Comparison of morphology and electrical conductivity of various thin films containing nano-crystalline praseodymium oxide particles

It is well known that sensing performances depend critically on nature of sensor material, its structure and morphology. Praseodymium oxide nanoparticle has currently been receiving much attention as a new sensor material. Thus, three methods for the preparations of praseodymium oxide nanoparticles namely (i) direct heat treatment of praseodymium nitrate powder; (ii) precipitation of praseodymium nitrate solution as hydroxide nanoparticles followed by heat treatment; and (iii) synthesis of hydroxide nanoparticles in reverse micromulsion followed by heat treatment are hereby intensively studied. Powder X-ray diffraction and transmission electron microscopy (TEM) are employed to characterise the size and morphology of the praseodymium oxide particles. It is found that the microemulsion method gives the smallest particle size while the direct heat treatment gives the largest oxide particle size. In addition, the prepared oxide nanoparticles are fabricated as thin films on tin-doped indium oxide (ITO) electrode surface for electrochemical AC impedance characterisation. The impedance measurements of the films reveal that their electrical conductivity is inversely proportional to particle size, which is attributed to the decreasing resistance of grain boundaries as the grain size decreases.