Thermal expansion of organic superconductor α-(BEDT-TTF)₂ NH₄Hg(SCN)₄ Available to Purchase

The temperature dependence of the linear thermal expansion coefficients (LTEC) of a single crystal of α-(BEDT-TTF)₂NH₄Hg(SCN)₄ where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene was studied by the meth­od of precision capacitive dilatometry in the temperature range 2-250 K along the crystallographic direction b (per­pendicular to the crystal layers). Negative values of LTEC were found below 4 K. Probably it is due to charge fluc­tuations as the temperature approaches the temperature of transition to the superconducting state T_c. It has been suggested that the bends on temperature dependence of LTEC observed in the temperature range 25-45 K are relat­ed to order-disorder arrangement of $NH4+$ ions. Weak maximum of the LTEC, detected at a temperature of about 200-220 K, can be caused by the processes of charge redistribution and the associated intermolecular interaction fluctuations.