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Modulations in B8-type Intermetallics

Elding-Pontén, Margareta LU (1997)
Abstract
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... (More)
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. (Less)
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author
opponent
  • Dr Landa-Canovas, Angel
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Electron diffraction, X-ray diffraction, Superspace group, Edshammar polyhedron, Mn-Sn, Cu-In, B8-type, Ni2In, NiAs, Modulation, Superstructure, Inorganic chemistry, Oorganisk kemi
pages
133 pages
publisher
Inorganic Chemistry, Chemical Center, Lund University
defense location
Room F, Chemical Center, Lund
defense date
1997-04-11 13:15
external identifiers
  • other:ISRN: LUTKDH/(TKOO-1018)/1-71/1997
ISBN
91-628-2413-9
language
English
LU publication?
yes
id
17fdab80-5265-47df-a98e-738bca536adf (old id 29120)
date added to LUP
2007-06-14 09:20:17
date last changed
2016-09-19 08:45:10
@phdthesis{17fdab80-5265-47df-a98e-738bca536adf,
  abstract     = {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.<br/><br>
<br/><br>
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.<br/><br>
<br/><br>
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.<br/><br>
<br/><br>
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.},
  author       = {Elding-Pontén, Margareta},
  isbn         = {91-628-2413-9},
  keyword      = {Electron diffraction,X-ray diffraction,Superspace group,Edshammar polyhedron,Mn-Sn,Cu-In,B8-type,Ni2In,NiAs,Modulation,Superstructure,Inorganic chemistry,Oorganisk kemi},
  language     = {eng},
  pages        = {133},
  publisher    = {Inorganic Chemistry, Chemical Center, Lund University},
  school       = {Lund University},
  title        = {Modulations in B8-type Intermetallics},
  year         = {1997},
}