Optical, electrical and magnetic properties of potassium metal loaded into channel-type zeolite L

Potassium metal was loaded into K-form zeolite L crystals which have one-dimensional (1D) main-channels with an inside diameter of ≈1 nm. The loading density of K atoms per unit cell, n, was changed from 0 to 9.6. Optical, electrical and magnetic properties were measured for the powders of K-loaded zeolite L crystals. A resonant optical absorption-reflection band is observed at ≈1.1 eV in all K-loaded samples. Another reflection band at ≈1.8 eV appears at n ⪆ 5. The 1.1 and 1.8 eV bands are assigned to the respective excitations from 1s to 1p and from 1p to 1d states of s-electrons confined in main-channels. A mid-infrared absorption around 0.3 eV is observed at n ⪆ 3 and increases with n. This absorption is assigned to a Drude term of s-electrons. A temperature-dependent semiconducting resistivity is observed at 3 ⪅ n ⪅ 9. A nearly metallic resistivity is observed at 9 ⪅ n. The semiconducting and metallic resistivities are assigned to the polaron hopping between main-channels and the three-dimensional (3D) band conduction, respectively. A temperature independent spin-susceptibility is extracted from the integrated intensity of ESR signal, and increases at n ⪆ 5. This term is assigned to the Pauli paramagnetism. These properties are interpreted in terms of an insulating state of 1s and 1p states at n ⪅ 5, a 1D metallic state of 1s and 1p states at 5 ⪅ n ⪅ 9 and a 3D metallic state of 1d state at 9 ⪅ n for s-electrons in the bundle of main-channels. (author)