Properties of Oxide Nanoparticles : The current knowledge on oxide materials allows to affirm that most of their
physical-chemical properties display an acute size dependence. Physical-chemical properties of special relevance
in Chemistry are mostly related to the industrial use of oxides as sensors, ceramics, absorbents and/or catalysts.
A bunch of novel application within these fields rely on the size-dependence of the optical, (electronic and/or
ionic)transport, mechanical and, obviously, surface/chemical (redox, acid/base) properties of oxide
nanomaterials. We should stress that size effects in oxide chemistry have frequently two interrelated faces,
structural/electronic quantum-size and size-defect or non-stoi chiometry effects. Hence, here we will describe
the influence of these two phenomena in the main physic-chemical properties of oxides
Oxide Nanoparticles play a very important role in many areas of chemistry, physics and materials science. The
metal elements are able to form a large diversity of oxide compounds. These can adopt a vast number of
structural geometries with an electronic structure that can exhibit metallic, semiconductor or insulator character.
In technological applications, oxides are used in the fabrication of microelectronic circuits, sensors, piezoelectric
devices, fuel cells, coatings for the passivation of surfaces against corrosion, and as catalysts. In the emerging
field of nanotechnology, a goal is to make nanostructures or nano arrays with special properties with respect to
those of bulk or single particle species. Oxide nanoparticles can exhibit unique physical and chemical properties
due to their limited size and a high density of corner or edge surface sites. Particle size is expected to influence
three important groups of basic properties in any material.
Oxide Nanoparticles first one comprises the structural characteristics, namely the lattice symmetry and cell
parameters. Bulk oxides are usually robust and stable systems with well-defined crystallographic structures.
However, the growing importance of surface free energy and stress with decreasing particle size must be
considered: changes in thermodynamic stability associate with size can induce modification of cell parameters
and/or structural transformations and in extreme cases the Oxide Nanoparticles can disappear due to
interactions with its surrounding environment and a high surface free energy. In order to display mechanical or
structural stability, a nanoparticle must have a low surface free energy. As a consequence of this requirement,
phases that have a low stability in bulk materials can become very stable in nanostructures.
Oxide Nanoparticles structural phenomenon has been detected in TiO2, VOx, Al2O3 or MoOx oxides. Sizeinduced structural distortions associated with changes in cell parameter shave been observed, for example, in
Oxide Nanoparticles of Al2O3, NiO,Fe2O3,ZrO2,MoO3,23 CeO2,22 and Y2O3.23 As the particle size decreases,
the increasing number of surface and interface atoms generates stress/strain and concomitant
structuralperturbations.24 Beyond this “intrinsic” strain, there may be also “extrinsic” strain associated with aparticular synthesis method which may be partially relieved by annealing or calcinations. Also, nonstoichiometry is a common phenomenon. On the other hand, interactions with the substrate on which the
nanoparticles are supported can complicate the situation and induce structural perturbations or phases not
seen for the bulk state of the oxides
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