CN103247752B - Ge-Pb-Te-Se composite thermoelectric material and preparation method thereof - Google Patents

Abstract

The invention provides a Ge-Pb-Te-Se composite thermoelectric material and a preparation method thereof, which are suitable for the technical field of novel energy materials. The chemical formula of the thermoelectric material is Ge1-xPbxTe1-ySey, wherein x represents the quantity that Pb replaces Ge, the value of x is larger than or equal to 0.10 and is smaller than or equal to 0.90, y represents the quantity that Se replaces Te, and the value of y is larger than or equal to 0.10 and is smaller than or equal to 0.70. The composite thermoelectric material provided by the invention has lower thermal conductivity, higher non-dimensional figure of merit and good thermoelectric property, and the non-dimensional figure of merit ZT reaches 1.58 at the temperature of 40 DEG C. The invention further provides the preparation method of the composite thermoelectric material.

Description

Ge-Pb-Te-Se composite thermoelectric material and its preparation method

technical field

The invention relates to the technical field of new energy materials, in particular to a medium-temperature composite thermoelectric material and a preparation method thereof.

Background technique

Thermoelectric material is a special functional material, which can realize temperature control, temperature difference power generation and energized refrigeration by using the thermoelectric effect that produces a temperature gradient when a current passes through it, and generates an electromotive force or current when there is a temperature difference between the two ends. These refrigeration and power generation systems have the advantages of small size, light weight, no mechanical rotating parts, no noise during operation, no environmental pollution, long service life, and easy control. They are considered to be very competitive energy alternative materials in the future. It has broad application prospects in future green environmental protection energy engineering and refrigeration engineering.

The conversion efficiency of thermoelectric devices is determined by the performance of thermoelectric materials, and the performance of thermoelectric materials is measured by the dimensionless figure of merit ZT=S ² σT/k, where S is the Seebeck coefficient, σ and k are the electrical and thermal conductivity of the material, respectively, and T is the absolute temperature. A thermoelectric material with excellent performance must have high Seebeck coefficient, high electrical conductivity and low thermal conductivity.

IV-VI semiconductor thermoelectric materials, including PbTe, GeTe and PbSe are medium-temperature semiconductor thermoelectric materials, which can be used in thermoelectric power generation devices working in temperature range (400-800K), especially in the recovery of industrial waste heat and the utilization of waste heat from automobile engines. Compared with PbTe-based thermoelectric materials, although GeTe has higher electrical conductivity, its thermal conductivity is also higher, resulting in a smaller thermoelectric figure of merit ZT.

An effective way to reduce the thermal conductivity of GeTe-based composite thermoelectric materials is to introduce a nano-second phase to increase the scattering of phonons, but has little effect on the electrical conductivity, so that it can have a high dimensionless figure of merit.

Contents of the invention

The technical problem to be solved by the present invention is to provide a composite thermoelectric material and its preparation method, aiming to provide a composite thermoelectric material containing a small amount of PbTe cubic structure nanophase and GeTe trigonal structure matrix phase, which has very low thermal conductivity and good thermoelectric performance.

The present invention is achieved in this way. According to the GeTe-PbTe pseudo-binary phase diagram with the phase formation rule of amplitude modulation decomposition transformation, the composition and heat treatment process of the alloy are designed, and a GeTe-based composite thermoelectric material is prepared. The chemical formula of the thermoelectric material is Ge _1-x Pb _x Te _1-y Se _y , where x is the amount of Ge replaced by Pb, the range of x is 0.10≦x≦0.90, y is the amount of Te replaced by Se, and the range of y is 0.10≦y≦0.70 .

A preparation method of the GeTe-based composite thermoelectric material, comprising the steps of: according to the values of x and y in Ge _1-x Pb _x Te _1-y Se _y , using metal Ge, Pb, Te and Se simple substances as raw materials, according to Proportionally weigh the raw materials; make the Ge _{1- x} Pb _x Te _1-y Se _y single-phase alloy from the weighed raw materials; grind the Ge _1-x Pb _x Te _1-y Se _y alloy into powder and perform discharge plasma After sintering, a composite thermoelectric material comprising a nanophase of a PbTe cubic structure and a matrix phase of a GeTe cubic structure is obtained.

The composite thermoelectric material provided by the present invention, the alloy composition and process design are carried out through the phase formation rules of related systems, a single solid solution is obtained by smelting and heat treatment, and a nanophase containing a small amount of PbTe cubic structure and a GeTe trigonal structure are obtained by a spark plasma sintering preparation process The composite material Ge _1-x Pb _x Te _1-y Se _y of the matrix phase, the thermoelectric material has very low thermal conductivity and high thermoelectric performance, and the dimensionless figure of merit ZT reaches 1.58 at 400°C .

Description of drawings

Figure 1 is the X-ray diffraction pattern of Ge _1-x Pb _x Te _0.5 Se _0.5 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5) composite thermoelectric material.

Fig. 2 is a high-resolution electron micrograph of Ge _0.75 Pb _0.25 Te _0.5 Se _0.5 composite thermoelectric material.

Figure 3 is a graph showing the relationship between the resistivity and temperature of Ge _1-x Pb _x Te _0.5 Se _0.5 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5) composite thermoelectric materials and GeTe compounds.

Figure 4 is a graph showing the relationship between Seebeck coefficient and temperature of Ge _1-x Pb _x Te _0.5 Se _0.5 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5) composite thermoelectric materials and GeTe compounds.

Figure 5 is a diagram showing the relationship between thermal conductivity and temperature of Ge _1-x Pb _x Te _0.5 Se _0.5 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5) composite thermoelectric materials and GeTe compounds.

Figure 6 shows the relationship between the dimensionless figure of merit (ZT) and temperature of Ge _1-x Pb _x Te _0.5 Se _0.5 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5) composite thermoelectric materials and GeTe compounds picture.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

A GeTe-based composite thermoelectric material, the chemical formula of the thermoelectric material is Ge _1-x Pb _x Te _1-y Se _y , wherein x is the amount of Ge replaced by Pb, and the value range is 0.10≦x≦0.90, and y is Se The amount of replacing Te has a value range of 0.10≦y≦0.70.

Among them, a small amount of PbTe cubic structure is dispersed in the nanophase GeTe trigonal structure matrix phase, and x determines the content of PbTe phase distributed in GeTe and the thermoelectric properties of the material.

Preferably, the value of y is 0.5, and the range of x is 0.10≦x≦0.50.

A preparation method of the GeTe-based composite thermoelectric material, comprising the steps of:

In the first step, according to the values of x and y in the Ge _1-x Pb _x Te _1-y Se _y , the metal Ge, Pb, Te and Se simple substances are used as raw materials, and the raw materials are weighed according to the proportion;

In the second step, the weighed raw materials are prepared to obtain Ge _1-x Pb _x Te _1-y Se _y single-phase alloy;

In the third step, the Ge _1-x Pb _x Te _1-y Se _y alloy is ground into powder and then subjected to spark plasma sintering to obtain a composite thermoelectric material comprising a nanophase of PbTe cubic structure and a matrix phase of GeTe cubic structure.

Wherein, in the first step, the proportions of different metals Ge, Pb, Te and Se can be obtained according to the values of x and y. The value range of x is 0.10≦x≦0.90, and the value range of y is 0.10≦y≦0.70.

In the second step, put the weighed raw materials into a quartz tube, pump the vacuum to 6×10 ^-3 Pa, seal and weld the quartz tube and place it in a muffle furnace for reaction melting. The reaction temperature is 1000°C. The time is 20 hours, then slowly lower the temperature to 600°C, and keep at 600°C for 4 hours for solid solution treatment and then quenching to obtain Ge _1-x Pb _x Te _1-y Se _y single-phase alloy

In the third step, the Ge _1-x Pb _x Te _1-y Se _y alloy is ground into powder and then subjected to spark plasma sintering, the vacuum degree is 1×10 ^-2 Pa, the pressure is 30-50 MPa, and the sintering temperature is 450-500°C , the holding time is 5-10 minutes, and the composite thermoelectric material can be obtained.

The obtained composite thermoelectric material Ge _1-x Pb _x Te _1-y Se _y is characterized by the X-ray diffraction pattern shown in FIG. 1 . Figure 1 shows the X-ray diffraction pattern of the composite thermoelectric material when x is 0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5, and y is 0.5, and Figure 2 shows the composite thermoelectric material Ge _0.75 Pb _0.25 Te _0.5 Se _0.5 ( x is 0.25, y is 0.5), and Fig. 1 and Fig. 2 show that the composite thermoelectric material prepared by the present invention contains a small amount of PbTe cubic structure nanophase and GeTe trigonal structure matrix phase.

Please refer to Figure 3, the resistivity of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 changes with the increase of temperature. At the same temperature, the resistivity of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 is greater than the conductivity of GeTe, and the resistivity of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 increases with the value of x And increase.

Please refer to Figure 4, the Seebeck coefficient of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 changes with increasing temperature. At the same temperature, the Seebeck coefficient of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 is greater than that of GeTe, and the Seebeck coefficient of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 increases with increases with increasing x values.

Please refer to Figure 5, the thermal conductivity of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 decreases with increasing temperature. Moreover, at the same temperature, the thermal conductivity of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 is significantly lower than that of GeTe. Moreover, at the same temperature, as the value of x increases, the thermal conductivity value of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 decreases. It can be concluded from Fig. 5 that the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 can reduce the thermal conductivity of the thermoelectric material compared with GeTe.

Please refer to Figure 6, the dimensionless figure of merit of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 increases with increasing temperature. Moreover, at the same temperature, the dimensionless figure of merit of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 is greater than the thermal conductivity of GeTe. Moreover, at the same temperature, as the value of x increases, the dimensionless figure of merit value of the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 roughly increases. It can be concluded from Figure 6 that the composite thermoelectric material Ge _1-x Pb _x Te _0.5 Se _0.5 can increase the dimensionless figure of merit of the thermoelectric material and increase the thermoelectric performance of the material compared with GeTe.

In this technical solution, the figure of merit of the pure GeTe compound in Fig. 3 to Fig. 6 is based on the figure of merit of the pure GeTe compound reported by Gelbstein et al. For details, please refer to Y.Gelbstein, B.Dado, O.B.Yehuda, Y. Sadia, Z. Dashevsky and M.P. Dariel, Chem. Mater., 2010, 22, 1054–1058.

In the following, the composite thermoelectric material provided by the present technology and its preparation method will be described in detail with examples.

Use metal Ge, Pb, Te and Se simple substances as raw materials, and weigh the raw materials according to the ratio according to the value of Ge _0.75 Pb _0.25 Te _0.5 Se _0.5 ; put the weighed raw materials into a quartz tube, pump to 6×10 ^-3 After Pa vacuum, the quartz tube is sealed and welded and placed in a muffle furnace for reaction smelting. The reaction temperature is 1000°C, the reaction time is 20 hours, then slowly lower the temperature to 600°C, keep at 600°C for 4 hours for solid solution treatment, and then quench. A Ge _0.75 Pb _0.25 Te _0.5 Se _0.5 single-phase alloy was obtained. Grinding the Ge _0.75 Pb _0.25 Te _0.5 Se _0.5 alloy into powder and then carrying out spark plasma sintering, the vacuum degree is 1×10 ^-2 Pa, the pressure is 30-50 MPa, the sintering temperature is 450-500°C, and the holding time is 5-10 minutes. Composite thermoelectric material Ge _0.75 Pb _0.25 Te _0.5 Se _0.5 containing a small amount of PbTe cubic nanophase and GeTe trigonal matrix phase.

The phase, microstructure and thermoelectric properties of the composite thermoelectric material Ge _0.75 Pb _0.25 Te _0.5 Se _0.5 prepared in this example are shown in Figure 1-6, and its thermal conductivity is 0.66W/mK at 673K, which is the same as pure GeTe 20% of 3.23W/mK at temperature; and its maximum figure of merit (ZT) is 1.58, 209% higher than pure GeTe's 0.51.

It can be understood that composite thermoelectric materials Ge _1-x Pb _x Te _1-y Se _y . with different values of x and y can be prepared by using the same or similar method as above. Wherein, when x is 0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5, and y is 0.5, the properties of the prepared composite thermoelectric material Ge _1-x Pb _x Te _1-y Se _y can be seen in Fig. 3-6.

The composite thermoelectric material provided by the present invention, the alloy composition and process design are carried out through the phase formation rules of related systems, a single solid solution is obtained by smelting and heat treatment, and a nanophase containing a small amount of PbTe cubic structure and a GeTe trigonal structure are obtained by a spark plasma sintering preparation process The matrix phase composite material Ge _1-x Pb _x Te _1-y Se _y , the thermoelectric material has very low thermal conductivity and high thermoelectric performance, and the dimensionless figure of merit ZT reaches 1.58 at 400°C.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (3)

1. a kind of preparation method of composite thermoelectric material, the chemical formula of described thermoelectric material is Ge_1-xPb_xTe_1-ySe_y, wherein x is Pb replaces the amount of Ge, and x span is 0.10 x 0.40, and y replaces the amount of Te for Se, and y span is 0.10 y 0.70；Wherein PbTe cubic structure nanometer is mutually scattered in GeTe trigonal crystal structure matrix phase；

Described preparation method includes step：

According to Ge_1-xPb_xTe_1-ySe_yThe numerical value of middle x and y, with metal Ge, Pb, Te and Se simple substance as raw material, weighs former according to proportioning Material；

The raw material weighing is made and obtains Ge_1-xPb_xTe_1-ySe_ySingle-phase alloy；And

By Ge_1-xPb_xTe_1-ySe_yCarry out discharge plasma sintering after alloy grind into powder, obtain comprising PbTe cubic structure The nanometer mutually composite thermoelectric material with GeTe trigonal crystal structure matrix phase；

The raw material weighing is made and forms Ge_1-xPb_xTe_1-ySe_yMethod be：The raw material weighing is loaded in quartz ampoule, is extracted into 6 ×10^-3After Pa vacuum, the good quartz ampoule of soldering and sealing is placed in Muffle furnace carrying out smelting, and reaction temperature is 1000 DEG C, the response time For 20 hours, then, slow cooling, to 600 DEG C, quenches after 600 DEG C of insulations carry out solid solution treatment in 4 hours, obtains Ge_{1- x}Pb_xTe_1-ySe_ySingle-phase alloy.

2. the preparation method of composite thermoelectric material as claimed in claim 1 is it is characterised in that y is 0.5.

3. the preparation method of composite thermoelectric material as claimed in claim 1 is it is characterised in that by described Ge_1-xPb_xTe_1-ySe_y Carry out discharge plasma sintering, the method obtaining composite thermoelectric material is after alloy grind into powder:By Ge_1-xPb_xTe_1-ySe_yClose Carry out discharge plasma sintering, vacuum is 1 × 10 after golden grind into powder^-2Pa, pressure 30～50MPa, sintering temperature 450～ 500 DEG C, temperature retention time 5～10 minutes, the spinodal decomposition using GeTe-PbTe system changes, and obtains described composite thermoelectric material.