Cryocooler regenerator material, cryogenic regenerator, regenerative cryocooler and system comprising regenerative cryocooler

1. A cryogenic regenerator, which is filled with a cryogenic regenerator material containing as a main constituent at least one compound (A), wherein a half width of a main peak obtained by a powder X-ray diffraction measurement on the compound (A) is 0.2 degrees or more,

wherein said at least one compound (A) is represented by a composition formula Ma 2 X or MbW 2 X 8 ,

wherein, in the composition formulae,

Ma represents a metallic element selected from Cu, Ag, Au, Pd and Pt, or two or more metallic elements comprising at least one selected from Cu, Ag, Au, Pd and Pt as the main constituent element,

Mb represents a metallic element selected from Zr and Hf, or two or more metallic elements comprising at least one selected from Zr and Hf as the main constituent element, and

X represents at least one non-metallic element selected from O, S and N.

2. The cryogenic regenerator of claim 1 , wherein the cryogenic regenerator material is a bulk body.

3. The cryogenic regenerator of claim 1 , wherein the cryogenic regenerator material contains the compound (A) in an amount of 40% or more with respect to the whole volume of the cryogenic regenerator material.

4. The cryogenic regenerator of claim 1 , wherein a density of the cryogenic regenerator material is 60% or more with respect to a theoretical density of the compound (A).

5. The cryogenic regenerator of claim 1 , wherein the compound (A) has a crystal structure containing at least one unit structure selected from a tetrahedral framework and octahedral framework each comprising the at least one non-metallic element X and the at least one metallic element Ma or Mb, wherein the tetrahedral framework and the octahedral framework are such that each vertex is occupied by the metallic element Ma or Mb with the center occupied by the non-metallic element X, or each vertex is occupied by the non-metallic element X with the center occupied by the metallic element Ma or Mb.

6. The cryogenic regenerator of claim 5 , wherein the compound (A) comprises two or more unit structures selected from the tetrahedral framework and the octahedral framework in the crystal structure, and at least one of the unit structures shares one vertex with at least one neighboring unit structure.

7. The cryogenic regenerator of claim 1 , wherein the compound (A) has a negative thermal expansion coefficient in a whole temperature range from 4 K to 100 K.

8. The cryogenic regenerator of claim 1 , wherein the cryogenic regenerator material further contains a substance with a positive thermal expansion coefficient in a temperature range from 4 K to 100 K.

9. The cryogenic regenerator of claim 1 , wherein the cryogenic regenerator material further contains a ductile metal.

10. The cryogenic regenerator of claim 1 , wherein the cryogenic regenerator material further contains a material with a higher thermal conductivity than that of the compound (A).

11. The cryogenic regenerator of claim 1 , containing at least one compound (A) represented by the composition formula Ma 2 X.

12. The cryogenic regenerator of claim 1 , wherein the half width of the main peak obtained by a powder X-ray diffraction measurement on compound (A) is 0.2 degrees −3 degrees.

13. A regenerative cryocooler comprising the cryogenic regenerator of claim 1 .

14. A system comprising the regenerative cryocooler of claim 13 .

15. The cryogenic regenerator of claim 1 , wherein the half width of the main peak obtained by a powder X-ray diffraction measurement on compound (A) is 0.3 degrees −2.5 degrees.

16. The system of claim 14 , wherein said system is a superconducting magnet apparatus, a magnetic resonance imaging (MRI) apparatus, a cryopump apparatus, a Josephson voltage standard system, or a magnetic field-applied single crystal pulling apparatus.

17. The cryogenic regenerator of claim 1 , containing at least one compound (A) represented by the composition formula MbW 2 X 8 .