Electric conductivity of doped triglycine sulphate crystals

Abstract

crystals. Single crystals of pure and doped TGS crystals were grown from seeds by slow cooling of a saturated solution of glycine, constituent acid and dopants in the stoichiometric ratio, at an initial rate of 0.2°C day-~ to a maximum of 1.0°Cday ~, under similar growth conditions. Transparent, flawless crystals of high optical quality were cleaved and silver electroded onto (0 1 0) faces so as to make the full face electrodes. The conductivity was measured using a three terminal sample holder by a Keighley 610C TABLE I Values of d.c. conductivity at room doped TGS crystals electrometer. The geometrical dimensions of the samples were chosen so that in the region of the phase transition, the readings could be taken at the lower section of the electrometer. Currents were measured one minute after the voltage switch on. The voltage used in the measurements was 100 V cm i. The ohmic contact of electrodes was verified by the linearity of the currentvoltage characteristics. During the measurements, the temperature was stabilized to within _+ 0.05 ° C. The values of conductivity of pure and doped TGS crystals, at room temperature and transition temperature are collected in Table I. Triglycine sulphate is an association compound, therefore, amino-acid glycine is expected to play a definite role in the conduction mechanism. It is possible that there is mixed conduction in these crystals, i.e. electronic, protonic and ionic conduction. The possibility of electronic conduction as in the case of protienes [5] can be ruled out. Because the band gap of glycine is