The effects of a low temperature irradiation on TTF-TCNQ and related compounds
We present measurements of the electrical conductivity of TTF-TCNQ, TSF-TCNQ and HMTSF-TCNQ samples irradited at 21 K with fast neutrons (≈ 1 MeV). At this temperature, a 6.1015 fast neutrons/cm2 neutron dose increases the resistivity of HMTSF-TCNQ by a factor of 5 and decreases the resivities of TTF - and TSF - TCNQ by an order of magnitude.
We present a phenomenological quantitative analysis of the resistivity versus dose curves. The irradiated TCNQ - salts are considered like inhomogeneous materials composed of small damaged volumes more (or less) conducting than the “pure material” and included at random in a matrix of undamaged crystal. With this effective medium model one can estimate the number n of atoms included in the transformed volume around a radiation induced defect. n (TTF-TCNQ) ≈ 7000n (TSF-TCNQ) ≈ 23000 n (HMTSF-TCNQ) ≈ 17000 (absolute values of n are known within a factor 4 or 5).
The annealing effects on the low temperature radiation induced defects are examined. An annealing peak is observed about 140 K in TTF-TCNQ and 85 K in TSF-TCNQ.
These results suggest that, at low temperatures, irradiated TCNQ salts crystals as well as “pure” ones contain macroscopic inhomogeneities due to defects. They are probably mixtures of more ar less distorted volumes.
A comparison of the low temperature irradiation induced defects in TCNQ salts and in polymeric sulphur nitride is presented. An attempt is made to explain irradiation effects in HMTSF-TCNQ with a homogeneous semi-metal model previou.sly used for (SN)x or bismuth