A rapid method for characterizing different phase structures of SrCoO 3-δ System oxygen stoichiometric ratio method

Abstract

The present invention discloses a method for quickly characterizing different phase structures of SrCoO 3‑δ The method of oxygen stoichiometric ratio in the system belongs to the field of analytical testing technology. The charge conservation and titration reaction relationship are used to calculate the different phase structures of SrCoO 3‑δ The non-stoichiometric ratio relationship of oxygen in the system sample; Based on the relationship between phase structure and oxygen content, the high and low oxygen content and the color change and titration range of different phase structures are preliminarily analyzed; SrCoO with different phase structures is added 3‑δ The system sample was ground and weighed, and a mixture of hydrochloric acid with an appropriate pH value and excess KI was prepared to dissolve the sample. KI was used to reduce all Co ions, and then Na2S2O3 was used to quickly titrate the generated I2 according to the estimated range. The different phase structures of SrCoO were calculated based on the consumed Na2S2O3. 3‑δ The non-stoichiometric oxygen content of the system. This method facilitates the complete reaction of the sample and accelerates the initial titration rate, preventing I2 volatilization and improving the accuracy of the results. This has guiding significance for the characterization of the oxygen stoichiometric ratio of transition metal oxides with different phase structures.

Description

Technical Field

[0001] The present invention relates to a method for rapidly characterizing different phase structures of SrCoO 3-δ The invention discloses a method for the stoichiometric ratio of system oxygen, and belongs to the technical field of analysis and testing. Background Art

[0002] Iodine titration is a type of redox titration. Redox titration uses an oxidizing agent (reducing agent) as a titrant to react with a reducing substance (oxidizing substance) in a solution, gaining electrons (losing electrons) to generate a reduction product (oxidation product). It is a titration analysis method widely used in organic or inorganic analysis. Iodine titration utilizes the oxidizing properties of elemental iodine (I2) and the iodide ion (I - ) is titrated based on its reducing properties, with the formation or disappearance of I2 being the endpoint of the reaction. Because I2 turns yellow when it comes into contact with water, and a very small amount of I2 turns blue when it comes into contact with starch, this provides a basis for the titration endpoint.

[0003] Currently, people are interested in SrCoO 3-δ The research of the system mainly focuses on the electromagnetic properties, especially the room temperature ferromagnetism and physical mechanism. Zhang et al. found that the oxygen stoichiometry of SrCoO 3-δ The magnetic properties of the system are greatly affected. The reason is that the oxygen stoichiometric ratio will change the Co 3+ content, resulting in a change in the spin state, which in turn causes T c Fukushima et al. believed that the A-site order leads to the oxygen vacancy order, and the magnetization is closely related to the oxygen vacancy order. They attributed the room-temperature ferromagnetism to the special superstructure formed by the excess oxygen vacancies order.

[0004] The analysis found that the oxygen stoichiometric ratio and oxygen vacancy order have an impact on the SrCoO 3-δ The physical properties of the system are affected by different phase structures of SrCoO 3-δ There are also few literatures on the oxygen content of the system. 3-δ The system samples also have different oxygen stoichiometric ratios, especially the ultra-low oxygen content of the hexagonal phase has not been characterized. The present invention gives different phase structures of SrCoO 3-δ To characterize the oxygen stoichiometric ratio of the system, a mixed solution of appropriate hydrochloric acid and excess KI is used to allow the sample to react completely, and the titration range is estimated in advance to speed up the early titration speed, effectively prevent the volatilization of I2, and improve the accuracy of the oxygen content results. Summary of the Invention

[0005] The present invention provides a method for rapidly measuring different phase structures of SrCoO 3-δThe iodine titration method for determining the oxygen content of the system uses a mixed solution of appropriate hydrochloric acid and excess KI to allow the sample to react completely, estimate the titration range in advance, speed up the initial titration, effectively prevent the volatilization of I2, and improve the accuracy of the titration results. The specific steps include:

[0006] (1) Assuming different phase structures of SrCoO 3-δ The average valence of Co ions in the system sample is 3+p, and the oxygen stoichiometric ratio is calculated using the charge conservation and titration reaction relationship:

[0007]

[0008] Where m is the sample mass, C is the concentration of Na2S2O3 solution, the volume of Na2S2O3 consumed in titration is V, and M is the molar mass of the sample, M=M0±δM oxygen , M0 is the molar mass of the SrCoO3 system sample without δ, M oxygen is the molar mass of the O atom.

[0009] (2) Obtain the range of values for δ through the structural formula, and substitute the value of δ into formula (1) to calculate the volume range of Na2S2O3 consumed in the titration; the prejudgment of this step can improve the titration efficiency and accuracy. It is also possible to analyze the oxygen atom sites in the crystal structure, such as the low oxygen content in the hexagonal phase (CoO6 octahedrons are coplanarly stacked, and there are few oxygen sites in the crystal), the high oxygen content in the cubic phase (CoO6 octahedrons are three-dimensionally symmetrically distributed, and there are many oxygen sites in the crystal), and the low oxygen content in the tetragonal phase (CoO4 tetrahedral layers appear, and there are fewer oxygen sites in the crystal). The oxygen content is determined by color change; the higher the oxygen content, the more intense the yellow color of the solution.

[0010] (3) Grind and weigh the sample from step (2), and dissolve the powdered sample in a mixture of hydrochloric acid and excess KI, and introduce high-purity nitrogen gas.

[0011] (4) titrating the solution obtained in step (3) with Na2S2O3, performing a rapid titration before the titration range obtained in step (2), and performing an accurate titration within the range.

[0012] (5) Titrate the solution from step (4) until it turns pale yellow. Add starch indicator and continue titrating until the blue color just disappears.

[0013] (6) Calculate the volume of SrCoO in different phase structures by the volume of Na2S2O3 consumed in steps (4) and (5). 3-δ Non-stoichiometric oxygen content of system samples.

[0014] Preferably, the SrCoO in step (1) of the present invention 3-δThe charge conservation relationship of the system is that the charge number of the cation is equal to the charge number of the anion;

[0015] Iodine titration reaction equation:

[0016] Co (3+p)+ +(I+p)I - =Co 2+ +0.5(1+p)I2

[0017] I2+2Na2S2O3=2NaI+Na254O6

[0018] Preferably, in step (2) of the present invention, the titration amount corresponding to 30 mg of sample is 2 to 5 mL.

[0019] Preferably, the pH value of the mixed solution in step (3) of the present invention is 2-5, and the amount of KI used is 2 to 3 times the stoichiometric amount.

[0020] Preferably, the mass fraction of the starch indicator in step (5) of the present invention is 1%, and the amount added is 1 mL per 100 mL of titrant.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention provides SrCoO with different phase structures 3-δ The titration method of oxygen content in the system is helpful to analyze the relationship between the structure and oxygen vacancies of hexagonal, cubic perovskite and tetragonal phases.

[0023] (2) The iodine titration method of the present invention has the advantage of using a mixed solution of appropriate hydrochloric acid and excess KI, which enables the sample to react completely and improves the accuracy of the titration result.

[0024] (3) The present invention is to study the non-stoichiometric ratio of SrCoO in different phase structures. 3-δ The system estimates the titration range in advance, speeds up the early titration, effectively prevents the volatilization of I2, and improves the accuracy of the titration results. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 SrCoO with hexagonal structure 3-δ Crystal structure diagram.

[0026] Figure 2 Sr with cubic phase structure 1-x Y x CoO 3-δ (x=0.1) Crystal structure diagram.

[0027] Figure 3 Sr with tetragonal structure 1-x Y x CoO 3-δ(x=0.25) Crystal structure diagram. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0029] Example 1

[0030] A method for measuring the hexagonal structure of SrCoO 3-δ The iodine titration method for the oxygen content of the sample specifically includes the following steps:

[0031] (1) Assuming a hexagonal SrCoO 3-δ The average valence of Co ions in the sample is 3+p, and the non-stoichiometric oxygen content relationship is calculated using the charge conservation and titration reaction relationship:

[0032] The charge conservation equation states that the charge of the cation is equal to the charge of the anion:

[0033]

[0034] Iodine titration reaction equation:

[0035] Co (3+p)+ +(1+p)I - =Co 2+ +0.5(1+p)I2

[0036] I2+2Na2S2O3=2NaI+Na2S4O6

[0037]

[0038] Oxygen stoichiometric ratio relationship:

[0039]

[0040] Where M is the molar mass of the sample, m is the mass of the sample, C is the concentration of the Na2S2O3 solution, and the volume consumed in the titration is V (M = M0-δM oxygen , M0 is the molar mass of SrCoO3 sample 194.55, M oxygen is the molar mass of the O atom16).

[0041] (2) Using the hexagonal phase structure in step (1) Figure 1 As shown in the figure, CoO6 octahedrons are stacked on the same plane, with few oxygen lattice sites and low oxygen content. According to the oxygen stoichiometric ratio, 30 mg of SrCoO 3-δ The range of Na2S2O3 consumed by the sample (0<δ<0.5) is around 4mL.

[0042] (3) Grind and weigh the sample from step (2), and dissolve 30 mg of the powdered sample in a mixture of 100 ml of hydrochloric acid (pH = 2-5) and excess KI. Pass high-purity nitrogen gas through the mixture. After the sample is dissolved, the solution turns light yellow.

[0043] (4) The solution obtained in step (3) is rapidly titrated using Na2S2O3 to a titration range slightly less than 1 mL obtained in step (2).

[0044] (5) Titrate the solution from step (4) until it turns light yellow. Add 1 mL of 1% starch indicator and continue titrating until the blue color just disappears.

[0045] (6) Calculate the hexagonal structure of SrCoO by the volume of Na2S2O3 consumed in steps (4) and (5). 3-δ The non-stoichiometric oxygen content of a sample.

[0046] Table 1 shows the hexagonal SrCoO 3-δ The titration results of the oxygen content of the sample were repeated 3 times, and the volumes of Na2S2O3 consumed were 4.02, 4.05, and 4.07 mL, respectively. The corresponding average oxygen stoichiometric ratio was SrCoO 2.625 , lower oxygen content and Figure 1 Corresponding to the hexagonal crystal structure.

[0047] Table 1 Hexagonal SrCoO 3-δ Titration results of sample oxygen content

[0048]

[0049] Example 2

[0050] A method for measuring cubic Sr 1-x Y x CoO 3-δ (x=0.1) The iodine titration method for oxygen content specifically comprises the following steps:

[0051] (1) Assuming a cubic phase structure of Sr 1-x Y x CoO 3-δ The average valence of Co ions in the sample is 3+p, and the non-stoichiometric oxygen content relationship is calculated using the charge conservation and titration reaction relationship:

[0052] The charge conservation equation states that the charge of the cation is equal to the charge of the anion:

[0053]

[0054] Iodine titration reaction equation:

[0055] Co (3+p)++(1+p)I - =Co 2+ +0.5(1+p)I2

[0056] I2+2Na2S2O3=2NaI+Na2S4O6

[0057]

[0058] Oxygen stoichiometric ratio relationship:

[0059]

[0060] Where M is the molar mass of the sample, m is the mass of the sample, C is the concentration of the Na2S2O3 solution, and the volume consumed in the titration is V (M = M0-δM oxygen ,M0 is Sr 0.9 Y 0.1 The molar mass of the CoO3 sample is 194.68, M oxygen is the molar mass of the O atom16).

[0061] (2) Using the cubic phase structure in step (1) Figure 2 As shown in the figure, CoO6 octahedron three-dimensional top-to-bottom stacking has many oxygen lattice sites and a high oxygen content. According to the oxygen stoichiometric ratio, 30 mg of Sr 0.9 Y 0.1 CoO 3-δ The range of Na2S2O3 consumed by the sample (0<δ<0.5) is higher than 4mL.

[0062] (3) Grind and weigh the sample from step (2), and dissolve 30 mg of the powdered sample in a mixture of 100 ml of hydrochloric acid (pH = 2-5) and excess KI. Pass high-purity nitrogen gas through the mixture. After the sample is dissolved, the solution becomes a thick yellow color.

[0063] (4) The solution obtained in step (3) is rapidly titrated using Na2S2O3 to a titration range slightly less than 1 mL obtained in step (2).

[0064] (5) Titrate the solution from step (4) until it turns light yellow. Add 1 mL of 1% starch indicator and continue titrating until the blue color just disappears.

[0065] (6) Calculate the volume of the cubic phase structure Sr by the volume of Na2S2O3 consumed in steps (4) and (5). 1-x Y x CoO 3-δ The non-stoichiometric oxygen content of a sample.

[0066] Table 2 shows the cubic phase Sr 1-x Y x CoO 3-δThe titration results of the oxygen content of the sample were repeated 3 times, and the volumes of Na2S2O3 consumed were 4.17, 4.12, and 4.2 mL, respectively. The corresponding average oxygen stoichiometric ratio was Sr 0.9 Y 0.1 CoO 2.7 , higher oxygen content and Figure 2 The cubic phase crystal structure corresponds to

[0067] Table 2 Cubic phase Sr 1-x Y x CoO 3-δ Titration results of sample oxygen content

[0068]

[0069] Example 3

[0070] A method for measuring tetragonal Sr 1-x Y x CoO 3-δ (x=0.25) The iodine titration method for oxygen content specifically comprises the following steps:

[0071] (1) Assuming a tetragonal Sr 1-x Y x CoO 3-δ The average valence of Co ions in the sample is 3+p, and the non-stoichiometric oxygen content relationship is calculated using the charge conservation and titration reaction relationship:

[0072] The charge conservation equation states that the charge of the cation is equal to the charge of the anion:

[0073]

[0074] Iodine titration reaction equation:

[0075] Co (3+p)+ +(I+p)I - =Co 2+ +0.5(1+p)I2

[0076] I2+2Na2S2O3=2NaI+Na2S4O6

[0077]

[0078] Oxygen stoichiometric ratio relationship:

[0079]

[0080] Where M is the molar mass of the sample, m is the mass of the sample, C is the concentration of the Na2S2O3 solution, and the volume consumed in the titration is V (M = M0-δM oxygen ,M0 is Sr0.75 Y 0.25 The molar mass of the CoO3 sample is 194.87, M oxygen is the molar mass of the O atom16).

[0081] (2) Using the tetragonal phase structure in step (1) Figure 3 As shown in the figure, CoO6 octahedron and CoO4 tetrahedron are stacked alternately, there are fewer oxygen lattice sites and the oxygen content is low; according to the oxygen stoichiometric ratio relationship, 30mg of Sr 0.75 Y 0.25 CoO 3-δ The range of Na2S2O3 consumed by the sample (0<δ<0.5) is about 3.5mL.

[0082] (3) Grind and weigh the sample from step (2), and dissolve 30 mg of the powdered sample in a mixture of 100 ml of hydrochloric acid (pH = 2-5) and excess KI. Pass high-purity nitrogen gas through the mixture. After the sample is dissolved, the solution turns yellow.

[0083] (4) The solution obtained in step (3) is rapidly titrated using Na2S2O3 to a titration range slightly less than 1 mL obtained in step (2).

[0084] (5) Titrate the solution from step (4) until it turns light yellow. Add 1 mL of 1% starch indicator and continue titrating until the blue color just disappears.

[0085] (6) Calculate the volume of tetragonal Sr by the volume of Na2S2O3 consumed in steps (4) and (5). 1-x Y x CoO 3-δ The non-stoichiometric oxygen content of a sample.

[0086] Table 3 shows the tetragonal Sr 1-x Y x CoO 3-δ The titration results of the oxygen content of the sample were repeated 3 times, and the volumes of Na2S2O3 consumed were 3.48, 3.4, and 3.46 mL, respectively. The corresponding average oxygen stoichiometric ratio was Sr 0.75 Y 0.25 CoO 2.642 , higher oxygen content and Figure 3 The tetragonal crystal structure corresponds to

[0087] Table 3 Tetragonal Sr 1-x Y x CoO 3-δ Titration results of sample oxygen content

[0088]

Claims

1. A method for rapid characterization of different phase structures of SrCoO 3-δ The method for the stoichiometric ratio of oxygen in a system is characterized in that The specific steps include: (1) Assuming different phase structures of SrCoO 3-δ The average valence of Co ions in the system sample is 3+p, and the oxygen stoichiometric ratio is calculated using the charge conservation and titration reaction relationship: Where m is the mass of the sample, C is the concentration of the Na2S2O3 solution, the volume of Na2S2O3 consumed in the titration is V, and M is the molar mass of the sample M = M0 ± δM oxygen , M0 is the molar mass of the SrCoO3 system sample without δ, M oxygen is the molar mass of the O atom; (2) Obtain the value range of δ through the structural formula, and substitute the value of δ into formula (1) to calculate the volume range of Na2S2O3 consumed by titration; (3) Grinding and weighing the sample from step (2), dissolving the powdered sample in a mixture of hydrochloric acid and excess KI, and introducing high-purity nitrogen; (4) titrating the solution obtained in step (3) with Na2S2O3, performing a rapid titration before the titration range is less than that obtained in step (2), and performing an accurate titration within the range; (5) Titrate the solution from step (4) until it turns pale yellow. Add starch indicator and continue titrating until the blue color just disappears. (6) Calculate the volume of SrCoO in different phase structures by the volume of Na2S2O3 consumed in steps (4) and (5). 3-δ Non-stoichiometric oxygen content of system samples.

2. Rapid characterization of different phase structures of SrCoO according to claim 1 3-δ The method for the stoichiometric ratio of oxygen in a system is characterized by: SrCoO in step (1) 3-δ The charge conservation relationship of the system is that the charge number of the cation is equal to the charge number of the anion; Iodine titration reaction equation: Co (3+p) +(1+p)I - =Co 2 ++0.5(1+p)I2 <h2 style=";text-align:left;direction:ltr">I2+2Na2S2O3 = 2NaI+Na2S4O<h2 style=";text-align:left;direction:ltr"> 6。 3. Rapid characterization of different phase structures of SrCoO according to claim 1 3-δ The method for the oxygen stoichiometric ratio of the system is characterized by: In step (2), the titration amount corresponding to 30 mg of sample is 2 to 5 mL.

4. Rapid characterization of different phase structures of SrCoO according to claim 1 3-δ The method for the stoichiometric ratio of oxygen in a system is characterized by: In step (5), the mass fraction of the starch indicator is 1%, and the amount added is 1 mL per 100 mL of titrant.

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