CN111847519A - Preparation method of bismuth ferrotitanate oxide single crystal particles - Google Patents

Preparation method of bismuth ferrotitanate oxide single crystal particles Download PDF

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CN111847519A
CN111847519A CN202010771250.0A CN202010771250A CN111847519A CN 111847519 A CN111847519 A CN 111847519A CN 202010771250 A CN202010771250 A CN 202010771250A CN 111847519 A CN111847519 A CN 111847519A
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bismuth
temperature
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reaction kettle
powder
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CN111847519B (en
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陆亚林
张圆喜
傅正平
王建林
李志昂
刘欢
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University of Science and Technology of China USTC
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    • C01G49/00—Compounds of iron
    • C01G49/009—Compounds containing, besides iron, two or more other elements, with the exception of oxygen or hydrogen
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids

Abstract

The invention provides a preparation method of bismuth ferrotitanate oxide single crystal particles. Firstly, uniformly mixing reaction raw materials (tetrabutyl titanate, bismuth source compound and iron source compound) with a solvent and a complexing agent, heating and evaporating the obtained mixed solution by a combustion method, burning the mixed solution into powder, and then pretreating the powder under certain heat treatment conditions; and then carrying out hydrothermal recrystallization reaction on the pretreated powder by using a supercritical reaction kettle, specifically, putting the powder and a mineralizer into a liner of the supercritical reaction kettle, adjusting the filling degree inside and outside the liner until the inside and outside of the liner reach an equilibrium state, sealing the reaction kettle, and carrying out supercritical recrystallization reaction under certain conditions. According to the invention, through the combination of the specific pretreatment and the supercritical recrystallization, the bismuth-layer perovskite structure oxide single crystal particles can be prepared, the morphology is regular, the size of the single crystal particles is larger and can reach more than 4 microns multiplied by 0.3 microns, and the single crystal particle crystals are highly oriented.

Description

Preparation method of bismuth ferrotitanate oxide single crystal particles
Technical Field
The invention relates to the technical field of single crystal materials, in particular to a preparation method of bismuth ferrotitanate oxide single crystal particles.
Background
At room temperature, single-phase multiferroic materials having ferromagnetism, ferroelasticity and ferroelectricity simultaneously have attracted attention in recent years, and the coexistence and mutual coupling of different multiferroic properties can generate some new characteristics, such as magneto-dielectric effect, electrically controlled magnetic effect and the like. Currently, multiferroic materials are being used in the fields of data storage, spintronics, converters, solar cells, capacitors, sensors, and the like.
In recent years, bismuth-layer perovskite structure oxide becomes a multiferroic material with comparative heat due to unique structure and doping tolerance, and the structural general formula of the bismuth-layer perovskite structure oxide is (Bi)2O2)(Am-1BmO3m+1) Of two-layer fluorite structure (Bi)2O2)2+Of layers and of multilayer perovskite structuresm-1BmO3m+1)2-Composition periodically arranged along c direction, wherein A may be Bi3+、Pb2+、Sr2+、Ca2+、Ba2+Etc., B may be Fe3+、Ti4+、V5+、Nb5+、Ta5+、W6+And m represents the number of perovskite structural units. The adjustability of the degree of freedom and the huge doping tolerance enable the material to become an important multifunctional single-phase multiferroic material, and can respond to the regulation and control of an optical field, an electric field, a magnetic field, a sound field and the like.
At present, the research on bismuth-layered perovskite oxide materials is mainly focused on ceramics and thin films, and a Chinese patent with publication number CN 102167584A discloses a five-layer bismuth-layered perovskite oxide ceramic material with multiferroic performance and a preparation method thereof, and the ceramic material is prepared by adopting a solid phase grinding and sintering process. Chinese patent publication No. CN 102875145a discloses a layered perovskite structure ceramic and a preparation method thereof, wherein a firing method is adopted to prepare powder, and then a high-temperature hot-pressing sintering method is carried out to prepare a ceramic material. Because bismuth element is easy to volatilize at high temperature, the stoichiometric ratio of the element is deviated, the crystal of the bismuth layered perovskite structure oxide material is difficult to prepare by using a pulling method and a Bridgman method, the solid phase sintering method or the high temperature hot pressing sintering method in the prior art can only prepare polycrystalline materials, and the single crystal has no regular appearance, disordered grain orientation, other impurity phases and small grain size, so that high-quality single crystal is difficult to prepare. However, the single crystal particles can be directly subjected to performance characterization, can be used for testing intrinsic properties of the single crystal particles, including magnetism, ferroelectricity, electric transportation performance and optical performance, can avoid the influence of other impurities, and meanwhile, large-size materials can be made into devices to study the properties of the devices. Therefore, the preparation of the bismuth-layer perovskite structure oxide single crystal material, especially the large-size single crystal material, is of great significance.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for preparing bismuth ferrotitanate oxide single crystal particles. The preparation method provided by the invention can be used for preparing large-size bismuth iron titanate oxide single crystal particles.
The invention provides a preparation method of bismuth ferrotitanate oxide single crystal particles, which comprises the following steps:
a) mixing reaction raw materials, a solvent and a complexing agent to obtain a mixed solution;
the reaction raw materials are tetrabutyl titanate, a bismuth source compound and an iron source compound;
b) treating the mixed solution by a combustion method to obtain combustion powder;
c) preheating the combustion powder to obtain powder;
d) putting the powder and a mineralizer into a liner of a supercritical reaction kettle, adjusting the filling degree of the inner part and the outer part of the liner until the inner part and the outer part reach a balanced state, sealing the reaction kettle, and carrying out supercritical recrystallization reaction to obtain iron bismuth titanate oxide single crystal particles shown in a formula (1);
Bim+1FexTim-xO3m+3-formula (1);
wherein x is more than 0 and less than or equal to m, m is more than or equal to 3 and m is an integer and less than or equal to 0;
the temperature conditions of the recrystallization reaction are as follows: constant temperature treatment or treatment under temperature gradient;
the temperature of the constant temperature treatment is 400-600 ℃;
the treatment under the temperature gradient is as follows: the bottom heating temperature of the reaction kettle is 500-600 ℃, the top heating temperature is 400-500 ℃, and the bottom heating temperature is 100-200 ℃ higher than the top heating temperature.
Preferably, in the step d), the filling degree of the inner container of the supercritical reaction kettle is 50-80%, and the filling degree of the outer container is 40-60%.
Preferably, in the step a), the bismuth source compound is one or more of bismuth nitrate, bismuth oxide and bismuth oxalate;
one or more of iron nitrate, iron oxide and ferric oxalate as iron source compounds.
Preferably, in the step d), the mineralizer is a fluoride solution;
the fluoride is potassium fluoride and/or sodium fluoride;
the concentration of the fluoride solution is 0.1-0.5 g/mL.
Preferably, in the step c), the temperature of the preheating treatment is 500-650 ℃, and the time is 1-8 hours.
Preferably, in the step b), the temperature of the combustion method is 400-450 ℃, and the time is 20-25 min.
Preferably, in the step d), the time of the recrystallization reaction is 1 to 7 days.
Preferably, in the step d), the adjusting of the filling degree inside and outside the inner container to reach the equilibrium state is: adjusting the filling degree of the inner part and the outer part of the inner container to balance the pressure of the inner part and the outer part of the inner container;
the pressure is 25-29 MPa.
Preferably, in the step a), the solvent is nitric acid solution;
the complexing agent is ethylenediamine tetraacetic acid and/or citric acid.
Preferably, in the step a), the molar ratio of the complexing agent to the metal ions in the reaction raw materials is (1-1.5) to 1;
the dosage ratio of the reaction raw materials to the solvent is 30g to (100-150) mL;
after the reaction raw materials, the solvent and the complexing agent are mixed, the pH value of the system is adjusted to 6-7, and therefore mixed liquid is obtained.
In the preparation method provided by the invention, reaction raw materials (tetrabutyl titanate, bismuth source compound and iron source compound) are uniformly mixed with a solvent and a complexing agent, the obtained mixed solution is heated, evaporated and burnt into powder by a combustion method, and then pretreatment is carried out under certain heat treatment conditions; performing hydrothermal recrystallization reaction on the pretreated powder by using a supercritical reaction kettle, specifically, putting the powder and a mineralizer into a liner of the supercritical reaction kettle, adjusting the filling degree inside and outside the liner to reach a balanced state, sealing the reaction kettle, and performing supercritical recrystallization reaction under certain conditions; wherein, the temperature condition of the recrystallization reaction is as follows: constant temperature treatment (400-600 ℃) or treatment under temperature gradient (the whole temperature is 400-600 ℃, the bottom of the reaction kettle is high in temperature, the top of the reaction kettle is low in temperature, and the temperature difference between the top and the bottom is 100-200 ℃). The bismuth-layer perovskite structure oxide single crystal particles shown in the formula (1) can be prepared by combining the specific pretreatment and the supercritical recrystallization, the shape is regular, the size of the single crystal particles is larger and can reach more than 4 microns multiplied by 0.3 microns, in some embodiments, the size is as high as 40 microns multiplied by 4 microns, and the crystal of the single crystal particles is highly oriented.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic sectional view of a supercritical reaction vessel and an inner vessel used in a recrystallization step;
FIG. 2 is a schematic view showing the positions of a tube furnace and a reaction vessel during constant temperature treatment;
FIG. 3 is a schematic view showing the positions of a tube furnace and a reaction vessel in the case of treatment under a temperature gradient;
FIG. 4 is an SEM photograph of the powder obtained after pretreatment in example 1;
FIG. 5 is the XRD spectrum of the product obtained in example 1;
FIG. 6 is an SEM photograph of the product obtained in example 1;
FIG. 7 is an atomic force microscope photograph of the product obtained in example 1;
FIG. 8 is an SEM photograph of the product obtained in example 2;
FIG. 9 is a TEM image of the product obtained in example 2;
FIG. 10 is an SEM photograph of the product obtained in comparative example 1 by the solid phase method.
Detailed Description
The invention provides a preparation method of bismuth ferrotitanate oxide single crystal particles, which comprises the following steps:
a) mixing reaction raw materials, a solvent and a complexing agent to obtain a mixed solution;
the reaction raw materials are tetrabutyl titanate, a bismuth source compound and an iron source compound;
b) treating the mixed solution by a combustion method to obtain combustion powder;
c) preheating the combustion powder to obtain powder;
d) putting the powder and a mineralizer into a liner of a supercritical reaction kettle, adjusting the filling degree of the inner part and the outer part of the liner until the inner part and the outer part reach a balanced state, sealing the reaction kettle, and carrying out supercritical recrystallization reaction to obtain iron bismuth titanate oxide single crystal particles shown in a formula (1);
Bim+1FexTim-xO3m+3-formula (1);
wherein x is more than 0 and less than or equal to m, m is more than or equal to 3 and m is an integer and less than or equal to 0;
the temperature conditions of the recrystallization reaction are as follows: constant temperature treatment or treatment under temperature gradient;
the temperature of the constant temperature treatment is 400-600 ℃;
the treatment under the temperature gradient is as follows: the bottom heating temperature of the reaction kettle is 500-600 ℃, the top heating temperature is 400-500 ℃, and the bottom heating temperature is 100-200 ℃ higher than the top heating temperature.
With respect to step a): mixing reaction raw materials, a solvent and a complexing agent to obtain a mixed solution; the reaction raw materials are tetrabutyl titanate, a bismuth source compound and an iron source compound.
In the invention, tetrabutyl titanate is used as a titanium source, and if other titanium sources such as titanium tetrachloride and the like are adopted, impurities such as residual chlorine and the like are added after the subsequent combustion method treatment, so that the product synthesis and the product quality are influenced. The bismuth source compound is preferably bismuth nitrate, bismuth oxide or bismuth oxalate. The iron source compound is preferably iron nitrate, iron oxide or iron oxalate. The feeding ratio of the tetrabutyl titanate, the bismuth source compound and the iron source compound is that the tetrabutyl titanate, the bismuth source compound and the iron source compound are fed according to the stoichiometric ratio of metal ions according to the structure of a target product, and in some embodiments of the invention, the bismuth iron titanate oxide Bi is obtained according to the molar ratio of Bi to Fe to Ti of 5 to 1 to 35FeTi3O15。
In the invention, the solvent is preferably nitric acid solution, and more preferably dilute nitric acid; nitric acid is used as a solvent and can be changed into nitrogen-containing gas through a subsequent combustion method, so that only a plurality of required elements of bismuth, iron and titanium oxide are left in a final product, and other impurities are not introduced. The dosage ratio of the reaction raw materials to the solvent is preferably 30g to (100-150) mL.
In the invention, the complexing agent is preferably ethylenediamine tetraacetic acid and/or citric acid; more preferably ethylenediaminetetraacetic acid and citric acid. When the complexing agent is ethylenediamine tetraacetic acid and citric acid, the molar ratio of the ethylenediamine tetraacetic acid to the citric acid is preferably 1: 0.8-1; in some embodiments of the invention, the molar ratio is 1: 0.8. The complexing agent can form a complex with bismuth ions, iron ions and titanium ions to enable raw materials to be uniformly mixed at a molecular level, wherein the ethylenediamine tetraacetic acid and the citric acid are matched for use, so that a better complexing effect can be achieved, the raw materials can be well mixed at a molecular level, and the complexing agent and the citric acid can be used as fuel to enable the solution to be fully combusted and remove redundant carbon, hydrogen and nitrogen elements.
In the invention, the molar ratio of the complexing agent to the metal ions in the reaction raw material is (1-1.5) to 1.
In the present invention, the order of mixing is preferably: firstly, dissolving reaction raw materials in a solvent to obtain a dissolved solution, and then adding a complexing agent to mix uniformly. After the complexing agent is added, the materials are preferably mixed uniformly through stirring, the stirring speed is preferably 500-1000 rpm, and the time is preferably 0.5-1 h.
In the present invention, after the mixing is completed, the method preferably further comprises: and adjusting the pH value to 6-7 to obtain a mixed solution. In the present invention, the manner of adjusting the pH is not particularly limited, and the pH may be adjusted by adding an acid solution or an alkaline reagent, for example, when the pH is too low, an alkaline reagent (e.g., ammonia water) is added for adjustment, and when the pH is too high, an acid solution (e.g., a nitric acid solution) is added for adjustment. The method can ensure that ions fully form a complex with the complexing agent by controlling the pH to be 6-7, and the combustion quality is influenced and the combustion is insufficient if the pH is too low.
With respect to step b): and treating the mixed solution by a combustion method to obtain combustion powder.
In the invention, the temperature of the combustion method is 400-450 ℃, and preferably 430 ℃; the treatment time is 20-25 min, preferably 22 min. During the combustion process, the mixture is heated to dryness and burned to form powder. In the present invention, the temperature of the combustion process is less than the temperature of the subsequent preheating treatment.
With respect to step c): and carrying out preheating treatment on the combustion powder to obtain powder.
In the invention, after the powder is obtained by a combustion method, the pretreatment is carried out for a certain time at a certain temperature. The temperature of the pretreatment is preferably 500-650 ℃; in some embodiments of the invention, the temperature is 500 ℃, 550 ℃, 600 ℃, 650 ℃. The pretreatment time is preferably 1-8 h; in some embodiments of the invention, the treatment time is 6h or 8 h. The invention carries out pretreatment after the combustion method treatment, which is beneficial to improving the quality of crystal products, and if the pretreatment is not carried out, impurities can be introduced after the subsequent recrystallization; wherein, if the pretreatment temperature is too low, the impurity content is high, and if the pretreatment temperature is too high, other impurity phases can be formed among the raw materials.
In the present invention, it is preferable to further perform grinding after the preheating treatment. The powders are agglomerated together by preheating treatment, and the dispersed powder is obtained by grinding.
With respect to step d): and (2) putting the powder and a mineralizer into a liner of a supercritical reaction kettle, adjusting the filling degree of the inside and the outside of the liner until the inside and the outside of the liner reach an equilibrium state, sealing the reaction kettle, and carrying out supercritical recrystallization reaction to obtain the bismuth iron titanate oxide single crystal particles shown in the formula (1).
In the invention, the powder prepared in the previous step is subjected to hydrothermal recrystallization reaction by using a supercritical reaction kettle. In the invention, a mineralizer is introduced in the recrystallization process. The mineralizer is preferably a fluoride solution. The fluoride is preferably one or more of potassium fluoride and sodium fluoride. The introduction of the fluoride mineralizer can improve the solubility of the powder, adjust the internal and external balance of the inner container and promote the stable reaction.
In the invention, the concentration of the fluoride solution is preferably 0.1-0.5 g/mL; in some embodiments of the invention, the concentration is 0.3 g/mL. The mass ratio of the powder to the mineralizer is preferably 1: 50-80.
In the present invention, the supercritical recrystallization is specifically performed by: and putting the powder and the mineralizer into an inner container of a supercritical reaction kettle, adjusting the filling degree inside and outside the inner container until the filling degree reaches an equilibrium state, sealing the reaction kettle, and carrying out supercritical recrystallization reaction. Referring to FIG. 1, FIG. 1 is a schematic sectional view of a supercritical reaction vessel and an inner vessel used in a recrystallization step; wherein, 1 is a powder raw material, 2 is a mineralizer, 3 is an inner container, and 4 is a supercritical reaction kettle body.
Wherein, adjusting the filling degree of the inner part and the outer part of the inner container to reach the equilibrium state means adjusting the filling degree of the inner part and the outer part of the inner container (namely, the cavity of the reaction kettle) to balance the pressure of the inner part and the outer part of the inner container. In the invention, the pressure of the reaction kettle is preferably 25-29 MPa, namely the pressure inside and outside the liner is adjusted to be under the pressure, and the internal pressure and the external pressure are kept the same, so that the whole reaction kettle is subjected to supercritical water thermal recrystallization under the pressure condition. In some embodiments of the invention, the pressure is 26 MPa.
In the invention, the filling degree of the inner container is the proportion of the volume of liquid in the inner container to the total volume of the inner container; the filling degree of the outer part of the inner container (namely the filling degree of the reaction kettle) is the proportion of the volume of liquid in the reaction kettle to the residual volume of the reaction kettle, and the residual volume is the total volume of the reaction kettle minus the volume of the inner container; the liquid in the reaction kettle is deionized water.
According to the invention, the internal and external pressures of the inner container are balanced by changing the filling degrees of the inner container and the outer container at a certain temperature, and the filling degrees have no reference and certain standards for the influence of the pressure balance, and long-term tests of an applicant show that the filling degree of the inner container of the supercritical reaction kettle is preferably controlled to be 50% -80% and the filling degree of the outer container is preferably controlled to be 40% -60%, so that the internal and external balance of the inner container is ensured, and stable reaction is facilitated. In some embodiments of the invention, the inner container has an inner filling degree of 80% and an outer filling degree of 60%.
In the invention, the inner container is preferably a noble metal inner container; in some embodiments, the silver liner has a purity of 99.9%.
In the invention, after the inner container and the outer container of the reaction kettle are completely charged and the balance state is adjusted, the reaction kettle is sealed. The manner of sealing is not particularly limited in the present invention, and it may be performed according to a conventional sealing operation well known to those skilled in the art, such as sealing it using a mechanical device.
In the invention, after the reaction kettle is sealed, the supercritical recrystallization reaction is carried out under certain conditions. Specifically, the reaction kettle is placed in a tubular furnace, and a high-temperature condition is provided for carrying out a supercritical recrystallization reaction. In the present invention, the temperature conditions of the recrystallization reaction are: constant temperature treatment or treatment under temperature gradient.
Wherein the temperature of the constant temperature treatment is 400-600 ℃; in some embodiments of the invention, the temperature is 550 ℃. The constant temperature treatment refers to that the whole reaction kettle is subjected to heat treatment reaction at the same temperature; referring to fig. 2, fig. 2 is a schematic diagram of the positions of the tube furnace and the reaction kettle during constant temperature treatment, and the reaction kettle is entirely placed in the same temperature zone of the tube furnace.
The treatment under the temperature gradient is as follows: the bottom heating temperature of the reaction kettle is 500-600 ℃, the top heating temperature is 400-500 ℃, and the bottom heating temperature is 100-200 ℃ higher than the top heating temperature. Specifically, the bottom of the reaction kettle is placed in a high-temperature area of a furnace, and the top of the reaction kettle is placed in a low-temperature area for heat treatment; the temperature of the high-temperature area is 500-600 ℃, the temperature of the low-temperature area is 400-500 ℃, and the temperature difference between the high-temperature area and the low-temperature area is 100-200 ℃. That is, the treatment under the temperature gradient means that the upper part and the lower part of the reaction kettle are heated at different temperatures, so that the temperature difference is formed between the upper part and the lower part of the whole reaction kettle. Referring to fig. 3, fig. 3 is a schematic diagram of the placement positions of the tube furnace and the reaction kettle during the treatment under the temperature gradient, wherein a cushion block is placed at the lower part of the reaction kettle, so that the top of the reaction kettle is higher than the heating cavity of the tube furnace, the bottom of the reaction kettle is in a high temperature region, and the top of the reaction kettle is in a low temperature region, thereby forming a temperature difference between the upper part and the lower part of the reaction kettle. In some embodiments of the invention, the temperature at the bottom of the reactor is 500 ℃, 550 ℃, 600 ℃ and the temperature at the top of the reactor is 400 ℃, 500 ℃.
The invention can achieve the best effect within the recrystallization temperature range; moreover, the temperature conditions of the two recrystallization reactions are preferably temperature gradient treatment, which can obtain better product quality and larger product size.
In the invention, the time of the supercritical recrystallization reaction is preferably 1-7 days; in some embodiments of the invention, the reaction time is 3 days. After the supercritical water thermal recrystallization reaction, taking the materials to obtain the bismuth iron titanate oxide single crystal particles shown in the formula (1): bim+1FexTim-xO3m+3-Formula (1); wherein x is more than 0 and less than or equal to m, m is more than or equal to 3 and m is an integer and less than or equal to 0. In some embodiments of the invention, x is 1, m is 4, and 0, and the compound of formula (1) is Bi5FeTi4O15。
In the preparation method provided by the invention, reaction raw materials (tetrabutyl titanate, bismuth source compound and iron source compound) are uniformly mixed with a solvent and a complexing agent, the obtained mixed solution is heated, evaporated and burnt into powder by a combustion method, and then pretreatment is carried out under certain heat treatment conditions; performing hydrothermal recrystallization reaction on the pretreated powder by using a supercritical reaction kettle, specifically, putting the powder and a mineralizer into a liner of the supercritical reaction kettle, adjusting the filling degree inside and outside the liner to reach a balanced state, sealing the reaction kettle, and performing supercritical recrystallization reaction under certain conditions; wherein, the temperature condition of the recrystallization reaction is as follows: constant temperature treatment (400-600 ℃) or treatment under temperature gradient (the whole temperature is 400-600 ℃, the bottom of the reaction kettle is high in temperature, the top of the reaction kettle is low in temperature, and the temperature difference between the top and the bottom is 100-200 ℃). The bismuth-layer perovskite structure oxide single crystal particles shown in the formula (1) can be prepared by combining the specific pretreatment and the supercritical recrystallization, the shape is regular, the size of the single crystal particles is larger and can reach more than 4 microns multiplied by 0.3 microns, in some embodiments, the size is as high as 40 microns multiplied by 4 microns, and the crystal of the single crystal particles is highly oriented.
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
In the following examples, the reagents used were all commercially available, and the reaction raw materials and the potassium fluoride mineralizer were all analytical reagents of the national drug group.
Example 1
1.1 preparation of samples
S1, dissolving tetrabutyl titanate, bismuth nitrate pentahydrate and ferric nitrate nonahydrate in a stoichiometric ratio of Bi to Fe to Ti of 5: 1: 3 in 30mL of dilute nitric acid solvent (with the concentration of 1mol/L), wherein the ratio of the total mass of the reaction raw materials to the amount of the solvent is 30g to 100 mL. Then, ethylenediamine tetraacetic acid and citric acid (the molar ratio of the total molar amount of the complexing agent to the total molar amount of the metal ions in the 3 reaction raw materials is 1.2:1, and the molar ratio of ethylenediamine tetraacetic acid to citric acid is 1: 0.8) were added, and after stirring at 800rpm for 1 hour, the pH was adjusted to 7 to obtain a mixed solution.
And S2, placing the mixed solution into a combustion dish, treating for 20min at 450 ℃, heating and evaporating the mixed solution to dryness, and combusting into powder.
S3, pretreating the powder at 550 ℃ for 6 hours, and grinding to obtain the powder.
The morphology of the obtained powder is shown in fig. 4, and fig. 4 is an SEM image of the powder obtained after pretreatment in example 1. It can be seen that the obtained powder is formed by agglomeration of a plurality of small crystal grains, and has irregular appearance and disordered crystal grain orientation.
S4, weighing 0.3g of powder, putting the powder into a noble metal liner (the length of the liner is 9cm, the diameter is 1.5cm), adding a potassium fluoride aqueous solution (the concentration is 0.3g/mL) to ensure that the filling degree of the liner is 80%, and sealing the liner by laser welding; the liquid in the cavity of the reaction kettle outside the inner container is deionized water, and the filling degree is 60%; and adjusting the filling degree of the inside and the outside of the metal liner to reach a balanced state, wherein the pressure is 26MPa, and sealing the reaction kettle by using mechanical equipment.
S5, placing the reaction kettle in a tubular furnace, wherein the placing position is shown in figure 3, the bottom of the reaction kettle is in a high-temperature region of 550 ℃ and the top of the reaction kettle is in a low-temperature region of 400 ℃, and performing supercritical recrystallization reaction for 3 days to obtain the layered iron bismuth titanate oxide Bi5FeTi3O15Single crystal particles.
1.2 characterization of the samples
(1) The X-ray diffraction test of the obtained product showed that fig. 5 shows the XRD spectrum of the product of example 1. It can be seen that the resulting product is Bi5FeTi3O15And has high crystallinity and no impurity phase.
(2) The scanning electron microscope test and the atomic force microscope test of the obtained product are respectively shown as fig. 6 and fig. 7, wherein fig. 6 is an SEM image of the product obtained in example 1, and fig. 7 is an atomic force microscope image of the product obtained in example 1. It can be seen that the obtained single crystal has a particle size of 40 μm × 40 μm × 4 μm, a regular morphology, and a high degree of orientation.
Example 2
1.1 preparation of samples
S1-S3: the same as in example 1.
S4, weighing 0.3g of powder, putting the powder into a noble metal liner (the length of the liner is 9cm, the diameter is 1.5cm), adding a potassium fluoride aqueous solution (the concentration is 0.3g/mL) to ensure that the filling degree of the liner is 80%, and sealing the liner by laser welding; the liquid in the cavity of the reaction kettle outside the inner container is deionized water, and the filling degree is 60%; and adjusting the filling degree of the inside and the outside of the metal liner to reach a balanced state, wherein the pressure is 26MPa, and sealing the reaction kettle by using mechanical equipment.
S5, placing the reaction kettle in a tube furnaceThe position is shown in figure 2, and the supercritical recrystallization reaction is carried out for 3 days in a constant temperature area of 550 ℃ to obtain the layered iron bismuth titanate oxide Bi5FeTi3O15。
1.2 characterization of the samples
(1) The X-ray diffraction test of the obtained product was carried out in accordance with example 1, and the result showed that the obtained product was Bi5FeTi3O15。
(2) The scanning electron microscope test of the obtained product shows that the result is shown in FIG. 8, and FIG. 8 is an SEM image of the product obtained in example 2. It can be seen that the size of the obtained single crystal particles was 4. mu. m.times.4. mu. m.times.0.3. mu.m.
(3) The transmission electron microscope test result of the obtained product is shown in FIG. 9, and FIG. 9 is a TEM image of the product obtained in example 2. It can be seen that the resulting product has four perovskite layers, the measured lattice length c4.1nm being compared with standard Bi5FeTi3O15The lattice length c4.1nm of the crystal is relatively consistent, and the crystal is further proved to be Bi5FeTi3O15。
Example 3
1.1 preparation of samples
S1: the procedure is as in example 1, except that the bismuth source is replaced by bismuth oxide and the iron source by iron oxide.
S2: the combustion temperature is 400 deg.C, and the treatment time is 20 min.
S3: the pretreatment temperature was 500 ℃ and the treatment time was 8 hours.
S4: the same as in example 1.
S5: according to the operation of example 1, the supercritical recrystallization reaction is carried out for 3 days at the bottom of the reaction kettle in a high temperature region of 600 ℃ and at the top of the reaction kettle in a low temperature region of 400 ℃ to obtain the layered bismuth iron titanate oxide Bi5FeTi3O15Single crystal particles.
1.2 characterization of the samples
The samples obtained were subjected to the characterization tests according to example 1, and the results showed that the product obtained was Bi5FeTi3O15(ii) a The obtained particles are single crystal particles, have regular shapes and sizes of 50 microns multiplied by 4 microns.
Example 4
1.1 preparation of samples
S1: the procedure is as in example 1, except that the bismuth source is replaced by bismuth oxalate and the iron source by iron oxalate.
S2: the combustion temperature is 450 deg.C, and the treatment time is 20 min.
S3: the pretreatment temperature was 650 ℃ and the treatment time was 6.
S4: the same as in example 1.
S5: according to the operation of example 1, the supercritical recrystallization reaction is carried out for 3 days at the bottom of the reaction kettle in a high temperature region of 600 ℃ and at the top of the reaction kettle in a low temperature region of 500 ℃ to obtain the layered bismuth iron titanate oxide Bi5FeTi3O15Single crystal particles.
1.2 characterization of the samples
The samples obtained were subjected to the characterization tests according to example 1, and the results showed that the product obtained was Bi5FeTi3O15(ii) a The obtained particles are single crystal particles, have regular shapes and the sizes of 45 microns multiplied by 3 microns.
Example 5
1.1 preparation of samples
S1: the procedure is as in example 1, except that potassium fluoride is replaced by sodium fluoride.
S2: the combustion temperature is 400 deg.C, and the treatment time is 20 min.
S3: the pretreatment temperature was 600 ℃ and the treatment time was 6 hours.
S4: the same as in example 1.
S5: according to the operation of example 1, the supercritical recrystallization reaction is carried out for 3 days at the bottom of the reaction kettle in a high-temperature region of 500 ℃ and at the top of the reaction kettle in a low-temperature region of 400 ℃ to obtain the layered bismuth iron titanate oxide Bi5FeTi3O15Single crystal particles.
1.2 characterization of the samples
The samples obtained were subjected to the characterization tests according to example 1, and the results showed that the product obtained was Bi5FeTi3O15(ii) a The obtained particles are single crystal particles, the shapes are regular, and the sizes are 30 micrometers multiplied by 4 micrometers.
Comparative example 1 conventional solid phase sintering method
1.1 preparation of samples
Adding Bi2O3、TiO2、Fe2O3Bi is weighed according to the molar ratio of 5:6:12O32.329g，TiO20.479g，Fe2O30.159g of the powder was put into a mortar and sufficiently ground for 2 hours, and the ground powder was put into an alumina crucible, transferred into a muffle furnace and kept at 550 ℃ for 6 hours to obtain a product.
1.2 characterization of the samples
The scanning electron microscope test of the obtained product shows that the result is shown in fig. 10, and fig. 10 is an SEM image of the product prepared by the solid phase method in comparative example 1. As can be seen, the obtained product has disordered orientation, irregular appearance and small size of about 10 mu m.
The embodiments show that the preparation method provided by the invention can prepare the layered bismuth iron titanate oxide single crystal particles, has regular morphology, larger size and high orientation degree, can directly perform performance characterization on a single particle, and is beneficial to promoting the research on the intrinsic properties (such as anisotropy of optical properties, anisotropy of electrical properties and the like) of the layered bismuth iron titanate oxide. In the supercritical recrystallization step, gradient temperature treatment is adopted, so that the size of single crystal particles can be further improved.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A method for preparing bismuth ferrotitanate oxide single crystal particles is characterized by comprising the following steps:
a) mixing reaction raw materials, a solvent and a complexing agent to obtain a mixed solution;
the reaction raw materials are tetrabutyl titanate, a bismuth source compound and an iron source compound;
b) treating the mixed solution by a combustion method to obtain combustion powder;
c) preheating the combustion powder to obtain powder;
d) putting the powder and a mineralizer into a liner of a supercritical reaction kettle, adjusting the filling degree of the inner part and the outer part of the liner until the inner part and the outer part reach a balanced state, sealing the reaction kettle, and carrying out supercritical recrystallization reaction to obtain iron bismuth titanate oxide single crystal particles shown in a formula (1);
Bim+1FexTim-xO3m+3-formula (1);
wherein x is more than 0 and less than or equal to m, m is more than or equal to 3 and m is an integer and less than or equal to 0;
the temperature conditions of the recrystallization reaction are as follows: constant temperature treatment or treatment under temperature gradient;
the temperature of the constant temperature treatment is 400-600 ℃;
the treatment under the temperature gradient is as follows: the bottom heating temperature of the reaction kettle is 500-600 ℃, the top heating temperature is 400-500 ℃, and the bottom heating temperature is 100-200 ℃ higher than the top heating temperature.
2. The preparation method according to claim 1, wherein in the step d), the filling degree of the inner container of the supercritical reaction kettle is 50-80%, and the filling degree of the outer container is 40-60%.
3. The preparation method according to claim 1, wherein in the step a), the bismuth source compound is one or more of bismuth nitrate, bismuth oxide and bismuth oxalate;
one or more of iron nitrate, iron oxide and ferric oxalate as iron source compounds.
4. The method according to claim 1, wherein in step d), the mineralizer is a fluoride solution;
the fluoride is potassium fluoride and/or sodium fluoride;
the concentration of the fluoride solution is 0.1-0.5 g/mL.
5. The method according to claim 1, wherein the preheating treatment is performed at 500 to 650 ℃ for 1 to 8 hours in step c).
6. The method according to claim 1, wherein the combustion process is carried out at a temperature of 400 to 450 ℃ for 20 to 25min in the step b).
7. The method according to claim 1, wherein the recrystallization time in step d) is 1 to 7 days.
8. The method for preparing the inner container according to claim 1, wherein in the step d), the adjusting of the filling degree of the inner container and the outer container to reach the equilibrium state is as follows: adjusting the filling degree of the inner part and the outer part of the inner container to balance the pressure of the inner part and the outer part of the inner container;
the pressure is 25-29 MPa.
9. The method according to claim 1, wherein in the step a), the solvent is nitric acid liquid;
the complexing agent is ethylenediamine tetraacetic acid and/or citric acid.
10. The preparation method of claim 1, wherein in the step a), the molar ratio of the complexing agent to the metal ions in the reaction raw materials is (1-1.5) to 1;
the dosage ratio of the reaction raw materials to the solvent is 30g to (100-150) mL;
after the reaction raw materials, the solvent and the complexing agent are mixed, the pH value of the system is adjusted to 6-7, and therefore mixed liquid is obtained.
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