Your browser has javascript turned off or blocked. This will lead to some parts of our website to not work properly or at all. Turn on javascript for best performance.

The browser you are using is not supported by this website. All versions of Internet Explorer are no longer supported, either by us or Microsoft (read more here: https://www.microsoft.com/en-us/microsoft-365/windows/end-of-ie-support).

Please use a modern browser to fully experience our website, such as the newest versions of Edge, Chrome, Firefox or Safari etc.

Modulations in B8-type Intermetallics

Author

  • Margareta Elding-Pontén

Summary, in English

The B8-type regions of the Mn-Sn and Cu-In systems have been investigated by means of electron and X-ray diffraction. The importance of the combination of these techniques in the study of B8-type phases is pointed out. In addition to the B8-type phases an alloy with a quasicrystal approximant structure has been studied.



In the Mn-Sn system at least three B8-type phases exist. An X-ray powder pattern of the low-temperature phase Mn3Sn2 has been refined with the Rietveld method. The structure of one of the high-temperature phases, Mn8Sn5, has been refined by using the JANA94 program for incommensurate structures, and for the other one, Mn12Sn7, a structural model has been proposed. All three structures are orthorhombic with different length of the a axis - 2ahex, 5ahex and 7ahex for Mn3Sn2, Mn8Sn5 and Mn12Sn7, respectively, in a commensurate approximation of the phases. ahex refers to the a axis of the base NiAs/Ni2In type cell.



In the Cu-In system at least four B8-type phases, A, B, C and Cu7In3, exist. A fifth phase, Cu11In9, is probably also based on the B8-type structure. The system is very complicated. The A, B and C phases seem to be related through gradual phase transitions. From the monoclinic high-temperature phase A the intermediate phase B is formed by a change in the modulation vector of the A-phase. There are different appearances of the B-phase because of the gradual change in its modulation vector. However, they all resemble each other, and all are closely related to the A-phase. At the end of this transition the C-phase appears as an orthorhombic superstructure with a=9ahex, b=sqrt(3)bhex, c=4chex.



The structure of the quasicrystal approximant (Mg,Na,Al)2(Al,Zn)3 has been refined from single-crystal data. The structure description is made in terms of successive shells of atoms with increasing size. The quasisymmetry of the phase arises from three shells with icosahedral (five-fold) symmetry. The fourth and outermost shell breaks this symmetry and reduces the symmetry to cubic.

Publishing year

1997

Language

English

Document type

Dissertation

Publisher

Inorganic Chemistry, Chemical Center, Lund University

Topic

  • Chemical Sciences

Keywords

  • Electron diffraction
  • X-ray diffraction
  • Superspace group
  • Edshammar polyhedron
  • Mn-Sn
  • Cu-In
  • B8-type
  • Ni2In
  • NiAs
  • Modulation
  • Superstructure
  • Inorganic chemistry
  • Oorganisk kemi

Status

Published

Supervisor

  • [unknown] [unknown]

ISBN/ISSN/Other

  • ISBN: 91-628-2413-9
  • ISRN: LUTKDH/(TKOO-1018)/1-71/1997

Defence date

11 April 1997

Defence time

13:15

Defence place

Room F, Chemical Center, Lund

Opponent

  • Angel Landa-Canovas (Dr)