JPH0242770B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a novel cation conductor. Cation conductors are important as solid electrolyte materials for solid batteries and ion sensors that can be used for electric vehicles, surplus electricity at night, etc. Conventional technology Until now, the most promising cation conductor is β-alumina, but this β-alumina is a two-dimensional material in which cations move in a plane, and its conductivity is low. Therefore, there was a demand to develop materials with even higher conductivity. Purpose of the Invention The present invention was made to eliminate the drawbacks of conventional cation conductors made of β-alumina, and its purpose is to transport cations not two-dimensionally but one-dimensionally. The purpose is to provide a cation conductor with high conductivity by aligning the movement directions of the cations. Structure of the Invention The present inventors first prepared the general formula M _x Ti _16-x Ga _16+x O ₅₆
(However, M is K, Rb, or Cs, x = 0.1 to 2.0
We have provided a novel compound represented by As a result of further research into the cation conductivity of this new compound, we were able to find that it conducts cations in a one-dimensional manner and has extremely high cation conductivity. The present invention was completed based on this knowledge. The cation conductor of the present invention has the general formula M _x Ti _16-x
Ga _16+x O ₅₆ (M is K, Rb, K or Rb
solid solution with Li or Na or Cs, x = 0.1 ~
2.0), which has a tetragonal one-dimensional tunnel structure. The tunnel structure of the cation conductor of the present invention is approximately
It has a large diameter of 6.5 Å, there is no bottleneck that acts as a structural barrier to the ion conduction path, and the ion conduction path has appropriate spacing and no interaction, which is an extremely effective structural feature for the ion conduction mechanism. have. K, Rb, a solid solution of K or Rb with Li or Na, and Cs act as conductive ions, all of which have excellent ionic conductivity, especially K,
Rb, K, and a solid solution of Rb with Li or Na are excellent. In addition, in this compound, a part of Ti (0 to 50%) is replaced by Mn ⁴⁺ and a part of Ga (0 to 50%)
may be replaced with Al ³⁺ , Fe ³⁺ or Cr ³⁺ . The value of x in the above general formula needs to be within the range of 0.1 to 2.0, but the preferable value is 0.6 to 2.0.
It is 1.2. When the value of x is less than 0.1, it is impossible to form a compound having a tetragonal one-dimensional tunnel structure,
When it exceeds 2, conductivity decreases. The shape of the cation conductor made of the compound of the present invention may be granular, powdery, fibrous, bullet-like, or lump-like as long as it is crystalline. However, due to the specificity of the conduction mechanism, it is most preferable to use a crystal that has developed a plane perpendicular to the tunnel structure axis, in other words, a plane perpendicular to the crystal C axis. In addition, it is most preferable if it can be used as a single single crystal, but depending on the synthesis method, needle-shaped fibrous crystals that are parallel to the crystal C axis can be obtained, so in such a case, it is necessary to bundle them with the same orientation. Accordingly, crystal C
Just make a large surface perpendicular to the axis. The method for producing the cation conductor crystal of the present invention may be any of the sintering method, melting method, hydrothermal method, and flux method, but it must be a flux method using molybdate or tungstate as a flux. is preferred. It is easy to manufacture because the basicity of the melt can be easily controlled, relatively large single crystals are easy to manufacture, and since high pressure is not required during manufacturing, there is no danger, and it can be manufactured at relatively low temperatures. There is no need to worry about pollution caused by evaporation, and it is easy to create various solid solutions.By dissolving ionic species with small ionic radius and high conductivity, such as Na and Li ions, with K and Rb ions, it is possible to create solid solutions with properties. This is because different ion conductors can be easily manufactured and obtained. Effects of the Invention Since the cation conductor of the present invention uses alkali metals such as K, Rb, and Cs as conductive ion species, when it is used as a solid battery, it cannot handle active and dangerous gases like conventional fuel cells. There is no need to use it, and
Because it has a unique large-diameter tunnel, it has the excellent effect of increasing its conductivity at high frequencies by 100 to 1000 times the value of β-alumina at room temperature by aligning the ion conduction direction one-dimensionally. can be played. Example 1 (1) Production of single crystal Potassium oxide, titanium oxide, and gallium oxide powders with a purity of 99.9% were mixed in molar proportions (K ₂ O).
They were mixed to have a ratio of _0.7 (TiO ₂ ) _1.0 (Ga ₂ O ₃ ) _0.5 . This mixture and potassium oxide and molybdenum oxide powder as flux raw materials (K ₂ O) _1.0
(MoO ₃ ) with a mixture at a molar ratio of _1.5 ,
They were mixed at a mol% ratio of 20:80. Fill 130g of the obtained mixture into a platinum crucible,
It was heated and melted at 1300℃ for about 10 hours in a silicon carbide exothermic electric furnace. Thereafter, it was slowly cooled to around 1000°C at a rate of 4°C/h, taken out from the electric furnace, allowed to cool to room temperature, the flux was dissolved with boiling water, and the crystals were separated. The obtained crystals were needle-shaped and elongated in the C-axis direction and were pale gray in color. The average size of the needle-like crystals was 0.1 mm in diameter and 5 mm in length. The results of chemical analysis were K _1.0 Ti _15.0 Ga _17.0 O ₅₆ . In addition, if Rb ₃ CO ₃ is used instead of K ₂ CO ₃ ,
If you use Rb _1.0 Ti _15.0 Ga _17.0 O ₅₆ , Cs ₂ CO ₃
Similar needle-like crystals of Cs _1.0 Ti _15.0 Ga _17.0 C ₅₆ are obtained. (2) Measurement of ionic conductivity The conduction mechanism of the one-dimensional ionic conductor of the compound of the present invention is explained by a different theory from the conventional transmission mechanism of β-alumina. That is, this is explained by the fact that K ions existing in a one-dimensional tunnel move within a region surrounded by random potential disturbances. According to this, when the conductivity is expressed by the complex conductivity σ, it is expressed by the following equation, and the electrical equivalent circuit for analyzing the measured value is shown in FIG. σ＝iωε _fw ε ₀ +iωε _p ε ₀・C(iω)〓／iωε _p ε ₀
+C(iω)〓 In Fig. 1, ε _p = polarization of ions in the tunnel ε ₀ = inductivity of vacuum ε _fw = dielectric constant ω related to the tunnel structural framework = angular frequency i = imaginary number C = one-dimensional conduction The constant of the conductivity function (iω) = indicates the frequency-dependent term of the conductivity function of one-dimensional conduction. Conductivity can be determined by alternating current measurement using a deposited gold film as an electrode and under conditions that block K ions. Regarding the crystal obtained in (1) above, that is, the sample with a length of 5 mm and a diameter of 0.1 mm grown in the crystal C-axis direction,
The real part and imaginary part of AC complex conductivity from 10 ² Hz to 325 GHz were calculated using a broadband impedance measuring device and a microwave standing wave method. The measurement results were as follows.

【table】

[Table] From the above results, it can be seen that it has the following characteristics. The ionic conductivity of the compound of the present invention is significantly dependent on frequency, exhibiting an extremely high ionic conductivity in a high frequency range, and no ionic conductor comparable to this has hitherto existed. In addition, the temperature dependence is extremely small, and the activation energy is extremely small at 0.048 eV, and there is no comparable ionic conductor to date. Note that similar ionic conductivity was obtained when Rb ions or Cs ions were used instead of K ions, or when a solid solution of K or Rb with Li or Na was used. Also, one part of Ti is Mn, one part of Ga is Al, Fe,
Alternatively, similar ionic conductivity was obtained when replacing with Cr.

[Brief explanation of drawings]

FIG. 1 shows an electrical equivalent circuit that can be used to analyze the measurement results of the one-dimensional cation conductor of the present invention. ε _p : polarization of ions in the tunnel, ε ₀ : permittivity of vacuum, ε _fw : relative permittivity related to the tunnel structural framework, ω : angular frequency, i : imaginary number, C : conductivity function of one-dimensional conduction. Constant, (iω)〓: Frequency-dependent term of the conduction relationship for one-dimensional conduction.

Claims (1)

[Claims] 1. General formula M _x Ti _16-x Ga _16+x O ₅₆ (where M is K,
A cation conductor consisting of a compound having a tetragonal one-dimensional tunnel structure represented by Rb, K or a solid solution of Rb with Li or Na, or Cs (representing x=0.1 to 2.0). 2 General formula M _x Ti _16-x Ga _16+x O ₅₆ (M is K,
A compound having a tetragonal one-dimensional tunnel structure represented by Rb, K or a solid solution of Rb with Li or Na, or Cs, x = 0.1 to 2.0),
A cation conductor made of a compound in which a portion of Ti is replaced with Mn. 3 General formula M _x Ti _16-x Ga _16+x O ₅₆ (M is K,
A compound having a tetragonal one-dimensional tunnel structure represented by Rb, K or a solid solution of Rb with Li or Na, or Cs, x = 0.1 to 2.0),
A cation conductor made of a compound in which a portion of Ga is replaced with Al, Fe, or Cr.