Altering the structural properties of A2B12H12 compounds via cation and anion modifications

The recent discovery of unusually high cationic conductivity in Na2B12H12 above its entropy-driven, order-disorder phase transition near 529 K and the expected similar conductivity behavior in Li2B12H12 above its transition near 615 K have led us to investigate modifications of these two materials in an effort to reduce their transition temperatures and thus extend their high conductivities to more technologically favorable values. Differential scanning calorimetry measurements of perhalogenated Na2B12X12 (X = Cl and I), which are larger anion relatives of Na2B12H12, suggest unfavorably higher transition temperatures near 730 K and 816 K, respectively. New mixed-cation LiyNa2 yB12H12 phases show intermediate transition temperatures between those of Li2B12H12 and Na2B12H12. X-ray diffraction measurements and neutron vibrational spectra corroborate low-temperature ordered structures (for y = 0.67, 1, and 1.33) similar to Li2B12H12, with Li+ and Na+ disordered among the near-trigonal cation sites. (C) 2015 Elsevier B.V. All rights reserved.