This communication focuses on the development of an approach to improve the synthesis of [Ti8O12(H2O)24]Cl8.HCl.7H2O crystals which is one of the precursor for titanium dioxide TiO2 particles. This study provides a significant improvement in crystallization kinetics with a production rate increased by a factor nineteen by intensifying heat and mass transfers compared to the process in a close vessel. This enhancement was made possible by the development of a new reactor to control the heat and mass transfers involved. In parallel with the experimental set-up, a numerical model representative of the transfer phenomena was initiated. The first numerical results are encouraging and present a good agreement with the measurements. Keywords: Heat and mass transfer; Co-desorption, Modelling, Experiment

Recent results have demonstrated an exceptionally high permittivity in the range 200–330 K in crystalline titanium oxide Rb 2 Ti 2 O 5 . In this article, the possibility of a structural transition giving rise to ferroelectricity is carefully inspected. In particular, X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy are performed. The crystal structure is shown to remain invariant and centrosymmetric at all temperatures between 90 K and 450 K. The stability of the C 2/ m structure is confirmed by density functional theory calculations. These important findings allow the existence of a conventional ferroelectric phase transition to be ruled out as a possible mechanism for the colossal permittivity and polarization observed in this material.

We have deposited transparent p-type semiconductive NiO thin films by reactive HiPIMS which appeared to be a powerful method to produce thin films exhibiting gradients of chemical compositions and opto-electronic properties. For a fixed amount of oxygen in the discharge (9%), the influence of the pulse duration was investigated. The position of the valence band with respect to the Fermi level was evaluated by X-ray Photoelectron Spectroscopy (XPS), for two different pulse durations, 15 and 30μs. We have then investigated the dependence of optical properties of NiO films using spectroscopic ellipsometry (1.5–5.0eV range). Refractive index n, extinction coefficient k, and gap energy of the NiO films were determined with a refractive index gradient decreasing along the film growth direction.

The present work aims at investigating the microstructure of Zn(O,S) buffer layers relative to their deposition route, namely either chemical bath deposition (CBD) or RF co-sputtering process (PVD) under pure Ar. The core of the study consists of cross-sectional transmission electron microscopy (TEM) characterization of the differently grown Zn(O,S) thin films on co-evaporated Cu(In,Ga)Se2 (CIGSe) absorbers. It shows that the morphology of Zn(O,S) layer deposited on CIGSe using CBD process is made of a thin layer of well oriented ZnS sphalerite-(111) and/or ZnS wurtzite-(0002) planes parallel to CIGSe chalcopyrite-(112) planes at the interface with CIGSe followed by misoriented nanometer-sized ZnS crystallites in an amorphous phase. As far as (PVD)Zn(O,S) is concerned, the TEM analyses reveal two different microstructures depending on the S-content in the films: for [S]/([O]+[S])=0.6, the buffer layer is made of ZnO zincite and ZnS wurtzite crystallites grown nearly coherently to each other, with (0002) planes nearly parallel with CIGSe-(112) planes, while for [S]/([O]+[S])=0.3, it is made of ZnO zincite type crystals with O atoms substituted by S atoms, with (0002) planes perfectly aligned with CIGSe-(112) planes. Such microstructural differences can explain why photovoltaic performances are dependent on the Zn(O,S) buffer layer deposition route.

In this paper, we characterize high transparency p-type semiconducting NiO thin films deposited by Direct Current Reactive Magnetron Sputtering from a pure Ni target in a mixture of oxygen and argon gases on Corning glass/SnO2:F substrates at different oxygen contents ranging from 0% at 30%. The influence of the O2/Ar ratio and thickness on transmittance has been examined using ultraviolet–visible spectroscopy. The results show that whatever the oxygen proportion into the discharge, the nickel oxide films exhibit a polycrystalline structure. At low oxygen content, the preferential orientation is (111), for stoichiometric films the XRD diagram is powder-like whereas the preferential orientation is (200) for higher oxygen content. For low and high oxygen content, the transmittance is low. Thanks to plasma method and its ability to tune the oxygen content in the discharge and therefore the film composition, we have been able to explore carefully the intermediate zone and obtain transparent films. The optical absorption coefficient α has been calculated from the transmittance and the variation of (αhν)2 versus the photon energy (hν) for nickel oxide is presented. The optical band gap energy has been evaluated and varies from 3.2 to 3.8eV.

Nickel oxide thin films were deposited by Direct Current magnetron reactive sputtering from Ni target onto SnO2:F conductive glass substrates. The process was carried out without intentional heating, in an argon/oxygen gas mixture with various oxygen contents and discharge currents. The polycrystalline NiO thin films were deposited with controlled growth of the structure along [111] and [200] crystallographic directions for chosen conditions. Morphology of as-deposited films was found to depend on the preferentially oriented NiO crystals. Moreover, on the basis of discharge voltage as a function of the O2 partial pressure for a constant discharge current, we present here the method to estimate the deposition conditions allowing us to achieve the desired preferential growth of transparent p-type semiconductor NiO, by Direct Current magnetron reactive sputtering.

In this study, sodium hydroxo titanates were synthesized using the reflux process in an alkaline medium. Three distinct morphologies were obtained, nanotubes and nanoribbons as classically encountered in the literature and a new nanosphere-like morphology. After ionic exchange of Na+ ions by protons and annealing, sodium titanates transform into TiO2 nanoparticles with anatase and TiO2(B) structures. We clarified the origin of this polymorphism. Nanoribbons transform into TiO2(B) at 400 degrees C, whereas nanospheres and nanotubes are converted to TiO2 anatase at 400 and 500 degrees C, respectively. The quantification of the anatase/TiO2(B) ratio performed by Raman spectroscopy allows us to establish an original ternary morphological diagram. The latter depicts the relative proportion of nanotubes, nanoribbons, and nanospheres composing each titanate and is of great utility in controlling the morphologies of the sodium titanates and correlating them to the synthesis parameters.

Nanoparticles of TiO2 crystallizing as anatase and TiO2(B) phases with different ratios were synthesized by a three step treatment including an initial reflux process in highly alkaline medium. For the first time, the ratio of each variety has been quantified by analysing the galvanostatic curves during the lithium electrochemical insertion. The weight percentage of TiO2(B) reaches 95% (110 m2 g−1 specific surface area). In order to get quantitative information based on the ratios deduced from electrochemistry, the same TiO2 samples have also been investigated by Raman spectroscopy. This technique shows a sensitivity seven times higher for anatase than TiO2(B) detection compared to electrochemical method. The equation deduced from Raman refinement and electrochemical quantification permits, for the first time, to quantify the anatase/TiO2(B) ratio simply by using Raman spectroscopy.

We report the synthetic and physical procedures for obtaining the Lanthanum-substituted Bi4Ti3O12 (BLT) ferroelectric films, Bi3.25La0.75Ti3O12, with its polarisation axis (a) oriented perpendicular to the surface of the electrode by employing partially oriented (001) polycrystalline thin films of La2Ti2O7 (LTO) as a buffer onto Si-wafers. The LTO thin film was achieved by dip coating and annealing at high temperatures while the BLT film was deposited using RF magnetron sputtering and annealing at a temperature as low as 650°C. Furthermore, the dependence of the thickness, grain size and orientation of the LTO films on the withdrawal speed of the dip-coating and annealing temperature is reported.

Well crystallized BLT thin films were deposited by RF magnetron sputtering using a target of Aurivillius phase Bi3.25L4.75Ti3O12 (BLT0,75), elaborated in our institute. RF sputtering experiments were performed at room temperature with an argon/oxygen mixture, in a pressure range of 20-50 mTorr. Optimisation of the plasma parameters, namely deposition pressure, RF power and oxygen content in the gas phase, allows obtaining BLT films with a chemical composition close to Bi3.25La0.75Ti3O12. After ex-situ annealing under oxygen atmosphere at 650 degrees C, BLT films deposited on Pt/TiO2/SiO2/Si (multilayer) substrates exhibit well defined rod-like grains morphology. A two step deposition process appeared to be necessary in order to reach satisfying dielectric properties. The effect of the plasma parameters on the chemical composition and electrical properties are presented and discussed.

We report the synthetic and physical procedures for obtaining the Lanthanum-substituted Bi4Ti3O12 (BLT) ferroelectric films, Bi3.25La0.75Ti3O12, with its polarisation axis (a) oriented perpendicular to the surface of the electrode by employing partially oriented (001) polycrystalline thin films of La2Ti2O7 (LTO) as a buffer onto Si-wafers. The LTO thin film was achieved by dip coating and annealing at high temperatures while the BLT film was deposited using RF magnetron sputtering and annealing at a temperature as low as 650 degrees C. Furthermore, the dependence of the thickness, grain size and orientation of the LTO films on the withdrawal speed of the dip-coating and annealing temperature is reported.

Well crystallized BLT thin films were deposited by RF magnetron sputtering using a home made target of Aurivillius phase Bi3.25La0.75Ti3O12 (BLT0.75). RF sputtering experiments were performed at room temperature with an argon/oxygen mixture, in a pressure range of 20-50 mTorr. Optimisation of the plasma parameters, namely deposition pressure, RF power and oxygen content in the gas phase, allows obtaining BLT films with a chemical composition close to Bi-3,25La0.75Ti3O12. After ex-situ annealing under oxygen atmosphere at 650 degrees C, BLT deposited on Pt/TiO2/SiO2/Si (multilayer) substrates exhibits well crystallized films with granular morphology. A two step deposition process appeared to be necessary in order to reach satisfying dielectric properties. The effect of the plasma parameters on the chemical composition and electrical properties are presented and discussed.

New oxygen ion conductors have been prepared by substituting Ga3+ for Ge4+ in Nd4GeO8, Zn2+ and Mg2+ for Ga3+ in Nd3GaO6, and Ca2+ and Sr2+ for Nd3+ in Nd3GaO6. A combustion technique using ethylenediamine tetraacetic acid has been developed to synthesize these materials at similar to 900 degrees C, leading to powders with spherical particles of about 100-200 nm. The green pellets obtained through the combustion-synthesized powders could be sintered to similar to 98% at 1250 degrees C. It was found that Nd4Ge1-xGaxO8-x/2 are formed up to x = 0.10, Nd3Ga1-xMxO6-x/2 (M = Zn, Mg) up to x = 0.03, and Nd3(1-x)M'3xGaxO6-3x/2 up to x = 0.03 and 0.015 for M' = Ca and Sr, respectively. These relatively small substitution rates induce a significant increase in oxygen ion conductivity (sigma(800 degrees C) = 0.2 x 10(-2) S cm(-1) for Nd4Ge0.9Ga0.1O7.95; sigma(800 degrees C) = 0.5 x 10(-2) and 0.4 x 10(-2) S cm(-1) for Nd3Ga0.97M0.03O5.985 with M = Zn and Mg, respectively, and sigma(800 degrees C) = 0.6 x 10(-2) and 0.7 x 10(-2) S cm(-1) for Nd2.91Ca0.09GaO5.955 and Nd2.955Sr0.045GaO5.9775, respectively) with respect to pure Nd4GeO8 (sigma(800 degrees C) = 2.8 x 10(-4) S cm(-1)) and pure Nd3GaO6 (sigma(800 degrees C) 2.7 x 10(-4) S cm(-1)).

Bi4-xLaxTi3O12 (BLTx), (x=0 to 1) thin films were grown on silicon (100) and platinized substrates Pt/TiO2/SiO2/Si using RF diode sputtering, magnetron sputtering and pulsed laser deposition (PLD). Stoichiometric home-synthesized targets were used. Reactive sputtering was investigated in argon/oxygen gas mixture, with a pressure ranging from 0.33 to 10 Pa without heating the substrate. PLD was investigated in pure oxygen, at a chamber pressure of 20 Pa for a substrate temperature of 400-440 degrees C. Comparative structural, chemical, optical and morphological characterizations of BLT thin films have been performed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Photoelectron Spectroscopy (XPS), Spectro-ellipsometric measurements (SE) and Atomic Force Microscopy (AFM).Both sputtering techniques allow to obtain uniform films with thickness ranging from 200 to 1000 nm and chemical composition varying from (Bi,La)(2) Ti-3 O-12 to (Bi,La)(4.5)Ti3O12, depending on deposition pressure and RF power. In addition, BLT films deposited by magnetron sputtering, at a pressure deposition ranging from 1.1 to 5 Pa, were well-crystallized after a post-deposition annealing at 650 C in oxygen. They exhibit a refractive index and optical band gap of 2.7 and 3.15 eV, respectively. Regarding PLD, single phase and well-crystallized, 100-200 nm thick BLT films with a stoichiometric (Bi,La)(4)Ti3O12 chemical composition were obtained, exhibiting in addition a preferential orientation along (200). It is worth noting that BLT films deposited by magnetron sputtering are as well-crystallized than PLD ones. (c) 2005 Elsevier B.V All rights reserved.

The proton compounds Ba2In2(1-x)Ti2xO4+2x(OH)(y) [0 less than or equal to x less than or equal to 1; y less than or equal to 2(1 - x)] were prepared by reacting Ba(2)In(2(1-x))Ti(2x)O(5+x)square(1-x) (0 less than or equal to x less than or equal to 1) phases with watervapor at similar to 200 degreesC. For 0 less than or equal to x less than or equal to 0.20, the filling of oxygen vacancies is almost complete. For larger x values, it decreases significantly down to similar to 30% only for x = 0.7. The crystal structure of the end member Ba2In2O4(OH)(2) (x = 0) was reinvestigated by a combination of techniques including H-1 and D-2 NMR and electron, X-ray and neutron diffraction. The actual cell is eight times larger than that previously published. The structure analysis confirms that the sheet consisting of parallel chains of In(2)O-4 tetrahedra and parallel rows of oxygen vacancies in the parent structure of Ba(2)In(2)O(5)square has been converted into a In(2)O-6 octahedral perovskite-like sheet. It demonstrates that the protons are bonded only to the O atoms around this In(2) site.When x increases, the change in reduced perovskite cell volume, concomitant with the water uptake, remains small for x < 0.25 and negligible for larger x values.The proton conductivity was measured between room temperature and 180 degreesC. The highest conductivity at 180 degreesC, sigma(180) approximate to 10(-6) S cm(-1), is observed for x similar to 0.3. (C) 2003 Elsevier B.V. All rights reserved.

Ba(2)In(2(1-x))Ti(2x)O(5+x)square(1-x) (0 less than or equal to x less than or equal to 1) compounds have been prepared by solid state reaction. At room temperature (RT), when x increases, the progressive filling of oxygen vacancies, concomitant with the substitution of Ti for In, first induces (for 0 < x less than or equal to 0.075) a disorder in the plane of oxygen vacancies observed in Ba(2)In(2)O(5)square. Then, it suppresses the distortion to orthorhombic symmetry; for 0.075 < x less than or equal to 0.15, the symmetry becomes tetragonal and a formation of domains is observed. For 0. 15 < x < 1, all members adopt a disordered cubic perovskite (DCP) structure at RT.Conductivity measurements between 450 and 800 degreesC show that the change from brownmillerite to tetragonal structure when x increases from 0.075 to 0.1 induces a drastic decrease of the activation energy. The highest oxide-ion conductivity is observed for 0.1 less than or equal to x less than or equal to 0.33: similar to0.5 x 10(-2) S cm(-1) at 700 degreesC. (C) 2003 Elsevier B.V. All rights reserved.

A convergent beam electron diffraction (CBED) study of Bi2La2Ti3O12 was performed. As in the case of Bi3LaTi3O12, it reveals a lowering of symmetry with respect to the idealized structure (space group I4/mmm) of Aurivillius phases. The structure of Bi4-xLaxTi3O12 (x = 1 and 2) compounds has been refined from powder X-ray diffraction data, showing that the interlayer mismatch between fluorite-like and perovskite-like layers is relieved by the conjuction of cation disorder and lowering of symmetry. HREM studies performed on Bi4-xLaxTi3O12 (X = 0, 0.75, and 2) compounds show that the La-containing compounds exhibit intergrowth defects within a thickness of similar to5 nm from the crystal surface to bulk. Taking into account both the enrichment of the surface with La and Bi, and the preference of La3+ for a 12-fold coordination, a model is proposed for the formation of such defects. They correspond to the growth of A-site cation-deficient perovskite compounds, (Bi,La)(3.33)Bi2Ti2O12 and (Bi,La)(3.66)Bi3TiO12.

The interaction between Pt electrodes and ferroelectrics in Pt/Bi4Ti3O12(BTO)/Pt and Pt/Bi3.25La0.75Ti3O12(BLT)/Pt capacitors was investigated by ex situ x-ray photoelectron spectroscopy studies. The bare surface of crystals in BTO thin films consists of the regular Aurivillius structure, whereas that in BLT is composed of the intergrowth defects. At the annealed Pt-BTO and Pt-BLT interfaces,the Pt substitution at the BTO and BLT lattices results in Pt impurity defects, which can combine with oxygen vacancies (V-O) resulting in complex metal-impurity-oxygen-vacancy defect pairs. The complex defect pairs at the Pt-BTO interfaces are polar, nonswitchable, and able to pin polarizations of surrounding lattices inducing fatigue. In contrast, the intergrowth defects of BLT crystals behave as an intrinsic diffusion barrier to Pt, and therefore, the harmful defect pairs occurring at the Pt-BTO interfaces are practically absent for the Pt-BLT interfaces, which could be relevant to the reported different fatigue properties of BTO and BLT capacitors.

A previous study by Raman scattering of the Sr1−xLa1+xAl1−xMgxO4 solid solution evidenced a distortion from ideal K2NiF4 structure. X-ray powder diffraction and selected area electron diffraction studies were carried out and no lowering of symmetry was observed. All the reflections could be indexed in the space group I4/mmm with a=b=0.38 nm and c=1.27 nm. A coupled study by convergent beam electron diffraction and crystallographic image processing was performed. These techniques have been used to determine a crystal distortion due to small atom displacements from mirrors or axes, which lower the structure symmetry. The mm2 point group symmetry was determined. A microdiffraction study leads to the Imm2 space group. This orthorhombic distortion allows a better understanding of the ionic conductivity behavior of these compounds.

An alternative chemical approach was used to prepare the ferroelectric Aurivillius phase Bi3LaTi3O12 (BLT1.00) at low temperature (450°C) leading to well-crystallized compounds at 750°C. The existence of 90°-oriented twin domains, characteristic of a ferroelectric state, was revealed in selected area electron diffraction and microdiffraction studies. Though the 3D reconstruction of the reciprocal lattice enables to propose the non-centrosymmetrical orthorhombic space group (SG) B2cm, a further convergent-beam electron diffraction study was undertaken in order to ascertain the symmetry. The monoclinic symmetry was clearly identified. BLT1.00 crystallizes in the polar SG B1c1 (no. 7, non-standard setting of P1c1) instead of I4/mmm, as previously reported.