Phase transitions and thermal properties of gadolinium trifluoride

The temperature dependence of gadolinium trifluoride density in the solid a nd liquid states was determined by a gamma attenuation technique. Volume ch anges on solid-solid and solid-liquid transitions were measured. The densit y and volume coefficient of thermal expansion of the liquid salt at the mel ting point are equal to 5609+/-25 kg m(-3) and (16.2+/-0.5)x 10(-5) K-1, re spectively. The relative density reduction on melting equals 16.7+/-0.15%. The polymorphic transformation from the low-temperature orthorhombic modifi cation (a lattice of beta-YF3 type) into the high-temperature hexagonal pha se (LaF3 type) occurs with an increase BE the density (about 2.1%). The pec uliarities of the thermal expansion of the solid rare earth fluorides, unde rgoing phase transition beta-YF3-type-->LaF3-type, are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.