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Experimental diffusion measurements show that migration enthalpies of Cl−, Br− and I− in NaCl are comparable, while that of F− is considerably lower. Earlier studies had shown that migration enthalpies of Na+, K+, Rb+ and Cs+ in NaCl were similar. The polarised point ion model predicts migration energies of ions (by vacancy mechanism) to monotonically increase with ion size, contrary to experiment. Inversely, the shell model calculations rightly predict the variation of migration energies with ionic size. Thus, migration energies by vacancy mechanism do not vary significantly for ions larger than the host ions. However, in the case of the small ions, Li+ and F−, the migration energies by vacancy mechanism are much lower and in good agreement with experiment for F−.
Electrical conductivity measurements show that Ln 1−x Sr x CoO 3 , (Ln = Pr or Nd) undergoes a non-metal-metal transition when x≈0 3. The d.c. conductivity of compositions with 0<x<0.l obeys the T −1/4 law up to 400 K and the a.c. conductivity data follow the ω δ law with δ in the range 0.6-0.8. Surprisingly, however, δ seems to increase with increasing temperature. Thermopower measurements show clear evidence for a change in the mechanism of conduction (around 350 K) from variable range hopping to transport at E c . All these transport properties suggest that Co 4+ ions in Ln 1-x Sr x CoO 3 (0<x<0.1), considered as moving in a lattice of Co 3+ , form a degenerate gas and that the states at the Fermi energy are Anderson localized.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
For Abstract see ChemInform Abstract in Full Text.
