RU2019509C1 - Process for preparing yttrium-barium-copper oxide - Google Patents

Abstract

FIELD: preparation of yttrium-barium-copper oxide Ba₂Cu₃O_7-δ. SUBSTANCE: yttrium, barium and copper are precipitated in the form of an oxalate precipitate from a nitrite solution. In order to precipitate, the precipitant is a sodium-oxalate solution containing sodium hydroxide. The precipitation is carried out at a pH of 9.6-9.8. The precipitate is washed with water and alcohol heat treated at 800 C for 5 hr and at 920 C for 6 hr and is then subjected to oxidizing roasting in a stream of oxygen at 350 C. EFFECT: improved process. 1 tbl

Description

The invention relates to the technology of materials having high temperature superconductivity (HTSC), and in particular to methods for producing yttrium-barium-copper oxide YBa ₂ Cu ₃ O _7-δ .

 A known method for producing this compound by mechanical mixing of yttrium, copper and barium carbonate oxides with subsequent extraction and repeated intermediate grinding of annealing products (the so-called ceramic synthesis method).

 The disadvantages of the method are: the duration of the annealing (more than 24 hours), the complexity of the process associated with the need for multiple intermediate grinding of the annealing product, as well as the difficulty of achieving chemical uniformity of the product.

Also known chemical process for the preparation of HTSC oxide by reacting an aqueous solution of nitrates of yttrium, barium and copper with citric acid solution, followed by evaporation to a viscous state, by dehydrating in vacuo and annealing at 900-950 ^{° C} for 2 hours.

The disadvantages of the method: the method requires a long evaporation of the solution at 75 ^about C and does not provide a chemically homogeneous product, as evidenced by the data of x-ray phase analysis (on the x-ray lines there are lines of impurity unidentified phases).

Closest to the proposed technical solution is a method for producing yttrium-barium-copper oxide by precipitation of these metals in the form of oxalates from an aqueous solution containing their nitrates or acetates. Precipitation with oxalic acid is carried out at pH 3.5-4.0, at room temperature, followed by thermal decomposition of a mixture of oxalates and annealing thermolysis product in an oxygen stream at 950 ° ^C.

 The method allows to reduce the heat treatment time to obtain a more uniform product.

The disadvantage of this method is the difficulty in achieving stoichiometry for cations (1: 2: 3): since barium oxalate, unlike yttrium and copper oxalates, is noticeably soluble at pH 3.5-4.0, barium does not completely precipitate from solution, but at pH above 3.5 increases the solubility of copper oxalate, which makes it difficult to obtain a precipitate with a strictly stoichiometric ratio of yttrium-barium-copper equal to 1: 2: 3. To achieve this ratio, an analytical determination of the amount of barium and copper transferred to the precipitate and the introduction of additional quantities barium and m unity, which complicates the process of producing oxide YBaCu ₃ O _7-δ .

 The aim of the invention is to simplify the process.

 This goal is achieved by the fact that yttrium-barium-copper-oxide is obtained by reacting a nitrate solution of these cations taken in an atomic ratio of 1: 2: 3 with a solution of sodium oxalate containing sodium hydroxide at a pH of 9.6-9.8 s subsequent thermal decomposition of the precipitate obtained and annealing of the thermolysis product in an oxygen stream.

 Distinctive features of the invention is the use as a precipitant of a solution of sodium oxalate containing sodium hydroxide, as well as the pH of the process.

The resulting precipitate during precipitation gidroksooksalatny composition YBa ₂ Cu ₃ (C ₂ O _{4) 5-6} (OH) _1-3 ˙ mH ₂ O is washed with alcohol and then heat treated ^at 800 ^° C for 5-6 hours, then at 980 ^{° C} 6 hours and oxidative annealing in an oxygen stream, resulting in the formation of YBa ₂ Cu ₃ O _7-δ oxide with a transition temperature to the superconducting state T _c = 89-93 K, containing up to 93% HTSC phase.

The essence of the proposed invention consists in the fact that when a sodium oxalate solution containing sodium hydroxide is used as a precipitant, from a solution containing Y, Ba, Cu nitrates in an atomic ratio of 1: 2: 3, they are deposited on the middle oxalates of these metals, including noticeably soluble barium and copper oxalates under these conditions, and a mixture of sparingly soluble double hydroxooxalates of yttrium-barium and yttrium-copper. Since yttrium, barium, and copper under these conditions are almost completely deposited, their atomic ratio in the precipitate is 1: 2: 3, i.e. cation stoichiometry is easily achieved. The precipitate is a homogeneous mixture of two hyodroxoxalates of the same degree of dispersion, as evidenced by the nature of sedimentation of the precipitate. Upon heat treatment of such a mixture under the above conditions and oxidative annealing, triple HTSC oxide YBa ₂ Cu ₃ O _{7-δ is formed} . The pH of the mixture during precipitation should be 9.6-9.8. At lower pH values, barium is not completely precipitated, and at a pH above 9.8, copper is not completely precipitated, which leads to a violation of the stoichiometry of precipitation by cations (see table).

PRI me R. To 265 ml of a solution containing 4.4 g of yttrium nitrate, 8.4 g of barium nitrate and 9.0 g of copper nitrate (II) (atomic ratio of Y: Ba: Cu = 1: 2: 3) at ²⁰ ° C is poured 360 ml of a solution containing 8.7 g of sodium oxalate and 4 g of sodium hydroxide; The pH of the mixture after the formation of a precipitate is 9.0. The precipitate is washed on the filter 5 times with alcohol and 1 time with water. The precipitate yield of 10.5. The degree of deposition of Y, Ba, Cu more than 99%. The atomic ratio in the precipitate according to the chemical analysis of Y: Ba: Cu = 1.0: 2.00: 3.00. The resultant precipitate was subjected to heat treatment ^at 800 ^° C for 5 hours, then at 920 ^{° C} for 6 hours and oxidative annealing in an oxygen stream at 950 ° ^C. The result is a ternary oxide of yttrium-barium-copper atomic ratio of Y: Ba: Cu = 1: 2: 3 and the temperature of the transition to the superconducting state 89K; the content of the superconducting phase is 92.5%. The deposition conditions and data on the composition of hydroxo-oxalate precipitates obtained in other examples are presented in the table.

 Thus, the proposed method allows to simplify the achievement of stoichiometry of cations at the deposition stage, in comparison with the prototype, due to the almost complete deposition of yttrium, barium, copper. This eliminates the need for an analytical determination of the degree of deposition of barium and copper and their additional introduction into the solution to compensate for losses associated with incomplete deposition.

Claims (1)

METHOD FOR PRODUCING ITTRIUM-BARIUM-COPPER OXIDE γ Ba ₂ Cu ₃ O _7-δ , including the deposition of yttrium, barium, copper in the form of an oxalate precipitate, its thermal decomposition and annealing in an oxygen atmosphere, characterized in that, in order to simplify the process, as the precipitant use a solution of sodium oxalate containing sodium hydroxide, and the deposition process is carried out to a pH of 9.6 to 9.8.

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