The thermodynamics of the divalent metal fluorides. I. Heat capacity of lead tetrafluorostannate, PbSnF₄, from 10.3 to 352 K

Abstract

Can. J. Chem. 66,549 (1988).We have measured the heat capacity of the fast ion conductor PbSnF4 at 10.3 < T < 352 K by adiabatic calorimetry. Our resultsshow anomalous values in the C,,,, in the region 300 < T < 352 K . These are associated with the a-P crystallographic transition reported at 353 K. Because the upper temperature limit of our cryostat is around 354 K, it was impossible to follow the phase transition to completion. A more subtle anomaly in the C,,,,, was detected between 130 and 160 K. Standard molar thermodynamic functions are presented at selected temperatures from 5 to 350 K.

The thermodynamics of the divalent metal fluorides. II. Heat capacity of the fast ion conductor BaSnF4 from 7 to 345 K

“…1 are similar in shape. The small anomaly found previously in the PbSnF 4 salt between 130 and 160 K [13] is not present in the BaSnF4. At the lowest temperatures below~20 K, the two curves are compared in Fig.…”

“…2 in an expanded plot. The smooth background curve drawn beneath the peak is given as the dashed line, which defines the temperature region of the anomaly as 210< T< 310 K. The heat capacity of PbSnF4 [13] is also shown in Fig. 1 for comparison with that of BaSnF4.…”

“…The ~ phase, which has a fluorite structure with space group Fm3,,,, is stable above 623 K up to fusion around 661 K [4,[10][11][12]. The heat capacity of PbSnF4 was recently measured by us over the range 10.3 < T< 352 K by adiabatic calorimetry [ 13 ]. A subtle anomaly in the heat capacity was detected between 130 and 160 K, which correlates nicely with the nuclear magnetic resonance (nmr) work by Chadwick et al [14], whose results show a gentle drop in the 19F spin-lattice relaxation time in that temperature region.…”