Igor Kosacki

RAMAN SCATTERING AND LATTICE DEFECTS IN NANOCRYSTALLINE CEO2 THIN FILMS

Abstract The results of Raman scattering studies of nanocrystalline CeO 2 thin films are presented. The spectra have been described using the spatial correlation model from which the correlation length has been determined as a function of grain size. A direct comparison between the concentration of defects related to correlation length and CeO 2 non-stoichiometry has been achieved. The relationship between the lattice disorder and the form of the Raman spectra in nanocrystalline CeO 2 is discussed.

Defect and transport properties of nanocrystalline CeO2−x

It is shown that unique defect thermodynamics and transport properties result for oxides of a few nanometers crystallite size. Fully‐dense CeO2−x polycrystals of ∼10 nm grain size were synthesized, and their electrical properties compared with those of samples coarsened from the same material. The nanocrystals showed reduced grain boundary resistance, 104 higher electronic conductivity, and less than one‐half the heat of reduction of its coarse‐grained counterpart. These properties are attributed to a dominant role of interfacial defect formation.

Electrical conductivity of nanocrystalline ceria and zirconia thin films

Abstract The results of studies of the preparation, structure and electrical conductivity of ZrO 2 :16% Y and CeO 2 thin films are presented. Dense films with grain size controlled in the region of 1–400 nm have been obtained on monocrystalline sapphire and polycrystalline Al 2 O 3 substrates using a polymeric precursor spin coating method. The electrical conductivity of nanocrystalline thin films has been studied as a function of oxygen activity and temperature and correlated with the microstructure. Nanocrystalline specimens are characterized by enhanced electrical conductivity and different stoichiometry compared with microcrystalline material.

Microstructure–electrical conductivity relationships in nanocrystalline ceria thin films

A study of nanocrystalline oxide thin film processing and influence of microstructure on the electrical properties of nanocrystalline Gd3+-doped CeO2 thin films was reported. Nanocrystalline films on sapphire substrate were prepared using a polymeric precursor spin coating technique. The grain size of these films depends upon the annealing temperatures and the dopant content, where higher content of dopant realized smaller grain size. The electrical conductivity of nanocrystalline Gd3+-doped CeO2 thin films was studied as a function of temperature and oxygen activity, and correlated with the grain size. The results show that the electronic conductivity of CeO2 increases, whereas the ionic conductivity increases in doped samples as the grain size decreases. From these results, the enthalpy of oxygen vacancy formation was determined as a function of grain size. For CeO2 sample, an enhancement of electronic conductivity was observed with decreasing grain size below 100 nm. In the case of Gd3+-doped CeO2, the electrical conductivity results show that an increase of the ionic conductivity was observed as the grain size decreased, which is related to a decrease in the activation energy for the ion mobility.

Nonstoichiometry and Electrical Conductivity of Nanocrystalline CeO\({2 - x} \)

AbstractWe synthesized dense CeO

Mixed conductivity in SrCe0.95Yb0.05O3 protonic conductors

{2 - x}

Nonstoichiometry and electrical transport in Sc-doped zirconia

polycrystals of ∼10 nm grain size and characterized their electrical conductivity, in order to determine whether the defect properties of nanocrystalline solids fundamentally differ from those of conventional materials. The nanocrystals exhibit enhanced electronic conductivity, greatly reduced grain boundary impedance, and a heat of reduction more than 2.4 eV lower per oxygen vacancy compared to their coarse-grained counterparts. We propose that defect formation at low energy grain boundary sites is responsible for these properties, and that nanocrystalline oxides represent bulk materials possessing the defect thermodynamics of interfaces.

The structure and electrical properties of SrCe0.95Yb0.05O3 thin film protonic conductors

The results of optical absorption measurements on nanocrystalline ZrO2:16%Y thin films are presented. Dense 0.7 μm thick films with 1–300 nm grain size have been obtained on sapphire substrate using a polymeric precursor spin coating technique. The relationship between the energy gap and microstructure of ZrO2:16%Y has been determined and discussed. The quantum confinement effect was observed at the grain size lower than 100 nm with the band gap energy shift of 0.25 eV when the microstructure was changed up to 1 nm. Some limitation of the model has been observed and discussed. The band gap energy of 5.62±0.05 eV has been determined as microstructure independent value.