Method of synthesising monocrystalline iron selenides

FIELD: chemistry.

SUBSTANCE: invention can be used for laboratory and industrial production of monocrystalline materials. A method of synthesising tetragonal iron monoselenide includes heating a hermetic vial with a charge from selenium and iron placed in one of its ends and filled with a salt melt. The vial heating is performed with the temperature gradient from a value of 450°C-350°C from the side of the charge location to a temperature, reduced by 30°C-100°C from the opposite side. As the salt melt used are mixtures of eutectic composition, which includes aluminium chloride. Heating is performed for the time necessary for the transfer of the selenium and iron charge into the opposite end of the vial.

EFFECT: invention makes it possible to increase coarseness of FeSe crystals with reduction of their synthesis temperature.

2 cl, 1 dwg, 4 ex

 

The invention relates to inorganic chemistry, namely, to technology creation and processing of crystalline materials, which is included in the list of critical technologies of the Russian Federation, namely the laboratory and the industrial production of monocrystalline iron selenides, including superconducting tetragonal FeSe1-x.

The prior art synthesis of Fe-Se from melts when the crystals grow when you own cooling of the melt (V. Tsurkan, J. Deisenhofer, A. Günther, Ch. Kant, H.-A. Krug von Nidda, F. Schrettle, A. Loidl, European Physical Journal 79, 2011, 289.) The disadvantage is the high temperature synthesis, in which the most unstable substances, or have a faulty structure, and/or a large deviation from the equilibrium conditions caused by the cooling of the starting substances.

The known method of synthesis of single-crystal iron selenides using the method of gas transport, when the mixture is added a small amount of transport of the reagent (catalyst), and a crystal grows from the gas phase in the temperature gradient. (A. Serafin, A.I. Coldea, A.Y. Ganin, M.J. Rosseinsky, K. Prassides, D. Vignolles, and A. Carrington, Phys. Rev. 82, 104514, 2010).) However, this method also does not work for phases stable at low temperature.

Known for the synthesis of single crystals in the molten tin with diluted Fe and Se during slow cooling. (N. Ni, S.L. Bud'ko, A. Kreysig, S. Nandi, G. E. Rustan, A.I. Goldman, S. Gupta, J.D. Corbett, A. Kracher, and P.C. Canfield, Phys. Rev. 78, 014507, 2008.) The disadvantage of this method is the difficulty of separating tin from the fusion products and the gradual change of temperature synthesis of single crystals in the growth process, which leads to a gradual change of properties of single crystals (zoning).

Closest to the claimed technical solution is the method of synthesis of single crystals in the molten halide salts of alkali metals with dissolved therein Fe and Se during slow cooling. As the environment using a combination of chlorides of alkali metals. (R. Hu, N. Lei, M. Abeykoon, E.S. Bozin, S.J.L. Billinge, J.B. Warren, T. Siegrist, and C. Petrovic, Phys. Rev. 83, 224502, 2011.) The disadvantage of this method is the gradual change of temperature synthesis of single crystals in the growth process, which leads to a gradual change of properties of single crystals (zoning). In addition, most of chlorides of alkali metals crystallizes at temperatures apparently higher temperature stability of iron selenides, in particular superconducting FeSe.

The task and the technical result of the invention are to develop technologies that provide larger crystals FeSe decreasing the temperature of synthesis.

The problem is solved in that in the method of synthesis of iron selenides, including heat seal technics is Oh ampoule placed in one end of the mixture of selenium and iron, and filled with a salt melt, according to the invention, heating of the ampoule is performed with the temperature gradient of the value 450-350°C by placing the mixture to a temperature of minus 30 to 100°C from the opposite side, where the molten salt is a mixture of eutectic composition comprising aluminum chloride, and heating is carried out over time, providing transfer of the charge from selenium and iron in the opposite end of the ampoule. As the molten salt may be used a mixture of aluminium chloride and potassium chloride in a molar ratio of 1.5-2:1.

Thus, the technical result is achieved due to the use of the new method of synthesis, including the creation of certain conditions of the synthesis of crystals, when growth occurs during the migration of selenium and iron in salt eutectic under the action of the temperature gradient from the hot end to the cold. The temperature gradually decreases with distance from the hot end of the ampoule to the cold. In this respect, the temperature of the interval is significantly below the temperatures that are used in the known methods. This is achieved through the use of a transport medium low-melting molten salt with the participation of aluminium chloride.

The invention is illustrated by the drawing, which shows a circuit implementation of the invention. Position the s in the figure is displayed: 1 - the single crystals of iron selenides, 2 - vial, 3 - molten salt, 4 - oven, 5 - hot end of the ampoule, 6 - cold end of the ampoule, 7 - mixture of iron and selenium.

The method can be implemented using the device represented in the figure.

The growth of crystals 1 occurs in a sealed ampoule 2, filled with a salt melt 3, under conditions of high temperature exposure. Synthesis in sealed quartz glass can be implemented similarly to the method presented in the source of information - Kullerud, G. Experimental techniques in dry sulfide research. In: Ulmer, G.C. (ed.) Research Techniques for High Pressure and High Temperature, Spinger-Verlag, New York, pp.288-315 (1971). Synthesis in executions salts described in Moh GH, Taylor L.A., Laboratory techniques in experimental sulfide petrology. Neues Jahrb. Mineral. Monatsch. 1971, No 10, 450-459. The ampoule is placed in a furnace 4 in a horizontal position and creates a temperature gradient. Crystal growth occurs in the temperature gradient, the temperature of the "hot" end of the 5 ampoules, which initially have a mixture of selenium and iron 7 is 450-350°C, the temperature of the "cold" end of the 6 - 30-100°C below the temperature of the "hot" end. As the molten salt is a mixture of eutectic composition (or close to eutectic) with the obligatory presence of aluminium chloride. The mixture of selenium and iron in the process of "gradient" temperature effects (smooth continuous reduced the I temperature of the "cold" end of the ampoule to its hot end) is gradually transferred from the hot end of the ampoule in the "cold" end of the lower solubility of selenium and sulfur in salt melt when cooled. The growth of the crystals is not less than one month.

This method was tested at different temperatures:

Example 1. Capsules long 100 mm, an inner diameter of 8 mm quartz glass was filled with a mixture of 1000 mg of selenium, 700 mg of iron and were first covered with aluminium chloride and potassium chloride in a molar ratio of 2:1. The ampoule was sealed under vacuum and placed in a tube furnace resistance handmade at the temperature of 400°C for 3-4 weeks. The temperature gradient was provided by the proximity of the "cold" end of the ampoule to the edge of the furnace. The temperature of the cold end was 350°C. the samples were obtained FeSe single crystals with dimensions of at least 2×2×1 mm with a well-formed habit.

Example 2. Capsules of the same size with the same filling were placed in the same oven with a temperature of 457°C in the hot end and at a temperature of 400°C with a temperature at the cold end. The synthesis was continued for 21 days. This has resulted in a sample size of 1×1×0.5 with poorly formed by habit and probably with ferromagnetic impurity.

Example 3. Quartz ampoules of the same size with similar Fe/Se charge and eutectic mixture of AlCl3/NaCl/KCl were placed in the same oven temperature to 300°C at the hot end, and a temperature of 270°C at the cold end. The synthesis was continued for 45 days. As a result, cold to the price of the capsules were found only slight traces of powder FeSe.

Example 4. Quartz ampoules of the same size with similar Fe/Se charge and eutectic mixture of AlCl3/NaCl/KCl/AgCl (used a mixture of aluminium chloride, potassium chloride and sodium chloride in an approximate molar ratio of 1.5-2:1:1.) were placed in the same oven at a temperature of 360°C at the hot end, and a temperature of 280°C at the cold end. The synthesis was continued for 60 days. This has resulted in samples of FeSe single crystals with dimensions of not less than 1×1×0.2 mm to form a habit.

Thus, on the basis of these experiments, it was concluded that the optimum crystal growth is observed at the temperature of the hot end 450-350°C and the temperature of the cold end at 30-100 degrees below.

1. The method of synthesis of tetragonal monoselenide iron, comprising heating the sealed ampoule is placed in one end of the mixture of selenium and iron and filled with a salt melt, characterized in that the heating of the ampoule is performed with the temperature gradient on the value of 450°C-350°C by placing the mixture to a temperature of minus 30°C-100°C on the opposite side, where the molten salt is a mixture of eutectic composition comprising aluminum chloride, and heating is carried out in the course of time, providing transfer of the charge from selenium and iron in the opposite end of the ampoule.

2. The method according to claim 1, trichosis fact, as molten salt, a mixture of aluminium chloride and potassium chloride in a molar ratio (1.5 to 2):2.



 

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2 tbl, 1 dwg

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