Background
Strontium potassium niobate (KSr) of tungsten bronze structure2Nb5O15) The material has strong spontaneous polarization and obvious optical birefringence effect, and the electro-optic coefficient of the potassium strontium niobate single crystal is about LiNbO3The single crystal is 7 times of the single crystal, and has wide application space in the fields of photoelectricity, ferroelectricity, dielectric, laser and the like. Compared with single crystals, the strontium potassium niobate textured ceramic has the advantages of short preparation period and low cost, so that the texturing of the strontium potassium niobate ceramic is rapidly developed. If acicular strontium potassium niobate microcrystal powder with anisotropic morphology is used as a raw material, the microcrystal is directionally arranged through a coating and casting process,the compact strontium potassium niobate ceramic (L. Liu. contamination of grain-oriented KSr2Nb5O15 ceramics by a burst technique [ J. Liu. contamination of grain-oriented KSr2Nb5O15 ceramic) with higher texture degree can be prepared after high-temperature sintering]Materials Letters 186 (2017) 105-. In the process, the needle-shaped strontium potassium niobate microcrystalline powder is a key material in the preparation of the texture ceramics with related components.
The method for preparing anisotropic strontium potassium niobate microcrystal with shape at present is mainly a molten salt method (peak, a method for preparing needle-shaped strontium potassium niobate microcrystal powder [ P]Chinese patent application CN 102616852B), but the chemical components of the obtained powder deviate from the stoichiometric ratio, resulting in lower curie temperature of strontium potassium niobate ceramic synthesized by using the powder as raw material, which is only 82 ℃ (l, liu, microstruture, dielectric and pinned hysteresis loops of grain-oriented KSr2Nb5O15 ferroelectric ceramics[J]Journal of Materials Science Materials in Electronics 29 (2018) 9635-9642), greatly limited the development of strontium potassium niobate ceramic Materials. Therefore, the key to the development of the strontium potassium niobate microcrystalline powder preparation technology is to find a technology for preparing the stoichiometric ratio microcrystalline with strong anisotropy of powder morphology.
Disclosure of Invention
The invention aims to provide a method for preparing needle-shaped potassium strontium niobate microcrystalline powder with stoichiometric ratio.
The invention shortens the distance between the raw material powder by pressurizing, accelerates the diffusion of ions in a high-temperature molten salt environment, further promotes the high-efficiency synthesis of a target product, and avoids the uneven components caused by the layering of the density difference of the raw materials in the molten salt.
The invention provides a method for preparing needle-shaped potassium strontium niobate microcrystalline powder with stoichiometric ratio, which comprises the following steps:
the method comprises the following steps: preparing a raw material mixture:
analytically pure SrCO3And Nb2O5The powders were weighed in a molar ratio of 1: 1.25. The KCl powder was weighed. Weighing SrCO3、Nb2O5And KCl in a polyethylene ball mill. Adding into a polyethylene ball milling tankAdding absolute ethyl alcohol to ball mill for 10-24 hr. And (3) placing the wet material subjected to ball milling in an oven, and drying for 6-12 h at the temperature of 60-80 ℃ to obtain dry powder. And grinding the dried powder into powder by an agate mortar to obtain a raw material mixture.
KCl and weighed SrCO3And Nb2O5The ratio of the mass sum of (A) to (B) is 1.5 to 3.5: 1. The absolute ethyl alcohol and SrCO placed in a polyethylene ball milling tank3、Nb2O5The mass ratio of the powder to the KCl is 2-4: 1.
Step two: pressing the raw material mixture:
and placing the obtained raw material mixture into a mold, and pressing the raw material mixture into a raw material mixture block under the condition of 50-200 MPa.
Step three: preparing strontium potassium niobate microcrystalline powder:
the obtained raw material mixture block is placed in a corundum crucible to be calcined for 3 to 6 hours at the temperature of 1100 to 1250 ℃. Repeatedly washing and filtering the calcined product in distilled water at the temperature of between 80 and 100 ℃ until no Cl is detected in the filtrate-. And drying the washed powder at 60-80 ℃ to obtain the strontium potassium niobate microcrystalline powder.
Step four: preparing needle-shaped strontium potassium niobate microcrystalline powder:
and placing the obtained needle-shaped strontium potassium niobate microcrystal in a beaker, adding distilled water into the beaker, stirring the mixture on a magnetic stirrer for 10 to 40min, settling the mixture for 1 to 2min, and pouring out the supernatant. Drying the settled powder at 60-80 deg.c to obtain needle strontium potassium niobate microcrystal powder in stoichiometric ratio.
The needle-shaped potassium strontium niobate microcrystalline powder prepared by the preparation method has the stoichiometric ratio of 15-20 microns in length, the length-diameter ratio of more than 20, and the content ratio of elements in the microcrystalline is K: Sr: Nb ≈ 1:2: 5.
The invention has the beneficial effects that:
the invention provides a method for preparing needle-shaped strontium potassium niobate microcrystalline powder with stoichiometric ratio, which adopts an improved molten salt growth method to prepare the strontium potassium niobate microcrystalline powder. The method has simple and convenient steps, the obtained product has high purity, the chemical components conform to the stoichiometric ratio of the strontium potassium niobate, the length-diameter ratio is more than 20, the requirements of the anisotropic template are met, the mechanical pollution is small, the formula deviation is small, the process is easy to control, the reproducibility and the stability of the product are good, and the method can be used for mass production of the shape anisotropic template powder with the stoichiometric ratio of the strontium potassium niobate.
Detailed Description
The present invention is further illustrated by, but is not limited to, the following examples.
Example 1:
the embodiment is a method for preparing needle-shaped potassium strontium niobate microcrystalline powder with stoichiometric ratio, which comprises the following specific processes:
step 1: a raw material mixture is prepared. Analytically pure SrCO3And Nb2O5The powders were weighed in a molar ratio of 1: 1.25. The KCl powder was weighed. Weighing SrCO3、Nb2O5And KCl in a polyethylene ball mill. Adding absolute ethyl alcohol into a polyethylene ball milling tank, and ball milling for 12 hours on a ball mill. And (3) placing the wet material subjected to ball milling in an oven, and drying for 10 hours at 80 ℃ to obtain dry powder. And grinding the dried powder into powder by an agate mortar to obtain a raw material mixture. KCl and weighed SrCO3And Nb2O5The ratio of the sum of the masses of (a) to (b) is 1.5: 1. The absolute ethyl alcohol and SrCO placed in a polyethylene ball milling tank3、Nb2O5The mass ratio of the powder to the KCl is 2: 1.
Step 2: the raw mixture is pressed. And placing the obtained raw material mixture into a mold, and pressing the raw material mixture into a raw material mixture block under the condition of 100 MPa.
And step 3: system for makingPreparing the strontium potassium niobate microcrystalline powder. The obtained raw material mixture block is placed in a corundum crucible to be calcined for 4 hours at 1150 ℃. Repeatedly washing in distilled water at 100 ℃ after calcination and filtering until no Cl is detected in the filtrate-. Drying the washed powder at 80 ℃ to obtain the strontium potassium niobate microcrystalline powder.
And 4, step 4: preparing needle-shaped strontium potassium niobate microcrystalline powder. And placing the obtained needle-shaped strontium potassium niobate microcrystal in a beaker, adding distilled water into a magnetic stirrer, stirring for 20min, settling for 1min, and pouring out the supernatant. Drying the settled powder at 80 ℃ to obtain the needle-shaped strontium potassium niobate microcrystalline powder with stoichiometric ratio.
According to the invention, the distance between the raw material powder bodies is shortened by pressurization, the diffusion of ions is accelerated in a high-temperature molten salt environment, the high-efficiency synthesis of a target product is further promoted, and the uneven components caused by the layering of the density difference of the raw materials in the molten salt are avoided. The strontium potassium niobate microcrystalline powder prepared by the embodiment is as shown in fig. 1, and has weak shape anisotropy, wide size distribution, a length of about 1-20 μm and a diameter of about 0.5-1 μm; the strontium potassium niobate microcrystalline powder prepared after sedimentation treatment is as shown in figure 2, the length is about 15-20 μm, the length-diameter ratio is greater than 20, and the microcrystalline powder particles are very uniform and have good dispersibility; x-ray powder diffraction Pattern and KSr2Nb5O15The standard cards are fully conformed, as shown in fig. 3; EDS test results show that the content ratio of each element in the microcrystal is K to Sr to Nb to 1 to 2 to 5, and further prove that the microcrystalline powder prepared by the method has the components in accordance with the stoichiometric ratio of strontium potassium niobate.
In order to further confirm that the chemical components of the synthesized powder meet the stoichiometric ratio, the dielectric temperature spectrum line of the strontium potassium niobate ceramic is tested, as shown in fig. 4. Wherein, the strontium potassium niobate ceramic is synthesized by sintering the obtained microcrystalline powder as a raw material at 1320 ℃ for 2 h. The result shows that the Curie temperature of the strontium potassium niobate ceramic is about 170 ℃, which well proves that the chemical composition of the microcrystalline powder prepared by the invention conforms to the chemical composition of the strontium potassium niobate (KSr)2Nb5O15) Stoichiometric ratio.
Example 2:
step 1:a raw material mixture is prepared. Analytically pure SrCO3And Nb2O5The powders were weighed in a molar ratio of 1: 1.25. The KCl powder was weighed. Weighing SrCO3、Nb2O5And KCl in a polyethylene ball mill. Adding absolute ethyl alcohol into a polyethylene ball milling tank, and ball milling for 12 hours on a ball mill. And (3) placing the wet material subjected to ball milling in an oven, and drying for 10 hours at 80 ℃ to obtain dry powder. And grinding the dried powder into powder by an agate mortar to obtain a raw material mixture. KCl and weighed SrCO3And Nb2O5The ratio of the sum of the masses of (a) to (b) is 2.5: 1. The absolute ethyl alcohol and SrCO placed in a polyethylene ball milling tank3、Nb2O5The mass ratio of the powder to the KCl is 3: 1.
Step 2: the raw mixture is pressed. The obtained raw material mixture is placed in a mould and pressed into a raw material mixture block under the condition of 50 MPa.
And step 3: preparing the strontium potassium niobate microcrystalline powder. The obtained raw material mixture block is placed in a corundum crucible to be calcined for 6 hours at 1100 ℃. Repeatedly washing in 80 deg.C distilled water after calcination and filtering until no Cl is detected in the filtrate-. Drying the washed powder at 80 ℃ to obtain the strontium potassium niobate microcrystalline powder.
And 4, step 4: preparing needle-shaped strontium potassium niobate microcrystalline powder. And placing the obtained needle-shaped strontium potassium niobate microcrystal in a beaker, adding distilled water into a magnetic stirrer, stirring for 40min, settling for 1.5min, and pouring out the supernatant. Drying the settled powder at 60 ℃ to obtain the needle-shaped strontium potassium niobate microcrystalline powder with stoichiometric ratio.
Example 3:
step 1: a raw material mixture is prepared. Analytically pure SrCO3And Nb2O5The powders were weighed in a molar ratio of 1: 1.25. The KCl powder was weighed. Weighing SrCO3、Nb2O5And KCl in a polyethylene ball mill. Adding absolute ethyl alcohol into a polyethylene ball milling tank, and ball milling for 12 hours on a ball mill. And (3) placing the wet material subjected to ball milling in an oven, and drying for 10 hours at 80 ℃ to obtain dry powder. Introducing dry powderAnd grinding the mixture into powder by an agate mortar to obtain a raw material mixture. KCl and weighed SrCO3And Nb2O5The ratio of the sum of the masses of (a) to (b) is 3: 1. The absolute ethyl alcohol and SrCO placed in a polyethylene ball milling tank3、Nb2O5The mass ratio of the powder material to the KCl is 4: 1.
Step 2: the raw mixture is pressed. And placing the obtained raw material mixture into a mold, and pressing the raw material mixture into a raw material mixture block under the condition of 150 MPa.
And step 3: preparing the strontium potassium niobate microcrystalline powder. The obtained raw material mixture block is placed in a corundum crucible to be calcined for 5 hours at 1200 ℃. Repeatedly washing in distilled water at 90 ℃ after calcination and filtering until no Cl is detected in the filtrate-. And drying the washed powder at 60-80 ℃ to obtain the strontium potassium niobate microcrystalline powder.
And 4, step 4: preparing needle-shaped strontium potassium niobate microcrystalline powder. And placing the obtained needle-shaped strontium potassium niobate microcrystal in a beaker, adding distilled water into a magnetic stirrer, stirring for 10min, settling for 1.5min, and pouring out the supernatant. Drying the settled powder at 70 ℃ to obtain the needle-shaped strontium potassium niobate microcrystalline powder with stoichiometric ratio.
Example 4:
step 1: a raw material mixture is prepared. Analytically pure SrCO3And Nb2O5The powders were weighed in a molar ratio of 1: 1.25. The KCl powder was weighed. Weighing SrCO3、Nb2O5And KCl in a polyethylene ball mill. Adding absolute ethyl alcohol into a polyethylene ball milling tank, and ball milling for 12 hours on a ball mill. And (3) placing the wet material subjected to ball milling in an oven, and drying for 10 hours at 80 ℃ to obtain dry powder. And grinding the dried powder into powder by an agate mortar to obtain a raw material mixture. KCl and weighed SrCO3And Nb2O5The ratio of the sum of the masses of (a) to (b) is 3.5: 1. The absolute ethyl alcohol and SrCO placed in a polyethylene ball milling tank3、Nb2O5The mass ratio of the powder material to the KCl is 4: 1.
Step 2: the raw mixture is pressed. And placing the obtained raw material mixture into a mold, and pressing the raw material mixture into a raw material mixture block under the condition of 200 MPa.
And step 3: preparing the strontium potassium niobate microcrystalline powder. The obtained raw material mixture block is placed in a corundum crucible to be calcined for 3 hours at 1250 ℃. Repeatedly washing in distilled water at 100 ℃ after calcination and filtering until no Cl is detected in the filtrate-. Drying the washed powder at 80 ℃ to obtain the strontium potassium niobate microcrystalline powder.
And 4, step 4: preparing needle-shaped strontium potassium niobate microcrystalline powder. And placing the obtained needle-shaped strontium potassium niobate microcrystal in a beaker, adding distilled water into a magnetic stirrer, stirring for 30min, settling for 1min, and pouring out the supernatant. Drying the settled powder at 80 ℃ to obtain the needle-shaped strontium potassium niobate microcrystalline powder with stoichiometric ratio.