Structure and magnetic property of potassium intercalated pentacene: observation of superconducting phase in K x C 22 H 14

We report the results from systematic investigations on the structure and magnetic properties of potassium intercalated pentacene as a function of potassium content, K x C 22 H 14 (1 ⩽ x ⩽ 3). Synchrotron radiation powder x-ray diffraction technique revealed that there are two different stable phases can be obtained via potassium intercalation, namely, K 1 C 22 H 14 phase and K 3 C 22 H 14 phase. Structural phase transition was induced when the potassium content was increased to the nominal value x = 3. This phase transition is accompanied by drastic change in their magnetic property, where those samples with compositions K 1 C 22 H 14 shows ferromagnetic behavior and those with near K 3 C 22 H 14 lead to observation of superconductivity with transition temperature, T c , of 4.5 K. It is first time that superconductivity was observed in linear oligoacenes. Both magnetization study and synchrotron radiation powder x-ray diffraction clearly indicates that the superconducting phase belong to K 3 C 22 H 14 as a result of phase transition from triclinic to monoclinic structure induced by chemical doping.