Calculation of the nonstoichiometry area of nanocrystalline palladium (II) oxide films

Abstract

Nanocrystalline palladium (II) oxide films were synthesised using thermal oxidation in the oxygen atmosphere of the initial ultradispersed metal palladium layers with a thickness of ~ 35 nanometres that were obtained on SiO2/Si (100) substrates using the method of thermal sublimation in high vacuum. Using X-ray analysis, it was established that during thermal oxidation in the oxygen atmosphere within the temperature range T = 670–970 K the values of the a and c parameters of the tetragonal lattice as well as the unit cell volume of nanocrystalline PdO films increased monotonously with the rise of the temperature reaching the maximum values at T = 950–970 K. It was found that the parameters of the tetragonal lattice and the unit cell volume of nanocrystalline PdO films decreased as the oxidation temperature increased up to T > 970 K Based on the ratio of the c/a parameters, it was shown that the main contribution to the deformation phenomena of the tetragonal lattice were mostly due to the increase in the elementary translations along the coordination axes OX and OY. Based on an assumption that the ionic component of the chemical bond is essential to the palladium (II) oxide structure, we suggested a method for the calculation of the range of the nonstoichiometry area for nanocrystalline PdO films, using the reported data on the radii of cation Pd2+ and anion O2-taking into account their coordination environment. The results of the calculations showed that nanocrystalline PdO films synthesised with an oxygen pressure of ~ 105 kPa are characterised by the two-sided homogeneity region in relation to the stoichiometric ratio of the components. The homogeneity region of nanocrystalline PdO films is characterised by the retrograde solidus line in the range of the temperatures T = 770–1070 K

Keywords

• palladium (ii) oxide
• nanostructures
• thermal oxidation
• crystal structure
• nonstoichiometry
• point defects
• gas sensors