Investigations of the transport properties of single crystals and poly
crystalline pressed samples of K-(BEDT-TTF)213 are presented. In contr
ast to polycrystalline pressed samples of K-(BEDT-TTF)2Cu(NCS)2 and K-
(BEDT-TTF)2Cu[N(CN)2]Br those of K-(BEDT-TTF)2I3 show bulk superconduc
tivity indicating that the loss of superconductivity in the first two
types of samples is not due to the special structure of the K- phase,
but probably due to a disproportionation of Cu1+ under the anisotropic
pressure during the preparation of the samples. Annealing the single
crystals as well as the polycrystalline pressed samples of K-(BEDT-TTF
)2I3 at 75-degrees-C for a few days results in a structural transfomat
ion with an increase in the transition temperature for superconductivi
ty (about 8 K for the crystals). IR-spectra indicate a transfomation i
nto a structure which is identical with alpha(t) - (BEDT - TTF)2I3, wh
ich seems to be the thermodynamically most stable phase of the several
(BEDT-TTF)2I3 phases.