Rare-earth-doped transparent glass ceramics

Synthesis and photocatalytic performances of BiVO4 by ammonia co-precipitation process

In recent years, there has been a resurgence of interest in transparent ferroelectric glass-ceramics (TFGCs), which are a special class of glass-ceramic composites that combine the low cost of fabrication and forming of transparent glass with the superior nonlinear optical and electro-optical properties of ferroelectric crystals. In this paper, we present a review of the current status, focusing on the challenges of fabrication and opportunities for selectively creating nonlinear optical structures, which will be useful in realizing integrated optical devices. A successful fabrication of TFGC requires the nucleation and growth of crystallites that are too small to scatter light, yet large enough to have ferroelectric response. Early experiments on silica based glasses containing common ferroelectric oxides indicated that although the preparation of TFGC is feasible, such a balance of crystallite size is difficult to achieve. However, later studies have demonstrated successful fabrication of TFGCs with com...

Transparent Ferroelectric Glass-Ceramics

Crystallization of oxide glasses has a long history since the first proposal by Stookey in the 1950s, and nowadays various glass-ceramics (crystallized glasses) having potential for practical applications have been reported There has been great progress in the field of the crystallization of glasses such as the relationship between glass composition and crystalline phase Because crystal nucleation and growth start from atomic rearrangements in the nanometer scale (ie, nano-scale) level, information on the nano-scale glass structure is very important for an understanding of the crystallization mechanism and thus for the design and control of crystalline phase and morphology In this article, we review the basic concept of the oxide glass structure related to crystallization, the basic scenario and typical types of glass crystallization, and features of laser-induced crystallization The design and control of crystal morphologies and glass-ceramic properties are also reviewed with some examples The crystallization processing of glasses is becoming more and more important as a novel technique for the development of new functional glass/crystal hybrid materials and also as an approach for a deep understanding of the nano-scale heterogeneous structure of glasses

Design and control of crystallization in oxide glasses

This paper reports recent progress in the patterning of non-linear optical crystals on the glass surface by laser irradiation. Two techniques for the writing of crystal lines have been developed, i.e., rare-earth (samarium) atom heat processing and transition metal atom heat processing, in which a continuous wave Nd:YAG laser (wavelength: λ = 1064 nm) is irradiated to the glasses containing rare-earth (RE: Sm 3+ , Dy 3+ ) ions or transition metal (TM: Ni 2+ , Fe 2+ , V 4+ ) ions. The writing of crystal lines such as β-BaB 2 Ο 4 , Sm x Bi 1-x BO 3 , and Ba 2 TiGe 2 O 8 showing second harmonic generations has been successful. It is clarified from the azimuthal dependence of second harmonic intensity and polarized micro-Raman scattering spectra that crystal lines consist of highly oriented crystals along the crystal line growth direction. It is also possible to write two-dimensional crystal bending or curved lines by just changing the laser scanning direction. The mechanism of the laser-induced crystallization has been proposed.

Patterning of non-linear optical crystals in glass by laser-induced crystallization

Transparent glasses in the system (100−x)Li2B4O7–x(SrOBi2O3Nb2O5) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi2Nb2O9 (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (er) and the loss factor (D) for the lithium borate, Li2B4O7 (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix.

Nanocrystallization of SrBi2Nb2O9 from glasses in the system Li2B4O7SrOBi2O3Nb2O5

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9 phase in the SrO–Bi2O3–Nb2O5–Li2B4O7 glass system

The crystallization kinetics in the glass system (100−x)LiBO2−xNb2O5 (5≤x≤20, in molar ratio) prepared via the conventional metal-plate quenching technique have been studied by isothermal and non-isothermal methods using differential thermal analyses. X-ray powder diffraction studies carried out on heat-treated (500°C) glasses reveal the evolution of lithium niobate crystalline phase along with a minor phase of LiBO2. The exponent n in the Jhonson–Mehl–Avrami (JMA) equation applied to the isothermal process is 2.62, which is in excellent agreement with that obtained under the non-isothermal process (2.67). The activation energies for crystal growth obtained from JMA equation under isothermal condition, modified Ozawa and Kissinger equations under non-isothermal conditions, are 293, 311, and 306 kJ/mol, respectively.

Crystallization Kinetics of the LiBO2–Nb2O5 Glass Using Differential Thermal Analysis

Transparent glasses in the system $(100 - x)LiBO_{2}-xNb_{2}O_{5}$ (5 \leq = x \leq = 25, in molar ratio) were fabricated by the conventional melt quenching technique. The as-quenched samples were amorphous as established via X-ray powder diffraction (XRD) studies. Differential thermal analyses(DTA) confirmed their glassy nature. The glass transition temperature(T-g) and the crystallization temperature were found to be strongly composition (x) dependent. Lithium niobate $(LiNbO_{3})$ nanocrystals were produced within the glass by heat-treating it at 500 degrees C/3 h (for x = 15). Two-stage heat-treatment process has improved the optical transmission characteristics. Impedance analysis was done to rationalize the electrical behavior of these glasses embedded with 100nm sized $LiNbO_{3}$ crystallites. The observed pyroelectric response and ferroelectric (P vs E) hysteresis loop at room temperature confirmed the polar nature of these composites.

Evolution of ferroelectric LiNbO3 phase in a reactive glass matrix (LiBO2–Nb2O5)

The nanocrystallites ( ≈ 3 nm) of LiNbO3, evolved in the (100−x)LiBO2-xNb2O5 (5x20, in molar ratio) glass system exhibited intense second-harmonic signals in transmission mode when exposed to infrared (IR) light at λ = 1064 nm. The second-harmonic waves were found to undergo optical diffraction which was attributed to the presence of self-organized submicrometer-sized LiNbO3 crystallites that were grown within the glass matrix along the parallel damage fringes created by the IR laser radiation. Micro-Raman studies carried out on the laser-irradiated samples confirmed the self-organized crystallites to be LiNbO3.

/pdf/optical-diffraction-of-second-harmonic-signals-in-the-libo2-1ik5peiz6e.pdf

N. Syam Prasad

Papers

Nanocrystallization of SrBi2Nb2O9 from glasses in the system Li2B4O7SrOBi2O3Nb2O5

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9 phase in the SrO–Bi2O3–Nb2O5–Li2B4O7 glass system

Crystallization Kinetics of the LiBO2–Nb2O5 Glass Using Differential Thermal Analysis

Evolution of ferroelectric LiNbO3 phase in a reactive glass matrix (LiBO2–Nb2O5)

Optical diffraction of second-harmonic signals in the LiBO2-Nb2O5 glasses induced by self-organized LiNbO3 crystallites