CONTINUOUS ORDER-DISORDER TRANSITION IN LI3NI2NBO6 AND CR-DOPED LI3NI2NBO6 ROCK SALT STRUCTURES

摘要

Li3Ni2NbO6 has a partially ordered rock salt superstructure in which Nb occupies fully one set: of octahedral sites and Li/Ni are distributed nonrandomly over three other sets of octahedral sites (Mather et at., J. Mater. Chem. 5, 1177 (1995)). Over the temperature range 25-1100 degrees C the Li/Ni site occupancy distribution is largely unchanged. Above 1100 degrees C, Nb increasingly occupies the Li/Ni sites until, above 1300 degrees C, the cations are completely disordered. The transition appears to be fully continuous, with no evidence of a transition enthalpy by DTA, Cr3+ ions are able to substitute partially into both ordered and disordered structures by a range of mechanisms. The temperature range of the order-disorder transition decreases with Cr content, as shown in the phase diagram of the vacancy solid solutions, Li3-xNi2-xCrxNbO6 (0 < x < 0.18). The materials are modest, semiconductors. (C) 1996 Academic Press, Inc. [References: 4]