Structural and electrical characterization of MxNb3Se4 (M = Cu, H)

The compounds Cu_xNb₃Se₄ (0≤x≤0,45) and H_xNb₃Se₄ (0≤x≤2·10⁻³) were prepared by electrochemical titration from Nb₃Se₄. The samples were characterized by X-ray analysis and q-probe conductivity measurements as a function of temperature. The Cu-compound is isostructural with Nb₃Se₄ for 0≤x≤0.2 and shows new phases for 0,2≤x≤0,45. The H-compound shows an impurity controlled conductivity in the temperature range from 20 to 200 °C and an intrinsic type conductivity in the temperature range from 330 to 450 °C. The activation engines are 0 and 0.15 eV, respectively. Rapid proton conduction in H_xNb₃Se₄ makes it difficult to control the composition as demonstrated by exposure of the samples to different atmospheres. An increasing H-concentration decreases drastically the conductivity by several orders of magnitude.