Determination structurale et proprietes de conduction d'un nouveau compose de type hollandite: K 1,8(Li 2,45Sb 5,55)O 16; mise en evidence d'une surstructure d'ordre 3

Abstract

The crystal structure of a synthetic hollandite phase K 1,8(Li 2,45Sb 5,55)O 16 has been refined by the full matrix least-squares method using 940 three-dimensional reflexions to a final R value of 0.046. The K atoms are randomly distributed on the special positions 2b (0 0 1 2 ) and 4e (0 0 ±z) with z = 0.340(4). A long-exposure rotation photograph along the c axis shows diffuse X-ray scattering between the layer line. After a thermal treatment the X-ray diffraction pattern shows weak but sharp reflexions that could be indexed by tripling the short axis. The structural studies indicate an ordering of the large K atoms within the channels. The ionic conductivity of this phase has been investigated on a single crystal by hyperfrequences method. The potassium ion conductivity is the ordre of magnitude of 10 −3 (ohm cm −1) at 30°C along the c axis.