The thermodynamics of the divalent metal fluorides. III. Heat capacity of the fast ion conductor SrSnF4 from 6 to 344 K

Abstract

The heat capacity of the fast ion conductor SrSnFl was measured by adiabatic calorimetry from 6 < T/K < 344. A phase transition was not detected, but an anomalous rise in the molar heat capacity was found above 280 K that showed no sign of lessening at 344 K. This rise is coincident with the temperature range where a rapid drop in the r9F spin-lattice relaxation time T, occurs. Standard molar thermodynamic functions are given at selected temperatures from 5 to 345 K. Q 1989 Academic PRSS. hc.

Mechanochemical Synthesis and Fluoride Ion Conductivity Studies in SrSnF4 Polymorphs

“…Furthermore, the absence of any discontinuities in the temperature-dependent conductivity plots (room temperature to 423 K) shows the absence of structural phase transitions over different temperatures in accordance with the earlier report on adiabatic calorimetry measurement. 12 The tetragonal SrSnF 4 phase consists of a layered structure favoring the faster diffusion of fluoride ions, whereas the random distributions of cations break the conduction plane resulting in lower ionic conductivity in the cubic phase (Figure 3). 19 The temperature-dependent conductivity plots of SnF 2 , milled SnF 2 (SnF 2 -BM-10 h), Sn 0.9 K 0.1 F 1.9 , 30 SrF 2 , milled SrF 2 (SrF 2 -BM-10 h), and Sr 0.7 Y 0.3 F 2.3 31 are shown in Figure 6a for comparison.…”

“…Various reports are known on the development of PbSnF 4 and BaSnF 4 materials in different forms and their applications on room-temperature FIBs. ,, However, the structural and transport details of the isostructural system SrSnF 4 are not known probably due to its low ionic conductivity value in comparison to the other MSnF 4 (M: Pb and Ba) materials. Earlier reports on SrSnF 4 mainly focused on the material development by a solid-state reaction method exhibiting a tetragonal structure. , A few reports are recently known on the XRD and impedance studies of both cubic and tetragonal BaSnF 4 systems. − In the current work, the structural and transport behaviors of SrSnF 4 crystallizing in cubic and tetragonal structures are compared by using XRD, scanning electron microscopy (SEM), and impedance spectroscopy techniques. The crystallite size is estimated from the broadening of the high intense diffraction peak by the Debye–Scherrer equation.…”

“…11 Earlier, the heat capacity and thermal expansion studies on SrSnF 4 using an adiabatic calorimetry technique have confirmed the absence of any structural phase transitions in the temperature range of 6 K < T < 344 K. 12 Earlier studies on the SrSnF 4 system have shown the preparation of the material by the solid-state reaction method at 773 K using an evacuated copper tube. 12,13 Earlier literature on the role of synthesis methodology in the ionic conductivity of an isostructural BaSnF 4 system by both dry (solid-state reaction and mechanochemical milling) and wet (coprecipitation) methods shows that the material prepared by mechanical milling exhibits the highest ionic conductivity. 14 It can also be seen that the mechanical activation reduced the preparation temperature from 773 K (solid-state reaction) to 573 K, and furthermore, the later method avoids complex synthesis procedures such as copper tube-based evacuation and heat treatment at higher temperatures.…”

“…Earlier reports on SrSnF 4 mainly focused on the material development by a solid-state reaction method exhibiting a tetragonal structure. 12,13 A few reports are recently known on the XRD and impedance studies of both cubic and tetragonal BaSnF 4 systems. 18−20 In the current work, the structural and transport behaviors of SrSnF 4 crystallizing in cubic and tetragonal structures are compared by using XRD, scanning electron microscopy (SEM), and impedance spectroscopy techniques.…”

“…The fluoride ion vacancies and interstitials in combination makes a large number of Frenkel defects which are known to be responsible for the anionic conductivity of these compounds . Earlier, the heat capacity and thermal expansion studies on SrSnF 4 using an adiabatic calorimetry technique have confirmed the absence of any structural phase transitions in the temperature range of 6 K < T < 344 K . Earlier studies on the SrSnF 4 system have shown the preparation of the material by the solid-state reaction method at 773 K using an evacuated copper tube. , Earlier literature on the role of synthesis methodology in the ionic conductivity of an isostructural BaSnF 4 system by both dry (solid-state reaction and mechanochemical milling) and wet (coprecipitation) methods shows that the material prepared by mechanical milling exhibits the highest ionic conductivity .…”