Picosecond Z-scan measurements on a glass-ceramic containing sodium niobate nanocrystals

doi:10.1016/S0030-4018(02)01189-6

Optics Communications

Volume 203, Issues 3–6, 15 March 2002, Pages 441-444

https://doi.org/10.1016/S0030-4018(02)01189-6 Get rights and content

Abstract

The third-order nonlinearity of a glass-ceramic containing sodium niobate (NaNbO₃) nanocrystals was studied using the Z-scan technique. The measurements were performed at 532 nm with 70-ps pulses at 5 Hz. Two-photon absorption coefficients and light-induced refractive index changes were determined. The results show dependence of the nonlinear parameters on the volume fraction of NaNbO₃ crystallites.

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Acknowledgements

We acknowledge the financial support by Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico (CNPq), Programa Nacional de Núcleos de Excelência (PRONEX), and International Science and Technology Center (ISTC: Grant #979). We also thank B.V. Tatarintsev for heat treatments, B.J.P. da Silva for polishing the samples and A.A. Vetrov for help in the electro-optical measurements. A.S.L. Gomes is acknowledged for sharing equipments.

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It is known that in such glasses with a high content of Nb2O5 the crystallization takes place via the segregation (liquid-liquid phase separation) process, and the formation of crystalline phases occurs in the segregation phase enriched with niobium and alkaline cations [1]. As a result, a heterogeneous structure (glass-ceramics) consisting of alkaline-niobate nanocrystals surrounded by the residual glass matrix forms [1–6]. Small-angle X-ray scattering (SAXS) shows that the resultant heat-treated glass contains crystals with a size of the order of 10 nm [1].
The dielectric response and the effect of heat treatment on the properties of a potassium-sodium-niobium-silicate glass with a high content of niobium are studied in wide temperature and frequency ranges. Heat treatment of the glass results in the formation of sodium niobate nanocrystals that leads to a significant decrease in the dielectric losses and an increase in the dielectric constant and the activation energy of the DC conductivity of the medium. It is shown that the crystallization process takes place in two stages – the first is the liquid-liquid glass separation (segregation), and the second is the crystals growth. Based on the classical Johnson-Mehl-Avrami-Kolmogorov theory, it is confirmed that the nanocrystals are anisotropic and that no new nuclei arise during the crystallization. The main contribution to the dielectric response of the initial and heat-treated glasses is made by the low-frequency relaxation process associated with the conductivity (charge polarization).
Effect of Al <inf>2</inf>O <inf>3</inf> addition on the formation of perovskite-type NaNbO <inf>3</inf> nanocrystals in silicate-based glasses
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It is, therefore, of extreme interest and importance to design and fabricate optically transparent composites, especially nanocomposites containing NaNbO3 or (Na,K) NbO3 nanocrystals. There have been several reports on the fabrication and characterization of crystallized glasses containing NaNbO3 crystals, and some studies are summarized in Table 1 [10–23]. Because of high kinetic fragility and, hence, crystallization tendency, it is practically impossible to prepare bulk glasses of stoichiometric composition (i.e., 50Na2O–50Nb2O5 (mol%)) corresponding to NaNbO3: the network-forming oxides such as SiO2, B2O3, TeO2, or GeO2 have to be added into the binary system of Na2O–Nb2O5.
The crystallization behavior of 30Na₂O–25Nb₂O₅–(45 − x) SiO₂–xAlO_1.5 (x = 0, 2.5, and 5) (mol%) glasses was examined and the effect of Al₂O₃ addition on the formation of perovskite-type NaNbO₃ crystals was clarified. It is found from X-ray diffraction analyses and transmission electron microscope observations that NaNbO₃ nanocrystals are formed in all glasses and the size of NaNbO₃ crystals decreases with the substitution of Al₂O₃ for SiO₂. A crystallized (heat-treated at 684 °C for 5 h) glass with x = 5, which contains NaNbO₃ nanocrystals with an average size of 50 nm, shows good optical transparency in the wavelength region of 500–2000 nm and a small hysteresis loop in the polarization–electric field curve. The lines containing NaNbO₃ crystals were patterned on the surface of NiO-doped glass with x = 5 by irradiations (power: 1.3–1.4 W, scanning speed: 10 μm/s) of Yb:YVO₄ fiber laser (wavelength: 1080 nm). The formation mechanism of NaNbO₃ nanocrystals in aluminosilicate glasses was also discussed.
Preparation and third-order optical nonlinearity of glass ceramics based on GeS<inf>2</inf>-Ga<inf>2</inf>S<inf>3</inf>-CsCl pseudo-ternary system
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Chalcohalide glass-ceramics based on GeS₂–Ga₂S₃–CsCl pseudo-ternary system were prepared by heat treatment method. X-ray diffraction and scanning electron microscope studies confirmed the formations of Ga₂S₃ and GeS₂ phase grains with sizes of 2–5 and 80 nm, respectively. Z-scan technology was employed to investigate the third-order nonlinear optical characteristics of both precursor glass and its glass ceramics at 800 nm. The results show that nonlinear refractive index n₂ as well as nonlinear absorption coefficient β increase after heat treatment, which is due to quantum effects, and the largest n₂ of the glass ceramics is 4.3 × 10^− 11 esu which is 4 times larger than that of the host.
Effect of ZrO<inf>2</inf> addition on crystallization and properties of the glass-ceramics contained NaNbO<inf>3</inf> crystals
2011, Current Applied Physics
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In general, the preparation process of NaNbO3 in a large single crystals form is preferred but it remains a difficult task because it has a strong tendency to be reduced at high temperatures required for the preparation procedures [1,3]. Thus, growing NaNbO3 crystal via devitrification process in the bulk glass specimen has been widely attempted [17,18]. Especially, in the silicate based composition of the Na2O–Nb2O5–SiO2 ternary system, that NaNbO3 precipitates out as a main phase.
Ferroelectric glass-ceramics containing NaNbO₃ crystals are prepared from the Na₂O–Nb₂O₅–SiO₂ system employing heat treatment process. ZrO₂ is systematically added to the glass compositions to study its effect on crystallization behavior of the glass and dielectric properties of the associated glass-ceramics. DTA trace measured from the as-quenched samples reveals shifting of the glass transition and the crystallization ranges to the higher temperature with increasing of ZrO₂ content. Then, the glass samples are subjected to heat treatment process at appropriate temperatures and times. Phase identifications through XRD analysis have shown that only the NaNbO₃ phase is devitrified in the glass-ceramics treated at 750 °C for 1 h. At 800 °C, precipitation of the secondary phase NaNb₃O₈ is additionally found but it present in only a small proportion. Crystallite size of the NaNbO₃ crystals determined from the X-ray diffracted peaks are in range 20–50 nm. The dielectric constants of the glass-ceramics measured at room temperature depend on the volume fraction of NaNbO₃ which varied with the ZrO₂ content.
Formation and laser patterning of perovskite-type KNbO<inf>3</inf> crystals in aluminoborate glasses
2011, Optical Materials
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Prasad and Varma [7] reported the evolution of ferroelectric LN crystals in LiBO2–Nb2O5 glasses. The crystallization of ferroelectric NaNbO3 (NN) in glasses has been also reported some researchers [43–46]. For instance, Radonjic et al. [44] succeeded in fabricating transparent crystallized glasses with NN nanocrystals in Na2O–Nb2O5–SiO2–Al2O3 glasses.
Perovskite-type nonlinear optical KNbO₃ (KN) crystals are synthesized from 40K₂O–25Nb₂O₅–35B₂O₃ (KNB) and 40K₂O–25Nb₂O₅–25B₂O₃–10Al₂O₃ (KNBA) (mol%) glasses by using a conventional glass–ceramics method. It is found from X-ray diffraction analyses and Raman scattering spectrum measurements that the addition of Al₂O₃ to glass is effective for the formation of perovskite-type KN crystals. A continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) is irradiated onto the surface of CuO-doped (2 mol%) KNB and KNBA glasses, and in particular, perovskite-type KN crystals are patterned in the condition of the laser power of 0.9 W and laser scanning speed of 8 μm/s for KNBA glass containing Al₂O₃. The formation of metastable (not perovskite-type) KN crystals is also confirmed in the samples crystallized in an electric furnace and in laser-patterned lines. The formation behavior of KN crystals in the glasses is discussed from the point of view of glass composition.

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Picosecond Z-scan measurements on a glass-ceramic containing sodium niobate nanocrystals

Abstract

Section snippets

Acknowledgements

Opt. Commun.

Solid State Commun.

Glasses for Photonics

Appl. Phys. Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.