CN111646798A - Preparation method of lanthanum calcium manganese oxygen low-doped samarium nitrate - Google Patents

Abstract

_The invention discloses a preparation method _of lanthanum calcium manganese _oxide low _{- doped samarium nitrate} . · 4H ₂ O, Mn(NO ₃ ) ₂ · 4H ₂ O and C ₆ H ₈ O ₇ · H ₂ O in a molar ratio of (0.7-x):x:0.3:1:4 (x=0.01-0.05) Calculate and weigh each component drug, use methanol as solvent and ethylene glycol as dispersant to chelate La _{0.7‑ x} Sm _x Ca _0.3 MnO ₃ wet gel, and then place it in a drying oven to dry, and the obtained After the dry gel was fully ground, it was kept at 500 °C for 8 hours for initial firing. The obtained initial fired powder was fully ground and tableted, and then held at 1400 °C for 12 hours for final firing, to prepare La _{0.7‑ x} Sm _x Ca _0.3 MnO ₃ A sample of crystalline ceramic target material; this method achieves a temperature coefficient of resistance (TCR) and a magnetoresistance (MR) of La _0.67 Sm _0.03 Ca _0.3 MnO ₃ polycrystalline ceramic material of 20.23% when 0.03 mol of samarium nitrate is low-doped by the sol-gel method. ·K ^-1 and 72.31%, so that the application of the material can better meet the needs of use, the method is convenient to prepare, has a short cycle, low preparation cost, and can be used for large-scale industrial production.

Description

A kind of preparation method of lanthanum calcium manganese oxide low-doped samarium nitrate

technical field

The invention relates to a preparation method of lanthanum calcium manganese oxygen low-doped samarium nitrate, which belongs to the technical field of electronic functional ceramics.

Background technique

La _0.7 Ca _0.3 MnO ₃ is a typical strongly correlated electron system. The metal-insulator transition near the Curie temperature can produce a large resistance mutation in a very small temperature range. As a strongly correlated oxide, LaCaMnO ₃ has many It has a special physical property, and its giant magnetoresistance effect and metal-insulator transition behavior have great research and application value in optoelectronic fast devices, bolometers, high-density magnetic storage heads, refrigerators and infrared detectors. . For the LaCaMnO ₃ material system, the temperature coefficient of resistance (TCR) indicates the sensitivity of the material to temperature, which determines the possibility of detecting device applications. At the same time, the high low-field magnetoresistance (LFMR) provides a basis for the fabrication of magnetic sensing devices and other devices that rely on magnetoresistive properties, while the low MR of the current pure _LaCaMnO3 largely limits this type of material. Applications.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the present invention provides a preparation method of lanthanum calcium manganese oxide low-doped samarium nitrate, so that the MR of the LaCaMnO ₃ system material can be greatly improved in the low-doped samarium nitrate, and the preparation method is simple. On the basis of La _0.7 Ca _0.3 MnO ₃ , samarium nitrate was directly combined with La _0.7 Ca _0.3 MnO ₃ by sol-gel method, so that samarium nitrate was uniformly doped to form La _0.7-x Sm _x Ca _0.3 MnO ₃ gel, and then Drying, initial firing and final firing are carried out to obtain La _0.7-x Sm _x Ca _0.3 MnO ₃ polycrystalline ceramic targets. When the doping amount is 0.03mol, the MR of La _0.67 Sm _0.03 Ca _0.3 MnO ₃ ceramics is as high as 72.31%, the preparation method can make the MR of the material as high as 72.31%, so as to better satisfy the use of the material.

The object of the present invention is to provide a kind of preparation method of lanthanum calcium manganese oxygen low-doped samarium nitrate, specifically comprising the following steps:

(1) The prepared sample is 2.5g of La _0.7-x Sm _x Ca _0.3 MnO ₃ polycrystalline ceramic target, lanthanum nitrate (La(NO ₃ ) ₃ ·nH ₂ O), samarium nitrate (Sm(NO ₃ ) ₃ ), calcium nitrate (Ca(NO ₃ ) ₂ ·4H ₂ O), manganese nitrate (Mn(NO ₃ ) ₂ ·4H ₂ O) and citric acid (C ₆ H ₈ O ₇ ·H ₂ O) in a stoichiometric ratio Calculate and weigh into a beaker, add methanol as a solvent in the beaker;

(2) place the beaker after the completion of step (1) on a magnetic stirrer and stir evenly, drop a small amount of ethylene glycol dropwise into the beaker simultaneously, and continue stirring until the medicine is completely dissolved;

(3) the mixed solution obtained in step (2) is heated in a water bath, while magnetic stirring, until the sol becomes a deep yellow, viscous and transparent gel;

(4) quickly put the gel obtained in step (3) into a drying oven, and obtain a dry gel after drying for 8-12 h;

(5) pour the xerogel obtained in step (4) into a mortar, and after fully grinding, put into a porcelain crucible, and place it in a box furnace for pre-firing to obtain nano-powder;

After the powder obtained in step (5) is fully ground in a mortar, the powder is pressed into a block with a tablet machine, loaded into a corundum crucible, and placed in a box furnace for final firing to obtain La _0.67 Sm _0.03 Ca _0.3 MnO ₃ polycrystalline ceramic target.

La(NO ₃ ) ₃ .6H ₂ O, Sm(NO ₃ ) ₃ , Ca(NO ₃ ) ₂ .4H ₂ O, Mn(NO ₃ ) ₂ .4H ₂ O and C ₆ in step (1) of the present invention The molar ratio of H ₈ O ₇ ·H ₂ O is (0.7-x):x:0.3:1:4, the amount of methanol is n _(methanol) :n _(CA) =3:1, methanol is used as colloidal chelate solvent.

The amount of ethylene glycol in step (2) of the present invention is n _(EG) :n _(CA) =1:2, ethylene glycol is used as a dispersant, and citric acid is used as a chelating agent.

The heating temperature of the water bath heating in the step (3) of the present invention is 85-88° C., and the stirring speed should slowly decrease in the process of the sol becoming viscous.

In step (4) of the present invention, the temperature of the drying box is 140-180° C., and the drying time is 8-12 h.

The initial firing process in step (5) of the present invention is to keep the temperature at 500°C for 8h, wherein in order to make the sample fully react, the temperature is respectively kept at 200°C and 400°C for 1 hour.

The final firing process in the step (6) of the present invention is to keep the temperature at 1400° C. for 12 hours.

The beneficial effects of the present invention: the preparation method of lanthanum calcium manganese oxide low-doped samarium nitrate according to the present invention, when the samarium nitrate is low-doped by sol-gel method 0.03mol, La _0.67 Sm _0.03 Ca _0.3 MnO ₃ polycrystalline The temperature coefficient of resistance (TCR) of the ceramic material and the resistance (MR) under 1T magnetic field reach 20.23%·K ^-1 and 72.31%, so that the application of this material can better meet the needs of use, the method is convenient to prepare and the cycle is short , the preparation cost is low, and large-scale industrial production can be carried out.

Description of drawings

Fig. 1 is the XRD pattern of the series of polycrystalline ceramic targets obtained in Examples 1-5;

Fig. 2-6 is the SEM map corresponding to embodiment 1-5;

Fig. 7 is the TCR curve of the series of polycrystalline ceramic targets obtained in Examples 1-5;

Fig. 8 is the MR curve of the series of polycrystalline ceramic targets obtained in Examples 1-5;

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and specific implementations, but the protection scope of the present invention is not limited to the above-mentioned contents.

Example 1

(1) Weighing and dissolving raw materials: First, calculate the amount of each raw material according to the stoichiometric ratio, and then weigh lanthanum nitrate, samarium nitrate, calcium nitrate, manganese nitrate and citric acid in a molar ratio of 0.69:0.01:0.3:1:4. , dissolve them in methanol solvent, and after they are completely dissolved, add an appropriate amount of ethylene glycol.

(2) heating and stirring to form a gel: the mixed solution obtained in step (1) is placed on a constant temperature water bath for constant temperature stirring treatment, the temperature is controlled at 88 ° C, heating is performed while stirring, the solvent is slowly evaporated, and when the solution evaporates to a certain amount , and the foaming phenomenon gradually appears to form a wet sol.

(3) Drying: the wet gel obtained in step (2) is immediately placed in a drying oven, the oven temperature is 180° C., and the holding time is 12 h to form a dry gel.

(4) Grinding and pre-firing: all the xerogels obtained in step (3) are poured into an agate mortar, fully ground for 30 min to form powder, put into a porcelain crucible, put into a box furnace for initial firing, and heated at 500° C. Incubate for 8h for initial firing to obtain black powder.

(5) Tablet sintering: After the black powder obtained in step (4) is fully ground with an agate mortar, it is pressed into a block with a diameter of 20 mm by a tablet machine, and then placed in a box furnace at 1400° C. The final sintering was carried out under heat preservation for 12 hours, and finally a La _0.69 Sm _0.01 Ca _0.3 MnO ₃ polycrystalline ceramic target was obtained.

Example 1 obtained is a La _0.69 Sm _0.01 Ca _0.3 MnO ₃ polycrystalline ceramic target with a low-doped samarium nitrate of 0.01 mol. As can be seen from Figures 1, 2, 7 and 8, the amount of low-doped samarium nitrate is At 0.01 mol, the La _0.69 Sm _0.01 Ca _0.3 MnO ₃ sample has a typical perovskite structure with no second phase, good crystalline quality, and low TCR and MR of 18.06%·K ^-1 and 52.50%, respectively.

Example 2

(1) Weighing and dissolving raw materials: First, calculate the amount of each raw material according to the stoichiometric ratio, and then weigh lanthanum nitrate, samarium nitrate, calcium nitrate, manganese nitrate and citric acid in a molar ratio of 0.68:0.02:0.3:1:4. , dissolve them in methanol solvent, and after they are completely dissolved, add an appropriate amount of ethylene glycol.

(2) heating and stirring to form a gel: the mixed solution obtained in step (1) is placed on a constant temperature water bath for constant temperature stirring treatment, the temperature is controlled at 88 ° C, heating is performed while stirring, the solvent is slowly evaporated, and when the solution evaporates to a certain amount , and the foaming phenomenon gradually appears to form a wet sol.

(3) Drying: the wet gel obtained in step (2) is immediately placed in a drying oven, the oven temperature is 180° C., and the holding time is 12 h to form a dry gel.

(4) Grinding and pre-firing: all the xerogels obtained in step (3) are poured into an agate mortar, fully ground for 30 min to form powder, put into a porcelain crucible, put into a box furnace for initial firing, and heated at 500° C. Incubate for 8h for initial firing to obtain black powder.

(5) Tablet sintering: After the black powder obtained in step (4) is fully ground with an agate mortar, it is pressed into a block with a diameter of 20 mm by a tablet machine, and then placed in a box furnace at 1400° C. The final sintering was carried out under heat preservation for 12 hours, and finally a La _0.68 Sm _0.02 Ca _0.3 MnO ₃ polycrystalline ceramic target was obtained.

Example 2 obtained is a La _0.68 Sm _0.02 Ca _0.3 MnO ₃ polycrystalline ceramic target with a low-doped samarium nitrate of 0.02 mol. It can be seen from Figure 1, Figure 3, Figure 7 and Figure 8 that the amount of low-doped samarium nitrate is At 0.02 mol, the La _0.68 Sm _0.02 Ca _0.3 MnO ₃ sample has a typical perovskite structure, no second phase, good crystalline quality, and low TCR and MR of 19.03%·K ^-1 and 69.63%, respectively.

Example 3

(1) Weighing and dissolving raw materials: First, calculate the amount of each raw material according to the stoichiometric ratio, and then weigh lanthanum nitrate, samarium nitrate, calcium nitrate, manganese nitrate and citric acid in a molar ratio of 0.67:0.03:0.3:1:4. , dissolve them in methanol solvent, and after they are completely dissolved, add an appropriate amount of ethylene glycol.

(2) heating and stirring to form a gel: the mixed solution obtained in step (1) is placed on a constant temperature water bath for constant temperature stirring treatment, the temperature is controlled at 88 ° C, heating is performed while stirring, the solvent is slowly evaporated, and when the solution evaporates to a certain amount , and the foaming phenomenon gradually appears to form a wet sol.

(3) Drying: the wet gel obtained in step (2) is immediately placed in a drying oven, the oven temperature is 180° C., and the holding time is 12 h to form a dry gel.

(4) Grinding and pre-firing: all the xerogels obtained in step (3) are poured into an agate mortar, fully ground for 30 min to form powder, put into a porcelain crucible, put into a box furnace for initial firing, and heated at 500° C. Incubate for 8h for initial firing to obtain black powder.

(5) Tablet sintering: After the black powder obtained in step (4) is fully ground with an agate mortar, it is pressed into a block with a diameter of 20 mm by a tablet machine, and then placed in a box furnace at 1400° C. The final sintering was carried out under heat preservation for 12 hours, and finally a La _0.67 Sm _0.03 Ca _0.3 MnO ₃ polycrystalline ceramic target was obtained.

Example 3 obtained is a La _0.67 Sm _0.03 Ca _0.3 MnO ₃ polycrystalline ceramic target with a low-doped samarium nitrate of 0.03 mol. As can be seen from Figures 1, 4, 7 and 8, the amount of low-doped samarium nitrate is At 0.03 mol, the La _0.67 Sm _0.03 Ca _0.3 MnO ₃ sample has a typical perovskite structure, no second phase, good crystalline quality, and the highest TCR and MR, 20.23% K ^-1 and 72.31%, respectively.

Example 4

(1) Weighing and dissolving raw materials: First, calculate the amount of each raw material according to the stoichiometric ratio, and then weigh lanthanum nitrate, samarium nitrate, calcium nitrate, manganese nitrate and citric acid in a molar ratio of 0.66:0.04:0.3:1:4. , dissolve them in methanol solvent, and after they are completely dissolved, add an appropriate amount of ethylene glycol.

(2) heating and stirring to form a gel: the mixed solution obtained in step (1) is placed on a constant temperature water bath for constant temperature stirring treatment, the temperature is controlled at 88 ° C, heating is performed while stirring, the solvent is slowly evaporated, and when the solution evaporates to a certain amount , and the foaming phenomenon gradually appears to form a wet sol.

(3) Drying: the wet gel obtained in step (2) is immediately placed in a drying oven, the oven temperature is 180° C., and the holding time is 12 h to form a dry gel.

(4) Grinding and pre-firing: all the xerogels obtained in step (3) are poured into an agate mortar, fully ground for 30 min to form powder, put into a porcelain crucible, put into a box furnace for initial firing, and heated at 500° C. Incubate for 8h for initial firing to obtain black powder.

(5) Tablet sintering: After the black powder obtained in step (4) is fully ground with an agate mortar, it is pressed into a block with a diameter of 20 mm by a tablet machine, and then placed in a box furnace at 1400° C. The final sintering was carried out under heat preservation for 12 hours, and finally a La _0.66 Sm _0.04 Ca _0.3 MnO ₃ polycrystalline ceramic target was obtained.

Example 4 obtained is a La _0.66 Sm _0.04 Ca _0.3 MnO ₃ polycrystalline ceramic target with a low-doped samarium nitrate of 0.04 mol. It can be seen from Figure 1, Figure 5, Figure 7 and Figure 8 that the amount of low-doped samarium nitrate is At 0.04 mol, the La _0.66 Sm _0.04 Ca _0.3 MnO ₃ sample has a typical perovskite structure with no second phase, good crystalline quality, and low TCR and MR of 15.48% K ^-1 and 61.40%, respectively.

Example 5

(1) Weighing and dissolving raw materials: First, calculate the amount of each raw material according to the stoichiometric ratio, and then weigh lanthanum nitrate, samarium nitrate, calcium nitrate, manganese nitrate and citric acid in a molar ratio of 0.65:0.05:0.3:1:4. , dissolve them in methanol solvent, and after they are completely dissolved, add an appropriate amount of ethylene glycol.

(2) heating and stirring to form a gel: the mixed solution obtained in step (1) is placed on a constant temperature water bath for constant temperature stirring treatment, the temperature is controlled at 88 ° C, heating is performed while stirring, the solvent is slowly evaporated, and when the solution evaporates to a certain amount , and the foaming phenomenon gradually appears to form a wet sol.

(3) Drying: the wet gel obtained in step (2) is immediately placed in a drying oven, the oven temperature is 180° C., and the holding time is 12 h to form a dry gel.

(4) Grinding and pre-firing: all the xerogels obtained in step (3) are poured into an agate mortar, fully ground for 30 min to form powder, put into a porcelain crucible, put into a box furnace for initial firing, and heated at 500° C. Incubate for 8h for initial firing to obtain black powder.

(5) Tablet sintering: After the black powder obtained in step (4) is fully ground with an agate mortar, it is pressed into a block with a diameter of 20 mm by a tablet machine, and then placed in a box furnace at 1400° C. The final sintering was carried out under heat preservation for 12 hours, and finally a La _0.65 Sm _0.05 Ca _0.3 MnO ₃ polycrystalline ceramic target was obtained.

Example 5 obtained is a La _0.65 Sm _0.05 Ca _0.3 MnO ₃ polycrystalline ceramic target with a low-doped samarium nitrate of 0.05 mol. As can be seen from Figure 1, Figure 6, Figure 7 and Figure 8, the amount of low-doped samarium nitrate is At 0.05 mol, the La _0.65 Sm _0.05 Ca _0.3 MnO ₃ sample has a typical perovskite structure, no second phase, good crystalline quality, and low TCR and MR of 14.51%·K ^-1 and 56.10%, respectively.

Claims (7)

1. A preparation method of lanthanum calcium manganese oxygen low-doped samarium nitrate is characterized by comprising the following steps:

(1) preparation of sample 2.5g of La_0.7-xSm_xCa_0.3MnO₃Polycrystalline ceramic target material prepared by mixing lanthanum nitrate (La (NO)₃)₃·nH₂O), samarium nitrate (Sm (NO)₃)₃) Calcium nitrate (Ca (NO)₃)₂·4H₂O), manganese nitrate (Mn (NO)₃)₂·4H₂O) and citric acid (C)₆H₈O₇·H₂O) calculating the stoichiometric ratio, weighing and placing into a beaker, and adding methanol into the beaker as a solvent;

(2) putting the beaker after the step (1) is finished on a magnetic stirrer, uniformly stirring, simultaneously dropwise adding a small amount of glycol into the beaker, and continuously stirring until the medicine is completely dissolved;

(3) heating the mixed solution obtained in the step (2) in a water bath, and simultaneously stirring by magnetic force until the sol becomes dark yellow, viscous and transparent gel;

(4) quickly putting the gel obtained in the step (3) into a drying box, and drying for 8-12h to obtain dry gel;

(5) pouring the xerogel obtained in the step (4) into a mortar, fully grinding, filling into a ceramic crucible, and placing in a box-type furnace for pre-sintering to obtain nano powder;

(6) fully grinding the powder obtained in the step (5) in a mortar, pressing the powder into blocks by using a tablet press, filling the blocks into a corundum crucible, and placing the corundum crucible in a box furnace for final burning to obtain La_0.7-xSm_xCa_0.3MnO₃Polycrystalline ceramic targets.

2. The method for preparing lanthanum calcium manganese oxygen low-doped samarium nitrate according to claim 1, which is characterized in that: la (NO) in step (1)₃)₃·6H₂O，Sm(NO₃)₃,Ca(NO₃)₂·4H₂O，Mn(NO₃)₂·4H₂O and C₆H₈O₇·H₂The molar ratio of O is (0.7-x) x:0.3:1:4, the amount of methanol is n_(methanol)：n_(CA)3: methanol as a solvent for colloidal chelation.

3. The method for preparing lanthanum calcium manganese oxygen low-doped samarium nitrate according to claim 1, which is characterized in that: the amount of ethylene glycol in the step (2) is n_(EG)：n_(CA)1: 2, ethylene glycol is used as a dispersant, and citric acid is used as a chelating agent.

4. The method for preparing lanthanum calcium manganese oxygen low-doped samarium nitrate according to claim 1, which is characterized in that: the heating temperature of the water bath heating in the step (3) is 85-88 ℃, and the stirring speed is slowly reduced in the process that the sol becomes viscous.

5. The method for preparing lanthanum calcium manganese oxygen low-doped samarium nitrate according to claim 1, which is characterized in that: the temperature of the drying box in the step (4) is 140-180 ℃, and the drying time is 8-12 h.

6. The method for preparing lanthanum calcium manganese oxygen low-doped samarium nitrate according to claim 1, which is characterized in that: the initial firing process in the step (5) is carried out for 8 hours at 500 ℃, wherein in order to ensure that the sample is fully reacted, the temperature is respectively kept for 1 hour when the temperature is raised to 200 ℃ and 400 ℃.

7. The method for preparing lanthanum calcium manganese oxygen low-doped samarium nitrate according to claim 1, which is characterized in that: the final firing process in the step (6) is heat preservation for 12 hours at 1400 ℃.

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