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Preparation of Mg: LN Polycrystalline Powders by Wet Chemical-Spray Drying Method and Investigation of Crystal Growth

Author: LiuQingBo
Tutor: XiaHaiBing；LiuHong
School: Shandong University
Course: Materials Engineering
Keywords: Mg-doped lithium niobate Liquid phase synthesis - spray drying Crystal growth UV absorption edge Optical homogeneity
CLC: O782
Type: Master's thesis
Year: 2011
Downloads: 32
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Abstract

Lithium niobate (LiNbO3, referred to LN) crystal is a set of ferroelectric, piezoelectric, nonlinear optics, electro-optic, and photorefractive properties of a multifunction artificial crystal material with stable chemical properties and thermal properties, crystal materials are cheap, easy to process, is widely used in the field of electronics and optics. Lithium niobate crystal filters, SAW devices, optical communications, optical waveguide substrate. With the surge in the number of social development, cordless phones and other communications devices, the demand for lithium niobate further increase, so far, lithium niobate crystal is still an enduring IOL material, its status can not be replaced by any other material. LN crystal commercialization on the general market is a typical non-stoichiometric crystal, with the growth of the traditional method of pulling congruent lithium niobate (Congruent LN CLN), the stoichiometric ratio of [Li] / [Nb] = 48.6/51.4. CLN crystal having a good consistency of the component, but due to the absence of Li, there are many of the intrinsic defects (such as anti-bit defects) in the crystal, greatly reducing the number of physical properties of the lithium niobate crystal, especially crystal hurt the ability of anti-light, in order to improve the optical damage threshold of the crystal, often incorporated in the CLN crystal MgO, reducing the impact because Nb antisite intrinsic defects on crystal performance. The preparation of high-performance powder (polycrystalline material) is a key factor to protect the quality of post-crystal growth. General lithium niobate powder synthesis method is the mixing of raw materials through the pro rata calcination at about 1200 ℃, after high-temperature solid-phase reaction of lithium niobate polycrystalline material. Easily cause the volatilization of Li lithium ion in the process of high temperature calcination, the component deviation occurs, resulting in defects such as inclusions, scattering particles, especially in the MgO-doped during the synthesis of the raw material, due to the high melting point of MgO, and the powders reunion, prone to the phenomenon of uneven distribution of doping elements. Hydroxide of niobium (Nb (OH) 5), lithium carbonate (Li2CO3), magnesium oxide (MgO), citric acid (CA), hydrochloric acid (HCl), aqueous ammonia (NH3H2O) used as raw material Liquid phase synthesis - spray drying prepared by the method of the precursor powder, and then calcined to obtain the doping uniformity MG: LN polycrystalline powder. The synthetic process comprises: niobium hydroxide was dissolved in concentrated hydrochloric acid in the water bath under heating; Nb-CA complexes generated by adding citric acid to form a stable niobium ion complex solution; using TGA accurate calculation solution the content of Nb ; based on the content of Nb is added the amount of lithium carbonate and magnesium oxide, and formulated into a precursor solution; spray-dried to obtain a powder of a precursor of the precursor solution; finally after calcination of the precursor is prepared by doping uniformity Mg: LN polycrystalline powder. The synthesis process and the product the following analysis: (1) study of the reaction mechanism of liquid phase synthesis; (2) by chelating substances before and after analysis, confirmed the generation of complex reactions occur and complexes; ( 3) using thermal gravimetric analysis and understanding of the thermal behavior of the precursor during calcination; infrared analysis (4) of the product was calcined under different temperatures, and to obtain the final temperature of the calcined precursor; (5) of the calcined product XRD characterization, confirmed the magnesium ions into the crystal lattice of lithium niobate, and the lattice parameters changed; (6) of the precursor powder obtained by the different concentration of the precursor solution, and calcined polycrystalline material for SEM test, observe and analyze the different morphology of the powders. The spray dried precursor particles are spherical and calcined polycrystalline material particles are formed by many nanoparticles spherical shell. In the crystal growth process, we have adopted grown by the Czochralski method in an air atmosphere in the components are uniformly high optical homogeneity MG: LN crystal, designed a unique growth system according to the crystal growth characteristics and habits discussed influence the crystal growth main factors: temperature field, seed, growth process parameters, the outside world, feeding. Then a series of characterization of crystals: (1) through the test Crystal UV absorption edge confirmed component uniformity and obtain the Li20 content of the crystals; (2) the use of the cone of the crystal center and edge positions of the optical interference pattern verified crystals having high optical uniformity; (3) Test the crystal center and edge positions of the refractive index, the refractive index significantly less than the CLN crystal; (4) through an optical homogeneity testing to obtain the crystal optical uniformity to achieve 2.02 X10-5.

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