Evidence for structural and electronic instabilities at intermediate temperatures in K-(BEDT-TTF){sub 2}X for X=Cu[N(CN){sub 2}]Cl, Cu[N(CN){sub 2}]Br and Cu(NCS){sub 2} : implications for the phase diagram of these quasi-2D organic superconductors

We present high-resolution measurements of the coefficient of thermal expansion {alpha}(T)={partial_derivative} ln l(T)/{partial_derivative}T of the quasi-two-dimensional (quasi-2D) salts {kappa}-(BEDT-TTF){sub 2}X with X=Cu[N(CN){sub 2}]Cl, Cu[N(CN){sub 2}]Br and Cu(NCS){sub 2} in the temperature range T