Li+ ion doping into KI-KBH4 solid solvent systems: The role of the BH4− anion

Abstract

In order to clarify the effect of BH4− anions on the Li+ ion doping into the KI-KBH4 solid solvent systems, the concentrations of the Li+ and BH4− ions in a solid solvent were separately controlled. The dissolving of LiI into the KI-KBH4 solid solvent was confirmed, while the formation of a solid solution between KI and LiI was not realized without the BH4− anions in the solid solvent. For the solid solvent doped with 10 mol% BH4− ions (9KI·KBH4), LiI could dissolve up to 6 mol%. The lattice parameters of the KI-KBH4 systems increased when the Li+ ions were doped. The 7Li MAS-NMR spectrum for the KI-KBH4 system dissolved with LiI showed one resonance peak at −0.72 ppm whose position is quite different from that for LiI (−4.57 ppm). These results indicated that the doped Li+ ions would not simply substitute the host K+ ions, but occupy the interstitial sites of the KI-KBH4 solid solvent. The results of the Rietveld analysis of the synchrotron radiation X-ray powder diffraction measurements showed that K+ vacancies are introduced by the doing of the interstitial Li+ ions as a charge balance.