Ion transport mechanism in anhydrous lithium thiocyanate LiSCN part II: frequency dependence and slow jump relaxation

Abstract

Specific aspects of the Li+ cation conductivity of anhydrous Li(SCN) are investigated, in particular the high migration enthalpy of lithium vacancies. Close inspection of impedance spectra and conductivity data reveals...

Ion transport mechanism in anhydrous lithium thiocyanate LiSCN Part I: ionic conductivity and defect chemistry

“…Li(SCN) breaks this relation, with a relatively low formation enthalpy and a high migration enthalpy. As will be shown in more detail in Part II, 40 this deviation is closely related to the specific ion transport mechanism in Li(SCN). The important difference between Li(SCN) and the lithium halides is the bidentate, anisotropic (SCN) − anion, since Li + can coordinate both to and − 〈NCS〉, with Li–N bonds being more favorable than Li–S bonds.…”

“…Although the highly polarizable anion facilitates defect formation, its very asymmetric interaction of sulfur and nitrogen with Li + cations hinders the migration of mobile defects, which renders the material a poor conductor. More details about this impact as well as the defect chemistry close to the melting point will be given in separate publications (Part II 40 and III 41 ).…”

“…10,11,23 This complexity is rooted in the frequency dependent conductivity of Li(SCN) and will be discussed in detail in Part II. 40 In the present work, only the DC resistance (low frequency intersection with the real axis) is of importance, thus only the low frequency part of the spectra was fitted with the circuit shown in Fig. 2.…”

“…All experimental and computational details are given in the ESI †. In Part II of this series of publications we discuss the frequency dependence of the ion conductivity in Li(SCN), 40 and Part III reports on the defect chemistry in the premelting regime. 41…”

Ion transport mechanism in anhydrous lithium thiocyanate LiSCN part III: charge carrier interactions in the premelting regime

“…However, Li(SCN) is Schottky disordered, which means that in order to become superionic, both cation and anion sublattices must have a defect concentration similar to the number of lattice sites, and at least one must have a high mobility. As discussed in Part II, 2 the mobilities of cation and anion can be (and indeed often are) correlated, and in case of a Schottky disordered material it is therefore more likely that the completely molten state is more stable. In contrast, in Frenkel disordered W< %" a stable situation can be reached in which only the cation lattice is molten (transition to M<2 3…”