The Crystal Structures of Thallium(I) Fluoride |
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Authors: | P. Berastegui S. Hull |
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Affiliation: | a Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91, Stockholm, Sweden;b The ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, United Kingdom |
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Abstract: | ![]() The effects of temperature and pressure on the crystal structures of thallium(I) fluoride have been investigated using powder neutron diffraction, with the aim of resolving the uncertainties present in the literature. Under ambient conditions, TlF adopts an orthorhombic structure in space group Pbcm with Z=4 and cell parameters a=6.09556(8) Å, b=5.48860(7) Å, and c=5.18300(7) Å. This structure can be derived from an idealized rocksalt-type arrangement, though with extensive distortions of the anion sublattice due to the presence of the 6s2 inert pair of the Tl+ Above 355 K TlF becomes tetragonal with Z=2, a=3.78283(2) Å, c=6.12312(5) Å, and space group P4/nmm. The behavior of the compound is also studied under hydrostatic pressure but, contrary to previous reports, no structural transition was observed and TlF remains orthorhombic up to at least 3.5 GPa. The compressibility is greatest along the a and b axes. The relationship between the ambient- and high-temperature structures of TlF is described and the influence of the inert pair discussed in relation to the massicot structured polymorph of PbO. |
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Keywords: | thallium(I) fluoride electron lone pairs neutron diffraction. |
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