A simple method is reported for the synthesis of monodispersed HfO2 nanoparticles by the ammonia catalyzed hydrolysis and condensation of hafnium (IV) tert-butoxide in the presence of surfactants at room temperature. Transmission electron microscopy shows faceted nanoparticles with an average diameter of 3-4 nm. As-synthesized nanoparticles are amorphous in nature and crystallize upon moderate heat treatment. The HfO2 nanoparticles have a narrow size distribution, large specific surface area and good thermal stability. Specific surface area was about 239 m2/g on as-prepared nanoparticle samples while those annealed at 500 °C have specific surface area of 221 m2/g indicating that there was no significant increase in particle size. This result was further confirmed by TEM images of nanoparticles annealed at 300 °C and 500 °C. X-ray diffraction studies of the crystallized nanoparticles revealed that HfO2 nanoparticles were monoclinic in structure. The synthetic procedure used in this work can be readily modified for large scale production of monodispersed HfO2 nanoparticles.

Nanorods composed of complex oxides have been synthesized using hydrothermal and sol-gel methods, but pulsed-laser deposition (PLD) provides precise, layer-by-layer control of growth, and is the method of choice for synthesizing complex structures. However, producing complex-oxide nanorods by PLD has proved elusive.

Here we report on our efforts to produce nanorods composed of the best-understood complex oxide, strontium titanate (STO). The results suggest it is indeed possible to produce STO nanorods via PLD by using a template of MgO nanorods.

A substitution of La3+ by Sr2+ in LaCoO3 induces holes in the low-spin ground state of the Co ions, which behave like magnetic impurities with a very high spin value (13 μB per hole). In this work, using single-crystal neutron spectroscopy, we prove that the charges introduced by strontium doping do not remain localized at the cobalt sites. Instead, each hole not only creates Co4+ in low-spin state, but it also transforms the six nearest neighboring Co3+ ions to the intermediate-spin state thereby forming a magnetic seven-site (heptamer) polaron. Spin-state polarons behave like magnetic nanoparticles embedded in an insulating nonmagnetic matrix. Therefore, lightly doped La1-xSrxCoO3 is a natural analog to artificial structures composed of ferromagnetic particles in insulating matrices.

We present a systematic study of semiconductor and dielectric properties as a function of annealing treatments at CCTO thin films deposited by pulsed laser deposition at 720 °C in 200 mTorr oxygen. The as-deposited thin film samples contain a high concentration of defects that contribute to the semiconductivity in the interior of grains. With increasing annealing temperature, the apparent dielectric constant decreases, and the resistance increases, both at a given temperature (e.g. room temperature). After annealing at 680oC, the semiconductivity was almost completely suppressed and CaCu3Ti4O12 behaved as a dielectric material. Knowing that oxygen vacancies are removed during annealing, one can infer that the dopant states are related to oxygen vacancies. A double plateau behavior in the dielectric constant vs temperature graph indicates that there are at least two defect levels in CaCu3Ti4O12 thin films. This was confirmed by simulating the capacitance response of a Schottky barrier containing two defect levels. Apart of the usual acceptor level, a trap at 500 meV from the valence band was identified. The finally achieved quasi intrinsic material exhibits a negative temperature dependency of the dielectric constant below 120 K.

A modified sol-gel approach to synthesize well-crystallized pure and doped ZnO nanocrystalline powders and thin films has been developed. The attachment of ZnO films onto quartz substrates was optimized by selecting suitable organic agents to control the viscosity of precursor solutions. Thermo-gravimetric analyses on pure and doped precursor solids suggested the need for annealing temperatures above 400 °C to assure the effective crystallization of the oxide phase. The average crystallite size in powders and thin films varied from 25.9 nm to 33.7 nm when pure ZnO films were annealed for 1 hour in the 450 °C - 600 °C range. The average crystallite size ranged between 30 nm and 33 nm in the presence of cobalt (5 at%) and decreased from 33.7 nm to 21.1 nm when scandium ions was used in the 0.0 at% - 10 at% range under similar annealing conditions. UV-vis measurements showed a sharp exciton peak centered at 370 nm whereas photoluminescence analyses detected the characteristic ZnO emission band in the UV region. No photoluminescence band in the visible region, usually attributed to defect states in ZnO, was observed in our measurements. Magnetization measurements revealed a weak ferromagnetism in Co-doped ZnO whereas a clear diamagnetism was evident in the Sc-doped sample.

Applications of nanocrystalline multiferroics in sensor development, massive memory storage or in the fabrication of new devices taking advantage of the electron charge and spin explains the need of investigating various options to synthesize these types of materials. Among promising candidates, Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits ferromagnetism, ferroelectricity and ferroelasticity. The present research is focused on the systematic study of the polyol synthesis of substrate-less nanocrystalline BiFeO3 particles and its structural and magnetic characterization. As an attempt to explore the possibility of tuning the ferrite magnetic properties, host BiFeO3 was doped with cobalt ions in the 5at. % -10at. % range. Our results suggested that the ferrite formation and its properties were strongly dependent on both, the annealing conditions of the precursors and the concentration of cobalt species. Well-crystallized pure BiFeO3 was produced after annealing the precursor powders for one hour at 800oC. Doping with cobalt ions lowered the temperature at which the nanocrystalline BiFeO3 host structure was developed. The saturation magnetization and coercivity in the nanocrystalline ferrite were strongly influenced by the selected annealing temperatures and dopant concentration. These magnetic parameters varied from 0.30 emu/g and 109.5 Oe up to 4.2 emu/g and 988 Oe for pure and 10 at % Co-doped ferrite, respectively.

High-density TiO2-CdS and ZnO-CdS core-shell nanocable arrays were synthesized on large-area Ti substrates. The CdS layers were deposited on the pre-grown vertically-aligned TiO2 (rutile) and ZnO nanowire arrays, with a controlled thickness (10~50 nm), using the vapor transport method. The ZnO-CdS nanocables consisted of single-crystalline wurtzite CdS shells whose [001] direction was aligned along the [001] wire axis of the wurtzite ZnO core, which is distinctive from the polycrystalline shell of the TiO2-CdS nanocables. We fabricated the photoelectrochemical cell using the ZnO-CdS photoelectrode exhibits much more efficient hydrogen generation than that using the TiO2-CdS one.

In this paper we present the results of the studies on proton conduction in composites polyantimonic acid (PAA)-potassium dihydrophosphate (KDP) obtained by precipitation technique as well as mechanical mixing. The highest conductivity (~10-2 Sm/sm at 300 K) is achieved in the precipitated samples with volume fraction of KDP close to f = 13 %. The results of X-ray diffraction showed the absence of reflections from KDP for the samples with f < 20% and slight change in the intensities of odd and even reflections from PAA, which is explained by the ion exchange between the phases through the interface. These indicate that conduction is occurred through the interface regions of the composite. The value of interface conductivity is estimated from the dependence of the composite conductivity on the volume fraction of KDP based according to the model by Uvarov et al. This gives σs ≈ 5 Sm/sm, however the equation derived in this model doesn't represent the experimental data properly. Probably the maximum of the dependence simply corresponds to the percolation through the interface's continuous cluster – it is close to the classical percolation threshold.

Well-controlled architectures (aligned or horizontally suspended) of CuO nanowire (average diameter ~75±18 nm)-Co3O4 nanoparticle (average diameter ~7±1 nm) heterostructures were fabricated in a simple and surfactant-free growth approach. This approach coupled microfabrication methods with a thermal growth method and wet-coating technique. The fabricated heterostructures were characterized by high resolution electron microscopy (SEM and TEM) and X-ray Photoelectron Spectroscopy (XPS) for their size, morphology, phases, interfaces, and composition of heterostructures. Finally, CuO nanowire–Cox3O4 nanoparticle heterostructures were utilized as photocatalyst to degrade organic dye (methyl orange) under a wide range of wavelengths (from UV, 265 nm, to visible region, 580 nm).

The in-situ aqueous synthesis of ZnO nanorods doped with Sb is presented. To control the inclusion of Sb into the ZnO nanorods structure ethylene glycol (EG) is added to the reaction solution. The addition of EG reduces the rate at which Sb is included in the ZnO rods and produces nanorods with a morphology that is similar to the undoped rods. This is contrary to the rods produced with Sb in the absence of EG which produce a less well ordered structure. An I/V curve taken from individual rods indicates a change in the diode behaviour. The change in I/V behaviour is associated with a change from the natural n-type behaviour of ZnO to a p-type behaviour due to the Sb doping.

New complex oxide Sr0.75-xCaxY0.25Co0.25Mn0.75O3-δ with a perovskite-like structure has been synthesized and characterized. DC and AC transport properties of ceramic samples have been studied in the temperature range 4.2K – 1173K. DC conductivity data at T > 300K are discussed in terms of the small polaron hopping model. Dependence of the polaron activation energy on the calcium content is found to correlate with the change of structural distortion parameters. Both the temperature dependence of DC conductivity and the frequency dependence of the real part of the admittance reveal hopping transport at low temperatures.

This paper addresses the characterization of the ferroelectric Ba0.6Sr0.4TiO3 on different substrates using three different microwave components. First, at low frequencies, metal-insulator-metal (MIM) capacitors are used to investigate the variation of the BST dielectric constant and loss tangent for different biasing voltages. BST shows a variation for the dielectric constant from 380 to 130, recording a tunability range of 66 %, and loss tangent of 0.027 to 0.005. In the range of frequency from 1 to 40 GHz, coplanar waveguides (CPW) are used to investigate the effective dielectric constant of BST on four different substrates, HR silicon substrates covered by silicon dioxide, silicon covered by silicon dioxide and silicon nitride, magnesium oxide (MgO (100)), and R-plane sapphire (Al2O3) substrate, all covered with 350 nm BST layer. The effective dielectric constant over silicon substrates covered by silica and BST is 7.2, 6.3 for Al2O3 substrates and 5.8 for MgO; and for the loss tangent, Al2O3 and MgO give about 0.03, while silicon substrates suffer higher values of 0.08 to 0.25. Finally, to study the tunability of microwave structures on the investigated substrates, interdigital capacitors (IDC) are fabricated and measured for different biasing voltages ranging from 0 to 55 V. IDCs over MgO show a tunability of 8.3%, while IDCs over sapphire show 20%.

The present work is devoted to study the development of yttria-stabilized zirconia membranes self-supported on silicon-based microplatforms, to be used as electrolytes on micro solid oxide fuel cells. The microfabrication process to obtain yttria-stabilized zirconia membranes is detailed, and some key aspects for the integration of yttria-stabilized zirconia films deposited by pulsed laser deposition on the silicon-based microplatform are shown. Moreover, the effect on the thermomechanical stability of different fabrication parameters is presented, as well as the way to control the pinhole generation on the membranes. Finally, some electrical characterization guidelines are included, in order to study the effects of the platform and the membrane dimensions on the different measurements performed.

Colloidal subwavelength nanostructured surfaces were fabricated by the deposition of uniform silica nanoparticles on a glass substrate by means of electrostatic attraction between charged colloidal particles and charged polyelectrolyte multilayers. The effects of surface morphology via the variation of nanoparticles on the antireflective properties of the nanostructured surfaces were investigated by the analysis of the reflection spectra and the SEM images. The Maxwell's equations were solved by a rigorous coupled-wave analysis (RCWA) to evaluate the experimental results. It was found that the reflective properties revealed by the simulation analysis were similar to the experimental results. The nanostructured surfaces with particles of ~120 nm in diameter yielded the most suitable performance for antireflection with respect to the visible-light region. In addition, the nanostructured surfaces showed the good anti-scratch when the nanoparticles were bound by polyethoxysiloxane.

Two Ag/CeO2 nanocomposite samples were prepared by deposition-precipitation (Ag/Ce nominal atomic ratio = 0.03 and 0.12). XPS data suggest the possible presence of traces of Ce(III). Beside Ag (0), oxidized silver species are also revealed in the Ag/CeO2 sample with lower metal content. The deposition of metal increases surface hydroxylation and carbonatation. Methanol interacts molecularly and dissociatively with the samples; oxidation products are observed from low temperature and depend on Ag content. Both the samples reveal a high activity in methanol complete oxidation; traces of partial oxidation products are observed in the sample with lower Ag content.

Indium Tin Oxide (ITO) films were deposited by RF sputtering onto glass and quartz substrates with no external heating. An ITO target containing 10 wt% SnO2 was used for the deposition in a Kurt Lesker PVD75 system, in an atmosphere of 50% O2 + 50% Ar. Post-deposition heat treatments were done on these coatings at 150°C, 300°C and 450°C in an atmosphere of commercial air or argon. The effects of these heat treatments on the microstructure and the properties of the films were evaluated using atomic force microscopy, resistivity measurements, and UV-visible absorption spectroscopy. The heat treatments were observed to significantly affect the properties such as transmittance in the visible region, optical band gap and the electrical resistivity of the films. The main differences are caused by the differences in thermal expansion coefficient of the substrates as compared to the sputtered ITO films.

In this work nanoclusters of vanadium dioxide (VO2) buried in 200 nm thick SiO2 on silicon have been irradiated with increasing fluences of He ions. The projected range of He was chosen to be 650 nm in order to avoid residual He in the VO2 nanoclusters and the surrounding SiO2. The VO2 nanoclusters have been synthesized by sequential ion implantation of the elements vanadium and oxygen followed by a rapid thermal annealing step. Irradiation with He ions leads to the generation of reversible lattice point defects in the nanocrystalline VO2 precipitates. Simultaneously there is no electronic doping by He incorporation. The effect of the local- and long-range structural disorder on the metal-to-insulator phase transition has been investigated as a function of He fluence by μ-Raman spectroscopy and temperature dependent spectral ellipsometry. The disappearance of a low-frequency Raman mode indicates increasing disorder in the long-range crystal structure due to He irradiation. At the same time the thermal hysteresis of the metal-to-insulator transition narrows.

In present paper we describe some unconventional adaptions of sol-gel method. Controlled sol-gel transformation processes of metal alkoxide based systems can lead to various novel shapes of metal alkoxide materials. Formation of different structures like tubular microstructures by gel sheet rolling, nano- and microfibres by direct drawing, as well as microtubes of metal oxides and gel dispersed liquid crystal materials are described. Different aspects of sol-gel processes leading to the formation of all of these structures are thereby discussed.

High-resolution piezoresponse force microscopy (PFM) was used to measure the out-of-plane (effective longtitudinal) and in-plane (effective shear) piezoresponse of zinc oxide films and microrods. Thin films were deposited by pulsed laser deposition (PLD) and micro rods formed from solution. Measurements of three components of piezoresponse, one out-of-plane (OPP) and two in-plane (IPP) signals, allowed the construction of 3D piezoelectric maps reflecting the polycrystalline nature of the films. Both the IPP and OPP piezoresponse signal distributions are analyzed based on the particular texture of the films. It was observed that the central part of microrods contains polarization inversion with head-to-head ferroelectric-like domains. The as-grown domain boundaries were always parallel to the (0001) basal plane. Analysis of the PFM piezoresponse images was done based on the hexagonal structure of ZnO and topographic features along the hexagonal axis.

The detailed structure of nanocrystalline BaTiO3 powder during ball milling has been studied using XRD & TEM. The study illustrates important advances in understanding atomic scale properties of this material. Ferroelectric BaTiO3 powder undergoes phase transformation along the sequence Cubic(Pm3m)-tetragonal(P4mm)-orthohombic (Amm2)-rhombohedral(R3m) structure when pressureless sintered samples are cooled from high temperature to low temperature. The high to low symmetry phases are not related to group subgroup symmetry as transformation is discontinuous and first order in nature and the twin relationship in the low symmetry is forbidden by Landau theory. In case of ball milled BaTiO3 powder a continuous and diffusionless phase transition occur via second order to and from a metastable intermediate phase. In this pathway crystallites in the aggregation are twinned and the twin structure is related to crystal point group m3m which in the present case is illustrated as having 6mm symmetry formed under low driving force. The unit cell evolution due to phase transition and the crystallographic relationship are established. The phase transformation, coalescence and twin structure of thermally annealed BaTiO3 nanocrystals under high vacuum has been investigated using in situ high temperature XRD. The structure analysis is performed with the use of the method of computer modelling of disorder structure and simulation of corresponding diffraction pattern.