Method for preparing phase-separated lead telluride-lead sulfide nanopowder using solution synthesis and phase-separated lead telluride-lead sulfide nanopowder prepared thereby

Abstract

The present invention relates to a method for preparing a phase-separated lead telluride-lead sulfide nanopowder using solution synthesis and a phase-separated lead telluride-lead sulfide nanopowder prepared by the method. The method includes: (a) mixing tellurium and a first solvent, followed by ultrasonic irradiation to prepare a tellurium precursor solution; (b) mixing an organosulfur compound and a second solvent, followed by ultrasonic irradiation to prepare a sulfur precursor solution; (c) mixing lead oxide, a third solvent, and a fourth solvent and heating the mixture to prepare a lead precursor solution; (d) adding the tellurium precursor solution to the lead precursor solution and allowing the mixture to react; (e) adding the sulfur precursor solution to the reaction mixture of step (d) and allowing the resulting mixture to react; and (f) cooling the reaction mixture of step (e) to room temperature to prepare a phase-separated lead telluride-lead sulfide nanopowder.

Claims

1. A method for preparing a phase-separated lead telluride-lead sulfide nanopowder using solution synthesis, comprising: (a) mixing tellurium (Te) and a first solvent, and exposing the mixture of the tellurium (Te) and the first solvent to ultrasonic irradiation to prepare a tellurium precursor solution; (b) mixing an organosulfur (S) compound and a second solvent, and exposing the mixture of the organosulfur (S) compound and the second solvent to ultrasonic irradiation to prepare a sulfur precursor solution; (c) mixing lead oxide (PbO), a third solvent, and a fourth solvent and heating the mixture of the lead oxide (PbO), the third solvent, and the fourth solvent to prepare a lead precursor solution; (d) adding the tellurium precursor solution prepared in step (a) to the lead precursor solution prepared in step (c) to form a first reaction mixture and allowing the first reaction mixture to react; (e) adding the sulfur precursor solution prepared in step (b) to the first reaction mixture of step (d) to form a second reaction mixture and allowing the second reaction mixture to react; and (f) cooling the second reaction mixture of step (e) to room temperature to provide a phase-separated lead telluride-lead sulfide nanopowder.

2. The method according to claim 1, wherein the first solvent used in step (a) is selected from the group consisting of trioctylphosphine (TOP), tridiethylaminophosphine (TDP), tributylphophine (TBP), and mixtures thereof.

3. The method according to claim 1, wherein the organosulfur compound used in step (b) is selected from the group consisting of bis(trimethylsilyl)sulfide, dimethyl sulfide, and a mixture thereof.

4. The method according to claim 1, wherein the second solvent used in step (b) is selected from the group consisting of 1-octadecene, trioctylphosphine (TOP), oleylamine, and mixtures thereof.

5. The method according to claim 1, wherein the third solvent used in step (c) is selected from the group consisting of 1-octadecene, trioctylphosphine (TOP), oleylamine, and mixtures thereof.

6. The method according to claim 1, wherein the fourth solvent is selected from the group consisting of oleic acid, octanoic acid, stearic acid, and mixtures thereof.

7. The method according to claim 1, wherein, in step (c), the mixture is heated to 120 to 180 C.

8. The method according to claim 1, wherein the reaction time in step (d) is from 3 to 7 minute.

9. The method according to claim 1, wherein the reaction time in step (e) is from 1 to 5 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an X-ray diffraction pattern showing the phases of a phase-separated lead telluride-lead sulfide nanopowder prepared in Example 1.

(2) FIG. 2a shows HRTEM images of a phase-separated lead telluride-lead sulfide nanopowder prepared in Example 1.

(3) FIG. 2b shows HRTEM images of a phase-separated lead telluride-lead sulfide nanopowder prepared in Example 1.

(4) FIG. 2c shows that the planes did not coincide with each other with respect to the spinodal lines that were disconnected, as revealed by different contrasts.

(5) FIG. 2d shows that the phase-separated lead telluride-lead sulfide nanopowder was found to consist of lead telluride and lead sulfide that grew in the same plane direction, which was confirmed by FFT analysis.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention will now be described in more detail.

(7) The present invention is directed to a method for preparing a phase-separated lead telluride-lead sulfide nanopowder through chemical synthesis by a hot-injection method into precursors in the form of solutions. Specifically, the method of the present invention includes: (a) mixing tellurium (Te) and a first solvent, followed by ultrasonic irradiation to prepare a tellurium precursor solution; (b) mixing an organosulfur (S) compound and a second solvent, followed by ultrasonic irradiation to prepare a sulfur precursor solution; (c) mixing lead oxide (PbO), a third solvent, and a fourth solvent and heating the mixture to prepare a lead precursor solution; (d) adding the tellurium precursor solution prepared in step (a) to the lead precursor solution prepared in step (c) and allowing the mixture to react; (e) adding the sulfur precursor solution prepared in step (b) to the reaction mixture of step (d) and allowing the resulting mixture to react; and (f) cooling the reaction mixture of step (e) to room temperature to prepare a phase-separated lead telluride-lead sulfide nanopowder.

(8) The first solvent used in step (a) may be selected from the group consisting of trioctylphosphine (TOP), tridiethylaminophosphine (TDP), tributylphophine (TBP), and mixtures thereof.

(9) The organosulfur compound used in step (b) may be selected from the group consisting of bis(trimethylsilyl)sulfide, dimethyl sulfide, and a mixture thereof.

(10) The second solvent used to prepare the sulfur precursor solution in step (b) may be selected from the group consisting of 1-octadecene, trioctylphosphine (TOP), oleylamine, and mixtures thereof.

(11) The third solvent used in step (c) may be selected from the group consisting of 1-octadecene, trioctylphosphine (TOP), oleylamine, and mixtures thereof. The fourth solvent may be selected from the group consisting of oleic acid, octanoic acid, stearic acid, and mixtures thereof.

(12) In step (c), the mixture of the lead oxide (PbO), the third solvent, and the fourth solvent is heated to a predetermined temperature, preferably 120 to 180 C. Outside the range defined above, particularly if the temperature is lower than 120 C., oxygen and water may remain unremoved in the reaction flask when the tellurium precursor solution prepared in step (a) is added and may form impurities during the subsequent reaction for the preparation of the final nanopowder. Further, the lead oxide may not be completely dissolved in the third and fourth solvents. Moreover, the dissolved lead oxide may not react with the tellurium precursor solution. Meanwhile, if the temperature exceeds 180 C., the dissolved lead oxide may be thermally decomposed, resulting in reprecipitation, and as a result, it may fail to react with the tellurium precursor solution.

(13) The reaction times in steps (d) and (e), that is, the reaction time between the dissolved lead oxide and the tellurium precursor solution in step (d) and the reaction time between the reaction mixture of step (d) and the sulfur precursor solution in step (e), are very important factors in the method of the present invention. Preferably, the reaction time between the dissolved lead oxide and the tellurium precursor solution in step (d) is in the range of 3 to 7 minute and the reaction time between the reaction mixture of step (d) and the sulfur precursor solution in step (e) is in the range of 1 to 5 minutes.

(14) Outside these ranges, particularly if the reaction time in step (d) is less than 3 minutes, the sulfur precursor solution is introduced in a state in which a tellurium lead nanopowder is not sufficiently grown, resulting in the formation of a lead sulfide nanopowder. Meanwhile, if the reaction time in step (d) exceeds 7 minutes, a tellurium lead nanopowder and a lead sulfide nanopowder are formed separately. If the reaction time in step (e) is less than 1 minute, a core/shell nanopowder rather than the desired phase-separated nanopowder is synthesized. Meanwhile, if the reaction time in step (e) exceeds 5 minutes, it is unnecessary to continue the reaction because the shape and phase of the nanopowder prepared after completion of the reaction are maintained unchanged.

(15) The present invention also provides a lead telluride-lead sulfide nanopowder prepared by the method wherein the lead telluride and the lead sulfide are spinodally phase-separated.

(16) The lead telluride-lead sulfide nanopowder of the present invention has a size of 100 nm or less and has a structure in which the lead telluride and the lead sulfide are spinodally phase-separated. A super-lattice can be formed from the lead telluride-lead sulfide nanopowder by a simple process through nanoscale microstructure control. Lead telluride and lead sulfide cannot exist in the form of an alloy in a single nanopowder. In contrast, lead telluride and lead sulfide coexist in the nanopowder of the present invention. This coexistence facilitates the fabrication of a device through sintering of the lead telluride-lead sulfide nanopowder of the present invention. The two nano-sized materials have different bandgaps, facilitating control over the electrical properties of the nanopowder.

EXAMPLES

(17) The present invention will be explained in more detail with reference to the following examples, including test examples. These examples are merely illustrative and the present invention is not limited thereto.

Example 1

Preparation of Phase-separated Lead Telluride-lead Sulfide Nanopowder

(18) Step 1: Preparation of TOP-Te Mixture

(19) 5.104 g of tellurium was completely dissolved in 40 ml of trioctylphosphine (TOP) by sonication to prepare a trioctylphosphine-Te mixture (hereinafter referred to simply as TOP-Te).

(20) Step 2: Preparation of bis(trimethylsilyl)sulfide Solution

(21) 2 ml of bis(trimethylsilyl)sulfide was completely dissolved in 8 ml of 1-octadecene by sonication to prepare a bis(trimethylsilyl)sulfide solution.

(22) Step 3: Preparation of Tellurium Lead-lead Sulfide Nanopowder

(23) 0.23 g of lead oxide, 10 ml of 1-octadecene, and 2 ml of oleic acid were stirred in a 100 ml flask. After the temperature was maintained at 150 C., stirring was continued until the solution became homogeneous. 0.6 ml of the TOP-Te solution prepared in step 1 was rapidly introduced into the flask. The reaction was allowed to proceed for 5 min. Subsequently, 2 ml of the bis(trimethylsilyl)sulfide solution prepared in step 2 was rapidly introduced into the flask. The reaction was allowed to proceed for 3 min. The reaction solution was rapidly cooled to room temperature and washed several times with acetone and toluene to afford a phase-separated lead telluride-lead sulfide nanopowder.

Experimental Example 1

Phase Analysis of the Phase-separated Lead Telluride-lead Sulfide Nanopowder

(24) The phases of the phase-separated lead telluride-lead sulfide nanopowder were determined by X-ray diffraction analysis. The types and compositions of the phases were identified by X-ray diffraction (XRD) using an X-ray diffraction analyzer (Rigaku D/MAX-2500/PC, Tokyo, Japan). The results are shown in FIG. 1.

(25) Results

(26) As shown in FIG. 1, the phase-separated lead telluride-lead sulfide nanopowder was found to consist of pure lead telluride and pure lead sulfide without any secondary phase.

Experimental Example 2

TEM Analysis of the Phase-separated Lead Telluride-lead Sulfide Nanopowder

(27) FIGS. 2a to 2c show HRTEM images of the phase-separated lead telluride-lead sulfide nanopowder, which were recorded using a transmission electron microscope (FEI Tecnai G2 F30) operated at 300 kV.

(28) Results

(29) As shown in FIGS. 2a and 2b, the phase-separated lead telluride-lead sulfide nanopowder had a non-uniform shape and a size of 20-100 nm. Different contrasts were observed on the surface of the phase-separated powder, unlike in general single-crystal nanopowders. Domains distinguished by different contrasts were found to arise from the spinodal phenomenon.

(30) As shown in FIG. 2c, the planes did not coincide with each other with respect to the spinodal lines that were disconnected, as revealed by different contrasts. As shown in FIG. 2d, the phase-separated lead telluride-lead sulfide nanopowder was found to consist of lead telluride and lead sulfide that grew in the same plane direction, which was confirmed by FFT analysis.

(31) As shown in FIGS. 2c and 2d, the phase-separated lead telluride-lead sulfide nanopowder consisted of lead telluride and lead sulfide that were aligned in the same plane. However, black lines were formed due to the different transmittances of the two materials and lattices were broken and bent due to the different lattice constants of the two materials, which were attributed to the occurrence of spinodal phase separation in the nanopowder.