of film growth which is possible through ionization of the depositing flux, and leads to further understanding of the mechanisms involved. We have also used OES for the study of the laser plume during pulsed laser deposition of complex oxides, and have illustrated the formation of molecular oxide species as ablated material travels from target to substrate.

SrBi 2 Ta 2 O 9 films were deposited on single crystal LaSrAlO 4 (110) substrates by pulsed laser deposition at various growth temperatures and were characterized using x-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). XRD measurement and TEM observations revealed that the films were highly epitaxial and were fully a -/ b -axis oriented with excellent in-plane alignment with the substrate. AFM showed that films possessed a very smooth surface with RMS roughness of the order of 2-3 nm.

High quality polycrystalline YCrO3 samples were synthesized using solid-state-reaction method. The samples were subsequently characterized using X-ray diffraction and magnetometry. Further, temperature dependent Raman spectroscopy over a spectral range from 100 to 800 cm−1 was used to examine the variation of phonons as a function of temperature from 90 to 300 K. In the low temperature ferroelectric phase of YCrO3, the observed phonon spectra showed softening of some Raman modes below the magnetic ordering temperature (TN ∼ 142K), suggesting a coupling between the spin and phonon degrees of freedom.

Time-integrated optical emission spectroscopy has been used to observe the plume produced during pulsed laser deposition (PLD) in oxygen of the ferroelectric oxide SrBi2Ta2O9 (SBTO). Line emission from atomic and singly ionized target material was observed, together with emission from atomic oxygen. Band emission from strontium oxide was also observed. Spatially resolved analysis of oxide emission and atomic emission together with the assumption of an optically thin plasma plume distant from the point of ablation indicated that oxidation occurred most readily at the interface between the visible plume and the background gas. The oxide content in the visible plume was seen to increase as the plume passed through the background gas. Analysis of line intensity ratios and widths allowed the plasma electron temperature and density of the plume to be measured, with peak values of 7300 K and 1.2×1017 cm−3, respectively, measured at the laser spot. These results are of interest for the fabrication of SBTO thin fi...

SrBi2Ta2O9 (SBT) is an attractive material for nonvolatile ferroelectric memory applications. In this paper we report on the deposition of highly epitaxial and smooth SrBi2Ta2O9 films on (110) SrTiO3substrates. The films were grown by pulsed laser deposition at temperatures ranging from 600 to 800°C and at various laser fluences from a Bi-excess SBT target. The background oxygen pressure was maintained at 28 Pa during the film deposition. Structural characterization of the films was performed by x-ray diffraction. Atomic force microscopy was used to investigate morphology and growth of the films. The films grew with preferred (115) or (116) orientation. The roughness was of the order of unit cell height. The films display a growth pattern resulting in corrugated film morphology.

We demonstrate room temperature ferroelectricity in the epitaxial thin films of magnetoelectric GaFeO3. Piezo-force measurements show a 180o phase shift of piezoresponse upon switching the electric field indicating nanoscale ferroelectricity in epitaxial thin films of gallium ferrite. Further, temperature dependent impedance analysis with and without the presence of an external magnetic field clearly reveals a pronounced magneto-dielectric effect across the magnetic transition temperature. In addition, our first principles calculations show that Fe ions are not only responsible for ferrimagnetism as observed earlier, but also give rise to the observed ferroelectricity, making GFO an unique single phase multiferroic., 15 pages, 4 main figures

Here, we report a combined experimental-theoretical study showing that collective application of rare earth doping on A-site and epitaxial strain to ferroelectric bismuth titanate does not lead to a very large c-axis polarization as reported previously. Further first principles calculations based on the examination of polarization tensor suggest that simultaneous Bi and Ti site doping could result in moderate polarization along c-axis of bismuth titanate which is typically a preferential axis of film growth and thus enabling c axis oriented films to have appreciable polarization. This approach could also be applicable to other ferroic oxides where one can correlate the doping, epitaxial strain, and polarization to design materials compositions resulting in epitaxial films grown along desired directions yielding substantial polarization., 16 pages, two figures

We report experimental and theoretical investigation of anisotropy in optical properties and their origin in the ferroelectric and paraelectric phases of bismuth titanate. Room temperature ellipsometric measurements performed on pulsed laser deposited bismuth titanate thin films of different orientations show anisotropy in the dielectric and optical constants, Subsequent first-principles calculations performed on the ground state structures of ferroelectric and high temperature paraelectric phases of bismuth titanate show that the material demonstrates anisotropic optical behavior in both ferroelectric and paraelectric phases. We further show that O 2p to Ti 3d transition is the primary origin of optical activity of the material while optical anisotropy results from the asymmetrically oriented Ti-O bonds in TiO6 octehdra in the unit cell., Comment: 13 pages, 4 figures

Here, we report the observation of magneto-dielectric and magneto-structural coupling in (1 - x)BiFeO3-xPbTiO3 i.e.(1 - x)BF-xPT) solid solutions with compositions in the vicinity of morphotropic phase boundary, as manifested by a combination of temperature dependent magnetic, Raman and dielectric measurements. Whilst x-ray diffraction and Raman spectroscopy suggest absence of any structural phase transition between 90-300 K, temperature dependent magnetic studies reveal magnetic anomalies in the solid solutions. These results are complemented by identical observations in the dielectric measurements at similar temperatures indicating a coupling between magnetic and electric order parameters. Further, Raman studies on rhombohedral i.e. x = 0.20 samples reveal a coupling between the magnetic structure and the lattice, causing spin-phonon interactions that are possibly responsible for observed magneto-dielectric effects. Our results illustrate that the phase transitions in BiFeO3-PbTiO3 system are fewer than expected and are attributed to a spatial averaging in an inhomogeneous albeit single-phase material due to clustering of Fe- or Ti-ions on different length scales.

We present a combined experimental-theoretical study demonstrating the role of site disorder, off-stoichiometry and strain on the optical behavior of magnetoelectric gallium ferrite. Optical properties such as band-gap, refractive indices and dielectric constants were experimentally obtained by performing ellipsometric studies over the energy range 0.8 eV to 4.2 eV on pulsed laser deposited epitaxial thin films of stoichiometric gallium ferrite with b-axis orientation and the data was compared with theoretical results. Calculations on the ground state structure show that the optical activity in GaFeO3 arises primarily from O2p-Fe3d transitions. Further, inclusion of site disorder and epitaxial strain in the ground state structure significantly improves the agreement between the theory and the room temperature experimental data substantiating the presence of site-disorder in the experimentally derived strained GaFeO3 films at room temperature. We attribute the modification of the ground state optical behavior upon inclusion of site disorder to the corresponding changes in the electronic band structure, especially in Fe3d states leading to a lowered band-gap of the material., Comment: 18 Pages, 6 figures

In this letter we show the presence of a spin-glass like phase in single crystals of magnetoelectric gallium ferrite (GaFeO3) below ~210 K via temperature dependent ac and dc magnetization studies. Analysis of frequency dispersion of the susceptibility peak at ~210 K using the critical slowing down model and Vogel-Fulcher law strongly suggests the existence of a classical spin-glass like phase. This classical spin glass behavior of GaFeO3 is understood in terms of an outcome of geometrical frustration arising from the inherent site disorder among the antiferromagnetically coupled Fe ions located at octahedral Ga and Fe sites., 16 pages, 4 figures