AC conductivity and scaling studies of polycrystalline SnF2

doi:10.1016/j.matchemphys.2009.02.056

Materials Chemistry and Physics

Volume 116, Issue 1, 15 July 2009, Pages 81-87

https://doi.org/10.1016/j.matchemphys.2009.02.056 Get rights and content

Abstract

The conduction characteristics of SnF₂ from room temperature (300 K) to 463 K have been investigated by using impedance spectroscopy. The temperature dependent conductivity plot shows a break in conductivity around 443 K corresponding to the α → γ phase transition temperature. The electrical properties of SnF₂ are also investigated by extracting dielectric and modulus data from impedance values. The frequency dependent plots of M″ and Z″ show that the conductivity relaxation is non-Debye in nature. The activation energy responsible for relaxation has been calculated from the modulus spectra and is found to be almost the same as that from the temperature dependent dc conductivity data. The real part of conductivity and permittivity in addition to the modulus spectra of the present system show scaling behavior, which means σ′(ω), ɛ′(ω) and M′(ω) isotherms successfully collapse to a single master curve indicating that the relaxation mechanism is temperature independent. Different scaling approaches have been applied to arrive at a correlation between the scaling parameters.

Introduction

Fluoride ion conductors, which show high value of ionic conductivity among the anionic conductors due to the small size of the anion, are found to be useful in several solid state ionic devices such as solid state batteries, electrochromic devices and gas sensors [1]. The choice of the material, stannous fluoride for the present study is unique in the sense that unlike in the case of alkaline earth fluorides and lead fluoride, the dielectric and conduction characteristics of SnF₂ are not well explored. The good electrical performance of SnF₂ results due to the high polarizability of Sn²⁺ and weak coordination of F⁻ ion [2]. SnF₂ forms a number of solid electrolytes by combining with monovalent and divalent fluorides, which are found to be very attractive for various electrochemical applications [3]. SnF₂ is known to exist in three polymorphic forms. Among these α-SnF₂ (monoclinic) is known to be stable at room temperature. It transforms to γ-SnF₂ (tetragonal) in the temperature range of 413–453 K which is stable up to the melting temperature (488 K) and upon cooling γ-SnF₂ transforms to β-SnF₂ (orthorhombic) through a second order phase transition [4], [5]. $α -Sn F_{2} ⟶_{upon heating}^{413 - 453 K, I order} γ -Sn F_{2} ⇌_{upon cooling}^{340 K, II order} β -Sn F_{2}$

In this paper the dielectric and conduction characteristics of SnF₂ have been investigated through impedance spectroscopy and the impedance data have been analyzed under conductivity, permittivity and modulus formalisms in order to obtain a better insight of the relaxation properties of the material.

Section snippets

Experimental details

Powder sample of SnF₂ (Aldrich, 99%) was used in the present study as procured. For conductivity measurement, fine powder of SnF₂ was pelletized between thin layers of ultra fine graphite powder. The pellet was then mounted between two spring-loaded electrodes in an evacuated conductivity setup. The ac impedance data, ǀZǀ and phase angle were recorded using a HP4192A impedance analyzer over the temperature range of 300–463 K.

Impedance analysis

Fig. 1 shows typical complex impedance plots for SnF₂ at some selected temperatures. In all the cases the experimental complex impedance plot comprises of a depressed semicircle accompanied by a straight line on the low frequency side, suggesting electrolyte–electrode polarization at the blocking electrodes. Such depression of the semicircle may originate from the presence of distribution in relaxation times within the bulk response [6], [7]. The radius of the semicircle decreases with

Conclusion

The frequency dependent conductivity, permittivity and modulus behavior of SnF₂ have been investigated as a function of temperature. There is a decrease in conductivity during α → γ phase transition, associated with an increase in the activation energy for F⁻ ion migration from 0.53 eV (α-phase) to 0.76 eV (γ-phase). The real part of dielectric permittivity shows saturation at higher frequencies and a strong dispersion at lower frequencies. The frequency variation of M″ data has been characterized

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AC conductivity and scaling studies of polycrystalline SnF2

Abstract

Introduction

Section snippets

Experimental details

Impedance analysis

Conclusion

Solid State Ionics

Mater. Res. Bull.

Mater. Sci. Eng. B

J. Solid State Chem.

J. Solid State Chem.

Solid State Commun.

Solid State Ionics

Mater. Chem. Phys.

Solid State Ionics

Solid State Ionics

Inorg. Mater.

AC conductivity and scaling studies of polycrystalline SnF₂