ELECTROLESS DEPOSITION OF ORTHORHOMBIC COPPER (I) SELENIDE AND ITS ROOM-TEMPERATURE PHASE-TRANSFORMATION TO CUBIC STRUCTURE

A phase transformation from orthorhombic copper (I) selenide to its cubic (superionic conducting) structure has been carried out at room temperature by controlling the parameters of the electroless deposition. X-ray diffraction analysis of the film suggests that it has Berzelianite structure with a lattice constant 5.719 +/- 0.009 angstrom. It is found to be a direct band-gap semiconductor with a band gap of 1.31 eV and having a resistivity of 0.52 x 10(-3) OMEGA cm at 296 K. The transformations of cubic copper (I) selenide to orthorhombic copper (II) selenide and orthorhombic copper (I) selenide were carried out potentiostatically at +0.20 V and -0.78 V vs. saturated calomel electrode respectively. The lattice constants of orthorhombic copper (II) selenide have been evaluated from the X-ray diffraction data: a0 = 3.958 +/- 0.011 angstrom, b0 = 6.958 +/- 0.017 angstrom and c0 = 17.229 +/- 0.025 angstrom.