The Crystal Structures of Thallium(I) Fluoride

✍ Scribed by P. Berastegui; S. Hull

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 332 KB
• Volume: 150
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8587

✦ Synopsis

The e4ects of temperature and pressure on the crystal structures of thallium(I) 6uoride have been investigated using powder neutron di4raction, 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) A > , b ‫؍‬ 5.48860(7) A > , and c ‫؍‬ 5.18300(7) A > . 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 6s 2 inert pair of the Tl ؉ Above 355 K TlF becomes tetragonal with Z ‫؍‬ 2, a ‫؍‬ 3.78283(2) A > , c ‫؍‬ 6.12312(5) A > , 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 in6uence of the inert pair discussed in relation to the massicot structured polymorph of PbO.