CN1143061A - A Step-by-Step Synthesis Method of Single Phase Bi2Sr2Ca2Cu3O10+δ High Temperature Superconducting Phase - Google Patents

Abstract

The invention discloses a step-by-step synthesis method of single-phase Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10+δ high-temperature superconducting phase. First, Bi ₂ O ₃ , SrCO ₃ , and CaCO ₃ are used as raw materials, and the batch materials are mixed , ball milling, and firing the mesophase Bi ₂ Sr _x Ca _2-x O ₅ (x=0~1.50). Then, using the above-mentioned mesophase as raw material, add SrCO ₃ , CaCO ₃ and CuO, mix the batch materials, ball mill, and sinter the 2212 superconducting phase; finally use the above-mentioned 2212 phase synthesized through the mesophase as raw material, add SrCO ₃ , CaCO _3. CuO and PbO are mixed with 0-5wt% 2223 superconducting phase as the batch material, ball milled, and the 2223 phase is fired. The invention can effectively increase the formation speed of the 2223 superconducting phase, expand the temperature range for the formation of the 2223 phase, and increase the critical current density.

Description

A Step-by-Step Synthesis Method of Single Phase Bi2Sr2Ca2Cu3O10+δ High Temperature Superconducting Phase

The present invention relates to a new method for preparing single-phase Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10+δ high-temperature superconductor, especially relates to sequentially synthesizing Bi ₂ Sr ₂ via Bi ₂ Sr _x Ca _2-x O ₅ intermediate phase Stepwise synthesis of Ca ₁ Cu ₂ O _8+δ (2212) and Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10+δ (2223) superconducting phases.

Bi-based superconductors have a variety of superconducting phases, and their general formula is Bi ₂ Sr ₂ Ca _n-1 Cun _{O 2(n+2)+δ} , when n=1, 2 and 3, they are Bi ₂ Sr ₂ Cu ₁ O _6+δ (2201) phase, Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _8+δ (2212) phase and Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10+δ (2223) phase. They are around 20K, 85K and 110K respectively. Bi-based superconductors have the advantages of high superconducting transition temperature, good stability, non-toxic, rare earth-free, abundant raw materials and low price, and their superconducting phase structure is significantly layered, which can be obtained by melting texture process or deformation texture The process creates a texture to improve or even eliminate the weak connection problem of the grain boundary. Therefore, besides the Y-Ba-Cu-O system that can be melt-textured, the Bi-system can be prepared by the silver-coated high-quality textured strip, and its critical current density Jc has reached 10 ⁵ A/cm ² ( OT, 77K), showing the possible prospect of high-temperature superconductors for strong electric applications.

In addition to the preparation of low-dimensional materials such as thin films, at present, the preparation of oxide superconductors mostly adopts the solid-state firing method. For the Bi system, Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO, etc. are used as raw materials, and are composed in the name of 2223 phase to make batch materials, which are directly fired after grinding, mixing and molding. However, among the above three superconducting phases of the Bi system, 2201 and 2212 are easier to obtain single-phase materials through solid-state reaction or melt crystallization, while the 2223 high-temperature superconducting phase with Tc=110K is very slow because of its reaction speed , and the formation temperature range is narrow, and it is difficult to synthesize good single-phase materials, which has attracted extensive attention and research. The methods commonly used to solve this problem include: (1) adding an appropriate amount of PbO to accelerate the formation of 2223 phase and broaden its formation temperature range; (2) precisely control the firing temperature and atmosphere; (3) greatly prolong the firing process. (4) optimization and precise control of composition, etc. However, even so, there are still the following problems: (1) The firing time still needs to be as long as about 200h (Phys. Rev. B, 40 [7] 5266 (1989)); (2) There is still a small amount of 2201 accompanying, It is not easy to obtain high-quality single-phase materials; (3) because in the Bi-based superconducting phase, Sr/Ca is in a solid solution state, and its solid solution amount and structure have a great influence on the formation temperature, range, speed and electromagnetic properties of the 2223 phase. However, it is difficult to adjust and control the solid solution behavior of Sr/Ca in the current batch firing method directly.

The purpose of the present invention is to provide a step-by-step synthesis method of single-phase Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10+δ high-temperature superconducting phase.

In order to achieve the above object the present invention takes the following measures:

First, use Bi ₂ O ₃ , SrCO ₃ , and CaCO ₃ as raw materials, and prepare batches according to the atomic ratio of Bi:Sr:Ca=2:x:(2-x) (x=0~1.50), after mixing, ball milling 2-3 hours, press into tablets, and burn at 780-850°C for 5-15 hours to obtain the mesophase Bi-Sr-Ca-O solid solution, whose composition is: Bi ₂ Sr _x Ca _2-x O ₅ , where x =0～1.50, it belongs to the monoclinic crystal system, and its crystal saturation parameters vary with the value of x, as shown in Table 1.

Then, using the above synthesized mesophase as raw material, add SrCO ₃ , CaCO ₃ and CuO so that the atomic ratio of the batch composition is Bi:(Sr+Ca):Cu=2:3:2 (wherein 1/2≤Sr/ Ca≤5) After mixing and ball milling the batch materials, they are pressed into tablets and fired at 780-840°C for 10-15 hours to obtain the 2212 superconducting phase. The solid solubility and structure of Sr/Sr+Ca are controlled by the solid-solution properties of the mesophase .

Finally, using the above-mentioned 2212 phase synthesized via the mesophase as a raw material, CaCO ₃ , SrCO ₃ , CuO and PbO were added to make the atomic ratio of the batch material Bi:Pb:(Sr+Ca):Cu=(1.75～1.90):(0.25 ~0.40):(3.90~4.00):3 (wherein 0.68≤Sr/Ca≤1.16), add 0~5wt% of 2223 phase after mixing and ball milling, press into tablets at 800~865℃, after firing for 20~30h , Grinding and re-burning for 10-100 hours, the 2223 superconducting material with high single-phase property without 2201 phase coexistence can be obtained.

Compared with the direct synthesis method currently used, the present invention has the following advantages:

1. Effectively increase the formation speed of 2223 superconducting phase, and greatly shorten the firing time from 200h to about 50h (when Sr/Ca≈1:1).

2. Broaden the temperature range for the formation of 2223 phase, which is convenient to control the appropriate amount of liquid phase, prevent and eliminate a small amount of 2201 or 2212 phase residue, and improve the single-phase property and quality of the compound.

3. The superconductivity can be controlled and improved by adjusting and controlling the Sr-Ca solid solution characteristics of the mesophase.

4. On this basis, it is expected to provide a carefully controlled introduction of Sr-Ca solid solution defects or elutes as flux pinning centers to increase its critical current density.

Describe below in conjunction with embodiment.

First, use Bi ₂ O ₃ , SrCO ₃ , and CaCO ₃ as raw materials, and prepare batches according to the atomic ratio of Bi:Sr:Ca=2:x:(2-x) (x=0.8~1.20), mix and ball mill 2-3 hours, press into tablets, and burn at 790-830°C for 8-12 hours to obtain the mesophase Bi-Sr-Ca-O solid solution, whose composition is: Bi ₂ Sr _x , Ca _2-x O ₅ , where x=0.8～1.20;

Then, using the above synthesized mesophase as raw material, add SrCO ₃ , CaCO ₃ and CuO so that the atomic ratio of the batch composition is Bi:(Sr+Ca):Cu=2:3:2 (wherein 1.50≤Sr/Ca≤ 2.75) After the batch materials are mixed and ball milled, they are pressed into tablets and fired at 790-830°C for 8-12 hours to obtain the 2212 superconducting phase;

Finally, using the above-mentioned 2212 phase synthesized via the mesophase as a raw material, CaCO ₃ , SrCO ₃ , CuO and PbO are added to make the atomic ratio of the batch material Bi:Pb:(Sr+Ca):Cu=(1.75～1.90):(0.30 ~0.40):(3.90~4.00):3 (wherein 0.75≤Sr/Ca≤1.10), add 0~5wt% of 2223 phase after mixed ball milling, press into tablets at 800~850℃, after firing for 20~30h , Grinding and re-burning for 20-50 hours, the 2223 superconducting material with high single-phase property without 2201 phase coexistence can be obtained.

Example:

Using analytically pure Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ , CuO and PbO as raw materials, the atomic ratio is Bi:Sr:Ca=2:1:1 to make batches, and after mixing and dry grinding in a ball mill for 3 hours, Press into tablets at 250-300MPa, and then sinter at 785±5°C for 1h and 825±5°C for 10h in sequence to form a mesophase composed of Bi ₂ SrCaO ₅ .

For every 100 grams of the above mesophase, add 23.59 grams of SrCO ₃ and 25.42 grams of CuO, mix and ball mill for 2.5 hours, then press into tablets, and burn at 785±5°C and 825-830°C for 1 and 10 hours, respectively, to obtain Bi ₂ Sr ₂ Ca ₁ Cu ₂ O _{3+ δ} phase. Using this as a raw material, 1.83 grams of SrCO ₃ , 13.74 grams of CaCO ₃ , 11.91 grams of CuO and 9.55 grams of PbO were added to every 100 grams, and 3-5 wt% of 2223 phase was added as crystal nuclei. The batch materials are mixed, ball milled for 2 to 3 hours, pressed at 300MPa, fired at 800±5°C and 855°C for 2 hours and 30 hours respectively, ground and refired for 20 hours, and the single-phase Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10+δ Mutually.

Table 1 Unit cell parameters of mesophase (Bi ₂ Sr _x Ca _2-x O ₅ ) Mesophase composition a(nm) b(nm) c(nm) β(deg) Unit cell volume

v(nm ³ )Bi ₂ Ca ₂ O ₅ 1.8363 0.5366 1.4670 100.26 1.42241Bi ₂ Sr _0.5 Ca _1.5 O ₅ 1.8563 0.5356 1.4820 99.95 1.45129Bi ₂ Sr _0.66 Ca _1.34 O ₅ 1.8588 0.5345 1.4869 99.96 1.45501Bi ₂ SrCaO ₅ 1.8661 0.5341 1.4952 100.03 1.46747Bi ₂ Sr _1.34 Ca _0.66 O ₅ 1.8676 0.5330 1.4983 100.04 1.46861Bi ₂ Sr _1.5 Ca _0.5 O ₅ 1.8761 0.5331 1.5014 100.08 1.47845

Claims (2)

1. single phase property Bi ₂Sr ₂Ca ₂Cu ₃O _{10+ δ}The stepwise synthesis method of high-temperature superconductor phase is characterized in that:

At first, with Bi ₂O ₃, SrCO ₃, CaCO ₃Being raw material, is Bi: Sr: Ca=2: x by atomic ratio: (2-x) (x=0～1.50) preparation admixtion, and through mixing, ball milling 2～3h, compression molding burns till 5～15h in 780～850 ℃, and promptly getting intermediate phase Bi-Sr-Ca-O is sosoloid, and it consists of: Bi ₂Sr _xCa _2-xO ₅, x=0～1.50 wherein;

Then, be raw material with above-mentioned synthetic intermediate phase, add SrCO ₃, CaCO ₃The atomic ratio that admixtion is formed with CuO is Bi: (Sr+Ca): Cu=2: 3: 2 (wherein 1/2≤Sr/Ca≤5) admixtiones are after mixing and ball milling, and compression molding burns till 10～15h in 780～840 ℃ and promptly gets 2212 superconducting phases;

At last, with above-mentioned be raw material mutually via intermediate phase synthetic 2212, add CaCO ₃, SrCO ₃, to make the admixtion atomic ratio be Bi: Pb: (Sr+Ca): Cu=(1.75～1.90) for CuO and PbO: (0.25～0.40): (3.90～4.00): 3 (wherein 0.68≤Sr/Ca≤1.16), add 0～5wt% 2223 after mixing and ball milling, compression molding is in 800～850 ℃, after burning till 20～30h, grind and heavily burn 10～100h, promptly get 2223 superconducting materials that do not have the 2201 high single phase property that coexist mutually.

2. a kind of single phase property Bi according to claim 1 ₂Sr ₂Ca ₂Cu ₃O _{10+ δ}The stepwise synthesis method of high-temperature superconductor phase is characterized in that:

At first, with Bi ₂O ₃, SrCO ₃, CaCO ₃Being raw material, is Bi: Sr: Ca=2: x by atomic ratio: (2-x) (x=0.8～1.20) preparation admixtion, and through mixing, ball milling 2～3h, compression molding burns till 8～12h in 790～830 ℃, and promptly getting intermediate phase Bi-Sr-Ca-O is sosoloid, and it consists of: Bi ₂Sr _xCa _2-xO ₅, x=0.8～1.20 wherein;

Then, be raw material with above-mentioned synthetic intermediate phase, add SrCO ₃, CaCO ₃The atomic ratio that admixtion is formed with CuO is Bi: (Sr+Ca): Cu=2: 3: 2 (wherein 1.50≤Sr/Ca≤2.75), admixtion are after mixing and ball milling, and compression molding burns till 8～12h in 790～830 ℃ and promptly gets 2212 superconducting phases;

At last, with above-mentioned be raw material mutually via intermediate phase synthetic 2212, add CaCO ₃, SrCO ₃, to make the admixtion atomic ratio be Bi: Pb: (Sr+Ca): Cu=(1.80～1.90) for CuO and PbO: (0.30～0.40): (3.90～4.00): 3 (wherein 0.75≤Sr/Ca≤1.10), add 0～5wt% 2223 after mixing and ball milling, compression molding is in 800～850 ℃, after burning till 20～30h, grind and heavily burn 20～50h, promptly get 2223 superconducting materials that do not have the 2201 high single phase property that coexist mutually.