title: The phase transition of Pb8F14I2.
abstract: The reversible phase transition of Pb8F14I2is of continuous type and takes place at about 107 °C as monitored by temperature-dependent single crystal and powder X-ray diffraction measurements, optical microscopy, and differential scanning calorimetry. The low-temperature ferroelastic phase crystallizes in the orthorhombic crystal system (23 °C,Bmmb,Z= 2,a= 6.0699(6) Å,b= 6.0165(6) Å,c= 25.077(2) Å, 1487 structure factors, 41 parameter,R(F2) = 0.0346,wR(F2) = 0.0771) and changes its symmetry to the tetragonal crystal system into the high-temperature paraelastic phase (130 °C,I4/mmm,Z= 1,a= 4.2667(12) Å,c= 25.388(7) Å, 430 structure factors, 303 parameter,R(F2) = 0.0575,wR(F2) = 0.1564). Group-subgroup relationships between the two structures and a hypothetical intermediate structure are presented.
authors.affiliation: Division of Structural Chemistry, Institute for Chemical Technologies and Analytics, TU Wien, Getreidemarkt 9/164-SC, 1060 Vienna, Austria.
authors.forename: Matthias
authors.identifier: 0000-0001-5235-9910
authors.initials: M
authors.lastname: Weil
keywords: Crystal structure determination; Group–subgroup relationships; Lead fluoride halide; Thermal analysis