Tunable Synthesis of Bismuth Ferrites with Various Morphologies

From molecules to bismuth oxide-based materials: Potential homo- and heterometallic precursors and model compounds

A simple microwave synthesis procedure has been developed for the single-crystalline perovskite nanocubes composed of bismuth ferrite (BiFeO3). Typical nanocubes had sizes ranging from 50to200nm. The single-crystalline nature of nanocubes was confirmed by high resolution transmission electron microscopy and selected area electron diffraction pattern. X-ray diffraction pattern showed the rhombohedral phase with R3c space group. The material showed photoinduced water oxidation activity in both photoelectrochemical and photocatalytic modes. It could become a useful material for photoelectrode and photocatalytic applications.

Microwave synthesis of single-crystalline perovskite BiFeO3 nanocubes for photoelectrode and photocatalytic applications

1 What Do We Want With Fiber Crystals? An Introductory Overview.- 2 Fundamentals of Growth Dynamics of the ?-Pulling Down Method.- 3 Theoretical Analysis of the Micro-Pulling-Down Process.- 4 Practice of Micro Pulling Down Growth.- 5 Crystal-Chemistry and Fiber Crystal Growth of Optical Oxide Materials.- 6 Oxide Eutectic Crystals for High-Temperature Structural Application.- 7 Oxide Fiber Crystals Grown by ?-PD and LHPG Techniques.- 8 Growth of Micro and Bulk Crystals by Modified Micro-PD and their Properties.

Fiber Crystal Growth From the Melt

We report an optoelectronic feedback loop that permits the active stabilization of an interferometric setup for any chosen value of the phase between the interfering beams. This method is based on phase modulation and homodyne detection techniques. The phase can be stabilized with a precision of better than 1 deg for our experimental conditions.

Adjustable phase control in stabilized interferometry.

We present an analytical theory of vectorial wave coupling in photorefractive cubic crystals which are, in general, optically active. The theory is based on the systematic use of the spatial symmetry properties and the apparatus of the Pauli operators to deal with two-dimensional vectors and matrices. It allows one to give a unified description of a wide spectrum of photorefractive phenomena, including the efficiency and polarization properties of Bragg diffraction, polarization two-beam coupling enhanced by ac fields, the influence of the photoelastic effect, etc. Applications of the theory to crystals of the sillenite family and to particular photorefractive phenomena are given. A good qualitative agreement between the theoretical predictions and experimental data for ${\mathrm{Bi}}_{12}{\mathrm{TiO}}_{20}$ (BTO) crystals is shown.

Theory of photorefractive vectorial wave coupling in cubic crystals.

Evolution of the light-induced absorption in a Bi12TiO20 crystal is investigated at a wavelength of 633 nm. It is found that the absorption coefficient evolution consists of fast and slow components with different characteristic response time. The light absorption coefficient decreases from 0.9 to 0.16 cm-1 after keeping the sample in darkness for six months. We propose a new charge-transport model that includes the deep donors in three valence states and the shallow traps. It is shown that the theory developed provides an explanation for the observed features of the increase and dark decay of the light-induced absorption. The material parameters of the Bi12TiO20 crystal are estimated from the best fit of the theoretical model with the experimental data.

Light-induced absorption in a Bi12TiO20 crystal

Growth of single-crystal photorefractive fibers of Bi12SiO20 and Bi12TiO20 by the laser-heated pedestal growth method

We experimentally observed the self‐channeling of the light beam in photorefractive Bi12TiO20 fiberlike sample owing to the strong fanning effect. It results in significant speed up of the photorefractive response time in waveguides and in anomalous dependence of the response time on the applied ac electric field amplitude: the higher electric field, the faster response.

Nonlinear self‐channeling of a laser beam at the surface of a photorefractive fiber

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.

Victor V. Prokofiev

Papers

Theory of photorefractive vectorial wave coupling in cubic crystals.

Light-induced absorption in a Bi12TiO20 crystal

Growth of single-crystal photorefractive fibers of Bi12SiO20 and Bi12TiO20 by the laser-heated pedestal growth method

Nonlinear self‐channeling of a laser beam at the surface of a photorefractive fiber

Combined formation of a self-pumped phase-conjugate mirror and spatial subharmonics in photorefractive sillenites