Structure and phase composition of BiFeO3 : La films synthesized by chemical deposition from solutions

The transmission electron microscopy, energy-dispersive, and X-ray powder diffraction analyses have been used to study the changes in the structure and phase composition of lanthanum-doped BiFeO₃ and undoped BiFeO₃ thin films synthesized by chemical deposition from solutions and annealed in the temperature range 500?C700°C. It has been found that the temperature of the onset of crystallization with formation of the rhombohedral phase of BiFeO₃ is 500°C. As the annealing temperature increases, the phase composition of the film is changed: the Bi_3.43Fe_0.57O₆ and Bi₂Fe₄O₉ phases are formed. The lanthanum doping increases the crystallization temperature to 550°C; in this case, the film remains single-phase to T = 700°C.     

Swift heavy ion irradiation induced modification of BiFeO3 thin films prepared by sol-gel method

We report the preparation of multiferroic BiFeO₃ thin films on ITO coated glass substrates through sol-gel spin coating method followed by thermal annealing and their modification by swift heavy ion (SHI) irradiation. X-ray diffraction and Raman spectroscopy studies revealed amorphous nature of the as deposited films. Rhombohedral crystalline phase of BiFeO₃ evolved on annealing the films at 550°C. Both XRD and Raman studies indicated that SHI irradiation by 200 MeV Au ions result in fragmentation of particles and progressive amorphization with increasing irradiation fluence. The average crystallite size estimated from the XRD line width decreased from 38 nm in pristine sample annealed at 550°C to 29 nm on irradiating these films by 200 MeV Au ions at 1 × 10¹¹ ions cm⁻². Complete amorphization of the rhombohedral BiFeO₃ phase occurs at a fluence of 1 × 10¹² ions.cm⁻². Irradiation by another ion (200 MeV Ag) had the similar effect. For both the ions, the electronic energy loss exceeds the threshold electronic energy loss for creation of amorphized latent tracks in BiFeO₃.     

Structural and optical characterization of Bi4Ti3O12 thin films prepared by metallorganic solution deposition technique

Single phase and nanosized microstructure Bi₄Ti₃O₁₂ thin films were prepared on fused quartz substrate by metallorganic solution deposition technique using titanium butoxide and bismuth nitrate at relatively low annealing temperature. The structural properties were characterized by XRD and AFM, which revealed that the crystallite sizes and crystallite cluster sizes of Bi₄Ti₃O₁₂ were increased with the increase of the annealing temperature and about 8.65–18.3 nm by XRD study and 60–110 nm by AFM study, respectively. The refractive index and extinction coefficient of the films were calculated by Manifacier method from the spectral transmission measurement. They were increased with the increase of the annealing temperature and decreased with the increase of wavelength. The band gaps of the films were about 2.96, 2.88 and 2.80 eV for 450, 550 and 650°C annealing temperatures, respectively.     

Temperature dependent surface and spectral modifications of nano V<Subscript>2</Subscript>O<Subscript>5</Subscript> films

Nanocrystalline V₂O₅ films have been deposited on glass substrates at 300°C substrate temperature using thermal evaporation technique and were subjected to thermal annealing at different temperatures 350, 400, and 550°C. X-ray diffraction (XRD) spectra exhibit sharper and broader characteristic peaks respectively indicating the rearrangement of nanocrystallite phases with annealing temperatures. Other phases of vanadium oxides started emerging with the rise in annealing temperature and the sample converted completely to VO₂ (B) phase at 550°C annealing. FESEM images showed an increase in crystallite size with 350 and 400°C annealing temperatures followed by a decrease in crystallite size for the sample annealed at 550°C. Transmission spectra showed an initial redshift of the fundamental band edge with 350 and 400°C while a blue shift for the sample annealed at 550°C, which was in agreement with XRD and SEM results. The films exhibited smart window properties as well as nanorod growth at specific annealing temperatures. Apart from showing the PL and defect related peaks, PL studies also supported the observations made in the transmission spectra.     

Strangeness production in AA collisions at SIS18

Aluminium oxides doped with 1% ⁵⁷Fe were prepared by sol-gel method, and annealed for 3 hours at various temperatures between 550°C and 1100°C. Amorphous phases were obtained below 1000°C, and crystalline α–Al₂O₃ was formed at 1100°C. Although Al₂O₃ itself shows diamagnetism, the light doping of Fe ions into aluminium oxide induced a very weak ferromagnetism, but the ferromagnetism disappeared by longer annealing. M?ssbauer spectra were composed of paramagnetic Fe^2?+? and Fe^3?+? species for samples heated below 750°C, and of paramagnetic Fe^3?+? above 850°C, in addition to a magnetic sextet and relaxation peaks of Fe^3?+?. The magnetic and quadrupole interactions of the sextet and the relaxation peaks and the density functional calculations suggest that the lightly doped Fe^3?+? ions are substituted at Al sites in the Al₂O₃ lattice.     

Structure and piezoelectric properties of BiFeO3 and Bi0.92Dy0.08FeO3 multiferroics at high temperature

Multiferroic BiFeO₃ and Bi_0.92Dy_0.08FeO₃ ceramics were prepared to study their crystal structures and piezoelectric properties. BiFeO₃ exhibits rhombohedral phase below 810 °C. Although Bi_0.92Dy_0.08FeO₃ ceramic also shows rhombohedral phase at room temperature, it allows the coexistence of rhombohedral phase and orthorhombic phase at 460–650 °C. Both samples have maximum polarizations of >21 μC/cm² and piezoelectric d₃₃ values of ～37 pC/N at room temperature. Their polarized slices show the dielectric anomalies and impedance anomalies because of vibrating resonances below 500 °C, and the thickness vibration electromechanical coupling factor is ～0.6 and ～0.4 for BiFeO₃ and Bi_0.92Dy_0.08FeO₃, respectively. The vibrating resonances confirm piezoelectric responses. Furthermore, samples' impedance and resistance decrease fast with temperature increasing, which screens piezoelectric response above 550 °C.     

Microstructural investigation of Fe–Zr–B–Ag soft magnetic thin films

A microstructural study of DC-sputtered Fe_93−xZr₃B₄Ag_x films on Si(0 0 1) substrates has been carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). All samples were deposited as a function of additive Ag content (x=0–6 at%), and annealed in the range of temperature, 300–600°C, for 1 h in order to obtain enhanced soft magnetic properties. Through XRD and TEM investigation, Ag-free Fe₉₃Zr₃B₄ films on Si(0 0 1) substrates consisted of nano-crystalline Fe-based phases. In the presence of Ag additive element, the microstructure of as-deposited Fe_93−xZr₃B₄Ag_x films consisted of a mixture of majority of Fe-based amorphous and Ag crystalline phases. In this case, additive element, Ag played a role in retarding the formation of Fe-based crystalline phases during deposition, and insoluble nano-crystalline Ag particles were dispersed in the Fe-based amorphous matrix. As the content of Ag increased, the intensity of Ag crystalline XRD peak increased. Crystallization of Fe-based amorphous phase in the matrix of Fe₈₈Zr₃B₄Ag₅ thin films occurred at an annealing temperature of 400°C. In the case of Fe₈₈Zr₃B₄Ag₅ films annealed at 500°C, a much enhanced permeability of the Fe-based alloy thin films associated with nano-crystalline phases was achieved.     

Crystallization and thermochromism of annealed heterostructures containing titanium and tungsten oxide films

Crystalline phases in heterostructures containing titanium and tungsten oxide films are studied after step annealing in vacuum at temperatures between 500 and 750°C. The films are deposited on a silica glass substrate by dc reactive magnetron sputtering. It is found that crystalline phases in single layers and bilayer structures form in a different way. In the latter, crystallization is influenced by the order of layer arrangement on the substrate. Thermochromism in structures annealed in vacuum is due to the oxygen-deficient phase WO_{3 ? x} belonging to the hexagonal syngony. This phase intensely grows as the temperature rises from 650 to 750°C.     

Effect of annealing treatment on the uniformity of CeO2/TiO2 bilayer resistive switching memory devices

Bilayer CeO₂/TiO₂ films with high-k dielectric property were prepared by rf magnetron sputtering technique at room temperature. Effect of annealing treatment on resistive switching (RS) properties of bilayer CeO₂/TiO₂ films in O₂ ambient at different temperature in the range of 350–550 °C was investigated. Our results revealed that the bilayer films had good interfacial property at 500 °C and this annealing temperature is optimum for different RS characteristics. Results showed that bilayer CeO₂/TiO₂ film perform better uniformity and reliability in resistive switching at intermediate temperature (i.e. 450 °C and 500 °C) instead of low and high annealing temperature (i.e. 350 °C and 550 °C) at which it exhibits poor crystalline structure with more amorphous background. Less Gibbs free energy of TiO₂ as compared to CeO₂ results in an easier re-oxidation of the filament through the oxygen exchange with TaN electrode. However, the excellent endurance property (>2500 cycles), data retentions (10⁵ s) and good cycle-to-cycle uniformity is observed only in 500 °C annealed devices. The plots of cumulative probability, essential memory parameter, show a good distribution of Set/Reset voltage.     

Annealing induced transformations in structural and optical properties of Ge30Se70−xBix thin films

ABSTRACT

Thin films of Ge₃₀Se_70?xBi_x (x?=?5, 15, 20) were prepared by thermal evaporation method on glass substrates with thickness 800?nm. The films were annealed at 250°C and 320°C for 2?h to study the annealing-induced structural and optical change. The X-ray diffraction characterization revealed the amorphous to crystalline phase transformation with annealing. The indirect optical band gap decreased with annealing which is explained on the basis of phase transformation and density of localized states. The formation of surface dangling bonds around the crystallites during crystallization process reduced the band gap. The Tauc parameter and Urbach energy change show the degree of chemical disorderness in the films. The transmitivity decreased while the absorption coefficient increased with the annealing process. The microstructural study done by Field emission scanning electron microscopy shows the formation of crystallites upon annealing. Atomic force microscopy investigation on these films shows the influence of annealing on surface topography.     

57Fe conversion electron Mössbauer spectrometric study of boron and carbon ion implanted irons

Amorphous layers produced at the surface of iron by B⁺ and C⁺ implantation (50 kV, 1×10¹⁸ ions cm⁻²) were analyzed by CEMS. The CEM spectrum of B⁺ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400°C brought about precipitation of FeB, which was converted to Fe₂B by annealing at 500°C. The P(H) for C⁺ implanted iron was resolved to 3 subpeaks with H values of 11.0, 18.0 and 22.5 T. The amorphous FeC phase was strongly correlated to crystalline Fe₅C₂ and Fe₂C, which precipitated at 300°C and were transformed into Fe₃C at 500°C. The amorphous layer disappeared by annealing at 600°C.     

Preparation and structural instability of the 0.1BiFeO3-0.9Bi4Ti3O12 system

The solid solution of 0.1BiFeO₃-0.9Bi₄Ti₃O₁₂ (BF-BT) with bismuth-layered perovskite structure was obtained by conventional solid-state reaction. The lattice instability of BF-BT has been investigated by variable-temperature Raman scattering and X-ray diffraction. The results showed that there was a ferroelectric phase transition in the 450∼550 °C region in terms of the evolution of temperature dependence of Raman scattering frequencies. Some changes at about 530 °C in the XRD lines, the lattice parameters (a, b and c) as well as the orthorhombic distortion b/a have been detected in the high temperature X-ray diffraction, which can be interpreted by a phase transition and it is in good agreement with the results of high temperature Raman scattering. PACS 77.80.Bh; 61.10.Eq; 63.20.Dj     

Effect of annealing temperature on hardness, thickness and phase structure of carbonitrided 304 stainless steel

Carbonitriding of AISI 304 austenitic stainless steel was performed at a plasma-processing power of 450 W using inductively coupled radio frequency (rf) plasma in a gas mixture of 50% N₂ and 50% C₂H₂. The rate of carbonitriding, microhardness, phase structure of the compound layer, surface microstructure and cross-section morphology were studied before and after the annealing process. At the annealing temperature up to 800°C, the microhardness values of the compound zones decrease, while the associated values of the diffused zones increase. Little change was found in the thickness of the compound and diffused zones when the carbonitrided samples were annealed up to 400°C. However, at a higher annealing temperature, the thicknesses of both zones increase. The γ-Fe austenite is the main crystalline phase that can be detected by X-ray diffraction. As the annealing temperature increases up to 500°C, X-ray spectra show α-Fe and Fe₅C₂ phases. Nitrogen diffuses more deeply from the near surface to the interior of the treated sample as the annealing temperature increases up to 800°C and this might explain the extent of carbonitrided thickness and the enhanced microhardness of the diffused zone.     

Observation of metastable phase separation and amorphous phase in Fe67Co33 alloy thin films synthesized by pulsed laser depositions

Pulsed laser deposition technique has been used to manipulate the structural order of Fe₆₇Co₃₃ films grown at various substrate temperatures. Films deposited at room temperature exhibited two phases including the stable crystalline phase embedded in the amorphous phase. The crystalline phase separated into two distinct bcc phases as evident from the splitting of (110) reflections, as compared to the bulk counterpart which crystalize into the single phase bcc structure. Both crystalline phases and the amorphous phase were metastable. Films prepared at higher substrate temperatures (∼500 °C), crystallized into the single stable equilibrium bcc structure. Orientation dependent magnetic properties are also presented for the films prepared at both room temperature and higher substrate temperatures. As expected, the easy axes lie parallel to the plane of the substrate due to shape anisotropy. Out of plane magnetization for the films which exhibited short range ordering is found to saturate at smaller field compared to films where single phase bcc structure is stabilized.     

Investigation of thermal annealing effects on microstructural and optical properties of HfO2 thin films

In the present paper, we investigate the effect of thermal annealing on optical and microstructural properties of HfO₂ thin films (from 20 to 190 nm) obtained by plasma ion assisted deposition (PIAD). After deposition, the HfO₂ films were annealed in N₂ ambient for 3 h at 300, 350, 450, 500 and 750 °C. Several characterisation techniques including X-ray reflectometry (XRR), X-ray diffraction (XRD), spectroscopic ellipsometry (SE), UV Raman and FTIR were used for the physical characterisation of the as-deposited and annealed HfO₂ thin films. The results indicate that as-deposited PIAD HfO₂ films are mainly amorphous and a transition to a crystalline phase occurs at a temperature higher than 450 °C depending on the layer thickness. The crystalline grains consist of cubic and monoclinic phases already classified in literature but this work provides the first evidence of amorphous-cubic phase transition at a temperature as low as 500 °C. According to SE, XRR and FTIR results, an increase in the interfacial layer thickness can be observed only for high temperature annealing. The SE results show that the amorphous phase of HfO₂ (in 20 nm thick samples) has an optical bandgap of 5.51 eV. Following its transition to a crystalline phase upon annealing at 750 °C, the optical bandgap increases to 5.85 eV.     

The effect of substrate heating on the tunability of rf-sputtered Bi2O3-ZnO-Nb2O5 thin films

Reactively rf-sputtered Bi₂O₃-ZnO-Nb₂O₅ (BZN) thin films were prepared on Pt(111)/TiO₂/SiO₂/Si with substrate heating. The effects of substrate heating on the structures, morphologies, dielectric properties, and voltage-tunable dielectric properties of the films were investigated. With heating, the BZN thin films could be deposited in crystalline form as the cubic pyrochlore phase. The amounts of secondary phases, such as zinc niobate and bismuth niobate, depended on the substrate temperature. The more compounding of the BZN crystalline phase proceeded at deposition, the less formation of secondary phases and stoichiometric change occurred after post-annealing. Therefore, improvement of the dielectric constant and tunability of thin films by grain-size enlargement might be possible with proper substrate heating and post-annealing. The BZN thin films sputtered with a substrate temperature of 550 °C and annealed at 800 °C showed a maximum tunability of 26.5% at a dc bias field of 1000 kV/cm and measurement frequency of 1 MHz. PACS 81.15.Cd; 77.55.+f; 77.84.Dy; 81.40.Tv     

Effect of annealing temperature on K-shell X-ray fluorescence parameters of zinc oxide thin films prepared by the sol-gel method

Zinc oxide thin films were grown on a glass substrate by a sol-gel process using a spin-coating technique. The obtained thin films were annealed between 350?°C and 550?°C in 50?°C steps and were then characterized using X-ray diffraction, scanning electron microscopy, and X-ray fluorescence techniques. The samples were stimulated by 59.5?keV gamma rays emitted from an Americium-241 annular radioisotope source. K X-rays emitted by samples were counted using an ultra-low energy germanium detector with a resolution of 150?eV at 5.96?keV. It was found that there was generally a decrease in both the Kβ/Kα X-ray intensity ratios and the K X-ray fluorescence cross sections for zinc oxide between 350?°C and 500?°C, but not at 550?°C. In addition, the X-ray diffraction patterns of the films showed that the transition phase from an amorphous to a polycrystalline hexagonal wurtzite structure was complete at an annealing temperature of 500?°C. The results show that variations in these parameters can be explained by the reorganization of atoms and the charge transfer process due to the effect of the annealing temperature on the elements forming the compounds.     

Kinetics of the nanocrystalline structure formation

The kinetics of the nanocrystalline structure formation in the Fe_73.5Cu₁Nb₃Si_22.5?xB_x (x=6. 7. 8. 9 at. %) was followed during the annealing runs interrupted between 300 and 700°C.⁵⁷Fe room temperature Mössbauer spectra were taken and complemented by the electrical resistivity and X-Ray diffraction measurements. It has been found that for the 50 K/min temperature increase the formation of the nanocrystalline phase begins above 450°C reaching a maximum around 500°C and is followed by the second stage of crystallization of the disordered intergranular remainder above ca 600°C accompanied by the changes in the occupation of the iron sites in the crystalline α?Fe?Si phase. Thus gained composition-temperature dependence seems to witness for the inhibiting influence of the substitution of B by Si on the crystallization process.     

The effects of vacuum annealing on the structure and surface chemistry of iron nanoparticles

In order to increase the longevity of contaminant retention, a method is sought to improve the corrosion resistance of iron nanoparticles (INP) used for remediation of contaminated water and thereby extend their industrial lifetime. A multi-disciplinary approach was used to investigate changes induced by vacuum annealing (<5 × 10^?8 mbar) at 500 °C on the bulk and surface chemistry of INP. The particle size did not change significantly as a result of annealing but the surface oxide thickness decreased from an average of 3–4 nm to 2 nm. BET analysis recorded a decrease in INP surface area from 19.0 to 4.8 m² g^?1, consistent with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations which indicated the diffusion bonding of previously discrete particles at points of contact. X-ray diffraction (XRD) confirmed that recrystallisation of the metallic cores had occurred, converting a significant fraction of poorly crystalline iron to bcc α-Fe and Fe₂B phases. X-ray photoelectron spectroscopy (XPS) indicated a change in the surface oxide stoichiometry from magnetite (Fe₃O₄) towards wüstite (FeO) and the migration of boron and carbon to the particle surfaces. The improved core crystallinity and the presence of passivating impurity phases at the INP surfaces may act to improve the corrosion resistance and reactive lifespan of the vacuum annealed INP for environmental applications.     

Differential thermal analysis of phase transitions in (Bi1−xLax)FeO3 solid solution

(Bi_1?xLa_x)FeO₃ solid solution, a material exhibiting simultaneously electric and magnetic long range dipole order, is studied by the method of differential thermal analysis. The results confirm the data on ferroelectric phase transitions obtained from electric permittivity and dilatometric measurements above 500°C. The endothermal effect observed about 820°C is related to the ferroelectric phase transition of BiFeO₃.