Chemistry of inorganic compounds – Boron or compound thereof – Oxygen containing
Patent
1994-06-15
1995-12-05
Langel, Wayne
Chemistry of inorganic compounds
Boron or compound thereof
Oxygen containing
423279, C01B 3512
Patent
active
054726786
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for preparing alkaline earth metal borates and articles comprising such borates.
Beta-barium borate (.beta.-BBO) is one of the materials having non-linear optical properties, and more particularly having the capacity in a certain range of wavelengths, to produce a second harmonic generation (frequency 2x) when it is submitted to an incident radiation of frequency x. Unlike other materials with usual sources of incident radiation, this second harmonic generation (SHG) is of sufficient amplitude to be observed and manipulated.
Another advantage of .beta.-BBO is that its optical damage threshold is high, i.e. 3-4 times the threshold of potassium dihydrogenophosphate, which is used as a reference material in non-linear optics. This means that .beta.-BBO can be used with short pulse, high power lasers as sources of incident radiations without being damaged. Also, .beta.-BBO can be used for non-linear optics within a range of temperatures which is broader than for any other material.
However, to be actually usable as a non-linear integrated optical device, a material has also to be obtainable in crystalline thin film form, on appropriate substrates.
Substances such as BBO are usually prepared by solid state reaction and sintering of metal oxide and metal carbonate mixtures. However, the treatment of these physical mixtures requires prolonged grinding/heating cycles. These methods are complex, expansive, provide non-uniform films with uncontrolled stoichiometry and do not permit easily to introduce dopants in a quantitatively controlled manner. Some of these problems may be partially overcome by tedious and time consuming trial and error combinations of the chemical elements in question, in order to achieve materials and films with the desired composition ratios. Besides, certain alkoxides have an alkaline pH, and hydrolysis at alkaline pH produces powders; a stable solution is usually obtainable with the addition of acids. However, the undesirable consequence of the addition of acids is an inferior crystallinity and the increase of crystallization temperatures when the film is subjected to thermal treatments.
Because of these difficulties, there has been a strong interest in the preparation of oxide ceramics by chemical methods in order to achieve the desired stoichiometric composition and atomic level homogeneity, and to reduce processing time and temperatures. One of such methods is sol-gel method, which consists in a controlled hydrolysis of precursors which are generally alkoxides. These alkoxides are hydrolyzed and condensed to form an inorganic metal-oxygen-metal network. Further thermal treatments result in the formation of the desired crystalline phase. Sol-gel method has been described in references such as U.S. Pat. Nos. 4,789,563, 4,652,467, 4,849,252 and EP's 130,801, 232,941. Various hydrolysis methods are reported in the technical literature.
Chem. Lett. 11 (1979), 1341-1344, discloses the preparation of strontium borate by pouring a mixture of boron and strontium alkoxide into aqueous ammonia solution to form the precursor, which is decomposed by heating to form the borate.
Z. anorg. Allg. Chem. 460 (1980), pages 228-234, discloses the preparation of borates by adding alkaline earth metal to a water containing mixture of boron alkoxide in alcohol followed by boiling to obtain borate precursors.
JP-A-63293178 discloses the preparation of complex metal and boron containing compounds by reacting boron alkoxide, metal alkoxide, alcohol amines and carboxylic acid in an organic solvent. Alkaline earth metals and pH conditions are not disclosed. However, a requirement for the sol-gel method is that alkoxides must be hydrolyzed in a controlled manner. Boron alkoxides are very water-sensitive, i.e. they have a tendancy to hydrolyse too rapidly and to produce powders; thus, sol-gel method was thought not to be a good candidate for preparing .beta.-BBO, or related borates.
The present invention eliminates the above difficulties and provides a way to use the sol-gel met
REFERENCES:
patent: 4897249 (1990-01-01), Ross et al.
patent: 4931133 (1990-06-01), Gualtieri et al.
European Patent Application 269385 published Jun. 1, 1988.
Chemical Abstracts citation 92:33108u (1992).
Chemical Abstracts citation 93:124874c (1993).
Lurin Christian
Nie Wenjiang
Paz-Pujalt Gustavo R.
Eastman Kodak Company
Hawley J. Jeffrey
Langel Wayne
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