M. Boudard

Investigation of thickness-dependent stress in PbTiO3 thin films

X-ray diffraction (XRD) and Raman spectroscopy were used to investigate stress dependence on thickness in PbTiO3 (PTO) films grown by pulsed liquid injection metalorganic chemical vapor deposition on a LaAlO3 (001) substrate (LAO). Films on sapphire substrate (R plane) were used as the polycrystalline film reference. Epitaxial PTO films with a dominant c domain structure are grown on LAO substrate, whereas the films on sapphire are polycrystalline. A detailed investigation of the PTO/LAO film microstructure by XRD gives evidence of PTO twinning. Both techniques reveal that PTO films are under tensile in-plane stresses. The study of the film thickness dependence of microstrains, grain size, volume fraction of a domains, as well as surface morphology of PTO/LAO films indicates that these parameters are clearly correlated. A change in the relaxation mechanism between 65 and 125 nm of film thickness has been evidenced. A c parameter gradient occurs throughout the film depth; it originates in stress relaxation...

Layered Ni(OH) 2 -Co(OH) 2 films prepared by electrodeposition as charge storage electrodes for hybrid supercapacitors

Consecutive layers of Ni(OH)2 and Co(OH)2 were electrodeposited on stainless steel current collectors for preparing charge storage electrodes of high specific capacity with potential application in hybrid supercapacitors. Different electrodes were prepared consisting on films of Ni(OH)2, Co(OH)2, Ni1/2Co1/2(OH)2 and layered films of Ni(OH)2 on Co(OH)2 and Co(OH)2 on Ni(OH)2 to highlight the advantages of the new architecture. The microscopy studies revealed the formation of nanosheets in the Co(OH)2 films and of particles agglomerates in the Ni(OH)2 films. Important morphological changes were observed in the double hydroxides films and layered films. Film growth by electrodeposition was governed by instantaneous nucleation mechanism. The new architecture composed of Ni(OH)2 on Co(OH)2 displayed a redox response characterized by the presence of two peaks in the cyclic voltammograms, arising from redox reactions of the metallic species present in the layered film. These electrodes revealed a specific capacity of 762 C g−1 at the specific current of 1 A g−1. The hybrid cell using Ni(OH)2 on Co(OH)2 as positive electrode and carbon nanofoam paper as negative electrode display specific energies of 101.3 W h g−1 and 37.8 W h g−1 at specific powers of 0.2 W g−1 and 2.45 W g−1, respectively.

Morphological changes and electrochemical response of mixed nickel manganese oxides as charge storage electrodes

Nickel manganese (Ni–Mn) oxide films were prepared by potentiostatic electrodeposition over stainless steel and post-thermal annealing at 250 °C. Morphological and structural changes were observed depending on the Ni to Mn ratio in the electrolyte. Single-phase Ni1−xMnxO oxide was formed at low Mn content, whereas two phases composed of Ni1−xMnxO and NixMn3−xO4 were formed at high Mn content. Electrochemical studies revealed an increase of the specific capacitance of the mixed Ni–Mn oxide electrodes compared to the single metal oxides, thus pin-pointing a synergistic effect. The Ni–Mn oxide film displayed a specific capacitance of about 300 F g−1 in a potential window of 0.5 V at an applied current density of 1 A g−1. The rate capability of the oxides was 58% when the applied current was increased from 1 A g−1 to 10 A g−1. The Ni–Mn oxide film exhibits excellent cycling stability with 100% capacitance retention after 1500 cycles.

Influence of non-magnetic Ti4+ ion doping at Mn site on structural and magnetic properties of La0.67Ba0.33MnO3

We have investigated the effect of titanium substitution on the structure and the magnetic properties of manganites with La0.67Ba0.33Mn1?xTixO3 (0 ? x ? 0.3) nominal composition. The polycrystalline samples have been produced by the conventional ceramic method at 1523?K. The morphology, grain size and phase identification studies were carried out by scanning electron microscopy, diffraction techniques (neutron and x-ray) and the chemical compositions were precisely determined by the inductively coupled plasma atomic emission spectroscopy technique. The structural refinement at room temperature by the Rietveld method revealed that for x ? 0.1 the compounds are almost a single phase manganite crystallizing in a rhombohedral perovskite structure (LaAlO3 type). The more salient structural feature is an increase in cell parameter and inter-ionic distances with increasing Ti content. For x = 0 and x = 0.05 the samples exhibit two manganite phases with orthorhombic (Imma) and rhombohedral space groups. Compounds with x ? 0.1 are ferromagnetic with a Curie temperature decreasing with increasing x. More complicated magnetic behaviour is observed for larger Ti content.

Structural evolution, magnetic properties and electrochemical response of MnCo2O4 nanosheet films

MnCo2O4 spinel oxide nanosheets were prepared via electrodeposition and post thermal annealing on stainless steel substrates. The structural transformation of an electrodeposited hydroxide phase into a spinel phase was achieved by thermal annealing at different temperatures (250 °C, 350 °C, 450 °C and 650 °C). The surface morphology of the films revealed the presence of a nanosheet percolation network that was converted into nanoplatelets after annealing at 650 °C. The nanosheets are composed of nanocrystals and the crystal size of the MnCo2O4 spinel oxide increased from 10 nm after 250 °C annealing to 100 nm after 650 °C annealing, in which a twinning was observed. The magnetic transition temperature also increased from 101 K to 176 K for the films annealed at 250 °C and 650 °C, respectively. The spinel films displayed specific capacitance values above 400 Fg−1 at 1 Ag−1, making these spinel oxides promising pseudocapacitive materials.

Raman spectroscopy and X-ray diffraction studies of stress effects in PbTiO/sub 3/ thin films

The evolution of domain structure and in-plane and out-of-plane lattice parameters in PbTiO3 (PTO) films on SrTiO3 (STO), LaAlO3 (LAO) and MgO substrates was studied as a function of film thickness and temperature by X-ray diffraction (XRD). Microstrains and average grain sizes were determined in several crystallographic directions for films of different thicknesses using a Williamson-Hall and Langford analysis. Stress relaxation with film thickness was observed in different domains by Raman spectroscopy and greatly influences lattice parameters. Specific contributions of a-and c-domains on Raman spectra were analyzed and correlated to domains fraction. The high temperature structural phase transition was followed by Raman spectroscopy, showing that the transition depends on the nature of stress.

One-step process to form a nickel-based/carbon nanofoam composite supercapacitor electrode using Na2SO4 as an eco-friendly electrolyte

In this work, NiOx is anodically electrodeposited onto carbon nanofoam (CNF) to form a composite electrode devoted to supercapacitor applications. The use of NiSO4 as precursor in electrodeposition results in the formation of NiO and NiOOH species, as confirmed by XPS analysis, by means of a one-step anodic process. The presence of both NiO and NiOOH suggests the existence of pseudocapacitance, as observed in MnO2 and RuO2 materials. By employing Na2SO4, an eco-friendly electrolyte, the resulting composite delivers a specific capacitance of 150 F g−1 at 1 A g−1 considering the total mass of the electrode (deposit plus substrate). In addition, this composite electrode can operate in a very broad potential window, as high as 2.2 V, suggesting its application in high energy density electrochemical supercapacitors.

Yttria and ceria doped zirconia thin films grown by pulsed laser deposition

The Yttria stabilized Zirconia (YSZ) is a standard electrolyte for solid oxide fuel cells (SOFCs), which are potential candidates for next generation portable and mobile power sources. YSZ electrolyte thin films having a cubic single phase allow reducing the SOFC operating temperature without diminishing the electrochemical power density. Films of 8 mol% Yttria stabilized Zirconia (8YSZ) and films with addition of 4 weight% Ceria (8YSZ + 4CeO2) were grown by pulsed laser deposition (PLD) technique using 8YSZ and 8YSZ + 4CeO2 targets and a Nd-YAG laser (355 nm). Films have been deposited on Soda-Calcia-Silica glass and Si(100) substrates at room temperature. The morphology and structural characteristics of the samples have been studied by means of X-ray diffraction and scanning electron microscopy. Films of a cubic-YSZ single phase with thickness in the range of 1-3 µm were grown on different substrates.

Raman Spectroscopy and X-ray Diffraction Studies of Stress Effects in PbTiO 3 Thin Films

The evolution of domain structure and in-plane and out-of-plane lattice parameters in PbTiO3 (PTO) films on SrTiO3 (STO), LaAlO3 (LAO) and MgO substrates was studied as a function of film thickness and temperature by X-ray diffraction (XRD). Microstrains and average grain sizes were determined in several crystallographic directions for films of different thicknesses using a Williamson-Hall and Langford analysis. Stress relaxation with film thickness was observed in different domains by Raman spectroscopy and greatly influences lattice parameters. Specific contributions of a-and c-domains on Raman spectra were analyzed and correlated to domains fraction. The high temperature structural phase transition was followed by Raman spectroscopy, showing that the transition depends on the nature of stress.

Transport mechanism through metal-cobaltite interfaces

The resistive switching (RS) properties as a function of temperature were studied for Ag/La