JP2002029728A - Silicon and/or germanium clathrate compound and its production process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon and/or germanium clathrate compound which has a completely different bonding mode from that of a conventional silicon or germanium crystal and the physical properties of which can greatly be changed without changing its basic structure, and also to provide a production process of the clathrate compound. SOLUTION: This clathrate compound comprises, as its constitutional unit, a polyhedral cluster consisting of, as its constitutional units, (Si, Ge or a mixture of Si and Ge)20 and (Si, Ge or a mixture of Si and Ge)24, each of which is also a cluster of the Si and/or Ge element, and further, additionally contains a d- electron-containing element, an f-electron-containing element or a mixture of a d-electron-containing element and an f-electron-containing element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field of application in the electronics industry, and relates to a silicon and germanium clathrate compound used as a semiconductor, metal, or insulator material for producing a high-performance device, and a method for producing the same. It is about.

[0002]

2. Description of the Related Art At present, semiconductor devices (such as arithmetic logic circuit devices, storage devices, photoelectric conversion devices, etc.) that support computer technology and laser devices that support optical communication technology include III-V devices such as silicon, germanium, and gallium arsenide. It is made using II-VI compound semiconductors such as group III compound semiconductors and zinc sulfide. The performance of such devices has been developed mainly by miniaturization of devices by using LSIs. However, in the future, performance improvement due to miniaturization cannot be expected much, and the degree of element performance is more and more defined by the basic performance of the material constituting the element.

[0003] Therefore, in view of the further development of electronics, it is desired to develop a new material having properties significantly different from those of conventional electronic material materials.

[0004] One idea to find such a breakthrough from the material side is to use a nanostructured cluster / clathrate material that is created naturally. In a cluster / clathrate material, the bonding mode between elements constituting the material is significantly different from that of a conventional material, so that superconducting properties and magnetic properties can be controlled via high-frequency phonons or the like. Also, because the number of defects can be reduced by the structural integrity of the cluster / clathrate structure,
It is considered that the basic performance of the substance is greatly improved.

As an example of clusters / clathrates related to group IV Si and Ge elements, there has been known a crystal in silicon having a specific shape structure into which an alkali metal element is introduced under a certain condition. (Silicone clathrate) (eg, cloth, etc., Journal of Solid Chemistry, 2
Vol. 570, 1970).

However, this compound is in a form in which only alkali metal elements are included in cages of M ₂₀ and M ₂₄ (where M represents Si) having a cage structure constituting a silicon clathrate material. Yes, the electronic properties of the resulting compound can be changed from semiconductor to metal properties by controlling the amount of alkali metal introduced, depending on the amount of carrier introduced, but the main electronic properties are clathrate networks. It is almost completely determined by the structure.

[0007] Therefore, there is little possibility that the variety of controlled physical properties can be fully utilized, and it has not been expected that it will be widely used in the field of electronics. For this reason, despite the fact that it is a promising material system capable of controlling the nanostructure, no significant change was expected in the confidentiality of the material even after more than 20 years since these reports were made.

However, recently, in addition to the alkali metal elements Na and K contained in the Si ₂₀ cluster, Na ₂ Ba ₆ Si ₄₆ in which the alkaline earth element Ba is contained in the Si ₂₄ cluster is synthesized. It was reported that it could be done (Yamanaka et al., Fullerene Science and Technology, Vol. 3, p. 21, 1995).

It has also recently been reported that Ba ₈ Si ₄₆ can be synthesized under high pressure. This fact is noted as an indication that the nanomaterials of the present invention have potential applications in the electronics field. This is because, when an alkaline earth element is used, the d orbital of the alkaline earth element and the orbital forming the valence band of the Si ₄₆ clathrate are hybridized, and the electronic state of the obtained nanocrystal is greatly changed. This is because it is possible to make it possible. Actually, in the case of a silicon clathrate into which an alkaline earth element is not introduced, superconductivity is not exhibited, but in the case of a silicon clathrate into which Ba is introduced, metal and superconductivity are observed.

[0010] Such superconductivity is a characteristic characteristic of clathrate which is not observed in a normal silicon crystal having a diamond structure even when doped. This property is interpreted as being exhibited by a change in band structure caused by the introduction of an alkaline earth element.

[0011]

In view of such a situation, in order to add various electronic functions to the group IV clathrate material and utilize it widely in the field of electronics, not only Ba but also various other substances are required. It was necessary to introduce various elements, especially magnetic metal elements, into the group IV clathrate to achieve a variety of physical properties and high precision in material design control.

However, there has been no report on the synthesis of such a clathrate material so far, and in general, the realization of silicon or germanium clathrate and the diversification of its physical properties and material design for realizing it have not been reported. It was thought that high accuracy of control could not be expected.

The present invention eliminates the above problems and has completely different bonding modes from conventional silicon crystals or germanium crystals without changing the basic structure thereof.
An object of the present invention is to provide a silicon and germanium clathrate compound that can greatly change its physical properties and a method for producing the same.

[0014]

According to the present invention, in order to achieve the above object, [1] the structural unit is composed of silicon and germanium (Si,
In a clathrate compound having a polyhedral cluster composed of (Si or Ge or a mixture thereof) ₂₀ and (Si or Ge or a mixture thereof) _{24 as} a cluster of Ge) elements, a d-electron element or f- It is characterized by containing an electronic element or a mixture thereof.

[2] The structural unit is a cluster of Si
(Si, Ge)₂₀And (Si, Ge) _{twenty four}Is based on
(Si, Ge)₂₀And
And (Si, Ge)_{twenty four}Has Ba inside the cluster of
(Si, Ge)₂₀And (Si, Ge)_{twenty four}Cluster of
General formula B containing Mn as a d-electron element at the position connecting
a₈Mnx (Tr) y (Si, Ge)₄₀+ Z composition
Here, Tr represents a transition metal, and x, y, and z are x + y + z ≦
6 is a positive integer.

[3] The structural unit is a cluster of Si
(Si, Ge)₂₀And (Si, Ge) _{twenty four}Is based on
(Si, Ge)₂₀And
And (Si, Ge)_{twenty four}Ba and Ce inside the cluster
Having the general formula (Ce, Ba) ₈(Tr) x (Si, G
e)₄₀And represented by the general formula (Ba, Ce)₈(T
r) x (Si, Ge)₄₀+ Y composition, where Tr is transition
Represents a metal, x and y are positive integers satisfying x + y ≦ 6
There is a feature.

[4] In the method for producing a silicon and germanium clathrate compound, the structural unit is a cluster of silicon and germanium (Si, Ge) elements (Si or Ge or a mixture thereof) ₂₀ and (S
i or Ge or a mixture thereof) When introducing d- and f-electron elements into a clathrate compound having a polyhedral cluster composed of ₂₄ as a constituent unit, d- and f-
It is characterized in that the amount of the electron-based element is suppressed to about 2 to 4 per crystal lattice unit, and then the composition is melted and heated sufficiently under high-frequency heating and argon plasma.

[5] In the method for producing a silicon and germanium clathrate compound according to the above [4], the d-electron system / f-
It is characterized by stabilizing the electronic system and the Si and Ge clathrate compounds.

That is, the clathrate compound composed of Si and Ge dodecahedral and tetradecahedral d-
By using a clathrate compound in which magnetic electrons and f-magnetic electrons are incorporated in a crystal lattice, a new substance having a nanostructure capable of greatly changing magnetic properties can be produced.

[0020]

Embodiments of the present invention will be described below in detail.

The clathrate compound according to the present invention has the following structure: [1] The structural unit is silicon and germanium (Si,
In the clathrate compound having a polyhedral cluster composed of (Si or Ge or a mixture thereof) ₂₀ and (Si or Ge or a mixture thereof) _{24 as} a cluster of Ge) elements, a d- or f-electron element Or mixtures thereof.

That is, a clathrate compound composed of dodecahedral and tetradecahedral Si or Ge
A clathrate compound characterized by incorporating an electron element, an f-electron element, or a mixture thereof into a crystal lattice.

[2] In a clathrate compound whose structural unit is basically composed of (Si, Ge) ₂₀ and (Si, Ge) ₂₄ which are clusters of silicon, (Si, Ge) ₂₀
And (Si, Ge) having a Ba within the ₂₄ cluster, (Si, Ge) ₂₀ and (Si, Ge) general formula Ba ₈ containing Mn as d- electron system element to a position connecting the clusters ₂₄ Mnx (Tr) y (Si, Ge) ₄₀ + z composition, where Tr represents a transition metal and x, y, z are x + y
It is a positive integer satisfying + z ≦ 6.

That is, a general formula Ba ₈ Mnx (Tr) having Ba inside a clathrate compound composed of Si or Ge dodecahedron and tetrahedron and containing Mn as a d-electron element at a position connecting the clusters. ) Y (S
i, Ge) ₄₀ + z, wherein Tr represents a transition metal, and x, y, and z are positive integers satisfying x + y + z ≦ 6.

[3] Structural unit is a cluster of Si
(Si, Ge)₂₀And (Si, Ge) _{twenty four}Is based on
(Si, Ge)₂₀And
And (Si, Ge)_{twenty four}Ba and Ce inside the cluster
Having the general formula (Ce, Ba) ₈(Tr) x (Si, G
e)₄₀And represented by the general formula (Ba, Ce)₈(T
r) x (Si, Ge)₄₀+ Y composition, where Tr is transition
Represents a metal, x and y are positive integers satisfying x + y ≦ 6
is there.

That is, a clathrate compound composed of a dodecahedral and a tetrahedral Si or Ge has Ba and Ce inside, and has a general formula (Ce, Ba) ₈ (Tr)
x (Si, Ge) ₄₀ and represented by the general formula (Ba, C
e) A clathrate compound characterized by the composition of ₈ (Tr) x (Si, Ge) ₄₀ + y, wherein Tr represents a transition metal, and x and y are positive integers satisfying x + y≤6. I do.

In these compounds, the bonding mode of the silicon element and the germanium element is not the sp3 bonding mode found in the conventional silicon crystal and germanium crystal, but is the magic numbers 20 and 2 respectively.
Reflecting that the silicon and germanium cluster units composed of four silicon elements and germanium elements become the constituent units of each crystal, a special bonding mode located between sp3 and sp2 is adopted.
In addition, the clathrate compounds of the present invention each include (Si
(Ge) ₂₀ or (Si / Ge) ₂₄ clusters have a form in which an alkaline earth element is included or a Ce element is included in a special bonding mode.

Until now, the only alkaline earth element Ae that can be incorporated into such a structure is considered to be Ba in the case of Si, and such clathrate compounds are actually used in other elements. Did not exist. The Au element necessary for introducing Ce is as follows:
(Si / Ge) Crystallographically 6 binding ₂₀ clusters
introduced at a location called e. When Mn is used,
Mn is introduced at the position 6e.

According to the present invention, these clathrate compounds are mixed with substances having a desired composition, melt-heated in an inert atmosphere such as argon with a high-frequency heating device, and then reheated with argon plasma. Found to be produced by

FIG. 1 is a diagram showing the crystal structure of the synthesized silicon clathrate compound according to the present invention.
FIG. 1 (a) is a diagram showing the crystal structure of a clathrate compound of silicon ₂₀ and silicon ₂₄ , and FIG. 1 (b) is a crystal structure of a clathrate compound in which a transition metal of Au and Ba and Ce are simultaneously mixed into the silicon clathrate compound. FIG.

Basically, the d- and f-electron elements are Si
In addition, it is difficult to introduce it into a clathrate structure composed of Ge elements, but the amount is limited to about 2 to 4 per crystal lattice unit, and further, it is sufficiently melted and heated under high frequency heating and argon plasma. It has been newly found that silicon and germanium compounds can be synthesized through the process of the above.

In some cases, Au, Cu, Ag
It has been found that the d- / f-electron system and the Si and Ge clathrate structures can be stabilized by mixing transition metals such as these at the same time.

Further, when the physical properties of the clathrate compound of the present invention were examined, an interesting result that ferromagnetic transition occurred at 7K was obtained.

As described above, these Si / Ge clathrate compounds containing an f- (and / or) d-electron element in addition to Ba are the same as those of the conventional Si having a diamond structure.
Unlike the / Ge crystal, it exhibits an essentially narrow band structure due to the specific binding mode of Si clathrate. This band structure can be greatly modulated by a hybrid of the d orbital of Ba and the orbital forming the band of Si clathrate. Further, it is expected that a novel magnetic and electric conduction phenomenon will be exhibited through a process in which conduction electrons introduced from Ba interact with magnetic electrons of d- / f-electron elements.

Therefore, unlike the conventional Si crystal, by controlling the doping with the same substance, the physical properties of the material range from insulators to semiconductors having various band gaps, as well as metals and superconductors, ferromagnetic and antiferromagnetic. Can be changed.

This indicates that a highly functional electronic element can be manufactured using Si, an element having a high abundance ratio in the natural world. In addition, the narrow band dispersion feature is very sensitive to changes from outside,
Due to such physical properties, an unprecedented sensing function or a magnetoresistance change (eg, giant magnetoresistance) characteristic larger than that of a conventional material is developed.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0038]

As described above, according to the present invention, the following effects can be obtained.

(A) Si or Ge abundant in nature
Using a silicon clathrate or germanium clathrate in a material having a basic structure that is significantly different from a conventional Si crystal or Ge crystal, respectively, a semiconductor having various band gaps from an insulator,
Further, it is possible to provide a clathrate compound that can greatly change its physical properties such as a metal or a superconductor, and a ferromagnetic and an antiferromagnetic.

The fact that the physical properties can be widely changed from one material in this way leads to the production of an electronic device at a low price, and is of great industrial significance.

The band structure having a narrow dispersion characteristic of the clathrate compound of the present invention may show a larger change in magnetic and electronic conductivity with respect to a change from the outside than in the past. The impact in the electronics field on sensors and magnetoresistive elements using characteristics is great.

In particular, Si or Ge, which is abundant in nature,
With the use of alkali metal elements and alkaline earth elements, which have a very small amount of pollution and abundant amounts, the physical properties of insulators, semiconductors with various band gaps, and even metals can be significantly changed. This provides a clathrate compound. Being able to change the physical properties of such a wide range with one material leads to industrially low-cost production of electronic elements.

[Brief description of the drawings]

FIG. 1 is a view showing a crystal structure of a synthesized silicon clathrate compound according to the present invention.

Claims (5)

[Claims] 1. A polyhedral cluster composed of (Si or Ge or a mixture thereof) ₂₀ and (Si or Ge or a mixture thereof) ₂₄ whose constituent units are clusters of silicon and germanium (Si, Ge) elements. A silicon and germanium clathrate compound comprising a d-electron element, an f-electron element, or a mixture thereof. 2. The structural unit is a cluster of Si (S
i, Ge)₂₀And (Si, Ge)_{twenty four}Based on
In the lathrate compound, (Si, Ge) ₂₀and
(Si, Ge)_{twenty four}Has Ba inside the cluster of
(Si, Ge)₂₀And (Si, Ge)_{twenty four}Cluster of
General formula B containing Mn as a d-electron element at the position connecting
a₈Mnx (Tr) y (Si, Ge)₄₀+ Z composition
Here, Tr represents a transition metal, and x, y, and z are x + y + z ≦
6 is a positive integer satisfying 6
And germanium clathrate compounds. 3. The structural unit is a cluster of Si (S
i, Ge)₂₀And (Si, Ge)_{twenty four}Based on
In the lathrate compound, (Si, Ge) ₂₀and
(Si, Ge)_{twenty four}Ba and Ce inside the cluster
And the general formula (Ce, Ba)₈(Tr) x (Si, Ge)
₄₀And represented by the general formula (Ba, Ce)₈(Tr) x
(Si, Ge)₄₀+ Y composition, where Tr is the transition metal
X and y are positive integers satisfying x + y ≦ 6.
Silicon and germanium clasley characterized by
Compound. 4. A method for producing a silicon and germanium clathrate compound, wherein the constituent units are clusters of silicon and germanium (Si, Ge) elements (Si or Ge or a mixture thereof) ₂₀ and (Si or Ge or a mixture thereof) Clathrate compounds containing polyhedral clusters composed of ₂₄
When introducing the electron element and the f-electron element, the amount of the d-electron element and the f-electron element is suppressed from 2 to 4 per crystal lattice unit. A method for producing a silicon and germanium clathrate compound, wherein the composition is melted and heated sufficiently to synthesize. 5. The method for producing a silicon and germanium clathrate compound according to claim 4, wherein the d-electron system / f-electron system and the Si and Ge clathrate compounds are stabilized by simultaneously mixing transition metals. A method for producing a silicon and germanium clathrate compound, characterized in that: