JPH0524972B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a novel conductive vanadium digermanide with a C40 type crystal structure (chemical composition VGe ₂ ).
and its manufacturing method. Prior Art Many of the silicides and germanides of transition metals exhibit metallic properties with high electrical conductivity, as well as characteristic properties such as semiconductors, semimetals, and superconductors. Because magnets exhibit a wide variety of properties, including Pauli paramagnetism, helical magnetism, weak ferromagnetism, and diamagnetic properties, a wide range of basic and applied research has been conducted on them, with interest in crystal chemistry and physics. For example, CrSi ₂ , which exhibits semiconducting properties,
FeSi ₂ and other materials have low resistivity and large thermoelectric power, and are used as thermoelectric conversion materials. By the way, similar properties are expected for germanium compounds, and there is a possibility that new compounds with even better properties will be discovered. In other words, germanium has higher electrical conductivity than silicon, and also has higher mobility of electrons and holes, so it is possible that by creating a compound with a transition metal, it is possible to obtain something with higher electrical conductivity than silicon compounds. It is also believed that the energy band gap can be easily adjusted, and it is predicted that a wide variety of compounds with various properties can be designed. Therefore, research is currently being conducted on many germanium compounds. For example, four phases of vanadium germanium compounds have been reported so far. H.
V ₃ Ge (Monatsh
Chem., 94, 473 (1963)) and V ₅ Ge ₃ (Monatsh
Chem., 94, 497 (1963)), H. Vollenkle et al.
V ₁₁ Ge ₈ (Monatsh Chem., 95, 1544 (1964)) and V ₁₇ Ge ₃₁ (Z. Krist., 124, 9 (1967)).
All of these are manufactured by processing raw material powder with a Ge/V ratio of 0.3 to 2 in a vacuum at a temperature of 600 to 1000°C, but until now V
There is no known material having a stoichiometric composition in which the ratio of Ge and Ge is 1:2. In transition metal-germanium compounds, the band gap increases as the proportion of germanium increases, so a previously unknown thermal
It is thought that electrical properties can be obtained, but it is difficult to synthesize transition metal germanides with a stoichiometric ratio of 1:2, and especially in the vanadium-germanium system, phases with a high germanium content cannot be formed freely. Because of the increased energy, it was impossible to generate germanium compounds under normal pressure. OBJECTS OF THE INVENTION The present invention provides a novel conductive vanadium digermanide having a higher proportion of germanium than those conventionally known, and a method for synthesizing the same. Structure of the Invention The present invention is a novel conductive vanadium digermanide having a C40 type structure and represented by the compositional formula VGe ₂ . This vanadium digermanide is a single compound and exhibits one physical property, as will be explained in detail in Examples. The C40 type structure is of Zeitschrift fu¨r Kristallogrophie.
CrSi ₂
Also called type. This is a hexagonal space group D ⁴ ₆ consisting of TX ₂ atomic planes stacked with a certain regularity, in which metal atoms T and metalloid atoms X are tightly packed.
The structure is (P6 ₂ 22). It has the most dense structure among disilicides and digermanides. Therefore, the vanadium digermanide having the C40 type structure referred to in the present invention is a compound having a hexagonal system and a crystal lattice type of space group D ⁴ ₆ (P6 ₂ 22). The conductive vanadium digermanide having a C40 type structure of the present invention is synthesized by reacting vanadium and germanium under high temperature and high pressure. That is, in the second invention, vanadium and germanium are mixed in a ratio of 1:1 to 1:3.
Mix at a molar ratio of , pressure 1GPa or more, temperature 600~
Characterized by reacting under conditions of 1300℃,
This is a method for producing conductive vanadium digermanide having a C40 type structure. It is desirable to use highly purified vanadium and germanium as raw materials. In particular, if an oxide is present as an impurity, germanium oxide is generated and separation becomes difficult, so it is necessary to use a material containing as little oxide as possible. In some cases, it is preferable to use a raw material that has been subjected to a reduction treatment with hydrogen or the like. Reaction temperature is 600
If the temperature is lower than ℃, germanium will not dissolve and no reaction will occur. Also, since it will evaporate if the temperature exceeds 1300℃, the temperature should be set at 1GPa or higher to allow the reaction to occur in a state close to that of a solid phase reaction.
Preferably, conditions of 3 GPa or higher and a temperature of 600 to 1300°C are required. Note that if the reaction temperature is low, some germanium will remain unreacted, and if the reaction temperature is high, some V ₅ Ge ₃ will be produced.
A temperature range of 850-1250°C is desirable to obtain a single phase of _VGe2 . These unreacted substances and by-products can also be removed by treatment with nitric acid or the like. For high-temperature, high-pressure synthesis, a high-pressure and high-temperature generating device such as a belt-type high-pressure device that can maintain the above-mentioned conditions for the time required for a predetermined reaction is used. TG ₂ type compounds include C54 type (TiSi ₂ type, orthorhombic system) and C40 type (CrSi ₂ type) depending on the stacking method of the TX ₂ planes.
Type, hexagonal system) C11 _b type (MoSi ₂ type, tetragonal system), but digermanides of group elements of the periodic table are thought to be C40 type. The vanadium digermanium compound produced by the high temperature and high pressure reaction of the present invention is all C40 type VGe ₂ . Examples Example 1 After thoroughly mixing V powder and Ge powder with a purity of 99.99% or more in nitrogen at a molar ratio of approximately 1:2, 4.0 t/cm ²
It was molded into a disc shape of 5φ x 3mm by applying a load of .
This was filled into a nitrogen-boron reaction vessel, and treated for 2 hours at 5.5 GPa and 850°C using a belt-type high-pressure device. After the reaction was completed, the heating power was cut off and the mixture was rapidly cooled. The obtained compound had a dark gray color and was confirmed to be VGe ₂ by atomic absorption spectrometry and spectrophotometric analysis. Table 1 shows the results of powder X-ray diffraction of the vanadium digermanium compound obtained in Example 1. This diffraction pattern is similar to that of VSi ₂ and CrSi ₂ , and the diffraction intensity of each peak is also almost the same.
This indicates a C40 type structure. It also has a hexagonal crystal system, belongs to space group D ⁴ ₆ , and has a lattice constant a = 0.4806 nm.
It was determined that c=0.6634 nm.

[Table] Figures 1 and 2 show the results obtained in Example 1, respectively.
The temperature dependence of resistivity and the temperature dependence of thermopower of VGe ₂ are shown. According to these figures, resistivity is metallic and increases linearly with temperature in the range of 1.5 × 10 ^-4 to 4 × 10 ^-4 Ωcm, but the rate of increase is 1.1 × 10 ^-6 Ω.
cm/K. The thermoelectric power is - in the range of 80 to 300K.
It exhibits a small value of 4 to -5 μV/K compared to alloys such as platinum-rhodium, chromel-alumel, and constantan that are normally used in thermocouples, and is characterized by small temperature changes. Figure 3 shows the change in magnetic susceptibility of VGe ₂ with temperature. It was found that the material exhibits no special interaction above 80K, has a small magnetic susceptibility, and is a paramagnetic material that follows the Cuyrie-Weiss law. By the way, the effective Pohr magneton number and the Cuyuri-Weiss temperature were determined to be 0.82μ _B and -32K, respectively. This value is smaller than 1.73μ _B , which is the value when considering one unpaired electron. This means that the V-Ge bond distance is 2.61A, and the sum of the atomic radii is 2.64A.
Since it is shorter, this can be explained by considering that the spin is partially canceled out by electron transfer from Ge to V. Example 2 The treatment was carried out in the same manner as in Example 1, except that the reaction conditions were 4 GPa, 1000° C., and 1 hour. As a result of chemical analysis and X-ray diffraction, the obtained compound was found to be Example 1.
It is the same C40 type VGe ₂ and showed the same physical properties. Example 3 The treatment was carried out in the same manner as in Example 1, except that the reaction conditions were 4 GPa, 800° C., and 2 hours. As a result of analysis, the obtained compound contained VGe ₂ and a trace amount of unreacted Ge.
It has become clear that there is. Therefore, this was treated with 1N nitric acid to remove Ge. It was confirmed that the obtained sample was the same C40 type VGe ₂ as in Example 1 and exhibited the same physical properties. Example 4 The treatment was carried out in the same manner as in Example 1, except that the reaction conditions were 5.5 GPa, 1100° C., and 30 minutes. As a result of chemical analysis and X-ray diffraction, the obtained compound was found to be Example 1.
It is the same C40 type VGe ₂ and showed the same physical properties. Comparative Example 1 V powder and Ge powder were thoroughly mixed at a molar ratio of approximately 2:1, then placed in a silica tube and heated to 10 ^-3 mmHg.
After degassing and sealing, the reaction was carried out at a temperature of 880°C for 40 hours. The obtained sample was subjected to chemical analysis and powder
As a result of line diffraction, it was found to be V ₁₇ Ge ₃₁ with a Mn ₁₁ Si ₁₉ type structure and unreacted Ge. Comparative Example 2 V powder and Ge powder were mixed at a molar ratio of approximately 1:1, and as in Comparative Example 1, a reaction was carried out in vacuum at a temperature of 900° C. for 20 hours. Analysis of the obtained sample revealed that it was V ₁₇ Ge ₃₁ and V ₁₁ Ge ₈ . Effects The present invention provides a novel and useful vanadium digermanide having a C40 type structure, and also establishes a method for producing the same. As shown in the examples, this compound has low thermoelectric power and has extremely stable electrical resistance characteristics against changes in the outside air, especially heat and atmosphere, so it has a wide range of applications such as ultra-precision resistors and resistance materials for current control. This is a promising substance for development. For example, constantan wire with a volume resistivity of 50 μΩcm and a temperature change rate of resistance value of 2 × 10 ^-5 Ωcm/K is currently widely used as a resistor for current control, but the thermoelectromotive force against copper is as large as 40 μV, As a precision resistance material, the volume resistivity is rather 44.
±3μΩcm, temperature change rate of resistance value (5 to 100) ×
10 ^-6 Ωcm/K, thermal electromotive force of 2 μV compared to copper, and superior manganese wire is used for standard resistors. However, the new compound VG ₂ obtained by the present invention is
Volume resistivity is 1.5×10 ^-4 Ωcm, and the temperature change rate of resistance is
1.1×10 ^-6 Ωcm/K, thermoelectromotive force against copper is -4~
-5 μV and its temperature dependence is small, so it is expected to be used as a superior low-voltage antibody and is extremely useful industrially.

[Brief explanation of drawings]

Figure 1 shows VGe ₂ having a C40 type structure according to the present invention.
The graphs showing the results of measuring resistivity, and FIGS. 2 and 3, are also graphs showing the results of measuring thermoelectric power and magnetic susceptibility.

Claims (1)

[Claims] 1. A conductive vanadium digermanide having a C40 type structure and represented by the compositional formula VGe ₂ . 2 Vanadium and germanium 1:1 to 1:3
Mix at a molar ratio of , pressure 1GPa or more, temperature 600~
Characterized by reacting under conditions of 1300℃,
A method for producing conductive vanadium digermanide having a composition formula VGe ₂ and having a C40 type structure.