Content uploaded by Alexei Kamshilin
Author content
All content in this area was uploaded by Alexei Kamshilin on Apr 18, 2015
Content may be subject to copyright.
A preview of the PDF is not available
Combined Formation of a Self-Pumped Phase-Conjugate Mirror and Spatial Subharmonics in Photorefractive Sillenites
Abstract and Figures
We found that the formation of self-pumped phase-conjugate mirrors (SPPCM) in photorefractive Bi12TiO20 crystals under external alternating electric field is accompanied by strong enhancement of spatial subharmonics. This combined formation of the fundamental grating and its spatial subharmonics results in an expansion of the spatial-frequency band allowed for SPPCM recording. © 2001 American Institute of Physics.
Figures - uploaded by Alexei Kamshilin
Author content
All figure content in this area was uploaded by Alexei Kamshilin
Content may be subject to copyright.
... It is evident that the products are single-phase and highly crystalline BiFeO 3 after 65 min reaction, shown in Fig. 1(b). After that, only single-phase BiFeO 3 sample synthesized at 120 min. This indicates that the particle size increases with the reaction time. ...
... Bi(NO 3 ) 3 þ OH À / Bi(OH) 3 (1) ...
... The precipitates of Bi(OH) 3 and Fe(OH) 3 are formed at the high concentration of OH À condition before the heating process, as the Reaction 1 and 2. Reaction 3 and 4 could take place between the formed Bi(OH) 3 and Fe(OH) 3 at heated temperature, and then Bi 25 FeO 40 and BiFeO 3 could be formed. The formed Bi 25 FeO 40 could be transformed into BiFeO 3 along with the reaction proceeding (Reaction 5). ...
This paper describes on the fast synthesis of bismuth ferrite by the simple microwave-assisted hydrothermal method. The phase transformation and the preferred growth facets during the synthetic process have been investigated by X-ray diffraction. Bismuth ferrite can be quickly prepared by microwave hydrothermal method by simply controlling the reaction time, which is further confirmed by Fourier Transform infrared spectroscopy and magnetic measurement.
... BFO represents both magnetic and strong ferroelectric effect at room temperature only [12]. These wide properties have many variable properties like photochemical cells [13], non-volatile memories, optics [14] and thin films capacitors [15]. ...
Fuel crisis and atmospheric pollution have been major environmental issues from the advent of the nuclear era of 1945. Photocatalysis for water splitting and organic contaminant degradation in presence of sunlight is a promising and recently in-trend for solving current environmental problems. Photocatalytic oxidation offers distinct advantages such as its extensive applicability of total mineralization of organic compounds without any secondary pollution. Bismuth Ferrite (BiFeO3) and its doped materials have gained a lot of attention nowadays due to its very narrow band gap (≈2.1 eV), recycling nature, coexistence of magnetic and ferroelectric properties and distinctive crystal structure. Due to these elaborated properties, Bismuth Ferrite emerges as an interesting material as a photocatalyst. The focus of this article is to summarize BFO photocatalytic properties and how can it be used to remediate air pollutants and water pollutants multiple times. This review also broadly discusses about BiFeO3 as a visible light photocatalyst and its present shape of work, research gaps and future scope.
... These characteristics are beneficial to various applications including nonvolatile memory devices, [7] photoelectrochemical solar cells, [8] capacitors having magneto-capacitive effects, [9] and nonlinear optics. [10] For enhancing the electromagnetic behavior and structural properties of BFO, the researchers have doped it with numerous elements. This improvement in various physical properties exhibits an opportunity for the implementation of co-doped BFO nanostructures in our industry and different medical fields. ...
Nanohybrids containing graphene and bismuth ferrite have been actively employed as efficient photo-catalysts these days owing to the low rate of charge carrier's (e-'-h⁺) recombination, moderate surface area with a suitable range of band-gaps. We have synthesized nanohybrids of graphene oxide (GO) and doped BiFeO3 using a co-precipitation method and the doping elements were lanthanum and manganese, hence called BLFMO/GO nanohybrids. The surface area of BLFMO [La = 15% increased from 6.8 m²/g (for pure) to 62.68 m²/g (in nanohybrid)]. Also, the bandgap of the BLFMO/GO nanohybrid reduced significantly up to 1.75 eV. The resulting BLFMO/GO nanohybrid represents significantly higher catalytic activity (96% in 30 min) than the pure BiFeO3 (30% in 30 min).
... Sillenites exhibit various properties such as photorefractivity, photoconductivity, and enhanced velocity of ultrasound wave propagation, and such properties have potential applications. Sillenites, which contain tetrahedrally coordinated transition metal ions, e.g., Fe and Mn, offer tuning of electronic structure and photo-electronic features [4][5][6]. ...
Fe-doped Bi12MnO20–BiMn2O5 ceramics was sintered at 1130 K for 6 h in ambient air. Two centro-symmetric phases formed thermodynamically stable self-composite material that was deduced from X-ray pattern analysis. The lattice parameters were a = 10.147(8) Å—for the cubic I23 Bi12MnO20 phase; and a = 7.545(4) Å, b = 8.538(1) Å, c = 5.758(3) Å—for the orthorhombic Pbam BiMn2O5 phase. The ⁵⁷Fe Mössbauer spectrum, recorded at room temperature, has shown pure electronic quadrupolar split. The major doublets reflected the occurrence of Fe³⁺ ions distributed in two sites, i.e., octahedral Fe⁴⁺O6 and square pyramidal Fe³⁺O5, with preferential occupation of the pyramidal sites, that was consistent with the Pbam phase symmetry. The third doublet resulted from the presence of iron Fe³⁺ in tetrahedral Fe³⁺O4 coordination and corresponded to a small admixture of the I23 phase. The DC resistivity ρDC(T) dependence on temperature has shown thermally activated features, and the value of Ea,DC varied in the range of 0.22–0.37 eV. The electric impedance was measured in the f = 20 Hz–1 MHz and 100–690 K range. Two electrical relaxations were determined using the electric modulus formalism M″(T). Low-temperature relaxation has shown the temperature-dependent activation energy EA,1 = 0.14–0.20 eV and characteristic time values of τ01 = 10⁻¹⁰–10⁻¹² s in 100–200 K range. It was attributed to the charge transfer between Mn⁴⁺/Mn³⁺ sites. The other relaxation occurred in the 170–220 K range, and it exhibited the following values: τ02 = 10⁻¹¹ s, and EA,2 = 0.27 eV. A disorder-related VRH polaron model was proposed for ρDC(T) and for electric relaxation processes.
... The Bi 2 Ti 2 O 7 phase with sphere shapes has been obtained by hydrothermal processes with variations in the hydroxide ions concentration [81]. On the other hand, the selenite phases with general formula Bi 12 MO 20 (M=Ge, Ti, Ga, Fe, V, etc) exhibit several characteristics such as photo-refractivity, optical activity, photoconductivity and improved sound wave propagation velocity with applications in electro-optics, acoustic and piezoelectric devices [82]. Spherical nanoparticles of Bi 12 TiO 20 have been obtained by means of hydrothermal treatment using C 6 H 13 BiN 2 O 7 as a source of Bi, and TiCl 3 as a source of Ti for solving the agglomeration problems that normally occurs in the conventional hydrothermal method [83]. ...
The physical-chemical properties of bismuth and its oxides have been studied over the last two decades. As a result of this research, the growth of these materials with different crystallographic structures, showing micro and nanometric dimensions has been achieved by using several techniques (cathodic pulverization, laser pulsed deposition and hydrothermal method, among others). The dimensions reached have enabled thin films, nanotubes, nanospheres and nanowires to be obtained, allowing the developing of devices such as heavy metal detectors, optical filters and magnetic field sensors. Due to the progress in these materials in recent years, in this work a bibliographical review was carried out of some techniques employed for processing bismuth based materials with nanometric dimension and some technological applications.
In this communication, the synthesis (solid-state reaction) and characterization (XRD, SEM, EDX, and IS) of the (1 − x)BiFeO3 − x(BiNaKTiMnO3), (x = 0.05 and 0.1) ceramics were reported. The structural analysis suggests a rhombohedral crystal symmetry (#R3c) with an average crystallite size of 39.6 nm and micro-lattice strain of 0.000401 in x = 0.05 sample, whereas average crystallite size of 46.6 nm and lattice strain of 0.00133 in x = 0.1 sample, respectively. The growth and distribution of the grains and the position of grain boundaries were studied from a scanning electron microscope (SEM). The purity and compositional analysis of the prepared samples were checked from an energy-dispersive X-ray analysis (EDX) image. The study of the Fourier-transform infrared spectroscopy (FTIR) spectrum suggests the presence of a stretching band of the constituent elements in the modified bismuth ferrite. The presence of the Maxwell–Wanger type of dispersion was confirmed by a dielectric study. The investigation of impedance as a function of temperature and frequency reveals the existence of a negative temperature coefficient of resistance (NTCR). A non-Debye kind of relaxation mechanism is revealed by electric modulus analysis; however, a thermally induced relaxation process is confirmed by an ac conductivity study. The semi-circular arcs in the Nyquist and Cole–Cole plots indicate that the sample is semiconducting. BNKTM 5% has an energy bandgap of 2.9 eV, while BNKTM 10% has an energy bandgap of 2.7 eV, according to UV–visible spectra. The field-dependent hysteresis loop is analogous to the onset of ferroelectricity.
Recently, BFTO compounds attract much attention due to their potential as single-phase multiferroic materials. However, it is still challenging to synthesize pure phase BFTO nanocrystals due to their structural and compositional complexity. In this article, BFTO nanocrystals were successfully synthesized by adopting MOH (M = Li⁺, Na⁺ and K⁺) as mineralizers, and the critical role of M⁺ ion is expatiated in detail. Based on the anion coordination polyhedron growth unit model, growth unit/OH⁻/M⁺ core/shell capping layers would form during the syntheses process, and the outermost M⁺ layer can hinder the growth and formation of pure phase BFTO nanocrystals via the effective passivation beyond a certain critical concentration of M⁺, i.e., 0.5 M, 2.5 M and 0.5 M for LiOH, NaOH and KOH, respectively, proportional to 1/RM+ (the solvated cation radius) and \( {\text{K}}_{{\rm{D}}}^{{{\rm{MOH}}}} \) (the dissociation constant of MOH). The coefficient of \( {\text{R}}_{\text{Li + }} > {\text{R}}_{\text{Na + }} > {\text{R}}_{\text{K + }} \) and \( {\text{K}}_{\text{D}}^{\text{LiOH}} < {\text{K}}_{\text{D}}^{\text{NaOH}} < {\text{K}}_{\text{D}}^{\text{KOH}} \) results in the highest critical concentration of NaOH among all the MOH bases.
A PVA-assisted hydrothermal synthesis route was utilized to fabricate single-phase Bi25FeO40 crystallites. X-ray diffraction results indicated that sillenite Bi25FeO40 have been synthesized at the temperature of 200 °C using the KOH concentration of 7 M. Scanning electron microscopy showed the morphology of the as-prepared products were cubic shape with side length of 26 μm. The band gap of Bi 25FeO40 was determined to be 1.8 eV (688 nm) by using UV-vis diffuse reflectance spectroscopy. It was found that Bi 25FeO40 exhibited a high photocatalytic activity for the degradation of methyl orange under UV-Vis irradiation, being a potential material for photocatalytic decomposition of organic contaminants.
Manganese sillenite (Bi12MnO20) nanoparticles having average particle size between 22 and 43 nm were synthesized by a low temperature soft chemical route under refluxing conditions. A careful structural and microstructural characterization by means of high resolution X-ray diffraction experiments and transmission electron microscopy is presented. The as-cast powder displayed an isotropic superparamagnetic (SPM) behavior with a blocked state for temperatures below TB∼13.0K. We used three different measurement techniques to extract and compare the Bi12MnO20 blocking temperatures. First, we extracted TB with the modified Bean-Livingstone model from the coercive field temperature dependence obtained from hysteresis curves measured as a function of temperature. Then, the blocking temperature distribution function, f(TB), was obtained by deriving the zero field-cooled/field-cooled curves difference. For each applied field, the maximum of the distribution function gave us the mean blocking temperature value. Finally, the maximum of the magnetic susceptibility imaginary part as a function of frequency was used, combined with the Néel-Brown equation, to extract the blocking temperature. All measurement techniques yield an equivalent dependence of TB with H of the Bi12MnO20 superparamagnetic nanoparticles.
In this paper we discuss some fundamentals on uniform target ablation and present some new results on thin films of high-temperature superconductors, ferroelectrics, and polymers.
We present an experimental study of the self-pumped phase-conjugate-mirror (SPPCM) recording in a Bi12TiO20 sample due to the partial internal reflection of the pump beam from the rear face. SPPCM has been recorded under an external
alternating electric field of a square-wave form with response time equal to 170s at the pump beam intensity of 520mW/cm2. The mechanism of the SPPCM formation is similar to that of photorefractive double-phase-conjugate mirrors. The most effective
SPPCM is recorded at the much larger pump-beam-incident angle than it could be supposed from the typical angular dependence
of the two-wave-mixing gain factor. Strong dependence of the gain distribution on the pump-beam-propagation angle is observed.
It is found that the response time strongly depends on the preliminary history of the sample.
We investigated both analytically and numerically the simultaneous influence of higher-harmonic gratings and subharmonic gratings on the threshold for generation of the subharmonic K/2 grating. The higher-harmonic grating causes feedback to the fundamental grating, thus leading to a nonlinear correction in dissipation, and the threshold for subharmonic generation is substantially modified by the presence of more subharmonics. The numerical solution shows that the inclusion of five higher-harmonic components and four subharmonic components are sufficient to cover the entire spatial region. The discrepancy between the analytical and the numerical solution increases with increased electric-field amplitude.
Using the so-called ac field technique, we investigate experimentally the influence of optical beam coupling on the generation of subharmonic gratings in a photorefractive sillenite crystal. By the use of two different recording configurations, we are able to distinguish between effects caused by material nonlinearities and effects caused by optical beam coupling.
Detailed measurements of the self-pumped phase-conjugate emission that arises from internal reflections within crystals of BaTiO3 have been made. Four-wave mixing, possibly enhanced by stimulated photorefractive scattering around loops of light internally generated within the crystal, and four-wave mixing at coupling regions of a ring cavity set up between diagonal corners of the crystal are two mechanisms believed to give rise to phase-conjugate beams. An explanation is also given for the unstable effects often observed on the phase-conjugate beam and that give rise to frequency shifts, pulsations, and oscillations. The power of the beam incident upon the crystal determines the threshold characteristics for self-pumped phase-conjugate emission.
The theoretical analysis of unstationary holographic recording in photorefractive crystals under an external alternating electric field is presented. In particular, a step-like ac field resulting in a shifted phase hologram with an amplitude exceeding that of a hologram recorded under an external dc field is shown to be most efficient. The experimental curves for the gain factor Gamma obtained in Bi12TiO20 (lambda = 0.63mum) under an ac step-like field illustrate the field and spatial frequency dependencies of the hologram amplitude characteristics of the unstationary mechanisms of holographic recording.
The instability leading to the appearance of subharmonics in the presence of a square wave applied field is investigated both theoretically and experimentally. The threshold conditions are found for a range of parameters and the temporal variation of the subharmonic amplitude is measured. It is shown that a relatively simple theory, based on a set of material equations, gives good agreement with some of the experimental results but other experiments indicate that the materials equations alone cannot describe all the observations.
We report here for the first time the demonstration of self‐pumped phase conjugation in photorefractive semiconductors using 1.32 μm light. Using an ac field technique to enhance the gain coefficient in InP:Fe and a single input pump beam, phase conjugate reflectivities of 11% were measured using an input beam intensity of less than 1 mW/mm<sup>2</sup>. These results open up many possibilities for using photorefractive semiconductors in applications with low‐power infrared diode lasers.
A passive phase conjugate mirror based on four‐wave mixing in an optical ring cavity is described. Unlike previously demonstrated passive phase conjugate mirrors it generates only one of its pumping beams by nonlinear optical interactions, the other being provided by feedback of the probe after transmission through the nonlinear medium. The results of a theory yielding phase conjugate reflectivity and oscillation thresholds are presented together with an experimental demonstration of phase conjugation in barium titanate and strontium barium niobate. The device is self‐starting by four‐wave mixing, and has an oscillation threshold lower than that of other previously demonstrated passive phase conjugate mirrors with similar ease of alignment. The operation of a device which generates nonconjugate oscillation beams is also reported.
The appearance of subharmonics with the aid of an applied square-wave field is reported for the first time to our knowledge. It is shown that the intensity and the order of the subharmonics are dependent on the repetition rate of the square wave.